Monday, March 30, 2015

How Long Can Oceans Continue to Absorb Earth’s Excess Heat?

The main reason soaring greenhouse gas emissions have not caused air temperatures to rise more rapidly is that oceans have soaked up much of the heat.  But new evidence suggests the oceans’ heat-buffering ability may be weakening.

This map shows trends in global ocean heat content, from the surface to 2,000 meters deep. Yellow, orange, and red zones represent increases in ocean temperatures since 2006, as measured by the Argo network of 3,500 floating sensors. Green, blue, and violet zones depict temperature decreases, as measured in watts per square meter. The map shows that much of ocean warming in the past decade has occurred in the Southern Hemisphere. (Image credit: Roemmich et al., Nature Climate Change) Click to Enlarge.
For decades, the earth’s oceans have soaked up more than nine-tenths of the atmosphere’s excess heat trapped by greenhouse gas emissions.  By stowing that extra energy in their depths, oceans have spared the planet from feeling the full effects of humanity’s carbon overindulgence. 

But as those gases build in the air, an energy overload is rising below the waves.  A raft of recent research finds that the ocean has been heating faster and deeper than scientists had previously thought.  And there are new signs that the oceans might be starting to release some of that pent-up thermal energy, which could contribute to significant global temperature increases in the coming years. 

The ocean has been heating at a rate of around 0.5 to 1 watt of energy per square meter over the past decade, amassing more than 2 X 1023 joules of energy — the equivalent of roughly five Hiroshima bombs exploding every second — since 1990.  Vast and slow to change temperature, the oceans have a huge capacity to sequester heat, especially the deep ocean, which is playing an increasingly large uptake and storage role. 

That is a major reason the planet’s surface temperatures have risen less than expected in the past dozen or so years, given the large greenhouse gas hike during the same period, said Kevin Trenberth, senior scientist with the National Center for Atmospheric Research.  The phenomenon, which some call the “hiatus,” has challenged scientists to explain its cause.  But new studies indicate that the forces behind the supposed hiatus are natural  Ocean heat accumulation is the equivalent of five Hiroshima bombs exploding every second since 1990. — and temporary — ocean processes that may already be changing course.

Read more at How Long Can Oceans Continue to Absorb Earth’s Excess Heat?

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