Deep waters of the world's oceans have not warmed appreciably since 2005, a new NASA study revels, while a separate investigation shows surface temperatures warmed at a faster-than-expected rate.
Satellite and direct measurements data taken between 2005 and 2013 were analyzed by researchers from Jet Propulsion Laboratory. They found that oceans maintained a near-constant temperature below a depth of 1.24 miles.
During the 20th Century, global temperatures steadily rose, along with increasing levels of carbon dioxide in the atmosphere. Since that time, surface temperatures on the land have largely stayed steady, while levels of atmospheric CO2 have continued to climb. Surface water has become warmer during that time, possibly trapping some heat, but not enough to explain the entire discrepancy. Numerous theories have been proposed to explain where this missing energy has gone, including one idea that it is stored deep in the ocean.
The Argo Array, a network of 3,000 floating thermometers, has been in operation since 2005, allowing researchers the opportunity to accurately measure the temperature of surface waters around the world. Temperatures of water deeper under the surface is more difficult to obtain.
As water temperatures rise, the liquid expands, which leads to a rising sea level. Melting glaciers and ice sheets also contribute to this effect.
To make its determination, the team started with the increase recorded in sea levels. It then subtracted the increases due to surface temperature changes, and melt water. It found those two factors accounted for nearly the entire increase in sea levels, suggesting little to no rise in water temperatures far beneath the surface.
"The combination of satellite and direct temperature data gives us a glimpse of how much sea level rise is due to deep warming. The answer is - not much," William Llovel, lead author of an article announcing the study, said.
Researchers point out that although the deep ocean does not seem to be rising over the last decade, this finding should not be used to discount the effects of global warming. Even though temperatures deep in the ocean have remained steady over the last decade, the effects of warming on waters closer to the surface are easy to recognize.
"The sea level is still rising. We're just trying to understand the nitty-gritty details," Josh Willis of Jet Propulsion Laboratory told the press.
Felix Landerer, another researcher from JPL, found upper-level oceanic waters in the southern hemisphere have observed 24 to 58 percent more heat than earlier estimates had reported.
Discovery of a lack of heating in deep ocean waters since the start of the 21st Century was detailed in the journal Nature Climate Change.
