Ocean warming could also be earlier than expected

The seas are warming up – and researchers have again pondered how quickly ocean warming is occurring. They estimate that over the past 25 years, the oceans have absorbed at least 60% more heat than previous global estimates by the United Nations Intergovernmental Panel on Climate Change (IPCC).

And they calculate this heat as the equivalent of 150 times the annual production of electricity by the man.

"Imagine that the depth of the ocean does not exceed 10 meters," said Laure Resplandy, researcher at the Princeton Environment Institute in the United States. "Our data shows that it would have increased by 6.5 ° C per decade since 1991. In comparison, the estimate of the latest IPCC assessment report would correspond to a warming of only 4 ° C by decade."

The oceans cover 70% of the blue planet, but absorb about 90% of any excess energy produced by global warming. If scientists can accurately quantify this energy, then they can more accurately guess how warming the future surface will be, as humans continue to burn fossil fuels, release greenhouse gases such as carbon in the atmosphere and to raise the planetary thermometer.

At the university level, this is the search for a factor known to climatologists as climate sensitivity: the way the world reacts to the growing proportion of greenhouse gases in the atmosphere.

On the human side, this translates into increasingly extreme extremes of heat, drought and precipitation, with ever greater risks of catastrophic storms or floods, or failure of harvest, and more and more human suffering.

The global global measurements of ocean temperature date back to 2007 and the network of robot sensors that provide continuous data on the upper half of the ocean basins.

Dr. Resplandy and her colleagues reported in Nature that they used a sophisticated approach based on very high accuracy measurements of oxygen and carbon dioxide levels in the air.

Gas released

Both gases are soluble and the oceans become more and more acidic as the ocean absorbs ever higher levels of carbon dioxide. But as the sea heats up, they are also less able to retain their dissolved gases and release them into the atmosphere.

This simple consequence of the physics of the atmosphere meant that researchers could use what they call "the potential oxygen of the atmosphere" to find a new way to measure the heat that the oceans had to have absorbed over time.

They used the standard unit of energy: the joule. Their new budget for the heat absorbed each year between 1991 and 2016 is 13 zettajoules. This is a figure followed by 21 zeros, the type of magnitude that astronomers tend to use.

That the oceans are heating up is not surprising: the coarsest comparison of old naval data with modern surface checks has highlighted the fact that for years, researchers have argued that the temperature ever higher oceans could explain the so-called slowdown in global warming. the first twelve years of this century.

The new finding counts first as a school achievement: there is now a more accurate reading of the thermometer and new calculations can begin.

One of the researchers, Ralph Keeling of the Scripps Institution of Oceanography, said: "This result greatly increases the confidence we can place in estimates of global warming and thus helps to reduce the uncertainties associated with climate sensitivity. , in particular by limiting the possibility of very low climatic conditions. sensitivity."

But the result also suggests that internationally recognized attempts to maintain global warming at a maximum of 2 ° C – and the world has already warmed by about 1 ° C over the last century – have become more difficult.

This means that we will have to stop even more radical investment in fossil fuels and switch even more rapidly to renewable sources of energy such as solar and wind energy.

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