The United States has formally submitted notice to the United Nations that it plans to exit the Paris climate accord, in a decision French President Emmanuel Macron and scientists said was lamentable.
President Donald Trump went ahead with the pull out despite mounting evidence on the impact of climate change, with September the fourth month in the row that near- or record-breaking global temperatures were recorded.
US Secretary of State Mike Pompeo announced that the administration had started the process to withdraw “because of the unfair economic burden imposed on American workers, businesses, and taxpayers” by the agreement's terms.
The Paris accord set a goal of limiting temperature rises to well within two degrees Celsius from pre-industrial levels, a goal scientists say is vital to check the worst damage from global warming that is already increasing the severity of droughts, rising floods and intensifying storms.
Defending the decision to leave, Mr Pompeo said the US had reduced all types of air pollutants affecting human health and the environment by 74 per cent between 1970 and 2018, with greenhouse gas emissions dropping 13 per cent between 2005 and 2017.
“We will continue to offer a realistic and pragmatic model... showing innovation and open markets lead to greater prosperity, fewer emissions and more secure sources of energy,” he said of a US energy mix comprising fossil fuels, renewables and nuclear.
A spokesman for UN Secretary-General Antonio Guterres said the US had notified officials by letter that it was pulling out, under Article 28, paragraph 2 of the 2015 accord.
But the withdrawal will take a year, making the final exit date November 4, 2020 – one day after the next US presidential election. The Paris agreement's rules prevented any country from pulling out in the first three years after ratification in 2016.
Were a Democrat to win the US election next November, the decision could be reversed. This would potentially restore the conditions negotiated by President Barack Obama, Mr Trump's predecessor in the White House. Readmission would take 30 days.
Monday's decision makes America the only nation among 188 original signatories to pull out.
Mr Macron, who unsuccessfully tried to persuade Mr Trump to stay in the accord named after his nation's capital where it was negotiated, signalled that other alliances on climate would move forward regardless.
"We regret this and it makes the Franco-Chinese partnership on climate and biodiversity even more necessary," said a statement from the French presidency as Mr Macron visited China, the world's largest emitter of greenhouse gases blamed for climate change.
The US ranks second in global emissions.
The one-year period for exiting the accord leaves time for Mr Trump, who took office in 2017, to roll back environmental regulations as states such as California and New York try to take stronger action on their own.
The US president has sought to block California from setting tighter standards on car emissions and moved to let states set their own standards on existing coal-fired power plants.
Robert Menendez, the top Democrat on the Senate Foreign Relations Committee, said the Trump administration had “once again thumbed its nose at our allies, turned a blind eye to the facts and further politicised the world's greatest environmental challenge”.
A Washington Post poll last month found that even in his own party Mr Trump faces growing opposition on the issue, with 60 per cent of Republicans agreeing with the scientific consensus that human activity is causing climate change.
The European Union has sought to cut carbon pollution in 2030 by 40 per cent compared with 1990 levels, which is greater than America’s pledge, said Professor Rob Jackson of Stanford University, who is also chairman of the Global Carbon Project.
Britain has already exceeded that goal.
“The US agreement is not a tax on the American people. There is no massive wealth transfer,” said Climate Advisers chief executive Nigel Purvis, who was a lead State Department climate negotiator in the administrations of US presidents Bill Clinton and George W Bush.
“In fact, the agreement obligates no country to make any financial payments.”