In the tropical Pacific region, air will probably circulate less vigorously in a warmer world, according to a new study. The expected changes resemble the effects of El Niño, a warming of the tropical Pacific surface ocean that occurs every 3 to 7 years and causes a shift in global weather patterns.

Gabriel Vecchi from the US National Oceanic and Atmospheric Administration and Brian Soden from the University of Miami1 analysed simulations from 22 climate models that included a doubling of atmospheric CO2 by 2100. The models agreed that the tropical Walker circulation — which lifts air over Indonesia that later descends towards Peru in a giant vertical loop — will slow down as the temperature increases. This change will arise from the response of the global water cycle to increased temperature and result in a climatic pattern similar to El Niño. But contrary to El Niño events, the ocean will respond to, rather than cause slowing of atmospheric overturning.

Climate models are still divided on whether El Niño years will become more frequent or intense. But they agree that in a warmer world, Pacific climate will be closer to today's El Niño years, implying a decline in nutrient delivery to the surface ocean and in fishstocks off Peru and Ecuador.