The oceans and climate changeA welcome pause
When cold water meets hot air
THE rise in greenhouse-gas emissions means oceans are playing a bigger role in regulating the climate. In parts of the Pacific Ocean, huge upwellings from the bottom bring cold water from the depths and push warm surface water down. According to a new study in Nature Climate Change by Matthew England of the University of New South Wales and others, higher air temperatures are strengthening east-west trade winds at equatorial latitudes in the Pacific and speeding up this vast churn, sequestering heat that would otherwise have warmed the Earth’s surface. This, they say, explains much of the recent slowdown in the rise of surface temperatures that has puzzled climate scientists since it began in 1998.
The slowdown is clearly good news. But it may not last. Oceans also absorb carbon dioxide, which dissolves in sea water. They are the world’s biggest carbon sink. But there are limits to their absorptive capacity. A study in Nature by Samar Khatiwala and others in 2009 said their uptake of carbon dioxide declined by about 10% after 2000. That is disturbing. Less carbon in the oceans means more in the atmosphere—and implies that, at some point, the rise in surface temperatures is likely to resume.