Global warming is hiding, scientists say

22 สิงหาคม 2557

Global warming activists now have a better explanation for why global temperatures haven't been rising nearly as much as earlier predicted. The heat is temporarily trapped deep in the oceans, researchers say.

Global warming activists now have a better explanation for why global temperatures haven't been rising nearly as much as earlier predicted. The heat is temporarily trapped deep in the oceans, researchers say.

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Members of environmental group Greenpeace display a banner and life preservers with the names of world leaders to protest against global warming, in front of the venue for the Intergovernmental Panel on Climate Change (IPCC) Working Group II session in Yokohama, suburban Tokyo on March 30, 2014. AFP PHOTO / Yoshikazu TSUNO

Global warming is hiding, scientists say

On the one hand, global warming is often blamed for just about any damaging weather event, from severe storms, to floods to drought.

On the other hand, global warming sceptics point out that average temperatures have not been rising significantly for the past 15 years.

Scientists say everyone needs to take a longer-term look. Global warming is still with us, it's just hiding temporarily.

The apparent slowdown in the Earth's surface warming in the last 15 years could be due to that heat being trapped in the deep Atlantic and Southern Ocean, researchers said Thursday.

The findings in the journal Science suggest that such cycles tend to last 20-35 years, and that global warming will likely pick up again once that heat returns to surface waters.

"Every week there's a new explanation of the hiatus," said co-author Ka-Kit Tung, a University of Washington professor of applied mathematics and adjunct faculty member in atmospheric sciences.

"We looked at observations in the ocean to try to find the underlying cause."

Tung and Xianyao Chen of the Ocean University of China studied deep-sea temperatures from floats that sample the water as deep as 2,000 meters.

They found that more heat began to sink around 1999, just when the rapid warming of the 20th century began to flatline.

The movement of more heat into the water explains how surface temperatures could stay close to the same, even as mounting greenhouse gases trap more solar heat at the Earth's surface, the researchers said.

They also found that contrary to earlier studies, the Pacific Ocean was not the hiding place for the heat.

"The finding is a surprise," Tung said.

"But the data are quite convincing and they show otherwise."

The change also coincided with an increase in saltier, denser water at the surface of the northern part of the Atlantic, near Iceland.

This dynamic caused changes in the speed of the huge current in the Atlantic Ocean that circulates heat throughout the planet, the study said.

"When it's heavy water on top of light water, it just plunges very fast and takes heat with it," Tung said.

"There are recurrent cycles that are salinity-driven that can store heat deep in the Atlantic and Southern oceans," Tung added.

"After 30 years of rapid warming in the warm phase, now it's time for the cool phase."

Researchers said the current slowdown may last another decade, then the rapid warming is likely to return.

Adapted from an AFP story