diagrammatic representation of greenhouse effect

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greenhouse effect

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• UCAR Center for Science Education - The Greenhouse Effect
• University of California Museum of Paleontology - Understanding Global Change - Greenhouse effect
• British Geological Survey - The greenhouse effect
• National Geographic - Education - Greenhouse Effect
• Natural Resources Defense Council - Greenhouse Effect
• Library of Economics and Liberty - Greenhouse Effect
• greenhouse effect - Children's Encyclopedia (Ages 8-11)
• greenhouse effect - Student Encyclopedia (Ages 11 and up)

greenhouse effect , a warming of Earth ’s surface and troposphere (the lowest layer of the atmosphere ) caused by the presence of water vapour, carbon dioxide , methane , and certain other gases in the air. Of those gases, known as greenhouse gases , water vapour has the largest effect.

The origins of the term greenhouse effect are unclear. French mathematician Joseph Fourier is sometimes given credit as the first person to coin the term greenhouse effect based on his conclusion in 1824 that Earth’s atmosphere functioned similarly to a “hotbox”—that is, a heliothermometer (an insulated wooden box whose lid was made of transparent glass) developed by Swiss physicist Horace Bénédict de Saussure , which prevented cool air from mixing with warm air. Fourier, however, neither used the term greenhouse effect nor credited atmospheric gases with keeping Earth warm. Swedish physicist and physical chemist Svante Arrhenius is credited with the origins of the term in 1896, with the publication of the first plausible climate model that explained how gases in Earth’s atmosphere trap heat . Arrhenius first refers to this “hot-house theory” of the atmosphere—which would be known later as the greenhouse effect—in his work Worlds in the Making (1903).

The atmosphere allows most of the visible light from the Sun to pass through and reach Earth’s surface. As Earth’s surface is heated by sunlight , it radiates part of this energy back toward space as infrared radiation . This radiation, unlike visible light, tends to be absorbed by the greenhouse gases in the atmosphere, raising its temperature. The heated atmosphere in turn radiates infrared radiation back toward Earth’s surface. (Despite its name, the greenhouse effect is different from the warming in a greenhouse , where panes of glass transmit visible sunlight but hold heat inside the building by trapping warmed air.)

Without the heating caused by the greenhouse effect, Earth’s average surface temperature would be only about −18 °C (0 °F). On Venus the very high concentration of carbon dioxide in the atmosphere causes an extreme greenhouse effect resulting in surface temperatures as high as 450 °C (840 °F).

Although the greenhouse effect is a naturally occurring phenomenon, it is possible that the effect could be intensified by the emission of greenhouse gases into the atmosphere as the result of human activity. From the beginning of the Industrial Revolution through the end of the 20th century, the amount of carbon dioxide in the atmosphere increased by roughly 30 percent and the amount of methane more than doubled. A number of scientists have predicted that human-related increases in atmospheric carbon dioxide and other greenhouse gases could lead by the end of the 21st century to an increase in the global average temperature of 3–4 °C (5.4–7.2 °F) relative to the 1986–2005 average. This global warming could alter Earth’s climates and thereby produce new patterns and extremes of drought and rainfall and possibly disrupt food production in certain regions.

Understanding Global Change

Discover why the climate and environment changes, your place in the Earth system, and paths to a resilient future.

Greenhouse effect

Life as we know it would be impossible if not for the greenhouse effect, the process through which heat is absorbed and re-radiated in that atmosphere. The intensity of a planet’s greenhouse effect is determined by the relative abundance of greenhouse gases in its atmosphere. Without greenhouse gases, most of Earth’s heat would be lost to outer space, and our planet would quickly turn into a giant ball of ice. Increase the amount of greenhouse gases to the levels found on the planet Venus, and the Earth would be as hot as a pizza oven! Fortunately, the strength of Earth’s greenhouse effect keeps our planet within a temperature range that supports life

On this page

What is the greenhouse effect, earth system models about the greenhouse effect, how human activities influence the greenhouse effect, explore the earth system, investigate, links to learn more.

For the classroom:

• Teaching Resources

Global Change Infographic

The greenhouse effect occurs in the atmosphere, and is an essential part of How the Earth System Works. Click the image on the left to open the Understanding Global Change Infographic . Locate the greenhouse effect icon and identify other topics that cause changes to, or are affected by, the greenhouse effect.

Adapted from the Environmental Protection Agency greenhouse effect file

Greenhouse gases such as methane, carbon dioxide, nitrous oxide, and water vapor  significantly affect the amount of energy in the Earth system, even though they make up a tiny percentage of Earth’s atmosphere.  Solar radiation that passes through the atmosphere and reaches Earth’s surface is either reflected or absorbed . Reflected sunlight doesn’t add any heat to the Earth system because this energy bounces back into space.

However, absorbed sunlight increases the temperature of Earth’s surface, and the warmed surface re-radiates as long-wave radiation (also known as infrared radiation). Infrared radiation is invisible to the eye, but we feel it as heat.

If there were not any greenhouse gases in the atmosphere, all that heat would pass directly back into space. With greenhouse gases present, however, most of the long-wave radiation coming from Earth’s surface is absorbed and then re-radiated in all directions many times before passing back into space. Heat that is re-radiated downward, toward the Earth, is absorbed by the surface and re-radiated again.

Clouds also influence the greenhouse effect. A thick, low cloud cover can enhance the reflectivity of the atmosphere, reducing the amount of solar radiation reaching Earth’s surface, but clouds high in the atmosphere can intensify the greenhouse effect by re-radiating heat from the Earth’s surface.

Altogether, this cycle of absorption and re-radiation by greenhouse gases impedes the loss of heat from our atmosphere to space, creating the greenhouse effect. Increases in the amount of greenhouses gases will mean that more heat is trapped, increasing the amount of energy in the Earth system (Earth’s energy budget), and raising Earth’s temperature. This increase in Earth’s average temperature is also known as global warming.

This Earth system model is one way to represent the essential processes and interactions related to the greenhouse effect. Hover over the icons for brief explanations; click on the icons to learn more about each topic. Download the Earth system models on this page. There are a few ways that the relationships among these topics can be represented and explained using the Understanding Global Change icons ( download examples ).  

The greenhouse effect, which influences Earth’s average temperature, affects many of the processes that shape global climate and ecosystems.  This model shows some of the other parts of the Earth system that the greenhouse effect influences, including the water cycle and water temperature .

Humans directly affect the greenhouse effect through activities that result in greenhouse gas emissions. The Earth system model below includes some of the ways that human activities increase the amount of greenhouse gases in the atmosphere. Releasing greenhouse gases intensifies the greenhouse effect, and increases Earth’s average air temperatures (also known as global warming). Hover over or click on the icons to learn more about these human causes of change and how they influence the greenhouse effect.

Click the scene icons and bolded terms on this page to learn more about these process and phenomena.

Learn more in these real-world examples, and challenge yourself to  construct a model  that explains the Earth system relationships.

• Ancient fossils and modern climate change
• How Global Warming Works
• NASA:  Global Climate Change:  A Blanket Around the Earth
• UCAR Center for Science Education: The Greenhouse Effect
• IPCC:  What is the Greenhouse Effect?
• Indicators of Change (NCA.2014)
• Human influence on the greenhouse effect
• The Carbon Cycle and Earth’s Climate

Climate in Arts and History

Promoting climate literacy across disciplines.

Greenhouse Effect

What is the greenhouse effect.

• Earth’s atmosphere is composed of an assortment of gases, some of which trap heat. These gases, including carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O) water vapor (H 2 O), ozone (O 3 ), and more, are referred to as greenhouse gases.
• Greenhouse gases help insulate the planet, capturing heat from incoming solar radiation. This natural process is known as the greenhouse effect. The greenhouse effect plays a major role in maintaining a stable temperature and climate. To illustrate, if all carbon dioxide was removed from the atmosphere, the average global temperature would fall by 59°F (33°C).

How is it related to climate?

• Under the natural greenhouse effect, some heat from the sun is allowed to escape the atmosphere and radiate into space (image below – left). However, anthropogenic activity, mainly the burning of fossil fuels, is releasing large amounts of greenhouse gases into the atmosphere. With a higher concentration of greenhouse gases, more heat is being absorbed, causing the planet’s surface to warm (image below – right). The anthropogenic use of fossil fuels has caused the planet to warm on average by 2.1°F (1.2°C) in comparison to pre-industrial temperatures.

Diagram demonstrating the greenhouse effect, the process of heat-trapping gases absorbing radiation from the sun and keeping the Earth’s surface and atmosphere warm (from Lai, 2021). On the left, is a model of the natural greenhouse effect, and on the right is a model of the human-enhanced greenhouse effect. Burning fossil fuels releases carbon emissions into the atmosphere, amplifying the greenhouse effect and causing the planet’s surface to get hotter.

• Burning fossil fuels is not the only cause of global warming, although it is the primary contributor to carbon dioxide emissions. Land use changes and agricultural practices have contributed to the release of methane and nitrous oxide. Concentrations of these greenhouse gases have increased exponentially since the 18th and 19th centuries (image below), when fossil fuels became the dominant energy source for transportation, industry, electricity, and housing.

Graph depicting the change in three greenhouse gas concentrations in Earth’s atmosphere: carbon dioxide, methane, and nitrous oxide, from the years 0 to 2005 (from Lai, 2021). All three concentrations have been increasing since the 18th century, when fossil fuels became a dominant energy source. For current trends and values please see: https://gml.noaa.gov/ccgg/trends/ .

References and additional resources

• EPA. “Sources of Greenhouse Gas Emissions.” Environmental Protection Agency . May 2024. https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions .
• Lai, S. “Why Is The World Warming: An Introduction to Climate Change and Impact of Food.” What’s Up in Science? March 2021. https://sites.northwestern.edu/scienheal/2021/03/13/why-is-the-world-warming-an-introduction-to-climate-change-and-impact-of-food/ .
• NASA. “Global Temperature.” The National Aeronautics and Space Administration . 2023. https://climate.nasa.gov/vital-signs/global-temperature/?intent=121 .
• NASA. “What is the greenhouse effect?” The National Aeronautics and Space Administration . n.d. https://science.nasa.gov/climate-change/faq/what-is-the-greenhouse-effect/ .
• NOAA. “Trends in CO 2 , CH 4 , N 2 O, SF 6 .” NOAA: Global Monitoring Laboratory . May 2024. https://gml.noaa.gov/ccgg/trends/ .

The Greenhouse Effect, Simplified

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Modelling the greenhouse effect

In association with Nuffield Foundation

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Use this demonstration to illustrate the greenhouse effect and the role of carbon dioxide as a greenhouse gas

The demonstration includes two parts. In the first, students observe a model of the greenhouse effect in a greenhouse using transparent bottles containing air. In the second, they learn about the role of carbon dioxide by comparing the effects in two separate vessels containing air and carbon dioxide respectively.

The experiments in both parts demonstrate the greenhouse effect by comparing the temperature increases in suitable vessels containing the gases, on exposure to light from a powerful lamp.

Each part of the demonstration will take about 30 minutes. However, the second part can be started well before the first part has been completed if sufficient apparatus is available.

The experiments involve slow, gradual temperature increases. If the temperatures are monitored electronically, with data logging and a live display, the experiment can be allowed to proceed while the class carries on with other work. If ordinary thermometers or electronic thermometers with digital displays are used, the temperatures will have to be recorded at one minute intervals, requiring the attention of the class to time and record for the duration of the demonstrations.

For both parts

• Photoflood light bulb, 275 W, in a plain bulb holder (see notes 1 and 2 below)
• Temperature sensors with leads, 3, with data logger and computer display (see note 3)
• Plastic drink bottles, transparent, 1 dm 3 , x2 (see note 4)
• 2-hole bungs, to fit bottles (see note 4)
• Clock, with second hand
• Stand, boss and clamp, x2
• Beakers, 250 cm 3 , x2
• Black card discs, x2

Apparatus notes

• Photoflood bulbs are available from photographic suppliers on the internet, or from photography shops on the high street, at a cost of £10–15 each for a 275 W bulb. The bulb should be fitted in a plain bulb-holder suitably stabilised so that it stands securely on the demonstration bench, and is easily switched on and off by the demonstrator without disturbing the bulb.
• The photoflood bulb should be situated so that the three temperature sensors or thermometers can be placed equidistant from the bulb, as shown in figure 1 below.

