The Habitable PlanetHabitable Planet home page

Unit 2: Atmosphere // Section 4: Major Greenhouse Gases


Many GHGs, including water vapor (the most important), ozone, carbon dioxide, methane, and nitrous oxide, are naturally present in the atmosphere. Other GHGs are synthetic chemicals that are emitted only as a result of human activity. Anthropogenic (human) activities are significantly increasing atmospheric concentrations of many GHGs.

When atmospheric GHG concentrations increase, Earth temporarily traps infrared radiation more efficiently, so the natural radiative balance is disturbed until its surface temperature rises to restore equilibrium between incoming and outgoing radiation. It takes many decades for the full effect of greenhouse gases to be realized in higher surface temperatures, because the oceans have a huge capacity to store heat. They must be gradually warmed by excess infrared radiation from the atmosphere. Figure 4 illustrates the relative contributions from man-made emissions of various GHGs to climate change.

Importance of human-produced greenhouse gases

Figure 4. Importance of human-produced greenhouse gases
See larger image

Source: Courtesy Marian Koshland Science Museum of the National Academy of Sciences http://www.koshland-science-museum.org.

As we will see in section 8, "The Global Carbon Cycle," CO2 emitted from combustion of fossil fuel cycles between the atmosphere and land and ocean "sinks" (carbon storage reservoirs), which are absorbing a large fraction of anthropogenic carbon emissions. Ultimately, though, there are limits to the amount of carbon that these sinks can absorb. These sinks are more likely to delay than to prevent human actions from altering Earth's radiative balance.

Higher surface temperatures on Earth will have profound impacts on our planet's weather and climate. Before we consider those impacts, however, we need to understand how variables such as pressure, temperature, and moisture combine to create air currents, drive normal atmospheric circulation patterns, and create the overall climate.

top of page

© Annenberg Foundation 2014. All rights reserved. Legal Policy