NEW YORK: If you’re climate-curious, you’ve probably seen some of the research revealing why globally averaged surface air temperatures have warmed less quickly over the last decade or so than they did in the 1990s. The oceans are the dominant heat reservoir in the climate system, and they have been in a greedy phase lately, giving up a little less warmth to the atmosphere.
This has largely been the product of a string of La Niñas in the Pacific driven by stronger easterly trade winds. In those conditions, a pool of colder deep water takes the place of warmer surface water in the eastern Pacific. The warmer water that would normally be there is instead moved westward and mixed downward.
But here’s the puzzling thing: while records show a buildup of heat below the surface, the heat’s generally not in the Pacific. If that’s where so much downward mixing is taking place, where is the warm water going?
Using one dataset (a “reanalysis” that uses a model to generate global coverage from all the available measurements), over 70 percent of the heat accumulated in the upper 700 meters of the global ocean between 2003 and 2012 ended up in the Indian Ocean. Heat content in the Pacific, on the other hand, actually dropped a bit over that time period.
To find out why, a team led by University of Miami and NOAA researcher Sang-Ki Lee experimented with a global climate model. One configuration of the model was driven by the pattern of ocean surface heat exchange (determined by things like sunlight, water temperature, and air temperature) calculated by a historical reanalysis covering the last century. The model simulated the way the rest of the climate system responded to that two-way transfer of heat energy. For comparison, a second configuration of the model was driven by constantly average surface heat exchange.
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