Source: Royal Society of Chemistry

How to set up the apparatus to model the greenhouse effect in a greenhouse and compare temperature increases in each of the two bottles

• Check that all three temperature sensors show the same temperature on the computer display when placed in the same temperature environment. Fit two of the sensors through the rubber bungs that will fit into the drinks bottles. Each of the three temperature sensors should be wrapped with a lead (or prepared aluminium) foil ‘flag’. Each flag is made from a piece of lead foil about 3 x 2 cm such that after wrapping around the sensor, a flag approximately 1 cm wide and 2 cm high made of doubled foil is formed (see figure 2 below). The sensor should then be positioned so that the face of each flag will be perpendicular to the radiation from the bulb. The end result should be a set of three temperature sensors with flags that are as similar as possible. The sensors carrying their flags need to fit easily through the necks of the drinks bottles. The setting up of the datalogger and three temperature sensors will depend on the kit available in the school. The handbook for the datalogger will provide the necessary instructions. Suitable software should be used to display the temperature data as a function of time as three lines of different colour on screen(s) visible to the class. Two of the temperature sensors will be required again in part 2, but without the lead flags.
• The two drinks bottles for part 1 should be identical, colourless, transparent, PET plastic (recycling code 1) water bottles, fizzy drink bottles or similar, of 1 dm 3 capacity, capable of carrying a 2-hole rubber bung in the mouth (see figure 3). One hole is needed to carry the temperature sensor (or the thermometer if used), the other to allow air flow to prevent pressure build-up. One of the bottles should be painted matt black on one ‘side’ and allowed to dry thoroughly. The bottles should be secured in an upright position, without obscuring the light path from the lamp.

How to prepare the thermometers or temperature sensors and the half-painted bottle required for the first experiment

• Finally set up the apparatus for part 1 as in figure 1, clamping as necessary to ensure the arrangement is secure from accidental knocks, and at the appropriate point in the lesson, replace by the simple arrangement for part 2 as in figure 4. Note that the photoflood lamp is now positioned and clamped above the beakers, midway between them.

How to set up the apparatus to model the effect of carbon dioxide on temperature for the second experiment

• Lead foil pieces (TOXIC, DANGEROUS FOR THE ENVIRONMENT), about 3 cm x 2 cm, x3 (aluminium foil can be used as an alternative to lead foil but must be either painted black or darkened which happens after it has been in contact with food)
• Matt black paint (for example, blackboard paint)
• Source of carbon dioxide gas
• Methane (natural gas) (EXTREMELY FLAMMABLE)
• Pentane (EXTREMELY FLAMMABLE, HARMFUL, DANGEROUS FOR THE ENVIRONMENT), 1 cm 3
• Hexane (HIGHLY FLAMMABLE, HARMFUL, DANGEROUS FOR THE ENVIRONMENT), 1 cm 3

Health, safety and technical notes

• Read our standard health and safety guidance.
• Lead foil, Pb(s), (TOXIC, DANGEROUS FOR THE ENVIRONMENT) – see CLEAPSS Hazcard HC056 . In part 1 the lead foil pieces are for making the ‘flags’ around the temperature sensors (Note 3). The Lead foil can be replaced with darkened aluminium foil and the effect is still observed.
• Carbon dioxide, CO 2 (g) – see CLEAPSS Hazcard HC020a .  For use of a carbon dioxide cylinder also see Laboratory Handbook Section 9.9 about the safe storage and use of gas cylinders. If using solid carbon dioxide (dry ice), this should be obtained within 24 hours of the demonstration in substantially larger quantity than required for the experiment, and stored in a vented insulated container until required. All handling must be done using thermal gloves and handling tongs. If neither a carbon dioxide cylinder nor a supply of dry ice is available, carbon dioxide gas may be generated chemically – see these standard techniques for generating, collecting and testing gases . Replace the thistle funnel shown with a tap funnel or an unstoppered separating funnel. Use about 10 g of small marble chips (calcium carbonate) and about 100 cm 3 of hydrochloric acid (2 M) for the carbon dioxide generator. Add the acid a few cm 3 at a time to the marble chips to generate a steady stream of carbon dioxide. Either shortly before part 2 of the demonstration, or as part of the demonstration, allow a flow of carbon dioxide to displace the air from the beaker. Alternatively pieces of solid carbon dioxide can be allowed to evaporate in the bottom of the beaker.
• Methane (Natural gas), CH 4 (g), (EXTREMELY FLAMMABLE) – see CLEAPSS Hazcard HC045a .
• Pentane, C 5 H 12 (l), (EXTREMELY FLAMMABLE, HARMFUL, DANGEROUS FOR THE ENVIRONMENT) – see CLEAPSS Hazcard HC045a.
• Hexane, C 6 H 14 (l), (EXTREMELY FLAMMABLE, HARMFUL, DANGEROUS FOR THE ENVIRONMENT) – see CLEAPSS Hazcard HC045a.
• With the apparatus set up as in figure 1 above, start the datalogging programme with all three sensors at the same time (which should all show the same temperature), and immediately switch on the photoflood lamp.
• Allow the datalogging to proceed with the graphical display visible to the class. Ensure the class are aware of which graphical trace belongs to which sensor. In about 15 minutes, the three traces should level off, the ‘bare’ sensor showing a typical increase of around 5°C, the clear bottle about 8°C, and the blackened bottle about 13°C.
• If two further temperature sensors and a second datalogger are available, part 2 can be demonstrated while part 1 is running. Alternatively the class can proceed with other tasks until there is a clear result from part 1 on the display screen.
• Reset the datalogger and software to start again with inputs from two temperature sensors.
• Start the datalogger and switch on the lamp; the two traces should remain together, though showing a gradual rise.
• When this gradual rise levels off, introduce carbon dioxide as a steady flow into one of the beakers. The trace from that beaker should soon show a higher temperature than the beaker with only air – typically up to 8 degrees higher. If the gas flow is stopped, the carbon dioxide will slowly diffuse out of the beaker, replaced by air, and the temperature should begin to fall again.
• (Optional) Clear the carbon dioxide from its beaker, and repeat 1 and 2 above. Ensure all sources of ignition have been removed. Now introduce a slow stream of methane from the gas tap into the beaker and observe the effect on the temperature trace.
• (Optional) Again repeat 1 and 2 above and ensure all sources of ignition have been removed. Use a dropping pipette to drop about 1 cm 3 of the volatile liquid into the beaker. This will slowly evaporate, and the effect on the temperature trace can be followed as it does so.

Teaching notes

In a garden greenhouse, visible light passes through the glass and is absorbed by darker surfaces inside. This absorbed energy heats up the materials, also warming the surrounding air. But convection is restricted by the enclosing glass and the inside temperature of the greenhouse rises. This is the main cause of warming in a garden greenhouse.

However, in addition the warm surfaces re-radiate some of the absorbed energy, but at longer wavelengths in the infrared region of the spectrum. Some of this infra-red radiation is absorbed by glass and contributes to the warming of the greenhouse. It is this latter effect that is called the ‘greenhouse effect’. The greenhouse effect in the Earth’s atmosphere is caused by a number of gases that behave in a similar way to glass. They are transparent to visible light, but absorb in part of the infrared spectrum. Some of these gases are listed in the table. It can be seen that carbon dioxide is the most important greenhouse gas because of its relatively high concentration in the atmosphere rather than its intrinsic greenhouse efficiency.

In part 1, the experiment demonstrates the situation in a greenhouse using a plastic bottle. It also shows the effect of a black surface absorbing the energy from visible light.

In part 2, however, replacing the plastic bottles with open beakers removes the restriction on convection. The difference in temperature rise between the two beakers comes mainly from absorption by the gases of the radiant (infra-red) energy from the lead discs at the bottom of the beakers

Water vapour, carbon dioxide and ozone are the most important of the greenhouse gases, the first two because of their relatively high concentration in the atmosphere rather than because of their intrinsic greenhouse efficiency – indeed water vapour accounts for more than a third of the overall greenhouse effect. However, methane also makes a significant contribution, and it is the increasing proportion of carbon dioxide, and to a lesser extent methane, that seems to be producing the effect of global warming.

Additional information

This is a resource from the  Practical Chemistry project , developed by the Nuffield Foundation and the Royal Society of Chemistry.

Practical Chemistry activities accompany  Practical Physics  and  Practical Biology .

© Nuffield Foundation and the Royal Society of Chemistry

• 11-14 years
• 14-16 years
• Demonstrations
• Environment
• Environmental science

Specification

• Greenhouse gases in the atmosphere maintain temperatures on Earth high enough to support life. Water vapour, carbon dioxide and methane are greenhouse gases.
• Describe the greenhouse effect in terms of the interaction of radiation with matter.
• 8.24 Describe how various gases in the atmosphere, including carbon dioxide, methane and water vapour, absorb heat radiated from the Earth, subsequently releasing energy which keeps the Earth warm: this is known as the greenhouse effect
• C1.3.1 describe the greenhouse effect in terms of the interaction of radiation with matter
• C6.2c describe the greenhouse effect in terms of the interaction of radiation with matter within the atmosphere
• C6.3c describe the greenhouse effect in terms of the interaction of radiation with matter within the atmosphere
• 2.3.6 recall that the percentage of carbon dioxide in the atmosphere has risen from 0.03% to 0.04% because of combustion of organic compounds and is believed to have caused global warming;
• 2.5.28 demonstrate knowledge that the combustion of fuels is a major source of atmospheric pollution due to: combustion of hydrocarbons producing carbon dioxide, which leads to the greenhouse effect causing sea level rises, flooding and climate change;…
• 2.5.26 demonstrate knowledge that the combustion of fuels is a major source of atmospheric pollution due to: combustion of hydrocarbons producing carbon dioxide, which leads to the greenhouse effect causing sea level rises, flooding and climate change…
• The greenhouse effect and the influence of human activity on it.
• Possible implications of increased greenhouse effect.
• 3. Illustrate how earth processes and human factors influence Earth’s climate, evaluate effects of climate change and initiatives that attempt to address those effects.

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The Greenhouse Effect and our Planet

The greenhouse effect happens when certain gases, which are known as greenhouse gases, accumulate in Earth’s atmosphere. Greenhouse gases include carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), ozone (O 3 ), and fluorinated gases.

Biology, Ecology, Earth Science, Geography, Human Geography

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The greenhouse effect happens when certain gases , which are known as greenhouse gases , accumulate in Earth’s atmosphere . Greenhouse gases include carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), ozone (O 3 ), and fluorinated gases.

Greenhouse gases allow the sun’s light to shine onto Earth’s surface, and then the gases , such as ozone , trap the heat that reflects back from the surface inside Earth’s atmosphere . The gases act like the glass walls of a  greenhouse —thus the name, greenhouse gas .

According to scientists, the average temperature of Earth would drop from 14˚C (57˚F) to as low as –18˚C (–0.4˚F), without the greenhouse effect .

Some greenhouse gases come from natural sources, for example, evaporation  adds water vapor to the atmosphere . Animals and plants release carbon dioxide when they respire, or breathe. Methane is released naturally from decomposition. There is evidence that suggests methane is released in low-oxygen environments , such as  swamps or landfills . Volcanoes —both on land and under the ocean —release greenhouse gases , so periods of high volcanic activity tend to be warmer.

Since the  Industrial Revolution  of the late 1700s and early 1800s, people have been releasing larger quantities of greenhouse gases into the atmosphere. That amount has skyrocketed in the past century. Greenhouse gas emissions increased 70 percent between 1970 and 2004. Emissions of CO 2 , rose by about 80 percent during that time.

The amount of CO 2 in the atmosphere far exceeds the naturally occurring range seen during the last 650,000 years.

Most of the CO 2 that people put into the atmosphere comes from burning  fossil fuels . Cars, trucks, t rains , and planes all burn fossil fuels. Many electric power plants do as well. Another way humans release CO 2 into the atmosphere is by cutting down  forests , because trees contain large amounts of carbon.

People add methane to the atmosphere through  livestock  farming, landfills , and fossil fuel production such as  coal mining  and natural gas processing. Nitrous oxide comes from  agriculture  and fossil fuel burning. Fluorinated gases include chlorofluoro carbons (CFCs),  hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). They are produced during the manufacturing of refrigeration and cooling products and through aerosols.

All of these human activities add greenhouse gases to the atmosphere . As the level of these gases rises, so does the  temperature  of Earth. The rise in Earth’s average temperature contributed to by human activity is known as  global warming .

The Greenhouse Effect and Climate Change Even slight increases in average global temperatures can have huge effects.

Perhaps the biggest, most obvious effect is that  glaciers and  ice caps melt faster than usual. The  meltwater  d rains into the oceans , causing  sea levels to rise.

Glaciers and ice caps cover about 10 percent of the world’s landmasses. They hold between 70 and 75 percent of the world’s  freshwater . If all of this ice melted, sea levels would rise by about 70 meters (230 feet).

