Pacific warming 15 times faster than ever

Although the temperature of Earth’s atmosphere may have hit the “pause” button recently – with little global warming measured over the past few years – that hasn’t been the case with the oceans.

In a study out Thursday in the journal Science, researchers say that the middle depths of a part of the Pacific Ocean have warmed 15 times faster in the past 60 years than they did during the previous 10,000 years.

Most of the heat that humanity has put into the atmosphere since the 1970s from greenhouse gas emissions has likely been absorbed by the oceans, says a recent report from the Intergovernmental Panel on Climate Change, a United Nations-sponsored group of scientists that issues updates every few years about global warming.

“Increases in ocean heat content and temperature are robust indicators of global warming during the past several decades,” according to Thursday’s Science study.

“We may have underestimated the efficiency of the oceans as a storehouse for heat and energy,” said study lead author Yair Rosenthal, a climate scientist at Rutgers University.

Study co-author Braddock Linsley, a Columbia University climate scientist, said that in the past six decades the temperature of the Pacific Ocean water studied (from the surface to about 2,200 feet below) has increased by about one-third of a degree Fahrenheit. Researchers say that while the amount of warming might seem small, it’s the rate of warming that’s so alarming.

“It’s not so much the magnitude of the change, but the rate of change,” Linsley said.

The researchers found that Pacific Ocean water has generally been cooling over the past 10,000 years, until about 800 years ago, when temperatures started to slowly rise. After some temperature fluctuations since then, the past few decades have seen a dramatic rise in the rate of increase.

The Earth’s atmosphere has been about the same temperature for the past 15 years or so, providing fuel for skeptics of man-made global warming. However, this study, along with other recent research, finds that heat absorbed by the planet’s oceans has increased significantly.

Obviously, there were no thermometers taking measurements of ocean temperatures over the past few thousand years (records from buoys go back only to the 1960s). So scientists had to use “proxy” sources to measure temperature. In this case, it was fossils of ancient marine life that could be analyzed to reconstruct the climates in which they lived over millennia.

“This is a relatively new way of measuring past temperature data,” Rosenthal noted.

How long this pause in atmospheric temperature will last may be up to natural variability in the Pacific. When the La Niña climate pattern (cooler than average Pacific Ocean water) switches, and the Pacific reverts to warmer-than-usual El Niño, global temperatures may shoot up again, said Kevin Trenberth, a scientist at the National Center for Atmospheric Research in Boulder, Colo., who was not involved in the research.

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