By now, students have learned how minute quantities of air pollutants in the atmosphere can affect their health. Today they will learn how small amounts of certain gases can also affect the planet’s climate. Students will learn how greenhouse gases like carbon dioxide keep the Earth at a livable temperature, and how increasing amounts of these gases may cause the climate to change. Students will compute their carbon footprint and discuss alternative sources of energy. Students should come away with a sense of their own impact on the environment and what they can do to reduce the creation of more emissions.

The greenhouse effect is the warming of the Earth caused by certain gases in the atmosphere. The Figures on the next page show how this works. First, sunlight shines onto the Earth’s surface. The Earth absorbs some of this solar energy and radiates its own heat energy back toward space. Greenhouse gases are chemicals in the atmosphere that prevent some of the Earth’s heat from escaping into space, while letting sunlight pass through. Greenhouse gases include water vapor, carbon dioxide, methane, and chlorofluorocarbons.

The greenhouse effect is very beneficial to life on Earth because it warms the planet and moderates temperature extremes. Without greenhouse gases, the surface of the Earth would be too cold for liquid water! (For an interactive animation of the greenhouse effect, visit http://environment.nationalgeographic.com/environment/global-warming/gw-overview-interactive.html )

Figure 1: Credit: http://www.epa.gov/climatechange/kids/greenhouse.html

Greenhouse effect

While the greenhouse effect is necessary for most life on Earth, increasing levels of greenhouse gases can cause Earth’s temperature to rise. This is what scientists believe is currently happening to our planet. The burning of fossil fuels and the loss of forests have caused levels of greenhouse gases like carbon dioxide to increase significantly over the past century. Many greenhouse gases remain in the atmosphere for decades. As a result, more and more heat is being trapped in the Earth’s atmosphere, which is causing the Earth’s climate to warm.

Global warming is the increase in the average air temperature of Earth. Most climate scientists believe that the Earth’s average temperature has been rising over the past century, and that most of this warming has been caused by manmade emissions of greenhouse gases, such as the burning of fossil fuels.

Global warming can make it difficult for humans and natural ecosystems to adapt, especially if temperatures rise rapidly. Warm temperatures can melt major ice sheets and cause ocean water to expand, which could cause sea levels to rise significantly. Weather patterns could shift and become more extreme, with severe floods in some region and severe droughts in others. According to the Intergovernmental Panel on Climate Change, 11 of the 12 hottest years since thermometer reading became available occurred between 1995 and 2006!

Figure 2: Credit: http://www.globalwarmingart.com/wiki/Image:Mauna_Loa_Carbon_Dioxide_png

Atmospheric carbon dioxide concentrations have been increasing in recent decades

Figure 3: Credit: Intergovernmental Panel on Climate Change

Global temperatures and sea levels have been rising

So what can we do to prevent global warming? Burning of fossil fuels (coal, oil, and natural gas) is the biggest source of greenhouse gases. Fossil fuel use can be reduced by energy efficiency and conservation, and by switching to alternative sources of energy such as wind, solar, or nuclear power.

One way to calculate your impact on the environment and contribution to the heating of the earth is the “Carbon footprint.” A carbon footprint tells you how much carbon dioxide is emitted as a result of your day-to-day lifestyle and actions. It can also tell you what actions could reduce the amount of pollutants are released into the air. Toward the end of this lesson, students will compute their own carbon footprints using an EPA computer program online.

1. Greenhouse Effect

http://www.epa.gov/region01/students/pdfs/greenhouse.pdf

http://www.windows.ucar.edu/tour/link=/earth/interior/greenhouse_effect.html

2. Causes and Effects of Global Warming

http://environment.nationalgeographic.com/environment/global-warming/gw-causes.html

http://environment.nationalgeographic.com/environment/global-warming/gw-effects.html

3. Clean Fuels

http://www.epa.gov/region01/students/pdfs/rd_clean.pdf