Greenhouse Gases

Gases that trap heat in the atmosphere are called greenhouse gases. Two major greenhouse gases are carbon dioxide (CO2) and methane (CH4).

Carbon dioxide is the primary greenhouse gas emitted through human activities. Carbon dioxide in naturally present in the atmosphere as part of the Earth’s carbon cycle (the natural circulation of carbon among the atmosphere, oceans, soil, plants and animals). Human activities are altering the carbon cycle - both by adding more CO2 to the atmosphere and by influencing the ability of natural sinks (e.g., forests) to remove and store CO2 from the atmosphere. While CO2 comes from a variety of natural sources, human-related emissions are responsible for the increase that has occurred in the atmosphere since the industrial revolution.

Methane is emitted from natural sources (e.g., wetlands) and human activities (e.g., raising livestock). Methane’s lifetime in the atmosphere is much shorter than CO2, but CH4 is more efficient at trapping radiation than CO2, meaning its impact on climate change is greater than CO2, on a pound-for-pound basis.