The Intergovernmental Panel on Climate Change states that the global sea level rose about 1.8 millimeters (0.07 inches) per year from 1961 to 1993, and about 3.1 millimeters (0.12 inches) per year since 1993.

Rising sea levels cause  flooding in  coastal cities, which could displace millions of people in low-lying areas such as Bangladesh, the U.S. state of Florida, and the Netherlands.

Millions more people in countries like Bolivia, Peru, and India depend on glacial meltwater for drinking,  irrigation , and  hydroelectric power . Rapid loss of these glaciers would devastate those countries.

Greenhouse gas emissions affect more than just temperature . Another effect involves changes in  precipitation , such as  rain  and  snow .

Over the course of the 20th century, precipitation increased in eastern parts of North and South America, northern Europe, and northern and central Asia. However, it has decreased in parts of Africa, the Mediterranean, and southern Asia.

As climates change, so do the habitats for living things. Animals that are adapted to a certain  climate  may become threatened. Many human societies depend on predictable rain patterns in order to grow specific  crops for food, clothing, and trade. If the climate of an area changes, the people who live there may no longer be able to grow the crops they depend on for survival. Some scientists also worry that tropical diseases will expand their ranges into what are now more temperate regions if the temperatures of those areas increase.

Most climate scientists agree that we must reduce the amount of greenhouse gases released into the atmosphere. Ways to do this, include:

• driving less, using public transportation , carpooling, walking, or riding a bike.
• flying less—airplanes produce huge amounts of greenhouse gas emissions.
• reducing, reusing, and recycling.
• planting a tree—trees absorb carbon dioxide, keeping it out of the atmosphere.
• using less  electricity .
• eating less meat—cows are one of the biggest methane producers.
• supporting alternative energy sources that don’t burn fossil fuels.

Artificial Gas

Chlorofluorocarbons (CFCs) are the only greenhouse gases not created by nature. They are created through refrigeration and aerosol cans.

CFCs, used mostly as refrigerants, are chemicals that were developed in the late 19th century and came into wide use in the mid-20th century.

Other greenhouse gases, such as carbon dioxide, are emitted by human activity, at an unnatural and unsustainable level, but the molecules do occur naturally in Earth's atmosphere.

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What is the greenhouse effect?

The greenhouse effect is the process through which heat is trapped near Earth's surface by substances known as 'greenhouse gases.' Imagine these gases as a cozy blanket enveloping our planet, helping to maintain a warmer temperature than it would have otherwise. Greenhouse gases consist of carbon dioxide, methane, ozone, nitrous oxide, chlorofluorocarbons, and water vapor. Water vapor, which reacts to temperature changes, is referred to as a 'feedback', because it amplifies the effect of forces that initially caused the warming.

Scientists have determined that carbon dioxide plays a crucial role in maintaining the stability of Earth's atmosphere. If carbon dioxide were removed, the terrestrial greenhouse effect would collapse, and Earth's surface temperature would drop significantly, by approximately 33°C (59°F).

Greenhouse gases are part of Earth's atmosphere. This is why Earth is often called the 'Goldilocks' planet – its conditions are just right, not too hot or too cold, allowing life to thrive. Part of what makes Earth so amenable is its natural greenhouse effect, which maintains an average temperature of 15 ° C (59 ° F) . However, in the last century, human activities, primarily from burning fossil fuels that have led to the release of carbon dioxide and other greenhouse gases into the atmosphere, have disrupted Earth's energy balance. This has led to an increase in carbon dioxide in the atmosphere and ocean. The level of carbon dioxide in Earth’s atmosphere has been rising consistently for decades and traps extra heat near Earth's surface, causing temperatures to rise.

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Greenhouse Effect: Keeping the Balance

How do we keep the right balance of greenhouse gases in our atmosphere, greenhouse gases.

Besides CO 2 there are other greenhouse gases. These include water vapor, methane, nitrous oxide, and ozone. Without any greenhouse gases, Earth would be an icy wasteland. Greenhouse gases keep our planet livable by holding onto some of Earth’s heat energy so that it doesn’t all escape into space. This heat trapping is known as the greenhouse effect.

Just as too little greenhouse gas makes Earth too cold, too much greenhouse gas makes Earth too warm. Over the last century, humans have burned coal, oil, and gasoline in our cars, trucks, planes, trains, power plants, and factories. Burning such fossil fuels produces CO 2 as a waste product. Putting so much new CO 2 into the air has made Earth warmer. If we continue on our current path, we will cause even more warming.

Finding a Balance

CO 2 is a big part of the carbon cycle . The carbon cycle traces carbon's path from the atmosphere, into living organisms, then turning into dead organic matter, going into the oceans, and back into the atmosphere. Scientists describe the cycle in terms of sources (parts of the cycle that add carbon to the atmosphere) and sinks (parts of the cycle that remove carbon from the atmosphere).

The key to keeping everything in balance is for the sources and sinks to have the same amount of CO 2 .

The most important sinks are the ocean (which includes the seawater itself, the organisms living there, and the sediments on the sea floor) as well as plants and soil on land. The ocean stores most of the world's carbon, but forests are really important too. Forests and oceans each remove around one-fourth of the carbon we humans have added to the atmosphere.

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Greenhouse Effect

Table of Contents

What is the Greenhouse Effect?

Greenhouse gases, causes of greenhouse effect, effects of greenhouse effect, runaway greenhouse effect, greenhouse effect definition.

“Greenhouse effect is the process by which radiations from the sun are absorbed by the greenhouse gases and not reflected back into space. This insulates the surface of the earth and prevents it from freezing.”

A greenhouse is a house made of glass that can be used to grow plants. The sun’s radiations warm the plants and the air inside the greenhouse. The heat trapped inside can’t escape out and warms the greenhouse which is essential for the growth of the plants. Same is the case in the earth’s atmosphere.

During the day the sun heats up the earth’s atmosphere. At night, when the earth cools down the heat is radiated back into the atmosphere. During this process, the heat is absorbed by the greenhouse gases in the earth’s atmosphere. This is what makes the surface of the earth warmer, that makes the survival of living beings on earth possible.

However, due to the increased levels of greenhouse gases, the temperature of the earth has increased considerably. This has led to several drastic effects.

Let us have a look at the greenhouse gases and understand the causes and consequences of greenhouse effects with the help of a diagram.

Also Read:  Global Warming

“Greenhouse gases are the gases that absorb the infrared radiations and create a greenhouse effect. For eg., carbondioxide and chlorofluorocarbons.” Greenhouse Effect Diagram

The Diagram shows Greenhouse Gases such as carbon dioxide are the primary cause for the Greenhouse Effect

The major contributors to the greenhouse gases are factories, automobiles, deforestation , etc. The increased number of factories and automobiles increases the amount of these gases in the atmosphere. The greenhouse gases never let the radiations escape from the earth and increase the surface temperature of the earth. This then leads to global warming.

Also Read:  Our Environment

The major causes of the greenhouse effect are:

Burning of Fossil Fuels

Fossil fuels are an important part of our lives. They are widely used in transportation and to produce electricity. Burning of fossil fuels releases carbon dioxide. With the increase in population, the utilization of fossil fuels has increased. This has led to an increase in the release of greenhouse gases in the atmosphere.

Deforestation

Plants and trees take in carbon dioxide and release oxygen. Due to the cutting of trees, there is a considerable increase in the greenhouse gases which increases the earth’s temperature.

Nitrous oxide used in fertilizers is one of the contributors to the greenhouse effect in the atmosphere.

Industrial Waste and Landfills

The industries and factories produce harmful gases which are released in the atmosphere.

Landfills also release carbon dioxide and methane that adds to the greenhouse gases.

The main effects of increased greenhouse gases are:

Global Warming

It is the phenomenon of a gradual increase in the average temperature of the Earth’s atmosphere. The main cause for this environmental issue is the increased volumes of greenhouse gases such as carbon dioxide and methane released by the burning of fossil fuels, emissions from the vehicles, industries and other human activities.

Depletion of  Ozone Layer

Ozone Layer protects the earth from harmful ultraviolet rays from the sun. It is found in the upper regions of the stratosphere. The depletion of the ozone layer results in the entry of the harmful UV rays to the earth’s surface that might lead to skin cancer and can also change the climate drastically.

The major cause of this phenomenon is the accumulation of natural greenhouse gases including chlorofluorocarbons, carbon dioxide, methane, etc.

Smog and Air Pollution

Smog is formed by the combination of smoke and fog. It can be caused both by natural means and man-made activities.

In general, smog is generally formed by the accumulation of more greenhouse gases including nitrogen and sulfur oxides. The major contributors to the formation of smog are automobile and industrial emissions, agricultural fires, natural forest fires and the reaction of these chemicals among themselves.

Acidification of Water Bodies

Increase in the total amount of greenhouse gases in the air has turned most of the world’s water bodies acidic. The greenhouse gases mix with the rainwater and fall as acid rain. This leads to the acidification of water bodies.

Also, the rainwater carries the contaminants along with it and falls into the river, streams and lakes thereby causing their acidification.

This phenomenon occurs when the planet absorbs more radiation than it can radiate back. Thus, the heat lost from the earth’s surface is less and the temperature of the planet keeps rising. Scientists believe that this phenomenon took place on the surface of Venus billions of years ago.

This phenomenon is believed to have occurred in the following manner:

• A runaway greenhouse effect arises when the temperature of a planet rises to a level of the boiling point of water. As a result, all the water from the oceans converts into water vapour, which traps more heat coming from the sun and further increases the planet’s temperature. This eventually accelerates the greenhouse effect. This is also called the “positive feedback loop”.
• There is another scenario giving way to the runaway greenhouse effect. Suppose the temperature rise due to the above causes reaches such a high level that the chemical reactions begin to occur. These chemical reactions drive carbon dioxide from the rocks into the atmosphere. This would heat the surface of the planet which would further accelerate the transfer of carbon dioxide from the rocks to the atmosphere, giving rise to the runaway greenhouse effect.

In simple words, increasing the greenhouse effect gives rise to a runaway greenhouse effect which would increase the temperature of the earth to such an extent that no life will exist in the near future.

Also Read:  Environmental Issues

To learn more about what is the greenhouse effect, its definition, causes and effects, keep visiting BYJU’S website or download the BYJU’S app for further reference.

Frequently Asked Questions

What is global warming.

The gradual increase in temperature due to the greenhouse effect caused by pollutants, CFCs and carbon dioxide is called global warming. This phenomenon has disturbed the climatic pattern of the earth.

List gases which are responsible for the greenhouse effect.

The major greenhouse gases are: 1) Carbon dioxide 2) Methane 3) Water 4) Nitrous oxide 5) Ozone 6) Chlorofluorocarbons (CFCs)

What is the greenhouse effect?

What are the major causes of the greenhouse effect.

Burning of fossil fuels, deforestation, farming and livestock production all contribute to the greenhouse effect. Industries and factories also play a major role in the release of greenhouse gases.

What would have happened if the greenhouse gases were totally missing in the earth’s atmosphere?

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

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A student's guide to Global Climate Change

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The Greenhouse Effect

• Greenhouse Gases
• All About Carbon Dioxide

If it were not for greenhouse gases trapping heat in the atmosphere, the Earth would be a very cold place. Greenhouse gases keep the Earth warm through a process called the greenhouse effect. Play the video to learn more » ( Alternative version )

The Earth gets energy from the sun in the form of sunlight. The Earth's surface absorbs some of this energy and heats up. That's why the surface of a road can feel hot even after the sun has gone down—because it has absorbed a lot of energy from the sun. The Earth cools down by giving off a different form of energy, called infrared radiation. But before all this radiation can escape to outer space, greenhouse gases in the atmosphere absorb some of it, which makes the atmosphere warmer. As the atmosphere gets warmer, it makes the Earth's surface warmer, too.

Learn more about radiation . ( Alternative version )

Learn where the term “greenhouse effect” comes from . ( Alternative version )

Greenhouse gases keep the Earth warm through a process called the greenhouse effect.

What Is Radiation?

You might hear the word radiation and think that it's a bad thing. It's true that there are certain types of radiation that are bad for you, but other types of radiation are important parts of your life. When you feel heat from the sun, see all the colors around you, or listen to the radio, you are actually experiencing different types of radiation.

These types of radiation are all part of the electromagnetic spectrum, which means they involve energy traveling in the form of a wave. Different types of radiation have different wavelengths.

What's in a Name? The “Greenhouse Effect”

A greenhouse is a building made of glass that allows sunlight to enter but traps heat inside, so the building stays warm even when it's cold outside. Because gases in the Earth's atmosphere also let in light but trap heat, many people call this phenomenon the “greenhouse effect.” The greenhouse effect works somewhat differently from an actual greenhouse, but the name stuck, so that's how we still refer to it today.

