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Arctic thaw imperils climate goals

05 Oct 2018
Photo of Alaskan lake
Melting permafrost lets this Alaskan lake drain away to the sea. Image: US National Park Service (public domain), via Wikimedia Commons

Austrian researchers have bad news for those nations alarmed about climate change: the Arctic thaw means the chances that the world will exceed the global warming limit set by international agreement are high – and getting ever higher with every tiny shift in the planetary thermometer.

Warming in the Arctic is the fastest on the planet – and any warming will release ever more methane and other forms of stored carbon from the thawing permafrost.

Methane is a greenhouse gas far more potent than carbon dioxide. And as it seeps into the atmosphere, the chances that the world will overshoot its promise to contain planetary warming to “well below” 2 °C increase.

This target was agreed by 195 nations at a summit in Paris in 2015. The promise implicit in this historic decision was that the world would by 2100 be no hotter than 1.5 °C above historic levels.

Global average temperatures have already risen by about 1 °C in the last century, thanks to unconstrained combustion of fossil fuels that deposit ancient stored carbon back into the atmosphere in the form of ever more carbon dioxide.

But, says an international team led by Thomas Gasser of the International Institute for Applied Systems Analysis in Austria, there are prodigious amounts of carbon stored in the world’s once permanently frozen soils. As these are released, the chances are that global warming will accelerate.

“Permafrost carbon release from previously frozen organic matter is caused by global warming, and will certainly diminish the budget of CO2 we can emit while staying below a certain level of global warming,” Gasser says.

“It is also an irreversible process over the course of a few centuries, and may therefore be considered a ‘tipping’ element of the Earth’s carbon-climate system that puts the linear approximation of the emission budget framework to the test.”

The message behind the formal language of a paper in the journal Nature Geoscience is simple: the world has less time to act than the presidents and prime ministers who signed the Paris Declaration may think.

But this is no surprise. Right from the start, leading climate scientists were warning that the planet could already be much nearer its optimum target than anybody suspected.

Other researchers have repeatedly stressed the need for urgency, and the inadequacy of any of the prepared responses.

Concern about the permafrost, too, is not new: polar researchers have been arguing for years that any thaw will increase the atmospheric carbon burden, which will in turn accelerate further warning, with potentially catastrophic consequences.

It is one thing to slow the rate of global warming by drastically reducing fossil fuel emissions and restoring the world’s forests so as to arrive at a limit; quite another thing to overshoot the limit and then try to reduce the planetary temperature, the latest study suggests. There is no simple correlation between burning coal or oil and the planetary temperatures that follow.

“Overshooting is a risky strategy and getting back to lower levels after an overshoot will be extremely difficult. However, since we are officially on an overshooting trajectory, we have to prepare ourselves for the possibility that we may never get back to safer levels of warming,” Gasser says.

“Policymakers should understand that there is no elementary proportionality between cumulative CO2 emissions due to human activity and global temperature, as previously believed, and that overshooting may have serious consequences.”

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