A gas in the atmosphere that absorbs and emits radiation within the thermal infrared range. This property allows the earth to maintain its warm temperature which supports life on earth. Water vapor, carbon dioxide, ozone, and methane are good examples of gases with this property. When the concentration of these gases gets too high, the earth warms beyond its normal range and many catastrophic climate shifts occur.
Figure 4: Atmospheric concentrations of 3 greenhouse gases (carbon dioxide,methane, and nitrous oxide) over the last 2,000 years. Note that each of these gases has increased since 2005, and CO2 is now hovering around 400 ppm. You can see the most recent concentration values of these greenhouse gases at the Carbon Dioxide Information Analysis Center.[fn][[nid:328]][/fn]
Figure 3. The greenhouse effect. Solar short-wave radiation (light) entering the atmosphere is absorbed by the Earth’s surface and emitted as long-wave infrared radiation (heat) that is then absorbed by greenhouse gases which heats the atmosphere.[fn][[nid:327]][/fn]
Figure 2. A greenhouse is made of glass or plastic windows. Sunlight passes through the windows but heat is trapped inside. Vegetables and flowers can grow even during colder months.[fn][[nid:326]][/fn]
Concentration of greenhouse gases
IPCC, 2013: Climate Change 2013: The Physical Science Basis.