The oceans absorbed 60% more heat than we thought

According to a study conducted by researchers at Princeton and the Scripps Institution of Oceanography of the University of Washington, the world's oceans absorbed each year more than 150 calories of thermal energy. California-San Diego. The researchers found that global warming indicated that the Earth was more sensitive to fossil fuel emissions than previously thought.

The researchers reported in the newspaper Nature On 1 November, the world's oceans absorbed more than 13 zettajoules – one joule, the standard unit of energy, followed by 21 zeros – of thermal energy each year between 1991 and 2016. The study was funded by the National Oceanic and Atmospheric Administration and Princeton Environmental Institute.

The first author, Laure Resplandy, Assistant Professor in Geoscience and Princeton Environmental Protection Institute, stated that the estimate of her coauthors and her is greater than 60 % to that of the Fifth Assessment Report of the 2014 United Nations Intergovernmental Panel on Climate Change. Climate Change (IPCC).

"Imagine if the depth of the ocean was only 30 feet," said Resplandy, a postdoctoral researcher at Scripps. "Our data shows that it would have warmed by 6.5 degrees Celsius [11.7 degrees Fahrenheit] every decade since 1991. In comparison, the estimate of the latest IPCC assessment report would correspond to a warming of only 4 degrees Celsius. [7.2 degrees Fahrenheit] every decade. "

Scientists know that the ocean absorbs about 90% of all the excess energy produced by global warming. Knowing the amount of real energy thus allows one to estimate the surface warming that can be expected, said co-author Ralph Keeling, a Scripps oceanographer. geophysicist and former Resplandy postdoctoral counselor.

"The result greatly increases the confidence we can place in estimates of global warming and thus contributes to reducing uncertainties about climate sensitivity, particularly by limiting the possibility of very low climate sensitivity. "said Keeling.

Climate sensitivity is used to assess allowable emissions for mitigation strategies. Most climate scientists have agreed in the last decade that if global average temperatures exceed pre-industrial levels by 2? (3.6?), It is almost certain that society will face widespread and dangerous consequences of climate change.

The researchers' findings suggest that if society does not want the temperature to rise above this level, carbon dioxide emissions, the main greenhouse gas produced by human activities, must be reduced by 25% compared to what was been estimated before, said Resplandy.

The results of the researchers are the first to come from a measurement technique independent of the dominant method on which existing research is based, she said.

Previous estimates were based on millions of one – time measurements of ocean temperature, which were interpolated to calculate total heat content. Gaps in coverage, however, make this approach uncertain. A network of robotic sensors called Argo now performs comprehensive measurements of ocean temperature and salinity around the world, but the network only has complete data from 2007 and measures only the top half of the world. ocean. Several reevaluations of calorific content have been performed in recent years using data on ocean temperature, including the latest Argo data, which led to an upward revision of the data. IPCC estimate.

Resplandy and his co-authors used the high-precision measurements of oxygen and carbon dioxide in Scripps air to determine the amount of heat stored by the oceans during the period studied. They measured the heat of the oceans by examining the combined amount of O2 and CO2 in the air, a quantity that they call "atmospheric potential oxygen" or APO. The method depends on the fact that oxygen and carbon dioxide are less soluble in warmer waters.

As the ocean heats up, these gases tend to be released into the air, increasing APO levels. APO is also influenced by the burning of fossil fuels and an oceanic process involving the absorption of excess CO2 from fossil fuels. By comparing observed changes in APO observed with the expected changes due to the use of fossil fuels and to the absorption of carbon dioxide, the researchers were able to calculate the amount of APO emitted by the ocean that was warming. This quantity corresponds to the heat content of the ocean.

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More information:
Quantification of the heat absorption of the oceans by changes in the composition of atmospheric oxygen and CO2, Nature (2018). DOI: 10.1038 / s41586-018-0651-8, https://www.nature.com/articles/s41586-018-0651-8