Greenhouse Gases Shape Earth's Climate

Teaching about how scientists understand climate is supported by nine key concepts:

A. Nearly all the energy that flows through the Earth system comes from sunlight. Earth's climate is determined by the movement of energy through the Earth system—the ocean, atmosphere, clouds, ice, land, and life—and also includes energy and heat produced by humans and human activity. Learn more about Earth's energy balance

There are 8 more fundamental concepts. See them all...

B. Some of the sunlight that reaches Earth is reflected back to space by Earth's atmosphere and surface, but about 70% of it is absorbed by the atmosphere, land, and ocean. The warmed Earth radiates heat back into the atmosphere, where the heat is absorbed by greenhouse (also known as heat-trapping) gases that radiate some of this heat back toward Earth. This leads to the overall heating of Earth's surface—known as the greenhouse effect. Learn more about the greenhouse effect

C. Greenhouse gases added to the atmosphere by human activities intensify the greenhouse effect and drive global warming. The greenhouse gases produced by human activities include carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and fluorinated gases. Learn more about greenhouse gas emissions

D. Water vapor (H₂O) also traps heat, and a warmer atmosphere holds more moisture than a cooler one. As a result, water vapor amplifies the warming caused by the addition of human-produced greenhouse gases. Learn more about water vapor and the greenhouse effect

E. Some greenhouse gases are more effective at warming the planet than others. The heat-trapping ability of a greenhouse gas, plus how much of it is in the atmosphere and how long it endures, determines its contribution to total warming. For example, even though there is about 200 times more carbon dioxide in the atmosphere than methane, and carbon dioxide stays in the atmosphere for much longer, methane has contributed 20% to 30% of global warming to date. Learn more about the strength of greenhouse gases

F. Life—including microbes, plants, animals, and humans—is a major driver of the global carbon cycle and can influence global climate by modifying the chemical makeup of the atmosphere. The geologic record shows that life has significantly altered the atmosphere during Earth's history.

G. Carbon naturally moves very slowly between the atmosphere and reservoirs in the Earth, including rocks, soils, and the deep ocean. Human activities are disrupting this cycle by taking carbon out of storage underground and releasing it into the atmosphere, primarily by burning fossil fuels such as coal, oil, and natural gas. Learn more about how humans are changing the carbon cycle

H. While some of these human-caused carbon dioxide emissions are absorbed quickly by the ocean and forests, much of the carbon dioxide will remain in the atmosphere before it is absorbed by the ocean over thousands of years.

I. As concentrations of carbon dioxide and other greenhouse gases increase, Earth's average temperature rises in response. This rise in temperature causes a significant change in the climate averages and extremes that people and the natural environment experience. Learn more about carbon dioxide's role in Earth's climate

Bringing these ideas into your classroom

The natural greenhouse effect is a common area of misunderstanding. Educators should strive to explain this concept in a way that is as simple as possible but is still accurate.

Show a brief explanation of the greenhouse effect

Most of the Sun's energy that reaches Earth's surface is short wave radiation, which warms the surface and is transformed into long-wave infrared that radiates back toward space.
Most of the gases in the atmosphere do not trap the outgoing radiation.
However, greenhouse gases in the atmosphere such as water vapor, carbon dioxide, methane, and nitrogen oxides are very powerful in absorbing the outgoing radiation and re-radiating it in all directions.
The re-radiation of energy causes the lower atmosphere to warm, and in turn, warms Earth's land surface and oceans.

Attempts to oversimplify the greenhouse effect can be counter-productive and further confuse learners. For younger students, the mental model of how the natural greenhouse effect is like a "blanket" that keeps heat under the covers may be appropriate, but a key difference is that a blanket retains heat that is generated by your body (or the Earth, in the analogy). In reality, the heat energy is originally coming from the Sun, not from the Earth.

High school and certainly, college students should have a clearer understanding of the mechanics of the greenhouse effect. This concept is essential to understanding how human activities are impacting the climate system.

Full comprehension of the carbon cycle requires an understanding of biogeochemical systems. Students also have to understand the different time scales at which carbon exchange takes place in the different reservoirs. Learning about the carbon cycle lays an important foundation to the understanding of the impact of burning fossil fuels.

The terminology of positive and negative feedback in a system can often lead to misunderstanding because the words 'positive' and 'negative' have other meanings. It is clearer to use the term 'self-reinforcing cycle' to describe the way that positive feedback can amplify the initial input. Negative feedback can be termed a 'self-dampening cycle.'

Teaching materials from the CLEAN collection

Middle school

Carbon Cycle Role Play - Carbon cycle activity to demonstrate how carbon moves throughout the atmosphere. The activity ends with a discussion of how humans impact the carbon cycle.
What is Albedo? - In this lesson, students watch a 2-minute video explaining albedo. The video shows visualizations of albedo across Earth and how it can change. Students then interpret the images in the video and answer questions about albedo.
Heating it Up: The Chemistry of the Greenhouse Effect is part of a sequence of activities about climate change. Suitable for high school as well.
What makes a gas, a greenhouse gas? - Students act out 4 different molecules (nitrogen, oxygen, carbon dioxide and water vapor) to discover which ones are greenhouse gases and which ones are not.

High school

Global Warming: Carbon Dioxide and the Greenhouse Effect - This video segment demonstrates carbon dioxide's role in the greenhouse effect and explains how increasing concentrations of C02 in the atmosphere is contributing to global warming. The video includes an unusual demonstration of C02's heat-absorbing properties, using infrared film, a researcher's face, and a stream of C02 between them.
Decoding Antarctica's Climate History - Antarctica's Climate Secrets - This 10 minute video builds connections between topics that are important in climate science such as: the impact of variations in Earth's orbit and wobble on it's axis on climate; how the cores being sampled fit into the bigger climate picture; connecting greenhouse gases to melting ice and sea level changes; the sensitivity of the ice melt / sea level rise relationship; and computer model simulations showing connections between ice sheets and sea level. The companion website provides resources, an extensive list of activities, teacher guides, posters, and more.10-minute
Carbon on the Move is a 3-part lab activity where students investigate the global carbon cycle and study the effects of specific feedback loops.
Why Do Some Molecules Absorb Infrared Energy? - In this short, hands-on activity, students build simple molecular models of 4 atmospheric gases (O2, N2, C02, and methane), compare their resonant frequencies, and make the connection between resonant frequency and the gas's ability to absorb infrared radiation.

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