We have a new paper that has appeared in the Journal of Geophysical Research. The title is “Effects of biomass-burning-derived aerosols on precipitation and clouds in the Amazon Basin: a satellite-based empirical study” and is authored by J. C. Lin,T. Matsui, R. A. Pielke Sr., and C. Kummerow.
“Biomass burning in the Amazon provides strong input of aerosols into the atmosphere, with potential effects on precipitation, cloud properties, and radiative balance. However, few studies to date have systematically examined these effects at the scale of the Amazon Basin, over an entire burning season, using available data sets. We empirically study the relationships of aerosol optical depth (ta) versus rainfall and cloud properties measured from satellites over the entire Brazilian Amazon during the dry, biomass burning seasons (August–October) of 2000 and 2003. Elevated ta was associated with increased rainfall in both 2000 and 2003. With enhanced ta, cloud cover increased significantly, and cloud top temperature/pressure decreased, suggesting higher cloud tops.
The cloud droplet effective radius (Re) exhibited minimal growth with cloud height under background levels of ta, while distinct increases in Re at cloud top temperatures below -10C, indicative of ice formation, were observed with aerosol loading. Although empirical correlations do not unequivocally establish the causal link from aerosols, these results are consistent with previous observational and modeling studies that pointed dynamical effects from aerosols that invigorate convection, leading to higher clouds, enhanced cloud cover, and stronger rainfall. We speculate that changes in precipitation cloud properties associated with aerosol loading observed in this study could have important radiative and hydrological effects on the Amazonian climate system. The accelerated forest burning for agricultural land clearing and the resulting enhancements in aerosols and rainfall may even partially account for the observed positive trend in Amazonian precipitation over the past several decades.”
Excerpts from the paper read,
“Forest fires in the Amazon, which have accelerated over the past decades because of human activities [Crutzen and Andreae, 1990; Setzer et al., 1994], release large quantities of aerosols into the atmosphere.”
“On the basis of an empirical analysis of satellite observations, this study examined correlations between aerosol loading (primarily from biomass burning) and rainfall and cloud properties in the Amazon Basin, during the dry season. While this work cannot unequivocally establish causal links between aerosols and the observed changes, the analysis revealed the following correlations associated with increased aerosols that need to be reproduced in future modeling studies: (1) increased precipitation, (2) increased occurrence of intense rainfall events, (3) enhanced cloud cover, (4) elevated cloud tops, (5) increased water path, and (6) greater formation of ice.”
“The accelerated burning in the Amazon for agricultural land use over the past several decades [Crutzen and Andreae, 1990; Setzer et al., 1994] and the associated enhancements in aerosols and rainfall may even partly account for the observed multidecadal positive trend Amazonian precipitation [Chen et al., 2001; Easterling et al., 2000].”
Here is yet another study that documents why a focus on global average surface temperature trends completely misses a very important first-order human caused climate forcing which can have very significant effects on the regional and local environment. Moreover, when extrapolating these finds to other locations with biomass burning (e.g. Indonesia, central Africa), this clearly can have global climate consequences as the aerosol material is advected across long distances by the winds.