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Unit 4: Considering the Influence of Light and Thermal Phenomena on Global Climate

IV. Using Central Ideas about Light and Thermal Phenomena to Explain the Greenhouse Effect

The greenhouse effect is often mentioned in discussions about global climate. The name of this effect refers to an analogy between what happens when the Sun shines on the entire Earth and what happens when the Sun shines on a greenhouse in a garden here on Earth.

A. Considering what happens during the greenhouse effect in a garden greenhouse

A student noted that sometimes people have no idea what is happening in a greenhouse here on Earth:

I asked my sister if she knew anything about the greenhouse effect and she said nothing. So I asked if she ever heard of it before and she said no. Then I reminded her that greenhouses are used for gardens. She went ‘Oh, right’ but didn’t know what they did for the gardens …

Physics 111 Student, Spring 2016

Therefore it can be helpful to start this discussion with a focus on greenhouses in gardens here on Earth

Question 4.7 What is the greenhouse effect that occurs within a greenhouse in a garden?

 To explore the greenhouse effect in a greenhouse in a garden,  you will need:

• 2 identical clear glass or plastic containers,
• 2 thermometers that agree on the same number for room temperature or 2 digital temperature probes connected to a computer and calibrated so that they read the same temperature
• 2 moist paper towels
• access to a place to put the containers in the Sun or 2 identical lamps with identical incandescent bulbs* or one lamp that can shine equally on both containers with an incandescent bulb
• clear plastic wrap or glass cover for one of the containers.
• How could you use this equipment to explore what happens when an energy source (the Sun or a lamp) shines on an open versus a closed container?
• put two paper towels moistened in the same way in the bottom of each container
• check that two thermometers or two temperature probes connected to a computer give the same reading for room temperature
• place a ruler diagonally in each container with one end on the bottom and the other end resting on an edge of the container
• lay a thermometer on the ruler in each container so that the bulb of the thermometer is not resting on the bottom of the container but is supported at about a third of the height of the container, with the scale facing up so that the thermometer reading is visible (or place a digital thermometer on the ruler in each container)
• record the initial temperatures of the air in the containers; these should be the same
• At the top of your physics notebook page, record the Topic of this exploration. Under Before, draw a picture of the set up. What do you predict will happen to the temperatures of the containers after one container is covered and both are placed in the Sun or under identical lamps with incandescent bulbs placed the same distance away from the containers? Why do you predict this will happen?
• cover one of the containers with a clear glass plate or plastic wrap
• place the containers in the sun or place two identical lamps with identical incandescent bulbs so that they shine on the containers in the same way from the same distance away or place one lamp so it shines equally on the two containers
• monitor the temperatures every few minutes or so
• Under the During section of your physics notebook page, make a table recording the temperatures of the containers or draw or take a picture of the graph drawn by the computer connected to the temperature probes.
• Note any vocabulary that is new to you.
• Discuss your findings and formulate a relevant central idea. In the After section of the physics notebook page, report this central idea and the evidence on which it is based.
• Write a rationale that explains how the evidence supports this idea and why this is important
• Also reflect upon this exploration such as what connections can you make to other experiences? How might you use what you learned in your own classroom?
• What have you learned and what are you still wondering?

Write a summary of what you have learned about the greenhouse effect in a garden and explain why a greenhouse in a garden gets warm when light from the Sun shines upon it.

Complete documenting your exploration on your physics notebook page and writing a summary before looking at an example of student work about exploring the greenhouse effect in garden greenhouses.

• Use lamps with incandescent bulbs rather than lamps with LEDs so that the bulbs warm the air in the containers.

1. Example of student work about exploring the greenhouse effect in garden greenhouses

Greenhouse effect. (Figure 4.11) is a sketch of the experiment done in class.

The student labeled two lamps shining on two clear plastic tubs . Both tubs had wet paper towel s in the bottom and temperature probe s on ruler s leaning on one edge of the tub, with the ruler resting on the bottom. One tub had plastic wrap covering the top of the tub.

  Two plastic tubs were set up under lamps with a wet paper towel in each.  Both tubs also had a temperature probe attached to a ruler so we could track any changes in temperature that may have occurred.  One tub had plastic wrap covering the opening, and the other had no covering.  We predicted what would happen, and many of us thought that the one with plastic would be warmer, since heat could not escape as easily as the tub without plastic wrap.  At the beginning of this experiment both temperatures were about 22°C.  Later in the lab we returned to these tubs to see that the tub with plastic wrap had condensation on the plastic, and was much warmer than the other tub.  At the end of this experiment, the tub without plastic was 27.9° and the tub with the plastic wrap was 35.7°C.  Both tubs had an increase in temperature as a result of heat from the lamp.  However, with the plastic wrap blocking heat (energy) from leaving the tub, it was much hotter than the tub without a blocked exit.  Like this model, if greenhouse gasses block energy from leaving the Earth, then Earth’s temperature will drastically increase.

Physics student, Spring 2016

The greenhouse effect in this model of greenhouses in gardens involves an enclosed container getting warmer when more energy from the light source enters than leaves the container. The warmed air in the open container can circulate outside the container so the open container does not warm as much as the covered container.

Enclosed greenhouses in gardens prevent warmed air from circulating with cooler air outside. In addition, the garden greenhouse may be made out of glass that transmits visible light but not infrared light. Although the plants use some of the energy they absorb to grow, they also emit infrared radiation as they warm, as do the other contents of the greenhouse such as the soil, tables, and tools. If the infrared radiation cannot travel out through the glass and remains within the greenhouse, the temperature of the contents and the air increases. This mechanism differs from what happens when light from the Sun shines on the entire Earth, but the overall effect, an increase in temperature because of energy that does not leave the system, is the same.

If more energy enters than leaves, a system warms up. Within a garden greenhouse, the owner can use vents to modulate the energy flow in and out if the greenhouse gets too hot (see, for example, https://www.advancingalternatives.com/blog/getting-started-greenhouse-ventilation-systems/.  With a greenhouse effect operating within the entire Earth, however, what can the Earth’s “owners” do if the Earth gets too hot? That is the issue that concerns scientists and others convinced on the basis of evidence that the Earth is warming up now much more rapidly than in the past.

B. Considering what happens during the greenhouse effect on a global scale

Question 4.8 what is the greenhouse effect in the context of the entire earth.

• With your group members, talk about the greenhouse effect on a global scale.
• Where does this energy go?
• What changes does it undergo while on Earth?
• How does it leave the Earth?
• Plan and practice briefly what each group member will say when presenting your group’s diagram to the whole group.
• What patterns do you notice in these presentations?
• How are the groups’ ideas similar? How are they different?
• How do they help you think about the greenhouse effect on the Earth?

1.  Examples of students’ initial diagrams about the greenhouse effect

As shown in Fig. 4.12, Group 3’s diagram portrays the basic idea of the greenhouse effect, that thermal energy travels in rays from the Sun to the surface of the Earth and some of this thermal energy travels back out from the surface through the atmosphere to space. Some energy travels from the surface into the atmosphere but is trapped and returns back to the surface. The atmosphere includes two gases, water vapor and carbon dioxide that are relevant to this process.

As shown in Fig. 4.13, Group 5’s diagram portrays the basic idea of the greenhouse effect with some details. These include that rays from the Sun heat up the surface of the Earth ; that some rays cannot penetrate the atmosphere due to water vapor; that some rays bounce back and forth between the Earth’s surface and  clouds in the atmosphere ( It’s a TRAP!) , and some rays escape out to space, which raises an interesting question, does light disappear?? in space because Space is dark .  A red star draws attention to the statement light can only penetrate the atmosphere if it is not blocked by clouds!

As shown in Fig. 4.14, Group 2’s diagram portrays the basic idea of the greenhouse effect with some additional details. The Sun sends rays in many directions, including toward Earth . Implied is that some of these rays get through the atmosphere and interact with the surface, which keeps the earth warm – also heats it up! The surface includes our classroom, Room 328 , within a building within our country. Three clouds represent what happens in the atmosphere:   a cloud , this is also a cloud…and so is this. Just so you know . The water vapor heats up – doesn’t allow the light to go through.  The atmosphere contains : gases…oxygen and nitrogen.  These students recognized that the Sun affects other planets and they suggest use your imagination to consider the Sun’s effect there.

The students moved their chairs to form a circle and each group presented their whiteboard to the others. These examples demonstrate that the students already had useful knowledge about the importance of the Sun and the atmosphere, about some of the relevant processes, and about their effects. Many of the details needed elaboration and/or refinement but the small groups were able to make reasonable first attempts at creating these complex diagrams. The actions of talking with one another in the small groups, creating their group’s initial greenhouse effect diagrams, and sharing these ideas and diagrams through the circle conversation set the context for studying a controversial and complex topic in a respectful way.

2.  Greenhouse effect diagram provided by the Intergovernmental Panel on Climate Change

The Intergovernmental Panel on Climate Change (IPCC, www.ipcc.ch ) is an organization with 195 member countries through which scientists work together to collect and analyze information about climate change from studies all over the world. Figure 4.15 presents a diagram prepared by this organization to represent what happens to the energy that radiates to the Earth from the Sun.

• What do each of the three yellow rays represent?
• What does the narrow reddish ray represent?
• What does the thick reddish ray represent?
• What does each of the orange rays represent?
• Put “greenhouse effect diagram” in your computer browser and view the many versions available for representing the greenhouse effect. Select one or make your own and write your own interpretation of a diagram presenting the greenhouse effect.

3. Example of student’s written work about the greenhouse effect on the entire Earth

I went to the Internet to learn more about the process and the flow of energy surrounding the greenhouse effect. I came upon this diagram:

I used this diagram to help create my own diagram, because I learn best though my own creations. I decided to make a diagram that had steps to show how the radiation from the sun goes through a course to heat up the earth:

• Solar radiation is emitted from the sun, headed toward Earth.
• Most of the sun’s radiation is absorbed by the earth’s surface, thus warming the earth.
• Some of the solar radiation is reflected back out to space by the earth surface and atmosphere.
• As the solar radiation heats up the earth’s surface and lower atmosphere, the radiation is converted into thermal energy called infrared radiation.
• Some of the infrared radiation escapes Earth’s atmosphere, but most of it is absorbed and re-emitted to the earth by the greenhouse gasses in the atmosphere, warming the surface even more.

The earth should be able to keep a proper balance of energy in and energy out in order to keep the surface temperature stable for our current ecosystems; however this is no longer true. The earth’s “energy budget” has been disrupted by the presence of more than the natural amount of greenhouse gases in our atmosphere. Deforestation, excessive use of fossil fuels, and massive beef consumption all are factors that contribute to excess greenhouse gasses such as carbon dioxide and methane. Infrared rays have a hard time passing though these gases in the atmosphere, trapping more from escaping. This means that the earth is receiving the same amount of energy from the sun as it always had, but it is unable to release a balanced amount back out to space, throwing off the energy budget. Unfortunately, while there are things we as humans can do to aid in this issue, many people are not willing to make the necessary changes in order to save the planet.

Physics Student, Fall 2016

4. Nuances about the greenhouse effect and the Earth’s energy budget

A computer simulation provides many opportunities for students to explore various aspects of the greenhouse effect on their own or as part of small group activities in class, https://phet.colorado.edu/en/simulations/greenhouse/ . Some students are curious about what it means for the infrared radiation to be “trapped” by the green house gases. Some have questions about the details involved in what happens to the energy entering and leaving the Earth’s system. This section provides additional information for those interested.

(a) Mechanism that underlies the statement that energy is “trapped” by greenhouse gases. Discussions of the greenhouse effect often refer to energy being “trapped” by greenhouse gases in the atmosphere. What are greenhouse gases and what does being “trapped” mean in this context?

The Earth’s atmosphere is composed of a mixture of gaseous molecules (see, for example, https://climate.ncsu.edu/learn/climate-change-lessons/    (Part 1, slide 3, Earth’s Atmosphere). Most of the atmosphere consists of nitrogen molecules (N 2 ) and oxygen molecules (O 2 ). These molecules transmit the sunlight shining through them. Greenhouse gases, however, are molecules that interact with infrared radiation from the Sun as well as with infrared radiation emitted from the surface of the Earth. The major greenhouse gases are:

• water vapor, formed by two atoms of hydrogen bonded to one atom of oxygen, H 2 O
• carbon dioxide, formed by one atom of carbon and two atoms of oxygen, CO 2
• methane, formed by one atom of carbon and four atoms of hydrogen, CH 4 .

