This follow up to the Climate Science weblog of December 24th entitled
is to emphasize the significance of that weblog.
Using the climate metric of a large scale average (for 37 N to 37 S),
Matsui, T., and R.A. Pielke Sr., 2006:Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974,
found that the radiative forcing of the human contribution of well-mixed greenhouse gas and of aerosols were of the same order of magnitude (although of opposite sign). This is what is also concluded in the 2007 IPCC Report for the global average, as given in Figure SPM.2 in the Statement for Policymakers.
However, when evaluating the spatial gradient of these human radiative forcings, the radiative effect of the aerosol forcing is 60 times larger!
Since it is the spatial gradient of diabatic that forces atmospheric circulation patterns, the regional climate forcing metric is a much more valid climate metric to assess most climate impacts due to human activities than is a global, or other very large scale, average.
Land use/land cover change also has such large radiative effects as it is a spatially heterogeneous climate forcing; e.g. see
Pielke Sr., R.A., G. Marland, R.A. Betts, T.N. Chase, J.L. Eastman, J.O. Niles, D. Niyogi, and S. Running, 2002: The influence of land-use change and landscape dynamics on the climate system- relevance to climate change policy beyond the radiative effect of greenhouse gases. Phil. Trans. A. Special Theme Issue, 360, 1705-1719.
Since the other effects of aerosols are not considered (e.g. their effect on precipitation; e.g. see
Rosenfeld Daniel Atmosphere: Aerosols, Clouds, and Climate, Perspectives. Science 2 June 2006:Vol. 312. no. 5778, pp. 1323 – 1324 DOI: 10.1126/science.1128972,
the aerosol climate effect is even larger than its radiative effect alone.
Climate Science: Roger Pielke Sr. 