Climate sensitivity: What is it, and why is it important?

Authors: Dr Paulo Ceppi and Professor Jonathan M. Gregory

Climate sensitivity is a fundamental measure of global climate change. This briefing paper explains how climate sensitivity is estimated from different lines of evidence – modelling, observations, and palaeoclimate records – and why its exact value remains uncertain.

Headlines

• Climate sensitivity is defined as the global mean increase in surface air temperature resulting from a doubling of atmospheric CO2 concentration, once the system has reached equilibrium.
• Its exact value is uncertain and depends mainly on the strength of climate feedbacks that can amplify or dampen the effect of CO2 forcing. The most uncertain of these feedbacks is that related to clouds.
• Although based on a simple benchmark experiment, climate sensitivity is a good indicator of the rate of future global warming for a given scenario of greenhouse gas emissions. In turn, many societally relevant regional impacts, such as local changes in temperature and aridity, scale approximately linearly with global warming.
• All other things being equal, a higher climate sensitivity implies a lower remaining carbon budget for a given global warming limit. An understanding of climate sensitivity is thus central to carbon budget estimates for the Paris Agreement goals.

Download: Climate sensitivity: What is it, and why is it important? [PDF]

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[image: Jason Blackeye on Splash ]