BERLIN (AP) — World leaders breathed an audible sigh of relief that the United States under President Joe Biden is rejoining the global effort to curb climate change, a cause that his predecessor had shunned.

British Prime Minister Boris Johnson and French President Emmanuel Macron were among those welcoming Biden's decision to rejoin the the Paris climate accord, reversing a key Trump policy in the first hours of his presidency Wednesday.

“Rejoining the Paris Agreement is hugely positive news,” Johnson wrote on Twitter. Britain, which is hosting this year's U.N. climate summit, looked forward to working with the Biden administration on the issue, he said.

Macron likewise tweeted his joy at the U.S. rejoining the Paris pact, saying that with Biden, “we will be stronger to face the challenges of our time. Stronger to build our future. Stronger to protect our planet.”

The accord, forged in the French capital in 2015, commits countries to put forward plans for reducing their emissions of greenhouse gases such as carbon dioxide, which is released from burning fossil fuels.

Former President Donald Trump had questioned the scientific warnings about man-made global warming, at times accusing other countries of using the Paris accord as a club to hurt Washington. The U.S. formally left the pact in November.

By contrast, Biden put the fight against climate change at the center of his presidential campaign and on Wednesday immediately launched a series of climate-friendly efforts to bring Washington back in step with the rest of the world on the issue.

“A cry for survival comes from the planet itself,” Biden said in his inaugural address. “A cry that can’t be any more desperate or any more clear now.”

Experts say any international efforts to keep global warming well below 2 degrees Celsius (3.6 Fahrenheit), ideally 1.5C (2.7F), as agreed in the Paris accord would struggle without the contribution of U.S., which is the world's second biggest carbon emitter.

Scientists say time is running out to reach that goal because the world has already warmed 1.2 C (2.2 F) since pre-industrial times.

Italy said the U.S. return to the Paris accord would help other countries reach their own climate commitments. “Italy looks forward to working with the U.S. to build a sustainable planet and ensure a better future for the next generations,” Premier Giuseppe Conte tweeted.

The Vatican, too, was clearly pleased given the decision aligns with Pope Francis’ environmental agenda and belief in multilateral diplomacy. In a front-page editorial in Wednesday’s L’Osservatore Romano, Vatican deputy editorial director Alessandro Gisotti noted that Biden’s decision to rejoin Paris “converges with Pope Francis’ commitment in favor of the custody of our common home.”

German Chancellor Angela Merkel was more muted in her reaction, noting merely that her government would “probably have a more similar opinion” with Biden on issues such as the Paris climate accord, migration and the World Health Organization.

Merkel's conservative Union bloc has close ties to the German auto industry that's fought against tougher emissions rules for cars. Her potential successor, Armin Laschet, has defended the continued mining of coal in his home state even as Germany phases out the fossil fuel by 2038.

Germany's Environment Minister Svenja Schulze, of the center-left Social Democrats, voiced greater excitement at Biden's move. “The U.S. is rejoining the fight against the climate crisis with great verve and enthusiasm,” Schulze said, adding that she hoped the new U.S. administration would use the upcoming global summit to “reinforce their pursuit of climate neutrality with a concrete intermediate target for 2030.”

Youth activists who have been at the forefront of demanding leaders take the threat of global warming seriously said they now want to see concrete action from Washington.

“Many countries signed the Paris Agreement and they are still part of the Paris Agreement, but they make very free interpretations of what that implies," said Juan Aguilera, one of the organizers of the Fridays for Future movement in Spain. “In many cases, signing it has become a show, because at the end of the day the concrete measures that are being taken, at least in the short term, are not satisfactory.”

Biden has appointed a large team to tackle climate change both on the domestic and international front. Former Secretary of State John Kerry, named as the president's special climate envoy, on Thursday took part in a virtual event with Italian industry at which he touted the ‘green economy’ as an engine for jobs and said the U.S. planned to make up for time lost over the past four years.

Organizers of a meeting Monday on adapting to climate change said they hoped Kerry would take part too, and Biden himself has talked about inviting world leaders to a summit on the issue within his first 100 days in office.

Over the coming months the U.S. allies and rivals will closely watch to see by how much the administration offers to cut its emissions in the coming decade. A firm number is expected to be announced before the U.N. climate summit taking place in Glasgow, Scotland, in November.

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Nicole Winfield in Rome and Aritz Parra in Madrid contributed to this report.

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Follow AP’s climate coverage at https://www.apnews.com/Climate