Our planet is approaching the 'hothouse Earth' tipping point

August 7, 2018, 11:51 a.m.
Water floats on the top of the Greenland ice sheet in 2013 due to melting
Photo: Joe Raedle/Getty Images

It's been difficult to stay cool these past few months, and if the scientists behind a study published this week are correct, it's going to be even more difficult going forward.

Published in the journal American Proceedings of the National Academy of Sciences, the study says that even if countries meet the Paris Agreement's goal of keeping the global temperature from rising by 2 degrees Celsius, there's still a risk of the planet becoming a "hothouse Earth" due to other non-greenhouse gas warming factors.

Researchers envision this "hothouse Earth" as having temperatures 7 to 9 degrees Fahrenheit (4 to 5 degrees Celsius) higher than pre-industrial temperatures and sea levels at 33 to 200 feet (10 to 60 meters) higher than today.

"Human emissions of greenhouse gas are not the sole determinant of temperature on Earth. Our study suggests that human-induced global warming of 2 C may trigger other Earth system processes, often called 'feedbacks,' that can drive further warming — even if we stop emitting greenhouse gases," study lead author Will Steffen from the Australian National University said in a statement released by the Stockholm Resilience Centre.

The feedbacks Steffen alludes to are things like permafrost thaw, loss of methane hydrates from the ocean floor, weakening land and ocean carbon sinks, rainforest and boreal forest dieback, reduction of Northern Hemisphere snow cover, loss of Arctic summer sea ice and reduction of Antarctic sea ice and polar ice sheets. Any one of these goes and the others are much more likely to go as well.

The loss of summer sea ice is on display in the image above, a portion of the Greenland ice sheet melting in July 2013.

"These tipping elements can potentially act like a row of dominoes. Once one is pushed over, it pushes Earth towards another. It may be very difficult or impossible to stop the whole row of dominoes from tumbling over," explained co-author Johan Rockström, former executive director of the resilience centre and incoming co-director of the Potsdam Institute for Climate Impact Research.

It will require a global societal change to maintain what the researchers call a "stabilized Earth."

"Avoiding this scenario requires a redirection of human actions from exploitation to stewardship of the Earth system," Steffen said. This means not only eliminating fossil fuel use by the middle of this century, but also planting many, many trees, protecting forests and figuring out how to suck carbon emissions out of the air.

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