The Concept of Climate Sensitivity: History and Development

The concept of climate sensitivity has more than a century of history. According to this concept, a change in the global near-surface air temperature of the Earth, T , due to external disturbance of the Earth’s energy balance, can be linearly related to a change in the net radiation at some level in the atmosphere, F. Thus,
T F, where is the climate sensitivity. By doubling the pre-industrial atmospheric carbon dioxide concentration, estimates of climate sensitivity have been made using a variety of methods, ranging from “back of the envelope” to sophisticated mathematical models. Thus,
T2x has become a surrogate for and has played a central role throughout the history of the assessment reports of the Intergovernmental Panel on Climate Change (IPCC) in interpreting the output of numerical models, evaluating future climate changes from various scenarios, and in attributing the causes of the observed temperature changes. Estimates of
T2x have been published in all three IPCC assessment reports, and since 1979 the accepted range for the climate sensitivity, from 1.5 C to 4.5 C, has stayed unchanged. Recent studies, however, have shown there is a significant likelihood that T2x greatly exceeds 4.5 C. This means that different policy strategies in climate-change mitigation and adaptation need to be considered. Prior to the IPCC Fourth Assessment Report (AR4), the concept of climate sensitivity has been intensively examined by several recent scientific workshops. Here we briefly overview the concept of climate sensitivity and show possible ways of its future development.