Atlantic Ocean currents may be moderating global air temperatures

The foundational theory undperinning climate science says accumulating greenhouse gasses like carbon dioxide, methane and ozone trap heat within the Earth’s atmosphere. Yet, despite the continued rise in greenhouse gas concentrations, global air temperatures are not rising at the same rate as they did 15 years ago.

What’s going on?

If climate science is correct, why aren’t temperatures continuing to rise at the same rate as before? Where is all the heat going?

A new study in the journal Science suggests a possible answer: deep into the Atlantic Ocean.

Using new observational and measurement techniques, scientists have discovered massive heat sinks in the Atlantic and southern oceans — areas of the ocean where warm water temperatures have penetrated far deeper than previously known. This heat storage deep in the Atlantic Ocean has led to the current hiatus in rising average surface temperatures globally, according to the new study.

Ka-Kit Tung, an atmospheric scientist and applied mathematician at the University of Washington in Seattle, and Xianyao Chen of the Ocean University of China, deployed a series of sensors that included floats which dive up to 1500 meters below the ocean surface to measure the temperature and salt content of the water.

Prior to this study, scientists were relying largely on measurements of sea surface temperature to try to determine what was happening at greater depths, says Rick Spinrad, chief scientist at the National Oceanic and Atmospheric Administration in Washington. “So this is exciting new information,” he says.

Scientists have for years studied the global system of ocean currents known as the conveyor belt. This system carries warm, salty water from the Caribbean to the North Atlantic, where the water becomes colder and saltier. As the salt content increases, the water becomes denser and begins to sink. At the same time, the ocean current turns and heads south again.

Professors Tung and Chen suggest this sinking portion of the conveyor belt is what transports heat deep into the Atlantic Ocean.

Over 90 percent of the Earth’s heat resides in the ocean, Spinrad says, but until now scientists “didn't understand the dynamic nature of it: ‘How does it move around? Where does it move around? When does it move around? And ultimately, how does it exchange the heat with the atmosphere and drive our weather and climate?’”

The new data will force scientists to “re-think the energy balance for the whole Earth's system,” Spinrad says.

This story is based on an interview that aired on PRI's Science Friday with Ira Flatow