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World's oceans steadily heating up, new study finds

Trend in ocean heat content at depths between 0-2,000 meters. Image: Nature Climate Change
Scripps Institution of OCeanography
Trend in ocean heat content at depths between 0-2,000 meters. Image: Nature Climate Change

Ocean temperatures around the world are steadily creeping upward, according to a new study from the Scripps Institution of Oceanography.

On average, things are warming at a yearly rate of 0.005° C (0.009° F) in the top 500 meters of ocean.

Deeper down, between 500 meters and 2,000 meters waters are heating about 0.002° C (0.0036° F) a year.

Those numbers may seem small, but lead author Dean Roemmich says it takes a lot of energy to produce a change like that.

"The ocean is so large and its heat capacity, its ability to absorb heat, is so great that it's possible to push a  huge amount of heat into the ocean without changing its temperature by a whole lot."

In this case, Roemmich says the energy required is akin to two trillion 100-watt light bulbs blaring heat at the ocean continuously.

"That’s obviously a huge amount of heat,” he said.

Not all oceans heated equally though. Roemmich pointed out that waters in the southern hemisphere showed a greater increase in temperature, possibly because more of the world's oceans are there.

The data was gathered using a relatively new tool called Argo, it's a system of more than 3,700 buoys dropped in the world’s oceans about every 180 miles.

"That's really what made this study possible," Roemmich said.

(A map showing the location of the Argo buoys across the globe. Image by Mvanderburch via Wikimedia Commons.)

Argo has been in operation since the early 2000s but didn't have global coverage until 2006. This new study uses data from that point onward for its measurements.

The Argo instruments sink about 2000 meters in the water column of the ocean and rise, measuring temperature and salinity along the way.

Every 10 days they beam data to a satellite, Roemmich said.

The findings from this first-of-its kind study are consistent with long-term warming trends seen in past research. The team cited growing concentrations of heat-trapping greenhouse gases as the likely cause.

This new research also adds context to a widely reported haiatus in sea surface and lower atmosphere temperature increases dating back to 1998.

Phil Sutton with the National Institute of Waters and Atmospheric Research in New Zealand noted that this study shows much of that heat may have ended up in the deep ocean.

"The ocean is about 95% of where the heat energy is going in the whole global system," explained Sutton, who was also part of the study.

Warmer sea temperatures can have impacts on marine life and cause surface water to expand leading to higher sea levels across the globe.

Currently, water levels are rising at a rate of about an inch per decade, Roemmich said. He added that one-third of that is due to heat expansion.