This post provides a brief overview of why regional climate forcings are first order in terms of affecting atmospheric circulation patterns which are the reason for such weather events as droughts, floods, tropical cyclones and so forth. A global average radiative forcing, such as emphasized in the 2007 IPCC report, fails to capture these forcings, and indeed, obscures their significance.
Examples include (with excerpts from the papers)
1. Feddema et al. 2005: The importance of land-cover change in simulating future climates., 310, 1674-1678.
“Although land-cover effects are regional and tend to offset with respect to global average temperatures, they can significantly alter regional climate outcomes associated with global warming. Beyond local impacts, tropical land-cover change can potentially affect extratropical climates and nearby ocean conditions through atmospheric teleconnections.”
2. Marland, G., R.A. Pielke, Sr., M. Apps, R. Avissar, R.A. Betts, K.J. Davis, P.C. Frumhoff, S.T. Jackson, L. Joyce, P. Kauppi, J. Katzenberger, K.G. MacDicken, R. Neilson, J.O. Niles, D. dutta S. Niyogi, R.J. Norby, N. Pena, N. Sampson, and Y. Xue, 2003: The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy. Climate Policy, 3, 149-157
“Recent studies suggest that changes in the surface energy budgets resulting from land surface change can have a profound influence on the Earth’s climate…………….”
“Having observed that local and regional changes in climate may be as important as changes in the global mean climate, we suggest that attention be given to devising a regional climate change potential (RCCP) to encapsulate the effect that specific human actions have on the redistribution of energy within the Earth’s climate system.”
3. Pitman, A.J., N. de Noblet-Ducoudré, F.T. Cruz, E.L. Davin, G.B. Bonan, V. Brovkin, M. Claussen, C. Delire, L. Ganzeveld, V. Gayler, B.J.J.M. van den Hurk, P.J. Lawrence, M.K. van der Molen, C. Müller, C.H. Reick, S.I. Seneviratne, B. J. Strengers, and A. Voldoire, 2009: Uncertainties in climate responses to past land cover change: first results from the LUCID intercomparison study, Geophys. Res. Lett., doi:10.1029/2009GL039076, in press. [“Land-Use and Climate, IDentification of robust impacts” (LUCID)] (see)
“Seven climate models were used to explore the biogeophysical impacts of human induced land cover change (LCC) at regional and global scales. The imposed LCC led to statistically significant decreases in the northern hemisphere summer latent heat flux in three models, and increases in three models. Five models simulated statistically significant cooling in summer in near-surface temperature over regions of LCC and one simulated warming.”
4. McAlpine, C.A., J. Syktus, J.G. Ryan, R.C. Deo, G.M. McKeon, H.A. McGowan, and S.R. Phinn, 2009:A continent under stress: interactions, feedbacks and risks associated with impact of modified land cover on Australia’s Climate. Global Change Biology, in press. doi: 10.1111/j.1365-2486.2009.01939.x (see)
“The consequences of ignoring the effect of LUCC on current and future droughts in Australia could have catastrophic consequences for the nation’s environment, economy and communities”
5. Takata, K., K. Saito, and T. Yasunari, 2009: Changes in the Asian Monsoon Climate During 1700-1850 Induced by Pre-Industrial Cultivation. PNAS,(in press). (see)
“Pre-industrial changes in the Asian summer monsoon climate from the 1700s to the 1850s were estimated with an Atmospheric General Circulation Model (AGCM) using historical global land cover/use change data reconstructed for the last 300 years. Extended cultivation resulted in a decrease in monsoon rainfall over the Indian subcontinent and southeastern China, and an associated weakening of the Asian summer monsoon circulation. The precipitation decrease in India was marked, and was consistent with the observational changes derived from examining the Himalayan ice-cores for the concurrent period. Between the 1700s and the 1850s, the anthropogenic increases in greenhouse gases and aerosols were still minor; also, no long-term trends in natural climate variations, such as those caused by the ocean, solar activity, or volcanoes, were reported. Thus, we propose that the land cover/use change was the major source of disturbances to the climate during that period.”
6. 2002 Science paper entitled “Climate Effects of Black Carbon Aerosols in China and India” (subscription required) by S. Menon, J. Hansen, and L. Nazarenko and Y. Luo. (see)
“In recent decades, there has been a tendency toward increased summerfloods in south China, increased drought in north China, and moderate cooling in China and India while most of the world has been warming. We used a global climate model to investigate possible aerosol contributions to these trends. We found precipitation and temperature changes in the model that were comparable to those observed if the aerosols included a large proportion of absorbing black carbon (”soot”), similar to observed amounts. Absorbing aerosols heat the air, alter regional atmospheric stability and vertical motions, and affect the large-scale circulation and hydrologic cycle with significant regional climate effects. ”
7. 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.
“This paper diagnoses the spatial mean and the spatial gradient of the aerosol radiative forcing in comparison with those of well-mixed green-house gases (GHG). Unlike GHG, aerosols have much greater spatial heterogeneity in their radiative forcing. The heterogeneous diabatic heating can modulate the gradient in horizontal pressure field and atmospheric circulations, thus altering the regional climate.”
These example illustrate why the IPCC assessments must be broadened to include the diversity of heterogenous human climate forcings.