Global Warming: Deep Oceans Could Delay Effects for Decade-Long Periods

Earth's temperatures will likely stabilize for a period as deep ocean waters absorb enough heat to mask the effects of global warming for up to a decade, a new study indicates.

Earth's missing heat has long been a mystery for climate scientists as the last decade saw an incessant growth in greenhouse gas emissions did not elevate surface temperature as much as expected.

The joint U.S.-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 the National Center for Atmosperic Research 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, said the NCAR's Gerald Meehl, who led 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.

Meehl and the other researchers used the Community Climate System Model to run five simulations of global temperatures, accounting for the interactions among atmosphere, land, oceans and sea ice and factoring in human contributions like greenhouse gas emissions.

During these periods, the excess heat was absorbed into deep ocean water due to changes in ocean circulation, rather than released into the atmosphere.

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.

Kevin Trenberth, a study co-author and NCAR scientist, said: 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.

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.

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.