Other Greenhouse Gases

Water molecule Other greenhouse gases include water vapor, halocarbons, nitrous oxides, and ozone. Water vapor is the strongest greenhouse gas. The amount of water vapor (H2O) in the atmosphere is largely controlled by the temperature of the air and therefore varies from region to region. Warmer air can hold more moisture or water vapor. When the air becomes saturated (or holds as much moisture as the air can at that temperature), the excess moisture will condense into cloud droplets. If these droplets are large enough, they will fall as precipitation.

Water vapor plays an important role in the climate system. As air warms, it can hold more water vapor.  In turn, more water vapor can absorb and re-emit more infrared radiation. Any process that acts to amplify (positive feedback) or lessen (negative feedback) the initial cause of the change in climate is known as a climate feedback. The water vapor feedback is known as a positive climate feedback because increased amounts of water vapor amplify the warming trend.

Halocarbons, which are composed of carbon, chlorine, fluorine, and hydrogen, include chlorofluorocarbons (CFCs). CFCs are synthetic gases that were used in cleaning solvents, refrigerants, and plastic foam.

Nitrous Oxide Nitrous oxide (N2O), a relatively long-lived gas, has increased in atmospheric concentration due mainly to agriculture. Nitrate (NO3 ) and ammonia (NH4 +) are used as fertilizers. Bacteria convert a small amount of this nitrate and ammonia into the form of nitrous oxide. Internal combustion engines also produce nitrous oxide.

Ozone Ozone (O3) is also a relatively minor greenhouse gas because it is found in relatively low concentrations in the troposphere (the lowest layer of the atmosphere). In the troposphere, it is produced by a combination of pollutants––mostly hydrocarbons and nitrogen oxide compounds.


Humans have been altering the land for at least 8,000 years. They extract and use fossil fuels for energy and clear forests for agricultural production and grazing land. They use shallow swampy areas to grow rice. Humans also build roads and buildings. It is estimated that 46% of Earth’s land remains unmodified and most of this land is located in inhospitable regions of the planet. But how do we know if humans are causing climate change? In the following investigations, you will analyze several types of data to answer this question.