Earth's temperatures will likely stabilize for a period as a new study suggests that deep oceans may absorb enough heat to flatten the rate of global warming for periods as long as a decade.
Climate scientists have long wondered where this so-called missing heat was going, especially over the last decade, when greenhouse emissions kept increasing but world air temperatures did not rise correspondingly, Reuters reported.
The joint U.S. and Australian study, based on computer simulations of global climate, points to ocean layers deeper than 1,000 feet (300 meters) as the main location of the missing heat during periods such as the past decade when global air temperatures showed little trend.
The study conducted by scientists at NCAR and the Bureau of Meteorology in Australia was published in the Sept. 18 issue of the journal Nature Climate Change.
We will see global warming go through hiatus periods in the future, says NCAR's Gerald Meehl, lead author of the study. However, these periods would likely last only about a decade or so, and warming would then resume. This study illustrates one reason why global temperatures do not simply rise in a straight line.
The 2000s were Earth's warmest decade in more than a century of weather records and satellite measurements showed that the discrepancy between incoming sunshine and outgoing radiation from Earth actually increased which implies that heat was building up somewhere on Earth, according to a 2010 study published in Science by NCAR researchers Kevin Trenberth and John Fasullo.
The two scientists, who are coauthors on the new study, suggested that the oceans might be storing some of the heat that would otherwise go toward other processes, such as warming the atmosphere or land, or melting more ice and snow. But few measurements were available to confirm that hypothesis.
To figure out where the heat was going, Meehl and his colleagues ran five simulations on a computer model that portrays complex interactions between the atmosphere, land, oceans and sea ice.
The simulations indicated that temperatures would rise by several degrees during this century. But each simulation also showed periods in which temperatures would stabilize for about a decade before climbing again.
They found the vast area deeper than 1,000 feet (300 meters) warmed by about 18 to 19 percent more during the hiatus periods than at other times. Meanwhile, shallower global ocean above 1,000 feet warmed by 60 percent less than during non-hiatus periods in the simulation.
This study suggests the missing energy has indeed been buried in the ocean. The heat has not disappeared, and so it cannot be ignored. It must have consequences, said Trenberth.
The study also showed that oceanic warming during hiatus periods has a regional signature. During a hiatus, average sea-surface temperatures decrease across the tropical Pacific, while they tend to increase at higher latitudes.
Meehl says these patterns are similar to those observed during a La Niña event.
“Global temperatures tend to drop slightly during La Niña, as cooler waters reach the surface of the tropical Pacific, and they rise slightly during El Niño, when those waters are warmer,” he added.