What happens if US exits climate deal?
WASHINGTON: Earth is likely to hit more dangerous levels of warming even sooner if the US pulls back from its pledge to cut carbon dioxide pollution, scientists said. That is because America contributes so much to rising temperatures.
US President Donald Trump, who once proclaimed global warming a Chinese hoax, will soon decide whether the US stays in or leaves a 2015 Paris climate change accord in which nearly every nation agreed to curb its greenhouse gas emissions.
Other global leaders have been urging him to stay during highlevel security and economic meetings in Italy that began Friday. Pope Francis already made the case with a gift of his papal encyclical on the environment when Trump visited the Vatican earlier this week.
In an attempt to understand what could happen to the planet if the US pulls out of Paris, The Associated Press consulted with more than two dozen climate scientists and analyzed a special computer model scenario designed to calculate potential effects.
Scientists said it would worsen an already bad problem and make it far more difficult to prevent crossing a dangerous global temperature threshold.
Calculations suggest it could result in emissions of up to 3 billion tons of additional carbon dioxide in the air a year. When it adds up year after year, scientists said that is enough to melt ice sheets faster, raise seas higher and trigger more extreme weather.
“If we lag, the noose tightens,” said Princeton University climate scientist Michael Oppenheimer, co- editor of the peer-reviewed journal Climatic Change.
One expert group ran a worst-case computer simulation of what would happen if the US does not curb emissions, but other nations do meet their targets. It found that America would add as much as half a degree of warming (0.3 degrees Celsius) to the globe by the end of the century.
Scientists are split on how reasonable and likely that scenario is.
Many said because of cheap natural gas that displaces coal and growing adoption of renewable energy sources, it is unlikely that the US would stop reducing its carbon pollution even if it abandoned the accord, so the effect would likely be smaller.
But others say it could be worse because other countries might follow a US exit, leading to more emissions from both the US and the rest.
Another computer simulation team put the effect of the US pulling out somewhere between 0.1 to 0.2 degrees Celsius.
While scientists may disagree on the computer simulations they overwhelmingly agreed that the warming the planet is undergoing now would be faster and more intense.
The world without US efforts would have a far more difficult time avoiding a dangerous threshold: Keeping the planet from warming more than 2 degrees Celsius above pre-industrial levels.
The world has already warmed by just over half that amount — with about one-fifth of the past heattrapping carbon dioxide emissions coming from the US, usually from the burning of coal, oil and gas.
So the efforts are really about preventing another 0.9 degrees Celsius from now.
“Developed nations — particularly the US and Europe — are responsible for the lion’s share of past emissions, with China now playing a major role,” said Rutgers University climate scientist Jennifer Francis. “This means Americans have caused a large fraction of the warming.”
Even with the US doing what it promised under the Paris agreement, the world is likely to pass that 2-degree mark, many scientists said.
But the fractions of additional degrees that the US would contribute could mean passing the threshold faster, which could in turn mean “ecosystems being out of whack with the climate, trouble farming current crops and increasing shortages of food and water,” said the National Center for Atmospheric Research’s Kevin Trenberth.