Technical Report
Changes in atmospheric constituents and in radiative forcing
Forster, P; Ramaswamy, V; Artaxo, P; Berntsen, T; Betts, R; Fahey, DW; Haywood, J; Lean, J; Lowe, DC; Myhre, G; Nganga, J; Prinn, R; Raga, G; Schultz, M; Van Dorland, R
Cambridge University Press
Cambridge, United Kingdom
Climate change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
is a chapter of
1515270 Climate change 2007: The physical science basis
Radiative forcing (RF) is a concept used for quantitative comparisons of the strength of different human and natural agents in causing climate change. Climate model studies since the Working Group I Third Assessment Report (TAR; IPCC, 2001) give medium confidence that the equilibrium global mean temperature response to a given RF is approximately the same (to within 25%) for most drivers of climate change.
For the first time, the combined RF for all anthropogenic agents is derived. Estimates are also made for the first time of the separate RF components associated with the emissions of each agent.
The combined anthropogenic RF is estimated to be +1.6 [–1.0, +0.8] W m^(–2), indicating that, since 1750, it is extremely likely that humans have exerted a substantial warming influence on climate. This RF estimate is likely to be at least five times greater than that due to solar irradiance changes. For the period 1950 to 2005, it is exceptionally unlikely that the combined natural RF (solar irradiance plus volcanic aerosol) has had a warming infl uence comparable to that of the combined anthropogenic RF.
Increasing concentrations of the long-lived greenhouse gases (carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), halocarbons and sulphur hexafl uoride (SF6); hereinafter LLGHGs) have led to a combined RF of +2.63 [±0.26] W m–2. Their RF has a high level of scientifi c understanding.4 The 9% increase in this RF since the TAR is the result of concentration changes since 1998.
Solomon, S; Qin, D; Manning, M; Chen, Z; Marquis, M; Averyt, KB; Tignor, M; Miller, HL