The greenhouse gas molecules in the atmosphere “trap” energy by absorbing infrared radiation and then emitting infrared radiation in all directions, including back toward the surface of the Earth. These gases absorb and emit infrared radiation by vibrating in complex ways. Compare, for example, the Phet simulations of infrared versus visible photon absorption by methane, carbon dioxide, water, nitrogen, and oxygen molecules ( https://phet.colorado.edu/en/simulations/greenhouse/ ). Also see information about the effect of infrared radiation on the atmosphere ( http://energyeducation.ca/encyclopedia/Infrared_radiation  and https://www.youtube.com/watch?v=AauIOanNaWk  ) for forms of vibration in carbon dioxide molecules. A diagram of such vibrations is shown in Fig. 4.18.

The black dot represents a carbon atom, the two clear dots represent the oxygen atoms and the coils of springs represent the chemical bonds holding these atoms together as one molecule. The vibrations may involve (a) the two oxygen atoms both moving away from the carbon atom, (b) one oxygen atom and the carbon atom moving toward each other while the other oxygen atom moves away, or (c) the carbon atom moving one way perpendicular to the bonds while the two oxygen atoms move in the opposite direction.

This mechanism of the greenhouse gas molecules absorbing energy by vibration differs from the mechanism creating the greenhouse effect in greenhouses on earth. Green houses made out of glass panes that do not transmit infrared radiation warm up when incoming visible light is transmitted through the glass panes, absorbed by the contents of a greenhouse, emitted as infrared radiation, but not transmitted back out through the glass panes. Also, the greenhouse effect can occur simply by enclosing a container as in the exploration described in Question 4.7. However, the effects are the same in that the temperature of a system increases if more energy enters a system than leaves it. See  ( https://phet.colorado.edu/en/simulations/greenhouse/  ) to explore the difference between the greenhouse effect constrained by glass panes and open to the Earth’s atmosphere.

(b)  Details about what happens to energy entering and leaving the Earth’s system. Figure 4.19 presents a more detailed analysis of what would happen to the energy radiated from the Sun to the Earth during the greenhouse effect process if the Earth’s energy budget were balanced. To be in balance:

• the incoming energy at the edge of the atmosphere should equal the outgoing energy at the edge of the atmosphere;
• the incoming energy within the atmosphere should equal the outgoing energy within the atmosphere and
• the incoming energy absorbed by the surface of the Earth should equal the outgoing energy at the surface.

• What happens at the edge of the atmosphere if the Earth’s system is in balance? The thick yellow ray represents the incoming energy from the Sun (100%). The thinner yellow ray at the upper left corner of the diagram represents that 29% of that energy would be reflected back out into space from clouds, the atmosphere, and the surface. The somewhat thick red ray near the top right of the diagram represents that 71% of that energy would pass back out of the Earth’s atmosphere into space. If the Earth’s energy budget were in balance, the total incoming radiation would be balanced by the total outgoing radiation after reflection by the clouds, atmosphere and surface as well as after various absorption and emission processes within the atmosphere.
• What happens within the atmosphere if the Earth’s system is in balance? The thin yellow branch of the incoming ray that points into the atmosphere represents the 23% of the incoming energy absorbed by the atmosphere. Also entering the atmosphere are three sources from the surface: convection as in the sunny day at the beach (5%), evaporation (25%), and surface radiation (117%) for a total of 170%. Leaving the atmosphere is energy emitted by the atmosphere (50%), emitted by clouds (9%), and energy from the surface that gets through the “atmospheric window” directly out to space (12%) for a total of 71% and also energy emitted from greenhouse gases back in the direction of the surface (100%) for a total of 171%, which is balanced (the extra 1% probably due to rounding).
• What happens at the surface of the Earth if the Earth’s system is in balance? Incoming energy absorbed by the surface would be transferred to the atmosphere by several processes: The thin waving red ray, pointing upward, represents transfer of the incoming energy through convection (5%) in ways similar to those described in explaining sea breezes in Unit 3. Air warmed by the surface by conduction, expands, rises into the cool upper atmosphere, and cools as energy flows from the warm air into the cooler surrounding atmosphere. The red ray made out of horizontal segments, pointing upward, represents transfer of energy from the surface to the atmosphere through evaporation (25%) such as from puddles, streams, oceans and through transpiration by plants. When moist air is warmed, rises, and cools, the gaseous water releases energy as it condenses into droplets, forming clouds. The thick red ray with the arrow pointing upward represents the transfer of energy from the surface to the atmosphere when the surface emits infrared radiation (117%) at a rate determined by its temperature. The total energy from the surface to the atmosphere would be 148%. Some gases such as water vapor, carbon dioxide, and methane absorb most of the infrared radiation and re-emit it in all directions, including back down toward the surface of the Earth (100%), represented by the red ray with the arrow pointing downward. There would be a net sum of the energy emitted from the surface that would equal the incoming energy that is absorbed by the surface. Also some of the energy from the sun shines directly on the surface (48%) represented by the yellow ray pointed toward the surface. The energy reaching the surface (148%) would balance the energy leaving the surface (148%).

As the amount of water vapor, carbon dioxide, and methane gases in the atmosphere increases, however, more infrared radiation will be absorbed, emitted in all directions, including back toward the surface, with more and more energy staying in the Earth’s system, increasing the global temperature of the Earth. For more information about the Earth’s energy budget, search on the Internet for “Earth’s energy budget” and view, for example, a series of pages (4-7) at https://earthobservatory.nasa.gov/Features/EnergyBalance/page4.php

To deepen understanding about the influence of light and thermal phenomena on global climate read some students’ reflections about engaging a friend in learning about the greenhouse effect.

5.  Examples of student work reflecting upon engaging a friend or family member in learning about the greenhouse effect

The students explored websites that discuss the greenhouse effect and selected one or more to use in engaging a friend or family member in learning about the greenhouse effect. One student wrote:

I chose to explore the greenhouse effect with my two friends. Prior to exploring the website, they told me that they knew that the greenhouse effect was related to “gases getting trapped in the atmosphere and heating it up.” The website, https://energyeducation.ca/encyclopedia/Greenhouse_effect     is provided by Energy Education Canada. Both of them said that is was very helpful to observe a diagram depicting the greenhouse effect, which aided their understanding of the readings provided by the website. One of my friends said that the thing that hindered his understanding was that the arrow accompanying the text that reads, “Infrared radiation is emitted by the Earth’s surface,” emerges from water, rather than from land or a combination of land and water, which led him to believe that the diagram was indicating that only water emits infrared radiation.

Both of them asked me what infrared radiation is, and I explained to them that infrared emits energy in the form of heat, as well as that the color of an object when observed through night vision goggles indicates how much infrared radiation it emits, with objects that appear red emitting a lot of infrared radiation, and objects that appear blue emitting much less infrared radiation. Neither of them had prior knowledge of infrared radiation, and they stated that this was the most interesting thing they learned from the website. Additionally, neither of them had ever heard the term “enhanced greenhouse effect,” which is what is referred to in discussions of the greenhouse effect and climate change.

When I asked them how they felt about the potential consequences of climate change, including rising sea levels, they both wondered if climate change will drastically affect them personally in their lifetime. Additionally, they wondered how much of the greenhouse effect is due to livestock, which sparked an interesting discussion about how many cows and chickens are on the earth, as well as how the raising and consuming of animal products contributes to climate change. This experience taught me that sometimes a conversation may not go the way you expect it to, but it can still lead to beneficial discussion and learning. I was not expecting to discuss livestock with them, but they were very interested in the various layers of climate change, and I felt that they gained a lot from the website and grew in their curiosity throughout our discussion.

Both of my friends engaged in the NGSS Science practice of obtaining, evaluating, and communicating information during this exploration. Not only did they obtain information from the website that I showed them, but when our discussion shifted toward the effect of livestock farming on climate change, they both began to research articles on the topic, obtained knowledge from them, and shared that knowledge to enhance our discussion. They also engaged in the NGSS crosscutting concept of systems and system models, as the diagram from the website helped them to envision the system of the greenhouse effect and see how it works.

Physics student, Winter 2018

Another student chose to talk about the greenhouse effect with her father:

So I did this assignment with my father. I had a feeling it would not go well but I wanted to show him evidence of climate change. I first started by asking him what he knew about the greenhouse effect. He said “It causes global warming, climate change, and has something to do with too many cows giving off ethanol into the air.”  I then decided to show him the NASA website  https://climate.nasa.gov/causes/  because it was my favorite. We looked over the website. It was easy to navigate the website and the pictures were really helpful. The pictures helped the most and the website even had before and after photos of bad events around the world. We talked about the future effects of global warming but he did not ask any questions. After we finished exploring the website I explained the model diagram of the greenhouse effect again and explained that humans are the real cause of this. I then asked what my father thought about global warming. He said “the planet has always been changing and it always will.” So after showing all this proof to my father he then says “it’s propaganda.” My father just nodded while looking at the website.

I think my father did not have any questions because he is closed off and does not want to hear that humans are causing the Earth to heat up and it could harm/ is harming the environment. I went into more detail about the greenhouse gasses being the real cause and that human activity is the cause but he just wasn’t interested. Through this experience I think I have learned that it is hard to teach topics that people already think they know or feel strongly one way about. No matter how much evidence is shown. It is discouraging to think about how many people are out there, unable to face the facts that global warming is real. The older I get, the more I realize a lot of people do not listen to science and just believe what they want to. For example, learning about vaccines. It does not matter how much we show the scientific evidence of the safety and success of vaccines, people still believe they cause autism and make people sick.

The crosscutting concept of cause and effect is strongly shown in the topic of greenhouse gasses because we are showing that human activity is causing an effect on the Earth, causing it to warm up. One NGSS practice used was modeling. We used the model given on the website to help explain the greenhouse effect.

These students had very different experiences, with a welcome sharing of thoughts and additional learning for all concerned in the first and with a reluctant listener not yet open to alternative points of view in the second. Afterward, the second student raised in class the question of what to do. This is a difficult question to which there are no easy answers. To what extent is one willing to risk personal relationships in discussing controversial topics? How can one convey information based on evidence effectively? How can one keep one’s own spirits up in the face of such discouraging encounters? Our hope is that the small group activities and whole group discussions in class will at least make possible more positive experiences as well as increase information getting to the reluctant listeners whose friends or relatives choose to risk the conversation.

Exploring Physical Phenomena Copyright © 2020 by Emily Van Zee & Elizabeth Gire is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License , except where otherwise noted.

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RealClimate

Climate science from climate scientists...

What is the best description of the greenhouse effect?

12 Feb 2016 by rasmus

What exactly is the greenhouse effect? And what does it look like if we view it from a new angle? Of course, we know the answer, and Raymond Pierrehumbert has written an excellent paper about it ( Infrared radiation and planetary temperature ). Computer code used in climate models contain all the details.

But is it possible to provide a simple description that is physically meaningful and more sophisticated than the ‘ blanket around earth’ concept? I wanted a description that could be grasped by physicists. Without the clutter of too much details – just the essentials. A ‘back-of-the-envelope’ type derivation of the greenhouse effect.

The starting point was to look at the bulk – the average – heat radiation and the total energy flow. I searched the publications back in time, and found a paper on the greenhouse effect from 1931 by the American physicist Edward Olson Hulburt (1890-1982) that provided a nice description. The greenhouse effect involves more than just radiation. Convection also plays a crucial role.

How does the understanding from 1931 stand up in the modern times? I evaluated the old model with modern state-of-the-art data: reanalyses and satellite observations.

With an increased greenhouse effect, the optical depth increases. Hence, one would expect that earth’s heat loss (also known as the outgoing longwave radiation, OLR ) becomes more diffuse and less similar to the temperature pattern at the surface.

An analysis of spatial correlation between heat radiation estimated for the surface temperatures and that at the top of the atmosphere suggests that the OLR has become more diffuse over time.

The depth in the atmosphere from which the earth’s heat loss to space takes place is often referred to as the emission height . For simplicity, we can assume that the emission height is where the temperature is 254K in order for the associated black body radiation to match the incoming flow of energy from the sun.

Additionally, as the infrared light which makes up the OLR is subject to more absorption with higher concentrations of greenhouse gases ( Beer-Lambert’s law ), the mean emission height for the OLR escaping out to space must increase as the atmosphere gets more opaque.

There has been an upward trend in the simple proxy for the emission height in the reanalyses. This trend seems to be consistent with the surface warming with the observed lapse rate (approximately -5K/km on a global scale). One caveat is, however, that trends in reanalyses may be misleading due to introduction of new observational instruments over time (Thorne & Vose, 2010) .

Finally, the energy flow from the surface to the emission height must be the same as the total OLR emitted back to space, and if increased absorption inhibits the radiative flow between earth’s surface and the emission height, then it must be compensated by other means.

