In IPCC reports, equilibriumclimate sensitivity refers to the equilibrium change in global mean surface temperature following a doubling of the atmospheric (equivalent) CO2 concentration. This value is estimated, by the IPCC TAR, to be "likely to be in the range of 1.5 to 4.5°C" [1]. More generally, equilibrium climate sensitivity refers to the equilibrium change in surface air temperature following a unit change in radiative forcing (°C/Wm-2). In practice, the evaluation of the equilibrium climate sensitivity requires very long simulations with coupled global climate models. The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess the risk of human-induced climate change. The Panel is open to all members of the WMO and UNEP. Its... Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. ... A general circulation model (GCM) aims to describe geophysical flow by integrating a variety of fluid-dynamical, chemical, or even biological equations that are either derived directly from physical laws (e. ...
Schlesinger and Andronova (unsinge simple climate models) found that it could lie between 1 and 10 °C, with a 54 percent likelihood that the climate sensitivity lies outside the IPCC range [2]. The exact range depends on which factors are most important during the instrumental period: "At present, the most likely scenario is one that includes anthropogenic sulfate aerosol forcing but not solar variation. Although the value of the climate sensitivity in that case is most uncertain, there is a 70 percent chance that it exceeds the maximum IPCC value. This is not good news." said Schlesinger.
Some constraints are also available from observations: Gregory et al. (2002) estimate a lower bound of 1.6 oC from an observational estimate [3]; palaeoclimatic studies rule out very large values.
Climate sensitivity is not the same as the expected climate change at, say 2100: the TAR reports this to be and increase of 1.4 to 5.8 oC over 1990.
The Transient climate response (TCR) - a term first used in the TAR - is the temperature change at the time of CO2 doubling in a run with CO2 increasing at 1%/year.
The effective climate sensitivity is a related measure that circumvents this requirement. It is evaluated from model output for evolving non-equilibrium conditions. It is a measure of the strengths of the feedbacks at a particular time and may vary with forcing history and climate state. Details are discussed in Section 9.2.1 of Chapter 9 in the TAR[4]. TAR can mean: An abbreviation for Tar (file format) The Amazing Race, a reality television program An abbreviation for Tibet Autonomous Region The Third Assessment Report of the IPCC Thrombocytopenia Absent Radius syndrome For Tar or tar, see Tar (disambiguation). ...
References
An observationally based estimate of the climate sensitivity; JM Gregory, RJ Stouffer, SCB Raper, PA Stott, NA Rayner; Journal of Climate, 2002 .
In practice, the evaluation of the equilibrium climatesensitivity from models requires very long simulations with coupled global climate models, or it may be deduced from observations.
Schlesinger and Andronova (using simple climate models) found that it could lie between 1 and 10 °C, with a 54 percent likelihood that the climatesensitivity lies outside the IPCC range [3].
Climatesensitivity is not the same as the expected climate change at, say 2100: the TAR reports this to be an increase of 1.4 to 5.8 °C over 1990.
In recent usage, especially in the context of environmental policy, the term "climate change" is often used to refer only to the ongoing changes in modern climate, including the average rise in surface temperature known as global warming.
Many climate states, including the Pacific decadal oscillation, the North Atlantic oscillation, and the Arctic oscillation, have been recognized as modes within the climate system, owing their existence at least in part, to different ways that heat can be stored in the oceans and move between different reservoirs.
In their impact on climate, orbital variations are in some sense an extension of solar variability, because slight variations in the Earth's orbit lead to changes in the distribution and abundance of sunlight reaching the Earth surface.
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