Earth & Environment

Soot’s contributions to global warming may be overestimated, and unusual source of oceans’ methane discovered

Black carbon not so black
Black carbon, aka soot, may not have as big an effect on global warming as scientists had thought. Climate models generally assume that soot particles mix with other particles in the atmosphere in a way that enhances overall warming. Now, measurements of the air near Los Angeles, San Francisco and Sacramento suggest that instead of doubling this particular effect, black carbon increases it by an average of only 6 percent. Many simulations may thus overestimate warming attributable to black carbon — although soot contributes to atmospheric heating in other ways, as well as posing a major health threat. The work, led by Christopher Cappa of the University of California, Davis and Timothy Onasch of Boston College and Aerodyne Research in Billerica, Mass., appears in the Aug. 31 Science. —Alexandra Witze

Demystifying the ocean’s methane exhalations
A ubiquitous one-celled microbe may be behind the copious amounts of methane at the ocean’s surface. Methane, a greenhouse gas, is produced by anaerobic microbes, or those that aren’t dependent on oxygen, so scientists have puzzled over how the ocean surface could be saturated with the gas. In the Aug. 31 Science, William Metcalf of the University of Illinois at Urbana-Champaign and his colleagues show that archaea — common microbes unrelated to bacteria — make and decorate their shells with a phosphorus-rich food that aerobic bacteria crave. But when they eat it, the bacteria jettison methane as a by-product. The scientists also identified a second aerobic bacteria with the gene to make that methane feedstock: It’s Pelagibacter, one of the sea’s most abundant organisms. —Janet Raloff

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