A Sensitive Reaction

Global warming could speed up decomposition, but how much might decomposition speed up global warming?

By Kerry Grens

1 "In a sense there's some kind of natural break in the system that would bring this positive feedback to a halt," says Jerry Melillo at the Marine Biological Laboratory. For example, in a 10-year study Melillo led in the Harvard Forest, the response to warming, as measured in carbon flux, jumped an average of 28% in each of the first six years, but by the tenth year didn't respond at all to warming.2 In other words, the researchers found that, with elevated temperatures, decomposition (and therefore carbon dioxide) rises, but then returns to normal with time, breaking down the positive-feedback loop. Why?

Wallenstein suspects that microbial communities are acclimating to long-term increases in temperature, which may favor microbes with less temperature-sensitive enzymes. "In the microbial world we...

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