There is a new paper that provides yet another example that land cover change is first order climate forcing. [ and thanks to Souleymane Fall for alerting us to this paper!].
The paper is
Diffenbaugh, N. S., 2009:Influence of modern land cover on the climate of the United States. Climate Dynamics. DOI 10.1007/s00382-009-0566-z (in press).
The abstract reads
“I have used a high-resolution nested climate modeling system to test the sensitivity of regional and local climate to the modern non-urban land cover distribution of the continental United States. The dominant climate response is cooling of surface air temperatures, particularly during the warm-season. Areas of statistically significant cooling include areas of the Great Plains where crop/mixed farming has replaced short grass, areas of the Midwest and southern Texas where crop/mixed farming has replaced interrupted forest, and areas of the western United States containing irrigated crops. This statistically significant warm-season cooling is driven by changes in both surface moisture balance and surface albedo, with changes in surface moisture balance dominating in the Great Plains and western United States, changes in surface albedo dominating in the Midwest, and both effects contributing to warm-season cooling over southern Texas. The simulated changes in surface moisture and energy fluxes also influence the warm-season atmospheric dynamics, creating greater moisture availability in the lower atmosphere and enhanced uplift aloft, consistent with the enhanced warmseason precipitation seen in the simulation with modern land cover. The local and regional climate response is of a similar magnitude to that projected for future greenhouse gas concentrations, suggesting that the climatic effects of land cover change should be carefully considered when crafting policies for regulating land use and for managing anthropogenic forcing of the climate system.”
The conclusion has the text
“These results have important implications for future climate, energy, and land use policies. For instance, future conversion from crop to other land types could cause warming (particularly through urbanization (Kueppers et al. 2007)) and afforestation for carbon sequestration (e.g., Diffenbaugh 2005a; Jackson et al. 2008), while future expansion of crop area could cause cooling (particularly through expansion into marginal areas that require substantial irrigation). Further, in addition to direct influences on climate, the presence of agriculture could suppress regional and local warming at high greenhouse gas levels (Diffenbaugh et al. 2005; White et al. 2006), meaning that there could be secondary climatic effects of transitioning crops to forests as greenhouse gas concentrations continue to rise. The results presented here therefore suggest that the climatic effects of land cover change should be carefully considered when crafting policies for regulating land use and for managing anthropogenic forcing of the climate system.”
This study reinforces the 2005 National Research Council report on the need to broaden the assessment of the role of humans within the climate system, beyond that due to the emissions of well-mixed greenhouse gases. This scientifically robust perspective was ignored in the EPA report last week of the plan to regulate CO2 and several other gases due to their role as climate forcings.
The author could also expand his analysis to assess the heat content (moist enthalpy) changes that result from these land conversions (e.g. see and see). The change to agriculture, for example, would generally result in added water vapor and a darker surface albedo, both of which would elevate the moist enthalpy. Since moist enthalpy (in units of Joules per kilogram of air), rather than dry bulb temperature by itself, is the actual metric for heat, this would provide additional insight into the role of landscape change on the climate.