Cooking and Burning
A huge plume of air pollution, called the Asian Atmospheric Brown Cloud (ABC), emanates from Southern Asia and persists over much of the Indian continent and the Indian Ocean during the winter. It is so large and dense that its cooling effect may balance, or even surpass, the warming effect of greenhouse gases in the region. In order to know how to mitigate this scourge, its origin must be known. There are two major sources that contribute to the ABC--biomass burning and fossil fuel combustion--whose relative importance is unclear. Gustafsson et al. (p. _495_ (http://www.info-aaas.org/util/link.jsp?e=0-jkh8dWkT3n-qkJdT6KB-x1gZzuskeKJgc... eLEjlDfdQNDgEiwWG7Bw..A) ; see the Perspective by _Szidat_ (http://www.info-aaas.org/util/link.jsp?e=9hkWtoeqjSJbw-2wNomQH2ftvxBu__f9dAO... WW00evvrEUQ&s=8cAH8W7w42QgXi5scbyBzCg..A&v=9QieLEjlDfdQNDgEiwWG7Bw..A) ) measured radiocarbon in particles from the cloud, and between one-half and two-thirds of the carbonaceous aerosols were from biomass burning. Thus, controlling biomass combustion, particularly residential cooking and agricultural burning, will be important to mitigate climate effects and to improve air quality in the region.
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Dying Trees Tree mortality rates have more than doubled in recent decades in otherwise undisturbed forests of the western United States, possibly as a consequence of ongoing regional warming. Van Mantgem et al. (p. _521_ (http://www.info-aaas.org/util/link.jsp?e=3HAdVkrSLcAEJ1VfAFh0qQB5HmnlsgC85iP... W7w42QgXi5scbyBzCg..A&v=9QieLEjlDfdQNDgEiwWG7Bw..A) ; see the news story by _Pennisi_ (http://www.info-aaas.org/util/link.jsp?e=2O_odGyng9kHXsR_lt2roFsdP6gAdk9HY8G... ..A) ) use a long-term set of demographic data to reveal a pervasive increase in background mortality rates for trees in seemingly healthy forest. The increases occur regardless of elevations, tree size, taxon, or fire history and cannot be attributed to processes such as increasing competition or aging of large trees. The increases in mortality are likely to have been driven by environmental changes, with ongoing regional warming and its widespread effects on the western U.S. hydrologic cycle being the most probable contributors. Changes in tree mortality rates can affect future forest structure and composition, which in turn affect ecosystem services such as carbon sequestration, and thereby biological contributions and responses to climatic changes.
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