Temperature Trends

Global Warming Heat Not "Hiding" in the Deep Ocean After All


Argo Floats

One of the leading explanations for why the postulated rise in global average temperatures due to man-made warming has "paused" for nearly 18 years now is that the "missing heat" is hiding in the deep ocean. Two new papers in Nature Climate Change look at how much heat the oceans are supposed to have absorbed since the 1970s. The press release from the Jet Propulsion Lab whose researchers did much of the analysis notes:

The cold waters of Earth's deep ocean have not warmed measurably since 2005, according to a new NASA study, leaving unsolved the mystery of why global warming appears to have slowed in recent years.

Scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, analyzed satellite and direct ocean temperature data from 2005 to 2013 and found the ocean abyss below 1.24 miles (1,995 meters) has not warmed measurably. Study coauthor Josh Willis of JPL said these findings do not throw suspicion on climate change itself.

Basically, satellite measurements between 2005 and 2013 find that sea level has been increasing at rate of 2.78 millimeters per year. Some 0.9 millimeters results from expansion due to warming and 2.0 millimeters is due to additions of freshwater, e.g., melting glaciers. Since 2.9 millimeters is greater than the measured increase of 2.78 millimeters, the researchers concluded that the deep ocean is likely cooling down and thus contracting. 

By the way, at this rate of increase sea level would rise by about 11 inches over the next century—basically the amount of sea level rise experienced in the 20th century.* 

In any case, why do these findings not "throw suspicion" on man-made climate change? In a companion paper researchers cite recent data from the network of autonomous Argo floats that measure temperatures in the upper ocean. Combining those data with climate model simulations suggest that upper 700 meters of the oceans have absorbed a great deal of the extra heat resulting from anthropogenic increases in greenhouse gases in the atmosphere. The JPL press release continues: 

Landerer also is a coauthor of another paper in the same Nature Climate Change journal issue on ocean warming in the Southern Hemisphere from 1970 to 2005. Before Argo floats were deployed, temperature measurements in the Southern Ocean were spotty, at best. Using satellite measurements and climate simulations of sea level changes around the world, the new study found the global ocean absorbed far more heat in those 35 years than previously thought—a whopping 24 to 58 percent more than early estimates. 

It's always interesting when models find discrepancies in observational data. 

For more background, see my post, "Do Researchers Really Know Why Global Warming Is On Pause and When It Will End?"

*Addendum: One prominent estimate is that average sea level rose by 225 millimeters between 1880 and 2012, which amounts to an increase of almost 9 inches.