Explained: Climate sensitivity-If we double the Earth’s greenhouse gases, how much will the temp...

[OKIsItJustMe]

http://web.mit.edu/newsoffice/2010/explained-climate-sensitivity.html

Explained: Climate sensitivity

If we double the Earth’s greenhouse gases, how much will the temperature change? That’s what this number tells you.

David L. Chandler, MIT News Office

March 19, 2010

This is the second part of an “Explained” on climate change. http://web.mit.edu/newsoffice/2010/explained-radforce-0309.html">Part one dealt with radiative forcing.

Climate sensitivity is the term used by the Intergovernmental Panel on Climate Change (IPCC) to express the relationship between the human-caused emissions that add to the Earth’s greenhouse effect — carbon dioxide and a variety of other greenhouse gases — and the temperature changes that will result from these emissions.

Specifically, the term is defined as how much the average global surface temperature will increase if there is a doubling of greenhouse gases (expressed as carbon dioxide equivalents) in the air, once the planet has had a chance to settle into a new equilibrium after the increase occurs. In other words, it’s a direct measure of how the Earth’s climate will respond to that doubling.

That value, according to the most recent IPCC report, is 3 degrees Celsius, with a range of uncertainty from 2 to 4.5 degrees.

This sensitivity depends primarily on all the different feedback effects, both positive and negative, that either amplify or diminish the greenhouse effect. There are three primary feedback effects — clouds, sea ice and water vapor; these, combined with other feedback effects, produce the greatest uncertainties in predicting the planet’s future climate.

...