The Surface Of Oceans In The Southern Hemisphere Is Warming Twice As Fast As We Thought

Lined with bottles triggered at different levels of the ocean, this conductivity, temperature and depth profiler bearing a suite of sampling bottles is a mainstay of oceanography. It can be deployed to depths of 6,000 metres to study changes in ocean temperature and salinity. Image: Ann Thresher/CSIRO

The upper layer of the oceans in the southern hemisphere may be warming between 48% and 152% faster than we thought, according to the latest research.

A paper published in the journal Nature Climate Change says the rate of warming of the top 700 metres of the ocean in the Southern Hemisphere may have been underestimated

But another paper in the same journal finds the ocean 2 kilometres down has not warmed and has had a negligible contribution to sea-level rise.

The two studies provide insights into where heat is being stored in the ocean and the implications for atmospheric warming and sea-level rise.

The ocean is a major heat reservoir for the climate system, storing more than 90% of heat caused by human activities.

Paul Durack of the Lawrence Livermore National Laboratory in the US and colleagues combine climate model results with direct measurements and satellite sea-level data to study upper-ocean warming trends since the 1970s.

They find that the reported observational warming rates have poor agreement with the model results and they attribute this to poor sampling in the Southern Hemisphere.

Using data from the better sampled Northern Hemisphere, they suggest that estimates of the warming rates for the Southern Hemisphere should be increased by 48% to 152%.

To investigate deep-ocean warming, William Llovel of the Jet Propulsion Laboratory, Pasadena, and colleagues use satellite sea level and ocean mass change data, in combination with direct measurements.

They find that the deep ocean did not warm over the period 2005–2013.

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