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THE world’s oceans are the hottest they’ve ever been in the modern record. An analysis shared exclusively with 51���� 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 of the University of Hawaii in Honolulu analysed the most recent publicly available monthly data , 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 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 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.

“It’s a remarkable situation and I’ve never seen warming of the North Pacific like that”

Land surface temperatures are much more variable than ocean temperatures. The ability of the world’s oceans to absorb extra heat is believed by many to be behind the recent pause in global warming. Now some researchers say the increased ocean surface temperatures are a strong sign that this hiatus could be coming to an end.

“In the North Pacific, the hiatus is definitely finished,” says from the CSIRO, Australia’s national research agency in Melbourne. He says that while the global surface temperatures – which include land temperature too – aren’t at record highs yet, the slowdown in warming is more-or-less over: “In our mind the hiatus is already finished, because oceans are 70 per cent of the surface.”

But some are cautious about linking the peak to an upward trend. “Beware of single peaks,” says of the Scripps Institution of Oceanography in San Diego. He doesn’t interpret the data as showing a return to consistent warming.

Warmer seas are expected to affect marine ecosystems, including commercially valuable fish. “Many marine species have a strong association with specific temperature ranges, so if there is warm water, they move with it,” says Nate Mantua at the National Oceanic and Atmospheric Administration in Santa Cruz, California. Subtropical fish species like tuna have already moved further north. On the other hand, fish that do well in colder water, like Pacific salmon, typically grow more slowly and are less likely to survive in warmer waters, says Mantua.

Coral reefs could be hit too. When corals are stressed, they expel their symbiotic algae, turn white and die. When ocean temperatures were last at their highest, coral bleaching happened around the world. Although fewer coral reefs fall within the warmest regions this time, Timmermann says many corals are already being bleached in Hawaii.

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.

False forecast?

“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 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 51���� 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.FIG-mg29954001.jpg

This article appeared in print under the headline “Oceans get into hot water”