Maintaining Continental Slopes
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چکیده
Although water vapor is the most important greenhouse gas, it is not even agreed whether an increase in its concentration due to global warming will cause more warming or cooling. Warming (a positive feedback) will occur if the biggest effect is to absorb more outgoing long-wave radiation. Cooling (a negative feedback) will occur if the major result is to form more clouds, which would reflect more sunlight. Soden et al. (p. 727; see the Perspective by Del Genio) test these two possibilities by using observations of the atmospheric cooling and drying that occurred after the eruption of Mount Pinatubo in 1991 as targets for an atmospheric general circulation model. The cooling that followed the blast is consistent with the measured decrease in water vapor only if the vapor provides positive feedback. These results suggest that current climate models have correctly chosen the role of water vapor.
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