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The Pacific Ocean fills in another piece of the global warming puzzle

 
Jigsaw Puzzle

The global warming puzzle continues to be pieced together. Photograph: George Diebold/Getty Images

 

Powered by Guardian.co.ukThis article titled “The Pacific Ocean fills in another piece of the global warming puzzle” was written by Dana Nuccitelli, for theguardian.com on Tuesday 3rd September 2013 04.46 UTC

A new study published in the journal Nature incorporates temperature changes in the tropical Pacific Ocean into an advanced climate model, and finds that the model can reproduce observed global surface temperature changes remarkably well.

Global Surface Temperatures

This graph shows the good match between temperatures in the Nature paper model (in red) and measured temperatures (in black). Just accounting for human and solar climate influences doesn’t reproduce the recent surface warming slowdown (in purple).

Importantly, as authors Yu Kosaka and Shang-Ping Xie from the Scripps Institution of Oceanography explain, accounting for the changes in the Pacific Ocean allows the model to reproduce the slowed global surface warming over the past 15 years. It also accurately reproduces the regional and seasonal changes in surface temperatures, which adds confidence that their results are meaningful.

“Our results show that the current hiatus is part of natural climate variability, tied specifically to La-Niña-like decadal cooling … For the recent decade, the decrease in tropical Pacific sea surface temperature has lowered the global temperature by about 0.15 degrees Celsius compared to the 1990s”.

Despite only covering 8.2 percent of the Earth’s surface, these results suggest that the tropical Pacific Ocean plays a major role in short-term changes in the average global surface temperature. And over the past 15 years, it’s offset most of the global surface warming from the increased greenhouse effect.

These results are broadly consistent with several other important recent papers investigating the role of the oceans in global warming. For example, the model used in this study finds that the overall heating of the planet has not slowed when the warming of the oceans are taken into account, as studies led by John Abraham, myself, and several others have also concluded.

Research led by Gerald Meehl has similarly focused on the importance of the Pacific Ocean in short-term global surface temperature changes. His climate model predicts that there will be decades when surface temperature changes are relatively flat because more heat is transferred to the deep oceans, precisely as we have observed over the past decade. Meehl discussed the Kosaka & Xie study with Carbon Brief,

“This paper basically confirms, with a novel methodology, what we originally documented in our Nature Climate Change paper in 2011 and followed up with in our Journal of Climate paper … We went beyond [the new paper] to show that when the tropical Pacific was cool for a decade … more heat is mixed into the deeper ocean, something the new paper doesn’t address.”

Kevin Trenberth, who co-authored several of these important ocean studies, has likewise pointed to the important role of the Pacific Ocean in transferring more heat to the deep oceans.

“The cause of the shift is a particular change in winds, especially in the Pacific Ocean where the subtropical trade winds have become noticeably stronger, changing ocean currents and providing a mechanism for heat to be carried down into the ocean. This is associated with weather patterns in the Pacific, which are in turn related to the La Niña phase of the El Niño phenomenon.”

 

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