Record-breaking ocean temperatures wreak havoc

http://www.newscientist.com/article/mg22429954.000-recordbreaking-ocean-temperatures-wreak-havoc.html

12 November 2014 by Michael Slezak
Magazine issue 2995

THE world's oceans are the hottest they've ever been in the modern record. An analysis shared exclusively with New Scientist suggests that the global slowdown in the rise of air temperatures is probably over, and we are entering another period of rapid warming.

Since the last big El Niño event in 1998, when ocean temperatures last peaked, they have remained relatively stable. Such periods are not unexpected, but research is increasingly indicating that the recent slowdown in global surface air temperature rise is down to heat being absorbed by the world's deep oceans, leaving the surface, and therefore also the air, cool.

But when Axel Timmermann of the University of Hawaii in Honolulu analysed the most recent publicly available monthly data from the UK Met Office, he found that the ocean surfaces are now the hottest they have been since records began. In July this year, ocean surfaces were 0.55 °C (99F) above the average since 1890, just beating the previous record of 0.51 °C in 1998. In the North Pacific, the temperatures were about 0.8 °C (1.4F) above average, which is 0.25 °C warmer than the 1998 peak.

"It's a remarkable situation and I've never seen warming of the North Pacific like that," Timmermann says. The sea surface temperatures could drop back to what they've been recently, he says, but unless there is a dramatic drop soon, it will mean the end of the current hiatus in warming. "This will bias the trends over the next two or three years," says Timmermann.

•••••

Most climate scientists had expected the slowdown in global warming to be brought to an end by a large El Niño. These events happen when warm waters deep in the Pacific burst to the surface and raise global air temperatures.

But although a large El Niño was predicted for this year, we haven't had even a small one yet.

•••••

"For an El Niño to develop you need the atmosphere to play ball," says David Jones at the Bureau of Meteorology in Melbourne. Temperature differences across the Pacific Ocean are needed before an El Niño can kick in, so the consistently warm temperatures this year could be why the event forecasted for 2014 doesn't seem to be happening.

The warmer oceans make El Niño forecasts difficult, because they rely on looking at past events. "This is a flawed strategy when the climate is changing," says Kevin Trenberth at the National Center for Atmospheric Research in Boulder, Colorado.

Even though a large El Niño is yet to materialise, the warm Pacific temperatures mean some El Niño-like effects are occurring, says Trenberth. This includes more hurricanes in the Pacific, as well as more storms curling over into mainland US. Meanwhile, there have been fewer hurricanes in the Atlantic, just as happens during El Niño. Elsewhere, dry conditions have occurred across Australia, and the Indian monsoon was delayed – effects all arising from warm oceans, despite the lack of an El Nino event.

Cai compared recent temperature maps (see map) with historical patterns for New Scientist to see what to expect over the coming months. He found a correlation with rainfall changes that roughly matches those seen during El Niño, and so predicts that there may be increased rainfall over drought-stricken California. But unlike during El Niño, he says there should be drier than usual conditions in western Canada.