Global warming will exceed limit, UN says in a report that maps path to get back below danger zone

In a strategic retreat in the fight against climate change , the United Nations has acknowledged that Earth has lost its chance to prevent some of the worst of global warming's harms. So now the world must figure out how to get temperatures below the danger zone and back to safety, officials say.

Earth is soon going to exceed the safe temperature threshold agreed upon by the world in the 2015 Paris climate accord because of warming from the burning of coal, oil and gas , according to a bleak first-of-its-kind report issued by the United Nations Environment Programme Wednesday.

Instead of giving up, scientists and U.N. officials recommend trying to limit excessive warming and then bring the temperature back down to the agreed-upon threshold. But it still will mean decades of increased weather-related disasters , rising seas, extinctions and melting ice and glaciers.

“Humanity is speeding past the limit to avoid climate catastrophe,” United Nations Secretary-General António Guterres said.

After a period of over-the-limit warming, the new strategy envisions getting back below the limit by ending fossil fuel use and developing some kind of way to suck industries' carbon dioxide out of the air.

“It's a reality check. We have to live with this warmer world,” said report co-author Richard Betts, a climate scientist at the University of Exeter. “But there's still a lot we can do to limit warming.”

After the Paris climate accord, the United Nations ordered its climate science arm to study different warming limits. A goal of 1.5 degrees Celsius (2.7 degrees Fahrenheit) above mid-19th century temperatures became generally accepted after the scientists found dramatic impacts that affect people and the planet at 2 degrees Celsius (3.8 degrees Fahrenheit) but not at 1.5 degrees.

The world is now at 1.4 degrees Celsius (2.5 degrees Fahrenheit) above pre-industrial levels, some scientists have calculated. The measure is based on a 20-year average, rather than a single year's temperatures.

Despite experts saying there's no way to limit warming to 1.5 degrees, U.N. officials long maintained the 1.5 window was still open . Wednesday's report finally admitted that the world will cross the 1.5 threshold “in the next few years.”

The report said the most optimistic scenario has warming peaking at 1.8 degrees (3.2 degrees Fahrenheit) around mid-century if countries pursue ambitious climate goals, but that governments' current policies should push temperatures to 2.6 degrees (4.7 degrees Fahrenheit) above pre-industrial levels by 2100.

So instead of preventing warming of 1.5 degrees, now the UN said it wants policymakers to “prepare for and navigate a future'' in which the globe crosses that limit and then corrects course and cools temperatures. The report envisions that global temperatures will pass 1.5 “within the next few years,” follow a hump-shaped path of more warming, peak, then gradually cool to below the 1.5 mark, ideally by the end of the century. The report and experts call it “overshoot.”

“Let’s be very clear, 1.5 target is still the goal. But now we need to approach it differently from above,” said UNEP Executive Director Inger Andersen.

The 1.5 limit is not “some magical climate cliff” where it’s just game over, said University of Victoria climate scientist Andrew Weaver, who wasn’t part of the study. “Every tenth of a degree we avoid still means less damage.”

It's most important to first limit the new peak temperature and then reduce the amount of time above 1.5 degrees, Andersen said.

But the world likely will be in that overshoot period for “many, many decades,” Betts said.

Every five years of delay in reducing emissions adds at least a tenth of a degree to peak warming, said report co-author Joeri Rogelj, a climate scientist at Imperial College London.

“If we act now we can limit overshoot,” the report said. “Not a safe world, but safer than remaining above” 1.5 degrees for the long term.

“This is among the bleakest U.N. climate reports I have read. It carries the unmistakable tone of desperation, frustration and urgency — but not resignation,” Weaver said.

Climate scientist Bill Hare, CEO of Climate Analytics, said that “although UNEP does a good job of describing the hole we've dug ourselves into, it does a poor job of showing us that there's a way out.”

Governments need to increase efforts to adapt to worsening warming, which hits the poor hardest, “because some impacts simply cannot be avoided,” Andersen said.

The report calls this phase “coping and containment.”

During this overshoot period, more people will die or get sick because of the worsening climate change and its extreme weather, the report said. Food production will drop, people will go hungry, water shortages will worsen, economies will be hurt and species like coral will go extinct, the report said.

Although the triggers behind the recent deadly Nepal flooding that came as part of a Himalayan glacier dislodging are complex, Betts said “unfortunately we do expect to see more of such things and this is exactly why we need to limit peak warming.”

The report warns of “tipping points” with irreversible and cascading effects, including the loss of the West Antarctic and Greenland ice sheets, the loss of the Amazon rain forest and the shutdown of the Atlantic Ocean circulation system that keeps much of Europe warm.

“Some locations might become more or less uninsurable or even uninhabitable,” the report said.

The last phase in overshoot is cooling the planet by removing carbon dioxide from the air and storing it somewhere. The report said the traditional approach of this is planting more trees, but it says planting trees could, at most, shave a tenth of a degree off global temperatures. So the authors said more novel carbon removal approaches will be needed.

Other scientists called that unreliable and expensive.

“We were unable to stop the runaway train of global emissions to avoid 1.5 C of warming,” said Stanford University climate scientist Rob Jackson, who wasn't part of the report. “Now overshoot scenarios require us to stop the train quickly and to back it up. Is it our best hope? Absolutely. Is it likely? Absolutely not.”

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