What are climate feedbacks?
Climate changes caused by increased levels of greenhouse gases are amplified by other changes within the climate system, known as feedbacks, said Dr. James Hansen, director of NASA’s Goddard Institute for Space Studies, speaking at the 2008 Kansas Wind & Renewable Energy Conference in Topeka. Hansen said there are both fast and slow feedbacks.
Fast feedbacks — changes that occur quickly in response to temperature change — amplify the initial temperature change, resulting in additional warming. As the planet warms, fast feedbacks include increased levels of water vapor (due to higher evaporation rates), which traps additional heat; and less snow and sea ice, which exposes dark surfaces that absorb more sunlight.
Slower feedbacks also exist. Due to warming, forests and shrubs are moving poleward into tundra regions. Expanding vegetation, darker than tundra, absorbs sunlight and warms the environment. Another slow feedback is increasing wetness (i.e., darkness) of the Greenland and West Antarctica ice sheets in the warm season. Finally, as tundra melts, methane, a powerful greenhouse gas, is bubbling out. Paleoclimatic records confirm that the long-lived greenhouse gases — methane, carbon dioxide, and nitrous oxide — all increase with the warming of oceans and land.
These positive feedbacks amplify climate change over decades, centuries, and longer.
-- Steve Watson, CASMGS Communications