Warming is accelerating, threatening a cascade of tipping points that destabilize the climate. In a new paper, scientists say the risk of “hothouse Earth” is greater than once believed.
“After a million years of oscillating between ice ages separated by warmer periods, the Earth’s climate stabilized more than 11,000 years ago, enabling agriculture and complex societies,” said William Ripple of Oregon State University, lead author of the paper. “We’re now moving away from that stability and could be entering a period of unprecedented climate change.”
A decade ago, countries set forth in the Paris Agreement a target of capping warming at 1.5 degrees Celsius. Earth is now likely breaching that threshold. The world has not officially surpassed the Paris target, which will be judged according to the average temperature over 20 years, but the average temperature over the last three years exceeded 1.5 degrees.
Scientists say that the Earth is likely as hot or hotter than at any point in the last 125,000 years, while carbon dioxide levels are at their highest in at least 2 million years. And warming is gaining pace as the ability of the planet to soak up our emissions weakens. Forests that were once carbon sinks are becoming carbon sources as they succumb to fire and drought, while the oceans are losing the capacity to absorb carbon dioxide.
Beyond 1.5 degrees of warming, scientists see a potent risk that the Earth will cross key planetary tipping points, from the dieback of the Amazon rainforest to the thawing of Arctic permafrost, that would further hasten climate change. Already, the Greenland and West Antarctic ice sheets show signs of destabilizing, according to the paper, published in the journal One Earth.
Scientists warn that the crossing of one tipping point can push the Earth past another, in a domino effect. The melting of the Greenland ice sheet, for instance, could weaken Atlantic currents, disrupting rainfall over the Amazon. A cascade of tipping points could bring about “hothouse Earth,” said coauthor Johan Rockström, director of the Potsdam Institute for Climate Impact Research in Germany. “Our paper shows that we’re not there yet — but we’re very close.”
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