Science  30 Sep 2011:
Vol. 333, Issue 6051, pp. 1808

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  1. Aerosols Altered Asian Monsoons


    Summer monsoons provide much of the water for farming on the Indian subcontinent, but the pattern of rain shifted dramatically during the last half of the 20th century. In a study appearing online 29 September in Science, researchers pin the blame on soot and other aerosols from human activities.

    From 1951 to 1999, central-northern India became drier while Pakistan, northwestern India, and southern India got wetter. To determine whether these changes were due to natural variability or human interference (greenhouse gases or aerosols), climate scientists Massimo Bollasina, Yi Ming, and V. Ramaswamy of the Geophysical Fluid Dynamics Laboratory/NOAA in Princeton, New Jersey, compared the history of rainfall with simulations that singled out each climate “forcing” factor to observe its impact.

    Although greenhouse gases would have increased rainfall over north-central India, the aerosols, they found, caused the “very pronounced drying trend,” Ming says. Here's why: Under normal conditions, the northern hemisphere receives more energy from the sun from June to September; that imbalance drives the ocean-atmosphere circulation that powers the monsoons. But atmospheric aerosols shaded the northern hemisphere relative to the southern hemisphere, altering the energy balance between the two—weakening the circulation and altering where the rain falls.

  2. Study Casts Doubt on Aging Gene

    A study in Nature last week threw cold water on claims that a certain gene can extend life. Called SIR2, the feted gene seems to slow aging in a number of animals. Even more exciting, researchers have shown in recent years that calorie restriction, which also stretches lifespan, works by activating SIR2 and related genes, that make enzymes called sirtuins.

    But science is rarely straightforward, and a research group based mainly in the United Kingdom says that in their experiments, SIR2 did nothing to help worms and flies live longer. “We tried so hard to see any effects at all in many different settings, and we haven't seen any,” says biogerontologist David Gems of Imperial College London, who led the study.

    Sirtuin backers vehemently dispute the findings. Molecular biologist Leonard Guarente of the Massachusetts Institute of Technology, who led key work on SIR2 in worms, argues that “you can always get an experiment not to work.” Both sides are sticking to their views, and the debate is likely to continue.