Permafrost is far more sensitive to rising global temperatures than previously thought, scientists have discovered. Models now indicate that for every one degree Celsius of global warming, four million square kilometers of frozen soil could thaw—around 20 percent higher than previously estimated.
Permafrost is frozen ground that has been below zero centigrade for at least two years, but much of it has been this way for thousands of years. As global temperatures increase, this ground is now beginning to thaw, allowing the organic matter locked away inside to decompose, releasing methane and carbon dioxide into the atmosphere.
With an estimated three times more carbon locked up in permafrost than in all the Earth’s forests, its release would considerably increase the amount of carbon in the atmosphere, speeding up climate change in the process. As a result, scientists are currently working to estimate the rate of thawing.
In a study published in the journal Nature Climate Change, scientists have combined various climate models with observational data to create a more robust estimate of how much permafrost will be lost under different climate change scenarios.
The team, led by Sarah Chadburn of the University of Leeds, looked at the way permafrost changes in different regions and analyzed how this relates to air temperature, using only observational data, which is more robust as there are fewer biases.
The findings showed that the current spatial distribution of permafrost and air temperature reveal how sensitive it is to future global warming.
From this, they calculated that if global temperatures rise two degrees Celsius above pre-industrial levels, more than 40 percent of the world’s permafrost could thaw—amassing to six million square kilometers. Furthermore, for every additional degree Celsius of warming experienced, a further four million square kilometers (an area larger than India) could be lost.
However, if temperatures do not exceed 1.5 degrees Celsius, the target set out in the Paris Climate Agreement, two million square kilometers could be saved.
Chadburn told Newsweek: “It’s not a terrifying scenario, but there’s definitely some concerning impacts. Personally, I was surprised by how much permafrost loss we predicted, but in terms of how much carbon it might release into the atmosphere, that’s something which is still uncertain.
“The feedback will accelerate global warming a little bit, but it probably wouldn’t be a runaway climate change scenario.”
Thawing permafrost doesn’t just lead to an increase in greenhouse gasses. Ground that was once solid becomes unstable, as has been seen in Siberia, Russia, where large craters have emerged apparently as a result of methane build-up below ground. It can also cause huge damage to infrastructure in the towns and cities built in permafrost regions.
“As the permafrost thaws, at the beginning the ground would collapse and form into lakes,” Chadburn explains. “Then, as the ground thaws more and completely disappears, it drains and you get much drier ground so all the ecosystems would change. For humans, any infrastructure built there is going to have problems if the ground collapses.”
Max Holmes, deputy director of the Woods Hole Research Centre, a climate-change think tank, says the findings are not that surprising: “These studies show there really is a big difference between whether we halt global warming at 1.5 degrees Celsius or two,” he told Newsweek. “There’s more and more evidence to show that two degrees is too high—or at least that there will be some really big impacts, which are substantially reduced if we keep warming lower.
“However, the reality is that stopping at 1.5 degrees will be extraordinarily difficult and we’ll need everyone to cooperate in a hurry. Even two degrees is an enormous challenge, especially when not everyone is on board.”
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