Washington — Earth is likely to hit more dangerous levels of warming even sooner if the United States (US) pulls back from its pledge to cut carbon dioxide pollution, scientists said. That’s because America contributes so much to rising temperatures.
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 high level 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 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 (.18 to .36 degrees Fahrenheit).
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 (3.6 degrees Fahrenheit) above pre-industrial levels.
The world has already warmed by just over half that amount – with about one-fifth of the past heat-trapping carbon dioxide emissions coming from the United States, usually from the burning of coal, oil and gas.
So the efforts are really about preventing another 1.6 degrees Fahrenheit (0.9 degrees Celsius) from now.