Global warming strikes deep into oceans

The oceans have soaked up as much heat from global warming over the last two decades as during the preceding 130 years, according to a study published Monday.

While this accelerated absorption has helped keep human habitats cooler, in the long run it could be a ticking time bomb that disrupts weather and climate globally, scientists warned.

"We estimate that half of the total global ocean heat uptake since 1865 has accumulated since 1997," a team of scientists led by Peter Gleckler of the Laurence Livermore National Laboratory in California reported.

A third of that recent build up, they found, occurred at depths of 700 metres (2,300 feet) or greater, beyond the reach of sunlight.

This may explain a pause or "hiatus" in warming observed at the sea surface since the end of the 20th century, according to the study. 

Some had interpreted this as a slowdown in warming overall.

Surface waters are thought to have previously absorbed the bulk of heat taken up by the ocean. Why the ratio is changing is not fully understood.

The findings, published, in Nature Climate Change, were based in large part on observation.

The earliest data was gathered in the 19th century by the HMS Challenger expedition, a scientific foray launched by Britain's Royal Society that is often credited with laying the foundation for modern oceanography.

More recent inputs came from multi-decade ship logs, and for  measurements up to 2,000 metres (6,500 feet) deep so-called Argo floats scattered across the oceans.