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A major puzzle of paleoclimatology is why, after a long interval of cooling climate, each late Quaternary ice age ended with a relatively short warming leg called a termination. We here offer a comprehensive hypothesis of how Earth emerged from the last global ice age. A prerequisite was the growth of very large Northern Hemisphere ice sheets, whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation. The Southern Hemisphere westerlies shifted poleward during each northern stadial, producing pulses of ocean upwelling and warming that together accounted for much of the termination in the Southern Ocean and Antarctica. Rising atmospheric CO2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres.

"To help cool a warming world, some scientists have suggested fertilizing the oceans with iron. The idea is to stimulate vast blooms of phytoplankton, which sequester carbon dioxide. But such an approach could have deadly consequences. Experiments in the northern Pacific Ocean show that phytoplankton in waters far from land produce a molecule called domoic acid, a neurotoxin that has killed wildlife and people in coastal areas. "