There are no shortage of theories to explain why the rapid warming of the planet that began in the late 20th century has slowed. The climate science community has been grasping at straws to explain the mystery throwing out wild theories that range from volcanic activity to sunspots and air pollution.

Global warming

Last year, researchers were suggesting that an upwelling of cooler waters in the Pacific Ocean explained the slowdown in surface temperature increases.

But a new investigation, published online today in Science, suggests that it’s the Atlantic and Southern oceans that are responsible for the slowdown. Or rather, those oceans are storing all the extra heat.

Global warming: “Conveyor belts”

Oceanographer Xianyao Chen of the Ocean University of China in Qingdao and co-author Ka-Kit Tung of the University of Washington, wrote that there is a “conveyor belt” current that moves salty tropical water to the North Atlantic, where it sinks, carrying heat with it.

“Every week there’s a new explanation of the hiatus,” said  Ka-Kit Tung, a UW professor of applied mathematics and adjunct faculty member in atmospheric sciences. “Many of the earlier papers had necessarily focused on symptoms at the surface of the Earth, where we see many different and related phenomena. We looked at observations in the ocean to try to find the underlying cause.”

This “conveyor belt” is a slow-moving current in the Atlantic that carries heat between the two poles. The study suggests that it sped up around the turn of the century and is consequently drawing heat nearly a mile deep.

Global warming: Surprise deep water readings

“The finding is a surprise, since the current theories had pointed to the Pacific Ocean as the culprit for hiding heat,” Tung said. “But the data are quite convincing and they show otherwise.”

The two used observations from floats that sample the water down to 6,500 feet, the data show a rise in temperature beginning around 1999 when the slowdown began.

“There are recurrent cycles that are salinity-driven that can store heat deep in the Atlantic and Southern oceans,” Tung said. “After 30 years of rapid warming in the warm phase, now it’s time for the cool phase.”

The research was funded by the U.S. National Science Foundation and the National Natural Science Foundation of China.

While this is certainly good for the planet, it will most likely just add ammunition to arsenal of the global warming deniers.