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carbon dioxide levels

Climate feedbacks amplify or reduce direct warming and cooling effects. They do not change the planet’s temperature directly. Feedbacks that amplify changes are called positive feedbacks. Feedbacks that counteract changes are called negative feedbacks. Feedbacks are associated with changes in surface reflectivity, clouds, water vapor, and the carbon cycle.

Water vapor appears to cause the most important positive feedback. As Earth warms, the rate of evaporation and the ability of air to hold water vapor both rise, increasing the amount of water vapor in the air. Because water vapor is a greenhouse gas, this leads to further warming.

The melting of Arctic sea ice is another example of a positive climate feedback. As temperatures rise, sea ice retreats. The loss of ice exposes the underlying sea surface, which is darker and absorbs more sunlight than ice, increasing the total amount of warming.

Some types of clouds cause a negative feedback. Warming temperatures can increase the amount or reflectivity of these clouds, reflecting more sunlight back into space, cooling the surface of the planet. Other types of clouds, however, contribute a positive feedback.

There are also several positive feedbacks that increase GHG concentrations. For example, as temperatures warm:

  • Natural processes that are affected by warming, such as permafrost thawing, tend to release more CO2.
  • The ocean releases CO2 into the atmosphere and absorbs atmospheric CO2 at a slower rate.
  • Several types of land surfaces may release more methane (CH4).

These changes lead to higher concentrations of atmospheric GHGs and contribute to increased warming.