PerspectiveClimate Change

A Long View on Climate Sensitivity

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Science  24 Aug 2012:
Vol. 337, Issue 6097, pp. 917-919
DOI: 10.1126/science.1224011

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Humanity is engaged in an unprecedented climate experiment, the outcome of which is often framed in terms of an equilibrium “climate sensitivity.” This parameter encapsulates the amount of global warming that may be expected as a result of a doubling of the atmospheric carbon dioxide (CO2) concentration, which is equivalent to an additional 3.7 W m−2 of energy available to warm Earth's surface (1). The current best estimate of climate sensitivity is similar to the earliest estimates by Arrhenius (2) and Callendar (3), ranging from 2° to 4.5°C (4). Constraints on the lower limit of this range are much tighter than they are on the upper limit, with small but finite probabilities for very large climate sensitivities (4). Although the geological record provides strong support for climate sensitivities in this range, it also reminds us that a single value of climate sensitivity is unlikely to provide a complete picture of the climate system's response to forcing.