Global warming hiatus could be down to changing Atlantic currents

  • @SteveAConnor

The world would be an even warmer place had it not been for a change in the water currents of the North and South Atlantic which have transported huge amounts of heat from the sea surface to the deeper regions of the ocean, scientists said.

A study based on temperature data collected from deep-sea probes has found that since about 2000 there has been a greater flow of sinking water taking heat from the surface of the Atlantic which has helped to counteract man-made global warming.

The findings, published in the journal Science, are the latest possible explanation for why surface temperatures on land have not risen as fast as many computer climate models have predicted – resulting in the so-called global warming “hiatus”.

Temperatures readings taken by scientific Argos floats distributed in the Atlantic, which can sample water down to 2,000 metres, shows an increase over the past 15 years in the volume of water and heat that has been drawn down to depths of about 1,500 metres.

This could explain the “missing heat” of the hiatus and comes as a rival explanation to other possible reasons why surface temperatures have not risen as fast as they might, said Ka-Kit Tung of the University of Washington in Seattle.

“Every week there’s a new explanation for the hiatus. The finding is a surprise, since the current theories had pointed to the Pacific Ocean as the culprit for hiding heat. But the [Atlantic] data are quite convincing,” Dr Tung said.

The scientists believe the trend is part of a 30-year cycle of warming and cooling in the Atlantic and that even more rapid surface warming could occur in the near future when the ocean currents swing into a warming phase.

Piers Forster, professor of climate science at Leeds University, said: “This [study] is another a nail in the coffin of the idea that the hiatus is evidence that our projections of long-term climate change need revising down. Variability in the ocean will not affect long-term climate trends but may mean we have a period of accelerated warming to look forward to.”

Professor Andrew Watson of the University of Exeter said that further research is needed before any conclusive explanation of the hiatus is accepted.

“It will be very interesting to see whether their finding that during the last decade the heat has penetrated to depth mostly in the Southern and Atlantic Oceans stands up,” Professor Watson said.