Shifting Westerlies

摘要

The westerlies are the prevailing winds in the middle latitudes of Earth's atmosphere, blowing from west to east between the high-pressure areas of the subtropics and the low-pressure areas over the poles. They have strengthened and shifted poleward over the past 50 years, pos-sibly in response to wanning from rising concentrations of atmospheric carbon dioxide (CO_2) (1-4). Some-thing similar appears to have happened 17,000 years ago at the end of the last ice age: Earth warmed, atmospheric CO_2 increased, and the Southern Hemisphere westerlies seem to have shifted toward Antarctica (5, 6). Data reported by Anderson et al. on page 1443 of this issue (7) suggest that the shift 17,000 years ago occurred before the warming and that it caused the CO_2 increase. The CO_2 that appeared in the atmosphere 17,000 years ago came from the oceans rather than from anthropogenic emissions. It was vented from the deep ocean up to the atmosphere in the vicinity of Antarctica. The southern westerlies are important in this context because they can alter the oceanic circulation in a way that vents CO_2 from the ocean interior up to the atmosphere.