President Donald Trump said Monday he would again pull the United States out of the landmark Paris climate accord, dealing a blow world efforts to combat global warming and further distance the US from its closest allies.

The announcementwhich day has come Mr. Trump was sworn in for a second term, he repeated Trump’s actions in 2017when he announced that the US would leave the global Paris Agreement. President Biden later rejoined.

As signed by a a series of executive actions after his inauguration, Mr Trump said: “I am withdrawing immediately from the unfair, one-sided Paris climate agreement.” He also signed a letter informing the UN of his decision.

The pact is aimed at limiting long-term global warming to 2.7 degrees Fahrenheit (1.5 degrees Celsius) above pre-industrial levels or, if that is not possible, keeping temperatures at least well below 3.6 degrees Fahrenheit (2 degrees Celsius) above pre-industrial levels. USA is one of the world’s tops carbon pollution nations.

The 2015 Paris Agreement is voluntary and allows countries to set targets to reduce their own greenhouse gas emissions from burning coal, oil and natural gas. These targets are set to become more stringent over time, and countries face a February 2025 deadline for new individual plans.

The outgoing Biden administration last month offered a plan to reduce greenhouse gas emissions in the US by more than 60% by 2035.

Laurence Tubiana, chief executive of the European Climate Foundation and a key architect of the Paris accord, called the planned US withdrawal unfortunate, but said action to slow climate change was “stronger than the policies and politics of any individual country”.

The global context for Trump’s actions is “very different from 2017,” Tubiana said, adding that “there is unstoppable economic momentum behind the global transition, which the US has benefited from and led, but now risks losing.”

The International Energy Agency expects the global market for key clean energy technologies to triple to more than $2 trillion by 2035, she said.

“The impacts of the climate crisis are also worsening terrible forest fires in Los Angeles are the latest reminder that Americans, like everyone else, are affected by worsening climate change,” Tubiana said.

Gina McCarthy, who served as White House climate adviser under President Joe Biden, a Democrat, said that if Trump, a Republican, “really wants America to lead the global economy, become energy independent and create good-paying American jobs,” then he must “remain focused on growing our clean energy industry. Clean technologies are lowering energy costs for people across our country.”

The world is now 2.3 degrees Fahrenheit (1.3 degrees Celsius) above mid-19th century temperatures in the long term. Most, but not all, climate monitoring agencies said global temperatures exceeded the 2.7 degree Fahrenheit warming limit last year, and all said it was the warmest year on record.

Without major reductions over the next few years, the world is on track to experience a temperature rise of more than 3 degrees Celsius, according to October UN reportwhich warned that such an outcome “would have a debilitating effect on people, the planet and economies”.

The process of withdrawing from the Paris Agreement lasts a year. Trump’s previous withdrawal took effect the day after the 2020 presidential election, in which he lost to Biden.

While the first withdrawal was led by Trump from a key UN agreement — adopted by 196 nations — shocked and angered nations around the world, “no country has followed the US out the door,” said Alden Meyer, a longtime climate negotiations analyst at the European think tank E3G.

Instead, other nations have renewed their commitment to slowing climate change, along with investors, businesses, governors, mayors and others in the U.S., Meyer and other experts said.

Still, they lamented the loss of U.S. leadership in global efforts to slow climate change, even as the world is on track for another record-breaking hot year and teeters from drought to hurricanes, floods and wildfires.

“It is clear that America will not play a leading role in solving the climate crisis, the greatest dilemma humans have ever faced,” said climate activist and author Bill McKibben. “In the next few years, the best we can hope for is that Washington fails to destroy the efforts of others.”

About half of Americans “somewhat” or “strongly” oppose U.S. action to withdraw from the climate accord, and even Republicans aren’t overwhelmingly in favor, according to poll from the Associated Press-NORC Public Affairs Research Center. Only about 2 in 10 American adults are “somewhat” or “strongly” in favor of withdrawing from the Paris Agreement, while about one-quarter are neutral.

Much of the opposition to the US withdrawal comes from Democrats, but Republicans also show some ambivalence. Just under half of Republicans favor withdrawing from the climate accord, while about 2 in 10 oppose it.

A few years ago, China surpassed the United States as the country with the largest annual carbon dioxide emissions. According to scientists who monitor emissions for the Global Carbon Project, the US — the second largest annual carbon polluter — will release 4.9 billion metric tons of carbon dioxide into the air in 2023, an 11% drop from a decade earlier.

But carbon dioxide has been in the atmosphere for centuries, so the United States has dumped more of the heat-trapping gas that is now in the air than any other nation. According to the Global Carbon Project, the US is responsible for nearly 22% of the carbon dioxide released into the atmosphere since 1950.

While global efforts to combat climate change continued during Trump’s first term, many experts worry that a second Trump term will be more damaging, as the United States will further withdraw from climate efforts in a way that could cripple the efforts of future presidents. With Trump, a climate change denier, in charge of the world’s leading economy, these experts fear that other countries, particularly China, could use it as an excuse to relax their own efforts to reduce carbon emissions.

Simon Stiell, the UN’s executive secretary for climate change, expressed hope that the US will continue to embrace the global clean energy boom.

“Ignoring it just sends all that vast wealth to competing economies, while climate disasters like droughts, wildfires and superstorms get worse,” Stiell said. “The door to the Paris Agreement remains open and we welcome the constructive engagement of all countries.”