Earth’s climate is getting so hot that temperatures will likely exceed the level world leaders intended to set as a limit within a decade, according to a report released Monday that the United Nations described as “a code red for humanity.” .
“It’s just guaranteed to get worse,” said report co-author Linda Mearns, a climate scientist at the US National Center for Atmospheric Research. “I don’t see that any area is safe … There is nowhere to run, nowhere to hide.”
But the scientists also lowered the odds of the worst weather catastrophes a bit.
The report of the Intergovernmental Committee on Climate Change (IPCC), which describes climate change as “unequivocal” and clearly man-made, makes warmer and more accurate forecasts for the 21st century than in its previous edition. , published in 2013.
Each and every one of the five future scenarios, classified according to how much carbon dioxide emissions are reduced, exceed the strictest of the thresholds set by the 2015 Paris Climate Agreement.
World leaders then agreed to try to limit global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) compared to the end of the 19th century because problems would quickly add up from that point on. The limit is only a few tenths of a degree higher than the current level because the world has already warmed 1.1 degrees Celsius (2 degrees Fahrenheit) in the last century and a half.
In all scenarios, according to the report, the world will cross the 1.5 degree Celsius line in the 2030s, earlier than previous predictions. Warming has picked up speed in recent years, according to the data.
In three of the scenarios, the world would also exceed 2 degrees Celsius (3.6 degrees Fahrenheit) warming compared to the pre-industrial era, the other less stringent goal of Paris, and the heat waves, droughts and downpours that cause it would worsen. of floods “unless in the coming decades there are profound reductions in emissions of carbon dioxide and other greenhouse gases,” the report said.
“This report tells us that recent changes in climate are widespread, rapid, and intensifying, unprecedented in thousands of years,” said IPCC Vice President Ko Barrett, chief climate adviser for the National Oceanic and Atmospheric Administration Office. United States (NOAA). “The changes we experience will increase with more warming.”
The more than 3,000-page document, prepared by 234 scientists, points out that warming already accelerates the rise in sea levels, melts the planet’s ice and worsens extreme events such as heat waves, droughts, floods and storms. Tropical cyclones get stronger and wetter, while Arctic sea ice shrinks in summer and permafrost thaws. All of these trends will worsen, the report noted.
For example, heat waves that used to occur once every 50 years will now occur once a decade, and if the world warms another degree Celsius (1.8 degrees Fahrenheit), they will occur twice every seven years, the report warned. .
As the planet warms, the regions will be affected not only by extreme events, but by several simultaneous climatic disasters, the text noted. This is what is happening now in the western United States, where heat waves, drought and wildfires combine and cause more damage, Mearns said.
Some of the damage from climate change – the reduction of ice sheets, rising sea levels and changes in the oceans, which become more acidic as they lose oxygen – are “irreversible for centuries or millennia,” the report said.
The world is “assured” of a sea level rise of 6 to 12 inches (15 to 30 centimeters) by mid-century, according to report co-author Bob Kopp of Rutgers University.
Almost all of the warming that occurs on Earth can be attributed to emissions of heat-trapping gases in the atmosphere, such as carbon dioxide and methane. At best, natural forces like the sun or chance can explain a tenth or two of a degree of warming, the report noted.
The report outlined five possible future scenarios based on how much carbon dioxide emissions are reduced. They are: a future with incredibly large and fast pollution cuts; another with intense cuts but not so huge; a hypothesis of moderate emissions; a fourth scenario where current plans for small pollution reductions are maintained and a fifth possible future in which carbon dioxide pollution continues to grow.
In the previous five reports, the world was on the latter, often dubbed “business as usual.” But this time, the world is between the situation of moderate reductions and that of small emissions reductions, thanks to the progress in the fight against climate change, explained the co-author of the report Claudia Tebaldi, a scientist at the National Laboratory of the Pacific Northwest of the United States. United.
In a way, the world can stay on the 1.5 degree threshold with extreme and rapid cuts in its emissions. But even so, warming would reach 1.5 degrees in a decade, rise a bit and then subside, explained co-author Maisia Rojas Correda, director of the Center for Climate and Resilience Science in Chile.
United Nations Secretary General Antonio Guterres described the report as a “code red for humanity,” although he said there was a glimmer of hope that world leaders could avoid 1.5 degrees of warming, which he described as ” dangerously close ”.
“Anything we do to limit it, to stop it, it will pay off,” Tebaldi said. “And if we can’t get to 1.5, it will probably be painful, but it’s better not to give up.”
In a worst-case scenario, the world could warm by about 3.3 degrees Celsius (5.9 degrees Fahrenheit) by the end of the century. But that situation seems increasingly unlikely, said climate scientist and report co-author Zeke Hausfather, director of climate change at the Breakthrough Institute. The two extreme scenarios are looking increasingly unlikely, he noted.
“We are much less likely to be lucky and end up with less warm-up than we thought. We will not be able to meet the targets of the Paris Agreement without rapid reductions in our emissions in the short term, ”said Hausfather. At the same time, the likelihood of ending up in a much worse position than we expect if we actually cut our emissions is considerably lower. “
Ultra-catastrophic disasters, often called “tipping points,” such as the collapse of the polar ice caps and the sharp deceleration of ocean currents, are now “low-probability,” although they cannot be completely ruled out. The commented blockage of the Atlantic currents, which would cause huge changes in weather patterns, is unlikely in this century, Kopp said.
The report “offers a strong sense of urgency to do even more,” said Jane Lubchencho, White House deputy scientific adviser.
In new to the report, the scientists stressed how lowering levels of methane in the air, a powerful but rapidly dissipating gas that is at record levels, could help slow warming in the short term.
More than 100 countries have made informal pledges to achieve “neutral” human-made carbon dioxide emissions sometime in the middle of the century, which would be a linchpin of next fall’s climate negotiations in Scotland. Those commitments are essential, the report said.
“Many of the harshest impacts can still be prevented,” Barrett said.
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Follow Seth Borenstein on Twitter as @borenbears.
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