Dire warning: Earth may have crossed climate 'tipping points'

We're heading toward an unstoppable cascade of climate events that poses an "existential threat to civilization," scientists say.

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Smoke from intense fires rises over the Amazon rainforest in August 2019.

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A group of climate scientists have warned that Earth may have already crossed critical climate "tipping points," potentially resulting in irreversible changes to the environment. As greenhouse gas concentrations in Earth's atmosphere continue to rise, the authors of a new commentary piece, published in the journal Nature on Nov. 27, suggest we're already starting to observe some of the detrimental changes scientists once believed would occur only if the Earth got 5 degrees warmer than preindustrial levels.

"A decade ago we identified a suite of potential tipping points in the Earth system, now we see evidence that over half of them have been activated," said Tim Lenton, a climate scientist at the University of Exeter and lead author of the piece, in a press release.

Global tipping points, first introduced by the Intergovernmental Panel on Climate Change (IPCC) two decades ago, refer to large-scale unstoppable events caused by global warming, such as the loss of the West Antarctic ice sheet, corals in the Great Barrier Reef, circulation in the Atlantic and the Amazon rainforest.

The commentary piece says these events might unfold at a much more rapid pace than previously believed, with complex feedback loops causing a cascade of effects. For instance, losing the Arctic ice sheet might increase the risk of slowing down Atlantic circulation, which helps transport heat and salt around the oceans. As the Arctic sheet melts, the circulation slows... and if the circulation slows, the Amazon may be affected, as might Antarctic sea loss. Part of this process may already have begun.

It's a dire warning from the experts, tying together a wide range of evidence that humans are rapidly approaching some of the previously identified tipping points.

"In our view, the evidence from tipping points alone suggests that we are in a state of planetary emergency: both the risk and urgency of the situation are acute," the authors write.

The researchers agree it is difficult to understand the full extent of the interplay between Earth's myriad of climate-affected systems. But they note that carrying on with the business-as-usual approach will still put us on track for approximately 3 degrees of warming. Notably, the authors highlight that Earth's climate has been unstable across timescales before, caused by small changes in Earth's orbit. However, now humans are "strongly forcing the system" into a state that hasn't been seen for millions of years.

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