The energy flow is like the water in a river: it cannot just appear or disappear; it flows from place to place. In this case, the vertical energy flow is influenced by deep convection, which also plays a role in maintaining the lapse rate.

A popular picture of the greenhouse effect emphasises the radiation transfer but does not explicitly account for convection. As a result, it fails to explain the observed climate change.

Hulburt’s old model from 1931 included both radiative energy transfer and convection. It has now been validated against state-of-the-art data, and non-traditional diagnostics show a physically consistent picture.

An increased overturning can even explain a hypothetical slowdown in the global warming, and the association between these aspects can be interpreted as an entanglement between the greenhouse effect and the hydrological cycle, in which a reduced energy transfer associated with increased opacity is compensated by an acceleration of the hydrological cycle. This also makes a link with clouds.

The old conceptual model also explains why the so-called ‘saturation’ (which doesn’t exist on Venus ) is a red herring, which is also explained in the report by the Copenhagen Diagnosis . I think those who present this argument have a poor understanding of what the greenhouse effect is all about.

A bold proposal: One way to view the greenhouse effect is the vertical distance between the place where incoming energy is deposited and where the average outgoing heat loss takes place . This distance depends on the concentration of greenhouse gases, and at what height the OLR can escape to space without being reabsorbed by air above.

The graphics below provides a crude illustration: the OLR is determined by Stephan-Boltzman’s law and the temperature at the same height, and the surface temperature is then given by the emission temperature , the emission height, and the lapse rate.

A more elaborate description is given in (Benestad, 2016) , which was inspired by two posts here on RealClimate ( here and here ).

Not all of my colleagues may agree with my description of the greenhouse effect; it was a struggle to get this paper published. To my surprise, I realised that there are scholars with different ideas about it. However, I hope that my description will lead to more discussions and debate about the over-arching principles and our basic understanding of this phenomenon.

This also touches upon the question of climate sensitivity which is merely defined in terms of temperature change. A response to increased greenhouse gases could involve both a global warming and a speed-up of the hydrological cycle if the greenhouse effect and the hydrological cycle are intertwined. In other words, there could be more dramatic changes to the rainfall patterns than the temperature, but this doesn’t necessarily imply that the climate is less sensitive to the forcings.

• P.W. Thorne, and R.S. Vose, "Reanalyses Suitable for Characterizing Long-Term Trends", Bulletin of the American Meteorological Society , vol. 91, pp. 353-362, 2010. http://dx.doi.org/10.1175/2009BAMS2858.1
• R.E. Benestad, "A mental picture of the greenhouse effect", Theoretical and Applied Climatology , vol. 128, pp. 679-688, 2016. http://dx.doi.org/10.1007/s00704-016-1732-y

About rasmus

D. Phil in physics from Atmospheric, Oceanic & Planetary Physics, Oxford University, U.K. Funding: governmental (Norwegian Science Foundation)

Reader Interactions

85 responses to "what is the best description of the greenhouse effect".

12 Feb 2016 at 5:47 AM

Rasmus, I’m glad our paper made it – congratulations. I think it is a great contribution.

A way of looking at radiative transfer that I find useful but rarely mentioned is the Rosseland model. For some reason the best account I have seen is in a CFD manual . Maybe others know it under different names At high opacity, heat transfer is diffusive, with diffusivity inversely proportional to absorptivity. The rule of thumb for accuracy seems to be OD>3, so it doesn’t really apply to atmosphere (also it is a gray body model). But the concept helps. The “diffusive” flux induces a temperature gradient, which steepens the lapse rate. That is my way of seeing that the radiative equilibrium gradient tends to convective instability.

But does it get there? You have shown observations which seem to say that it does, at least sometimes. On the other hand, observed lapse rates seem to fall well short of DALR. Maybe moisture and latent heat is enough to make he difference? I see you talk about this toward the end of section 4.

Sorry this is a rather hasty comment, but it’s late here – I’ll look forward to reading the discussion in the morning.

12 Feb 2016 at 6:38 AM

I cite Hulbert’s paper as the first description of a radiative-convective model. It wasn’t until 1964 that Manabe and Strickland put one on a computer, giving us one of the first estimates of climate sensitivity due to doubled CO2 (among other things). But Hulbert figured the idea out first.

12 Feb 2016 at 7:20 AM

This video at around the 19 minutes mark http://topdocumentaryfilms.com/earth-the-climate-wars/

Laboratory experiment with CO2 and a candle and infrared visualisation. Showing the heat trapping properties of carbon dioxide.

12 Feb 2016 at 8:30 AM

Since you have added convection to the list, what about adding conduction? Any discussion on that possibility? It certainly seems to have some importance in surface level heat transfer.

12 Feb 2016 at 8:47 AM

The IR opacity sets the altitude from which the lapse rate is suspended. Mountains are cool, Death Valley is hot. Hoisting the lapse rate run with altitude by increasing the IR opacity raises Death Valley to the Plains and the Plains to the mountains. This seems like a widely understandable description.

12 Feb 2016 at 9:25 AM

Very interesting also from an historiographic point of view: Guy Callendar’s first paper on CO2-induced warming came out in 1938. Callendar has had considerable retrospective credit for resurrecting interest in the topic. I wrote in my article on Callendar that:

He read the papers of Fourier, Tyndall, Arrhenius, Ekholm and others, recording information and comments in voluminous notebooks. He saw that the work, though then not held in high regard, had merit—but was badly in need of updating.

This would have been in the years from about 1930 on. Was Hulburt one of the ‘others’? If so, how much did he contribute to the revival of interest in the question? Anybody have a copy of Fleming’s bio of Callendar they can check against?

12 Feb 2016 at 9:40 AM

The next step is to try and handle a simplified day/night model. No longer can you assume pointwise thermal equilibrium, but must include heat storage terms. Also convection in the lower atmosphere shuts down at night, and you often get a low level temperature inversion. But time integration of the atmosphere becomes messy, because of the behavioral discontinuity between a convective lapse rate, and no convection.

12 Feb 2016 at 10:44 AM

“To my surprise, I realised that there are scholars with different ideas about it.” – rasmus

This could be the least surprising scientific discovery of 2016! :-)

But please, tell us more – what was the pushback to your article about?

12 Feb 2016 at 11:16 AM

I like the thermal resistance model. Heat flows from a high temperature reservoir (the Sun) through Earth to the cold reservoir (the Cosmos). Greenhouse gases decrease the thermal conductance from Earth to space.

I like the photon tracking version of a simple explanation. Here is one version of that version. Corrections or improvements to it would be welcome.

The Greenhouse Effect 101. To balance incoming short-wave solar energy, the earth constantly radiates long-wave heat energy (infrared photons) back out to space. This is how the earth maintains a fairly constant temperature. Some of the outgoing radiation is absorbed & re-radiated back to earth by various trace gases like carbon dioxide, water vapor, methane, & ozone. This gives us the greenhouse effect, & keeps the earth from becoming a ball of ice. The warming effect works according to the laws of quantum physics. When an infrared heat photon of a specific energy collides with a greenhouse gas molecule, that photon will be absorbed & an excited electron will jump to a higher orbit. However, that new electron orbit is not stable & will soon fall back to its “rest” energy level & emit a photon of the same energy level (frequency) that was absorbed. While the original photons were on their way out to space when they were absorbed, the new photons will be radiated in a random direction. Some will continue up, some will return toward earth. It is this back-to-earth radiant energy that causes the underlying earth to warm to a new equilibrium temperature. Because of its complexity, only computer models can adequately quantify the greenhouse effect. The exact magnitude of this effect caused by gases humans are adding to the air is not yet precisely understood, but all models to date have shown various amounts of warming. None show the earth cooling or remaining the same.

12 Feb 2016 at 11:29 AM

A non-mathematical description of the GH effect is from the Barrettbellamy website: The Earth’s atmosphere is moderately trans­parent in the visible part of the spectrum and the majority of the solar radiation can pass through the atmosphere without being absorbed and is absorbed by the surface which is thus warmed. On the other hand, minor atmospheric constituents, the greenhouse gases, of which water vapor is the most important, ab­sorb strongly in the infrared region which is where the Earth’s surface emits. The atmosphere is largely opaque to the terrestrial infrared heat radiation.

What happens when the atmosphere absorbs radiation emitted from the surface of the planet? The atmosphere cannot steadily accumulate energy or it would become hotter and hotter. Instead, it emits radiation at the same rate as it absorbs when it has become hot enough to establish radiative equilibrium. The radiation is reemitted in all directions, and a substantial part of it is intercepted and absorbed by the surface. So the surface of the planet is heated not only by direct sunlight but also by infra­red radiation emitted by the atmosphere. For this reason the surface of a planet must radiate away more energy than it receives directly from the Sun, and the surface can have a temperature that exceeds the effective temperature of the planet. This is the greenhouse effect in simple outline

According to Fleming p. 70, Callendar’s notes do refer to Hulburt’s 1931 paper which Callendar said supports the CO2 theory. Hulburt was the first to add anything new to the subject since Arrhenius. Hulburt has a nice equation for heat balance that any student can understand. What is most important though is that no one paid any attention to Hulburt’s paper. Callendar did not cite it in his 1938 paper.

In a 1956 article in the popular magazine Weatherwise, Hans Panofsky (1918-1988) of Pennsylvania State University reviewed the different “Theories of Climate Change.” He classified them under the headings (1) Earth’s Crust: shifts in the position of the poles and mountain building; (2) Atmospheric: CO2 variations; and (3) Astronomical: changes in the Sun’s intensity or the Earth’s orbit. He did not mention Hulburt. Hulburt’s paper, which could have made a real difference, went virtually unnoticed and uncited.

12 Feb 2016 at 12:18 PM

//”A bold proposal: One way to view the greenhouse effect is the vertical distance between the place where incoming energy is deposited and where the average outgoing heat loss takes place.”//

I think this only makes sense in the limit where the atmosphere is perfectly transparent to solar radiation.

12 Feb 2016 at 1:29 PM

Hulburt’s paper deserves to be famous as a neglected discovery. To be sure, including convection should have been obvious… but it was not obvious to others for decades. Why was the paper overlooked (and almost never cited until recently)? I suspect its original sin was being published in the Physical Review, a top journal but one that otherwise was of not interest to climate/meteorology researchers of the time. Further, Hulburt was a government physicist who mainly worked on radio propagation, not someone in their community. The lesson is that it’s not enough to publish, scientists must also take some trouble to publicize their work to relevant communities.

12 Feb 2016 at 3:00 PM

#12–James, thanks for that response!

So Callendar was aware of the Hulburt paper. I wonder how well he knew it? Callendar’s paper emphasized the radiative effect at the surface, with arguably unfortunate effect. (Eg., Gerlich and Tscheuschner.)

Had Callendar latched on to the Hulburt model, things might have gotten quite a different spin, perhaps, in terms of the ‘mental model’ at least.

The 1938 paper was published with a ‘discussion’ which appears to have been viva voce. From it:

“…Callendar said he realized the extreme complexity of the temperature control at any particular region of the earth’s surface, and also that radiative equilibrium was not actually established, but if any substance is added to the atmosphere which delays the transfer of low temperature radiation, without interfering with the arrival or distribution of the heat supply, some rise of temperature appears to be inevitable in those parts which are furthest from outer space.”

That was in response to a comment by Sir George Simpson that:

“…it was impossible to solve the problem of the temperature distribution in the atmosphere by working out the radiation… the temperature distribution in the atmosphere was determined almost entirely by the movement of the air up and down. This forced the atmosphere into a temperature distribution which was quite out of balance with the radiation…”

12 Feb 2016 at 3:05 PM

I like the attempt to provide a simple description of the greenhouse effect. However, I find it misleading to mention the Beer-Lambert law when discussing the outgoing longwave radiation (OLR). The Beer-Lambert law can be applied on the incoming solar radiation, but it is not valid when emission is significant, that is the case for OLR. Yes, the emission from the surface will be absorbed following the Beer-Lambert law, but the strength of the emission is directly coupled to the absorption efficiency and this coupling is essential to understand the greenhouse effect.

In short, if the absorption is zero at some point in the atmosphere, at some wavelength, there is no emission from this point, at this wavelength. If there is absorption, there will also be emission. That is, absorption and emission can not be treated separately. For further reading, google “Schwarzschild’s equation”.

I am not sure about the reference to “saturation” (and I have not read the Copenhagen report), but that could be associated with this issue. If the Beer-Lambert law would totally govern OLR, I would say that a saturation could occur.

