Gives one a idea of the standard deviation of the distributions these assessments apply to. It is also useful to note what the real gorilla in atmospheric physics is and where it the atmosphere it each has the most weight.
Radiative forcing by well-mixed greenhouse gases:
Estimates from climate models in the
Intergovernmental Panel on Climate Change
(IPCC) Fourth Assessment Report (AR4)
http://www.agu.org/pubs/crossref/2006.../2005JD006713.shtmlCollins, W.D., V. Ramaswamy, M.D. Schwarzkopf, Y. Sun, R.W. Portmann, Q. Fu, S.E.B. Casanova, J.-L. Dufresne, D.W. Fillmore, P.M.D. Forster, V.Y. Galin, L.K. Gohar, W.J. Ingram, D.P. Kratz, M.-P. Lefebvre, J. Li, P. Marquet, V. Oinas, Y. Tsushima, T. Uchiyama, and W.Y. Zhong 2006. Radiative forcing by well-mixed greenhouse gases: Estimates from climate models in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). J. Geophys. Res. 111, D14317, doi:10.1029/2005JD006713.
The radiative effects from increased concentrations of well-mixed greenhouse gases (WMGHGs) represent the most significant and best understood anthropogenic forcing of the climate system. The most comprehensive tools for simulating past and future climates influenced by WMGHGs are fully coupled atmosphere-ocean general circulation models (AOGCMs). Because of the importance of WMGHGs as forcing agents it is essential that AOGCMs compute the radiative forcing by these gases as accurately as possible. We present the results of a radiative transfer model intercomparison between the forcings computed by the radiative parameterizations of AOGCMs and by benchmark line-by-line (LBL) codes. The comparison is focused on forcing by CO2, CH4, N2O, CFC-11, CFC-12, and the increased H2O expected in warmer climates. The models included in the intercomparison include several LBL codes and most of the global models submitted to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). In general, the LBL models are in excellent agreement with each other. However, in many cases, there are substantial discrepancies among the AOGCMs and between the AOGCMs and LBL codes. In some cases this is because the AOGCMs neglect particular absorbers, in particular the near-infrared effects of CH4 and N2O, while in others it is due to the methods for modeling the radiative processes. The biases in the AOGCM forcings are generally largest at the surface level. We quantify these differences and discuss the implications for interpreting variations in forcing and response across the multimodel ensemble of AOGCM simulations assembled for the IPCC AR4.
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[12] The specifications for each of the calculations requested from the LBL and AOGCM groups are given in Table 1. The concentrations of WMGHGs in calculations 3a and 3b correspond to conditions in the years 1860 AD and 2000 AD, respectively. The concentrations in 1860 are obtained from a variety of sources detailed in IPCC [2001]. Differences among these calculations cover several standard forcing scenarios performed by all AOGCMs in the AR4, including (1) forcing for changes in CO2 concentrations from 1860 to 2000 values (case 2a-1a) and from 1860 to double 1860 values (case 2b-1a), (2) forcing for changes in WMGHGs from 1860 to 2000 values (case 3b-3a), and (3) the effect of increased H2O predicted when CO2 is doubled (case 4a-2b). In addition to the four forcing experiments listed above, there are three additional forcing experiments for combinations of CH4, N2O, CFC-11, and CFC-12. The changes in WMGHGs and H2O in these seven forcing experiments are listed in Table 2.
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