This week’s Science carries two important articles. The first tackles the question of how much of carbonaceous aerosols in the South Asia and Indian Ocean’s atmospheric brown clouds can be attributed to either biomass (burning and cooking) or fossil fuel combustion (O. Gustafsson et al. Brown clouds over South Asia: biomass or fossil fuel combustion? Science 323:495-498, 2009). The authors estimate that 2/3 of the aerosols originate from biomass burning, suggesting where one should go first to mitigate atmospheric carbon emissions and air pollution in the region. These are conclusions with direct implications for the ongoing policy debate leading to the watershed Copenhagen climate convention meeting.
The second paper is a disturbing account of the rapid increase in the rate of tree mortality across the western United States (P. J. van Mantgem et al. Widespread increase in tree mortality rates in the western United States. Science 323:521-524, 2009). The authors describe how this phenomenon is significantly altering the composition, structure and function of the forests in response to climate change-driven regional warming, and associated drought stress. These results appear to be more consequential to the loss of carbon stocks across the affected temperate region than the dynamic observed in tropical forests driven by the same underlying cause. Climate change naysayers and conservationists alike need to look carefully at this disquieting analysis.