12 Feb 2016 at 4:38 PM

Rob Quayle @10 wrote: “ When an infrared heat photon of a specific energy collides with a greenhouse gas molecule, that photon will be absorbed & an excited electron will jump to a higher orbit. However, that new electron orbit is not stable & will soon fall back to its “rest” energy level & emit a photon of the same energy level (frequency) that was absorbed. ”

Please correct me if I am wrong, but this part does not seem right to me. My understanding is that photon absorption and excitation of a greenhouse gas molecule causes the molecular bonds to vibrate and/or bend, akin to a spring stretching and compressing and/or bending. That said, since molecular bonds are in fact shared electrons, the vibration/bending may well involve electron valence jumps, my understanding is fuzzy on that. In any case, although this molecular excitation is not stable and will soon spontaneously relax with the emission of a new photon, in the lower to mid troposphere relaxation is far more likely to occur through collision with another gas molecule than through emission of a new photon, thereby warming the atmosphere directly.

13 Feb 2016 at 12:38 AM

17 Jim Eager: “Infrared radiation and planetary temperature” by Raymond T. Pierrehumbert gives some of the greater complexity, but not too much. I take it that the quantum mechanics becomes very complicated very fast. Thanks Rasmus for the link. That thing about vibrations in bending versus what the electrons are doing is farther into quantum mechanics than I got too. I could guess that it could have something to do with p orbitals, but that is just a guess.

Thanks for the post and for Pierrehumbert’s article. I like them both and the animated graphic. Saturation fallacy: Now I know where that comes from. Tell Raymond T. not to ride a bicycle on the snow.

13 Feb 2016 at 2:43 AM

The main label in figure 1 says “relative humidity”, but the caption says total column water vapor — typo?

13 Feb 2016 at 3:20 AM

I agree with Jim Eager. The discussed statement is “When an infrared heat photon of a specific energy collides with a greenhouse gas molecule, that photon will be absorbed & an excited electron will jump to a higher orbit. However, that new electron orbit is not stable & will soon fall back to its “rest” energy level & emit a photon of the same energy level (frequency) that was absorbed.”

This comment seems to imply that emission only occurs when there is an absorbed photon, but this is not the case. It is rather the opposite, there is no direct connection between incoming radiation and emission.

To go on into details, this is in fact related to my comment above (@16), by something denoted as local thermodynamic equilibrium (LTE), that is assumed by the “Schwarzschild’s equation”.

LTE is a valid assumption for the atmosphere below about 50 km. LTE is a difficult concept, but it implies that the distribution of (the relevant) quantum states of the molecules is governed by the local temperature, not by radiation. This is basically explained by Rob in his last statement. Relaxation will most likely occur by collisions between the molecules, and not by emission of a photon. That is, LTE is valid when there are frequent collisions between the molecules. This is not the case at high altitudes, and LTE can not always be assumed in e.g. the mesosphere (but the exact altitude limit differs with wavelength).

To be clear, absorbed incoming radiation will tend to increase the local temperature, that indirectly can affect the emission. However, the main point is that there is no direct coupling.

This can seem to be contradictory to my comment above that absorption and emission can not be treated separately. What I meant is that you need to include both effects into your expression for radiative transfer, and then you get the Schwarzschild’s equation. When I wrote “absorption” I meant the efficiency for absorption, not the actual amount of radiation absorbed. I was a bit sloppy there, in an attempt to be brief. Being more detailed I would express is it as: If an air parcel is totally transparent at some frequency, there is no emission at this frequency. But if the air parcel has the potential to absorb at the frequency, then there will be emission. Note, for emission it suffices that the air parcel has the potential for absorption, no radiation has to be absorbed to induce emission. In technical terms, the absorption and emission coefficients (in e.g. 1/m) are equal.

Sorry if this got complicated, but nature is not always simple, especially when quantum physics is involved as happens to be the case here. But note that all this is of course taken into account in climate models, as well as when analysing remote sensing observations of the atmosphere (my profession).

13 Feb 2016 at 5:10 AM

“What exactly is the greenhouse effect?” It is easy to define the GHE, but it is difficult to calculate it. Consider a planet which is covered by a thin (some km’s thick) special layer: The absorption of the sunlight in the visible is small and the absorption of the IR radiation is large. The GHE is the difference of the surface temperature with and without the layer. The calculation is easy for a glassy planet. In this case the layer consists of fused quartz. Radiative transport through the layer is neglible. The heat transport is determined by the thermal conductivity of the glass which is diffusive and isotropic.So the GHE increases with the thickness and the thermal resistance of the layer. A similar case is the snowball-planet. The difference is that small ice crystals may cause a large albedo. Next we consider an aqua planet: no atmosphere, no land, only oceans. In this the case the radiative transport and the thermal conductivity by diffusion in the layer are neglible compared to convection. Convective transport is anisotropic:vertical and horizontal transport are different. The large meridonial transport indicates that you have to use a nonlocal model to get the right latitudinal dependence of the surface temperature. Next the GHE gas planet: the layer consists of an atmosphere with green house gases. In this case the radiative transport may not be neglible in the layer. Convective transport is complicated: the adiabatic lapse rate is modified by the condensation of water vapor. I doubt that a simple calculation can result in a good estimate of the GHE. In the abstract of the publication of E.O. Hulburt (1931) ‘The Temperature of the Lower Atmosphere of the Earth” a temperature rise of 4°C is predicted for doubling the CO2-concentration in the atmosphere. I think this estimate is too large. Unfortunately, this historical paper is paywalled. So I decided: fortget it and make your own calculations.

13 Feb 2016 at 6:21 AM

How about a murder whodunnit concept… Global heating has an unmistakable unique human fingerprint attached to it. Scars and blight on the landscape, acidosis, rapid oxidisation of vegetation.

Pathology of death: asphyxiation and hyperthermic stress by greenhouse gasses; bio-toxic ocean acidification by same. Extreme stresses on environment by out-of-control exponential human population growth.

Cause of death: sudden release of 100’s of millions of years worth of fossil hydrocarbons within the timeframe of 270 years.

Motive and intent of murder: Comes down I’m afraid to nothing more complex or substantial than just basic greed and/or theft coupled with rampant, ego driven ignorance and arrogance with absolutely no thought given to the future. Profile of perpetrator: Sociopathic, delusional and psychotic, as the Buddhist would call it, complete lack of innate awareness on every level.

13 Feb 2016 at 10:46 AM

Thanks Edward, I just downloaded Ray’s Infrared Radiation and Planetary Temperature.

13 Feb 2016 at 11:53 AM

Research Letter A revised picture of the atmospheric moisture residence time

Alexander Läderach1,* and Harald Sodemann1,2

Article first published online: 30 JAN 2016

DOI: 10.1002/2015GL067449

Our diagnostics yield an estimate of about 4–5 days for the global mean residence time, which is about half compared to depletion times that are commonly interpreted as proxies for the residence time. The discrepancies to depletion times are mainly explained by the fact that these are based on simplified representations of precipitation processes. The revised picture given by our results is supported by the overall consistency with the footprints of precipitation producing weather systems in different regions of the Earth.

13 Feb 2016 at 4:50 PM

This description of the GHE seems to imply that the primary mode of energy loss to space is from GHG emission; alternatively, it could also be interpreted to say that the atmosphere is behaving as a blackbody absorber/emitter.

If you look at a graph of the top-of-atmosphere OLR, the majority of power flux is in the region of about 8 to 25 or 30 microns, minus a sharp ozone absorption at 10 microns and a broad CO2 bending mode absorption at 13-17 microns (ignoring the almost continuous water absorption). The implication to me is that the main GHG effect is to warm the surface to a temperature where emission in the most transparent regions of the OLR spectrum is great enough to make up for the reduced transmission in the GHG absorption regions. Clearly convection plays a major role in heat transfer to the mid and upper troposphere, but it is largely irrelevant because greenhouse gas emission is still a smaller amount of energy loss from the planet compared with increased radiation from a warmed up surface through the more atmosphere-transparent portions of the OLR spectrum.

This is an argument based on qualitative examination of the top-of-atmosphere outward bound spectrum and not from any modelling, so I am receptive to more sophisticated argumentation.

13 Feb 2016 at 10:39 PM

This seems like the simplest explanation: To maintain thermal equilibrium, the earth must emit as must radiation energy to space as it receives from the sun. There is a point at the top of the atmosphere where photons make their final escape to space from excited CO2 molecules. Adding more CO2 molecules up there provides more opportunities for them to intercept such photons and redirect that energy downward. Everything after that is just a matter of tracking where the trapped energy goes, not whether it is trapped.

13 Feb 2016 at 11:27 PM

Can anyone comment on the truth of Moncton’s comment on WUWT? He claims: “The official theory is that CO2 warms the atmosphere and the atmosphere warms the surface.” With the apparent luke-warming of the troposphere, he claims that that disproves AGW.

[ Response: No, he’s making things up. Changes in GHGs change the flux of energy into the troposphere, which because of (tropical) convection, tends to react as a whole. The amplification of the signal above the surface is a consequence of the Clausias-Clapeyron equation (defining relative humidity) and its non-linear dependence on the surface temperature. Any surface warming should have the same amplification effect, and GHGs would still warm the climate even if the CC-eqn didn’t have non-linearities. Indeed, the amplification actually reduces the climate sensitivity (since the lapse rate change is a negative feedback). – gavin]

14 Feb 2016 at 4:23 AM

Hello Rasmus,

Thanks for a most interesting paper, and this article. For your information I have brought it to the attention of Roger Helmer MEP, who is the United Kingdom Independence Party spokesman on energy and industry.

My monologue on his blog is archived at: http://archive.is/6DEvk#selection-2151.0-2163.30

You will note that I have already been (un)reliably informed by one of the local denizens that:

RealClimate [is the] Home of arch-Mannipulator Gavin Schmitt and his rapid reaction ‘Crusher Crew’.

Personally, I prefer the ‘Beano’ myself.

More scientific credibility, you see.

[ Response: Their critiques would be more convincing if they actually knew what my name was… – gavin ]

14 Feb 2016 at 5:01 PM

Thanks for a most interesting paper and, particularly, for providing computer code enabling the results to be easily replicated and investigated. It is a great pity that so few professional climate scientists make their code available. If more followed your example, I think it would result in increased confidence in their work and results by scientifically and technically minded people who, quite reasonably, want to convince themselves of the validity of results before they will accept them.

The consistent, near linear, increase in bulk emission altitude that you find over 1979-2011, with a trend of just under 23 m/decade implies, as you say, GMST warming of 0.12 K/decade (0.117 based on your lapse rate of -5.07 K/km). Interestingly, this is almost the same as the forced trend of 0.122 K/decade over 1977-2008 found by Delsole et al. (2011; DOI: 10.1175/2010JCLI3659.1) after excluding unforced multidecadal variability.

[ Response: You know better than that. The DelSole et al decomposition is based on a method that only estimates the forced response based on subjective statistical criteria. It is not a clean decomposition into forced and internal variation. – gavin]

The GMST warming rate of 0.117 K/decade can of course be converted into an estimate of the transient climate response (TCR) by multiplying by the forcing from a doubling of CO2 concentration (3.71 W/m2) and dividing by the trend increase in forcing over 1979-2011. Using the IPCC AR5 forcing estimate timeseries, gives an estimate for TCR of 0.82 K. This is depressed by a positive trend in volcanic forcing, which seems to have a low efficacy, perhaps ~0.5. If only anthropogenic forcing is used (implying an almost zero efficacy for volcanic forcing), the TCR estimate would be 1.34 K.

[ Response: Now “of course” you are just trolling. Just because you can divide a trend by a forcing, that does not imply you are going to have an good estimate of the TCR. As you are well aware, doing this for short periods misses lags in the system and there are substantial uncertainties in the forcing itself, so this is not a particularly strong or useful constraint. It might be that you don’t like the models for whatever reason, but they provide excellent test-beds to demonstrate the utility of these kind of ‘back-of-the-agenda’ calculations. If this calculation doesn’t work for simulations, it won’t work in the real world either. – gavin]

14 Feb 2016 at 5:10 PM

I have made sure Mr. Helmer is aware of the correct spelling of your name Gavin. He has finally deigned to reply to me, but is prattling on about “negative CO2 climate sensitivity”. I feel certain he has yet to read Rasmus’ article, let alone the linked paper.

Looking on the bright side the ad homs have ceased, for the moment at least.

14 Feb 2016 at 8:09 PM

Nic Lewis :

It is a great pity that so few professional climate scientists make their code available. If more followed your example, I think it would result in increased confidence in their work and results by scientifically and technically minded people who, quite reasonably, want to convince themselves of the validity of results before they will accept them.

Oh sure. “Of course” scientists can’t be trusted to report their results truthfully, unless random “scientifically and technically minded people” can pick through their ad hoc data-reduction programs for bugs.

