Thanks to Fred Singer for alerting us to the following paper.
Jingfeng Wang, Frédéric J. F. Chagnon, Earle R. Williams, Alan K. Betts, Nilton O. Renno, Luiz A. T. Machado, Gautam Bisht, Ryan Knox, and Rafael L. Bras, 2009: Impact of deforestation in the Amazon basin on cloud climatology. PNAS, published online before print February 23, 2009, doi:10.1073/pnas.0810156106
The abstract is
“Shallow clouds are prone to appear over deforested surfaces whereas deep clouds, much less frequent than shallow clouds, favor forested surfaces. Simultaneous atmospheric soundings at forest and pasture sites during the Rondonian Boundary Layer Experiment (RBLE-3) elucidate the physical mechanisms responsible for the observed correlation between clouds and land cover. We demonstrate that the atmospheric boundary layer over the forested areas is more unstable and characterized by larger values of the convective available potential energy (CAPE) due to greater humidity than that which is found over the deforested area. The shallow convection over the deforested areas is relatively more active than the deep convection over the forested areas. This greater activity results from a stronger lifting mechanism caused by mesoscale circulations driven by deforestation-induced heterogeneities in land cover.”
An extract from the conclusions reads
”The atmosphere over the study domain behaves more like that over oceans with CAPE dominated by the humidity factor. The forested patches in the Amazon may be viewed as ‘‘green oceans’’ surrounded by ‘continents’. ’Mesoscale circulations induced by the contrast between forested and deforested surfaces with the existing length scales, have been identified as the likely dominant lifting mechanism for convection based on the existing evidence. Boundary layer turbulence appears to play a secondary role in the situation considered in this study. A lack of lifting mechanism is responsible for suppressed convective activity over extensive homogeneous forest surfaces even though CAPE was abundant during the period of study.”
This new study provides a clear demonstration of the role of landscape both as altering the atmospheric heat and moisture above it, as well as creating atmospheric circulations as a result of fragmented landscape change.
We have published similar conclusions in our papers; e.g. see
Lawton, R.O., U.S. Nair, R.A. Pielke Sr., and R.M. Welch, 2001: Climatic impact of tropical lowland deforestation on nearby montane cloud forests. Science, 294, 584-587.
Nair, U.S., R.O. Lawton, R.M. Welch, and R.A. Pielke Sr., 2003: Impact of land use on Costa Rican tropical montane cloud forests: 1. Sensitivity of cumulus cloud field characteristics to lowland deforestation. J. Geophys. Res. – Atmospheres, 108, 10.1029/2001JD001135
Pielke Sr., R.A., 2001: Influence of the spatial distribution of vegetation and soils on the prediction of cumulus convective rainfall. Rev. Geophys., 39, 151-177.
Pielke, R.A. Sr., J. Adegoke, A. Beltran-Przekurat, C.A. Hiemstra, J. Lin, U.S. Nair, D. Niyogi, and T.E. Nobis, 2007: An overview of regional land use and land cover impacts on rainfall. Tellus B, 59, 587-601.
Ray, D.K., U.S. Nair, R.O. Lawton, R.M. Welch, and R.A. Pielke Sr., 2006: Impact of land use on Costa Rican tropical montane cloud forests. Sensitivity of orographic cloud formation to deforestation in the plains. J. Geophys. Res., 111, D02108, doi:10.1029/2005JD006096.
This topic, of the effect of land use change on climate, was not adequately considered in the 2007 IPCC and 2009 CCSP Reports. This failure is one of the reasons that the policymakers are assuming, erroneously, that the climate is dominated by the radiative forcing of carbon dioxide.