There has been a slowdown in the global warming over the past 15 years and it is puzzle as to where all the heat is getting absorbed. It is only now that the exact methodology is becoming clearer. The key to this puzzle is the way oceans can act as heat sinks. The more researchers are trying to fathom this mystery, the more it becomes clearer that natural variability rather than any human triggered climate change.
Scientists from US and China have joined hands to find out exactly where this heat is hiding. The scientists attribute this slowdown in warming to heat taken up by oceans especially at depths below 2300 feet.
However the duo did not agree to a common belief- Most studies have concluded that the heat uptake was largely taken up by the Western Tropical Pacific. Xianyao Chen of the Ocean University of China and Ka-Kit Tung of the University of Washington feels that the Atlantic and Southern Oceans have done most of the heavy lifting. The team bases this conclusion on the umpteenth measurements of ocean heat gathered between 1970 and 2013 from the surface to the depths of 5000 feet. The findings by the team are going to be published on Friday in the Journal Science.
Dr. Tung says “Oceanographers have long known that the Atlantic and southern oceans are more efficient at storing heat than the Pacific. Based on the measured distribution of heat, trade winds alone – which have blown at unusually high levels during the hiatus – aren’t powerful enough to drive warm water very deep,”
However with the Atlantic the situation is markedly different. The heat is carried North by a powerful current system which is known as the Atlantic thermohaline circulation. The Gulf Stream is the result of this circulation.
When the water reaches the North Atlantic, the dense salt water, which is heavier, sinks to the depths and heads South at the same depths retaining some of the heat it had accumulated on the surface.
The researchers have also identified the cause of the multi-decadal swings in the intensity of the circulation. It is driven by the salinity of the water, Fresh water is more buoyant as compared to salty water and when water loses its salinity due to rainfall, snowfall or melting of the polar ice caps the circulation slows down.
Tung and Dr. Chen also feel that a small cooling period in global average temperatures in the mid-20th century which denoted another pause in the longer-term warming trend coincided with a fast phase in the Atlantic’s thermohaline circulation.