As a scientifically and technically minded person myself, I rely on my scientific meta-literacy to assess the credibility of a report. If a finding is accepted by the National Academy of Sciences, for example, I’m pretty sure I can trust it. For practical purposes, if I hear from a lopsided majority of the scientists who’ve put the time in that GMST will rise if carbon removed from the atmosphere millions of years ago is released back into it, that’s good enough for me. I don’t know about Nic Lewis’s friends, but I’ve got more productive things to do than replicate all science since Archimedes.

14 Feb 2016 at 8:44 PM

Some remarks on the discussions above set off by Rob Quale in 10

A useful marker of Local Thermodynamic Equilibrium is that the distribution of energy in all modes of motion (translational, rotational and vibrational) can be characterized by the same temperature.

A key to understanding what happens when a CO2 (or H2O) molecule absorbs an IR photon is that the radiative lifetime of CO2 is about 1.5 sec while the time between collisions in the atmosphere at the surface is about a tenth of a nanosecond, and it takes about 1000-10,000 collisions on average for vibrational to translational energy transfer. This means that a vibrationally excited molecule can only retain their excitation for a few microseconds.

OTOH, LTE tells you that some proportion of CO2/H2O molecules will be vibrationally excited by collisions at atmospheric temperatures. This produces a steady state population in the CO2 bending mode of about 5%.

This vibrational excitation is characterized by the local temperature, not the temperature of the levels from which radiation is absorbed.

Eli took a shot at a simple explanation http://rabett.blogspot.com/2010/03/simplest-explanation.html

Chris Colose had a more mathematical one https://chriscolose.wordpress.com/2010/02/18/greenhouse-effect-revisited/

But neither of us included the effects of convection although somebunny did point this out in the comments at Chris’

14 Feb 2016 at 9:50 PM

I was hoping Pierrehumbert would provide graphs and equations linking physical variables with temperature as Robinson & Catling did here: http://faculty.washington.edu/dcatling/Robinson2014_0.1bar_Tropopause.pdf

I find the R&C model to be pretty accurate considering it has only one “Up” radiation channel and two “Down” channels: https://diggingintheclay.wordpress.com/2014/04/27/robinson-and-catling-model-closely-matches-data-for-titans-atmosphere/

Currently I am trying to improve the R&C model by adding multiple cloud layers using Finite Element Analysis. This approach worked well for airless bodies: https://tallbloke.wordpress.com/2014/08/27/extending-a-new-lunar-thermal-model-part-ii-modelling-an-airless-earth/

15 Feb 2016 at 3:46 AM

An interesting and useful discussion, but I was mildly surprised to find that I needed to scan down to Jim Eager’s contribution (#17) to see mention of the importance of vibrational/rotational modes in the GHG molecules in causing the heating. GHG molecules (CO2, CH3, H2O…) are typically asymmetric polyatomic molecules, whereas the dominant atmospheric gases (N2, O2) are too tightly bound to absorb at IR frequencies.

As Eli Rabett (#32) points out, the main de-excitation mode will be via a collision with N2 or O2, and the excitation energy of the GHG molecule is removed as kinetic energy of the colliding molecule. The image I have is of a ping-pong ball tossed into a rotating fan – it comes out faster than it went in, and this kinetic energy is then dispersed through the surrounding gas as heat. To use a chemical analogy, GHGs can be seen as catalysts converting radiant energy into heat.

The point of this description is that it directly addresses the fundamental basis of the Greenhouse Effect in a way that can be readily understood by a non-specialist. It doesn’t have to be seen as something mysterious that must be taken on trust.

15 Feb 2016 at 6:27 AM

Personally, I suspect a larger factor influencing confidence in the work and results of climate scientists might be the tendency of some scientifically and technically minded people to over-estimate their competence to comment on the field, often leading them to identify clearly spurious ‘errors’ based on their own lack of comprehension. When such work is widely disseminated to the public, less scientifically and technically minded people may, quite reasonably, find themselves confused as to whose results to trust.

15 Feb 2016 at 11:03 AM

Perhaps it’s tiring to keep getting comments like mine, but have you looked at this and/or commented on it?

http://www.sciencedirect.com/science/article/pii/S0012825215300349

15 Feb 2016 at 11:05 AM

Not sure my first attempt got through… Have you seen and/or commented on this?

15 Feb 2016 at 4:19 PM

How should we interpret the apparent absence of trend in total column water vapor in the paper’s Figure 1? Should we expect to see a rising trend (WV feedback) on these timescales, and if so, why don’t we?

Peter, the mere fact that Willie Soon is the lead author should tell you something.

15 Feb 2016 at 4:20 PM

Chris Machens (#3), looking at the video, it appears to me that the bit involving putting out the infrared image of the flame (but not the flame itself) begins at 20 minutes 50 seconds. Love the video, by the way.

I have the segment specific to the flame at the top of my webpage. (See the link in my name. The webpage is designed as an interactive resource for explaining the greenhouse effect, focusing primarily on radiation transfer, but it is best viewed on a desktop or laptop computer.) But I prefer having the entire series episode.

Another visual or two along these lines include satellite images of carbon dioxide concentrations. I have older ones on the same webpage on the other end of the link, as well as videos showing satellite infrared imaging of carbon dioxide concentrations over the months and years. The imaging is based off of the reduction in infrared radiation reaching space due to rising levels of carbon dioxide.

As such, what is being imaged is essentially the greenhouse effect in action. Moreover, the measurements obtained by satellite agree with independent air sampling (“flask”) measurements to within 1.5 ppmv, which is a good indication of just how well we understand the greenhouse effect in terms radiation transfer.

15 Feb 2016 at 11:30 PM

Rob Quayle (#10) said ” When an infrared heat photon of a specific energy collides with a greenhouse gas molecule, that photon will be absorbed & an excited electron will jump to a higher orbit. However, that new electron orbit is not stable & will soon fall back to its “rest” energy level & emit a photon of the same energy level (frequency) that was absorbed.” This is what happens with UV light, Electronic transitions, however in the IR spectrum it is Rotational and vibrational energy levels of the bonds that are involved, there is no excitation of electrons. While rot/vib levels can emit radiation they are unlikely to do so in the troposphere because the lifetime of the excited states is so long that they are more likely to be deactivated by multiple collisions with neighboring molecules. Around the tropopause conditions favor emission (far fewer collisions).

16 Feb 2016 at 7:24 AM

Where ever I comments dealing with Global warming I post the following comment usually with some minor changes depending on the context. I would be interested in any feedback and corrections from anyone on this site. A sample of my comment is:

“Global warming caused by burning carbon, from whatever form, is a reality. In order to understand why it is so, is fairly easy to explain, however, there are a few things that you have to be aware of.

Just about all of the energy that gives rise to the warmth of the earth comes from the sun (only a tiny amount derives from the earth itself). That energy comes via radiant energy, it is the only form of energy that can travel through the vacuum of space. Most of the gases in the atmosphere are transparent to the suns heat, which means that that they will not heat up the atmosphere significantly as a result of the suns heat passing through. However, the atmosphere contains a few gases that are not transparent to the suns heat. They are called the greenhouse gases, the most important one is water vapour, followed by carbon dioxide and a few others. The ground of course is significant as well, it heats up depending how dark it is. Next thing to be aware of, you may be familiar with the effect that when you get higher it gets cooler, A valley will be warm, the mountain tops are snow covered. The reason it gets warmer as you get nearer the ground is due to those green house gasses, that temperature relationship with altitude is called the “lapse rate”. You need to also appreciate that the earth looses all the heat it receives from the sun, if it did not, the earth would cook, think how hot the inside of a car parked in the sun gets. The only way that heat can escape from the earth, ultimately, is in the same way it came in, via radiant energy. It is the greenhouse gasses that act as a blanket, the radiant energy can only escape back into space when the amount of those greenhouse gas molecules thins out as the atmosphere becomes less dense. By adding more CO2 to the atmosphere it increases the altitude at which the radiant energy can escape the earth, however the lapse rate changes very little, as a result it gets warmer at the earth’s surface.

For many years, it was thought that as carbon dioxide is thermally saturated at sea level, that adding more would not make any difference. That was realised to be a silly idea during the 1950’s when heat seeking missile were being developed. The sea level saturation is irrelevant. A simple way that you can think about the effect of adding CO2 to the atmosphere, is that it is like making any point on the surface of the earth deeper in the atmosphere from a thermodynamic point of view, not of course, from a pressure point of view.

There is a Climate Scientist, Richard Lindzen, who came up with a theory that as the earth warmed, the amount of water vapour will get higher which is true, and as a result, more clouds will form reflecting the suns heat. However that has not been observed, and judging from the geological record, that does not happen.

Global warming is a reality, the question is the time scale. To deny human caused global warming is as silly as denying gravity.”

16 Feb 2016 at 10:11 AM

> However what matters isn’t so much the > amount of carbon dioxide per volume but > the amount of carbon dioxide per area > cross section of atmopheric column.

It’s too bad the AIRS imagery uses red to indicate more CO2. It gives people the wrong impression. Darker gray shading to black would be more apt since it’s opacity in the IR.

16 Feb 2016 at 11:20 AM

Lawrence McLean @42 wrote “the atmosphere contains a few gases that are not transparent to the suns heat. They are called the greenhouse gases”

Lawrence, this part is confused. Although some greenhouse gases, particularly water vapour, do absorb some incoming solar shortwave IR, their absorption of outgoing longwave IR light radiated by earth’s surface and atmosphere is of far greater importance to the greenhouse effect. See this comparison of the spectra of incoming solar radiation to earth’s outgoing radiant energy which shows practically no overlap of the two: https://upload.wikimedia.org/wikipedia/commons/7/7c/Atmospheric_Transmission.png

(Sorry to refer to wiki, but global warming art is no more.)

16 Feb 2016 at 11:38 AM

“In this case, the vertical energy flow is influenced by deep convection, which also plays a role in maintaining the lapse rate.”

How can convection “maintain” the lapse rate? I confess I am at a loss as to why convection is mentioned in an essay about the greenhouse effect; all convection can do is reduce net absorption by increasing radiation at the emission height.

“A popular picture of the greenhouse effect emphasizes the radiation transfer but does not explicitly account for convection. As a result, it fails to explain the observed climate change.”

Given that convection can only reduce absorption (cooling the planet), can you clarify what you mean when you say that accounting for convection helps to “explain the observed climate change?”

16 Feb 2016 at 7:34 PM

Now that the GHE is correctly described, I want to renew my call for GISTEMP to follow HadCrut and publish the monthly baseline that produces anomalies in the analysis so we don’t have to hear silly things like January was the hottest month. It is wrong and it lacks poetry.

17 Feb 2016 at 6:52 AM

Re: Peter Schwartz says: 15 Feb 2016 at 11:05 AM

Have you seen some of the ridiculous nonsense that Willie Soon puts his name to? If not then please see this topical example:

http://GreatWhiteCon.info/2016/02/for-life-on-earth-ice-is-not-generally-a-good-thing/

Quoting Soon et al.

It is legitimate to infer that the surface datasets have been altered to try to bring the reported warming closer to the failed but (for now) still profitable predictions. (That is, the altered datasets still bring profits in the form of money, fame and power to the failed prophets of climate doom.)

17 Feb 2016 at 6:57 AM

#44 Jim Eager, thanks for that, do you think it would be better if I change the wording to: “the atmosphere contains a few gases that are not completely transparent to the suns heat. They are called the greenhouse gases”?

17 Feb 2016 at 9:42 AM

For LM – I think Jim E’s point is that “the sun’s heat” isn’t some special kind of heat.

Most of the energy arriving at Earth from the Sun is visible and higher energy photons, not “heat” (not infrared) (energy reaching the top of the atmosphere, and some of that penetrating all the way to the solid and liquid surfaces before it encounters something that turns the photon’s energy into vibration — dirt, for example, gets warmer when sunlight hits it).

Most of the energy departing the Earth’s surface _is_ in the infrared.

17 Feb 2016 at 10:49 AM

Hank Roberts wrote:

You are right, of course. Actually that is what I do with water vapor at 4, 6.7 and 11 microns. It gives the earth a rather eerie appearance, and makes the cold tops of high altitude clouds appear dark while warmer land appears white. Like the images of carbon dioxide, the original images of water vapor (the three that I combined into one) showed water vapor as lighter in color against a dark planet. For a more “faithful false color”, I combined their negatives, representing the three channels in red, green and blue, and consequently the planet has predominantly pale violet and pale green colors, with the cold top of a tall tropical storm appearing almost black and relatively warm land showing through a drier troposphere appearing white. But as with infrared weather satellite imaging of water vapor used in weather reports where clouds and water vapor appear paler grey to white, the AIRS imagery favors familiarity over accuracy.

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