LONDON (Reuters) - Reports that Donald Trump is about to quit the Paris accord drew calls on Wednesday for other countries to rally round the climate pact, but warnings from some environmentalists that it would leave the deal badly weakened.
Trump will follow through on his campaign pledge to pull the United States out of the global agreement, a source briefed on the decision told Reuters. On Twitter the president said: "I will be announcing my decision on the Paris Accord over the next few days."
The accord, agreed on by nearly 200 countries in 2015, aims to cut emissions blamed for global warming. The United States committed to reducing its own by 26 to 28 percent, compared with 2005 levels, by 2025.
The agreement has been criticised as far too cautious to hold back the rise in temperatures by more than a fraction of what is needed - but its defenders say its enrolment of almost all the world's governments makes it crucial.
Steffen Kallbekken, Research Director at the Center for International Climate and Environmental Research in Oslo, called Trump's move "monumentally irresponsible".
"It is difficult to imagine a decision that would be a more devastating blow to the positive momentum behind the Paris Agreement, and to the prospects of raising climate ambition over time," he said.
Niklas Hoehne of Germany's New Climate Institute said a U.S. pullout could corrode the resolve of other nations, perhaps including hydrocarbon powers Saudi Arabia and Russia.
The big achievement of the Paris Agreement is that it was supported by all countries," he said. "If the U.S. is out that doesn't work any more."
Former President Barack Obama helped broker the Paris accord and praised it during a trip to Europe this month. Trump has called the idea of global warming a hoax.
Canada, the European Union and China have said they will honour their commitments to the pact if the United States withdraws.
Indian Prime Minister Narendra Modi met Spain's Mariano Rajoy in Madrid on Wednesday, and both countries reaffirmed their Paris commitments, without mentioning the United States.
French President Emmanuel Macron said at a weekend summit in Italy he was sure Trump would back the deal after listening to his G7 counterparts. That hope appears to have been quickly dashed.
At a Wednesday news conference, a government spokesman said Macron had told a cabinet meeting France would be "very pro-active" in working to ensure the Paris accord was implemented.
"Depending on the stance some people or others are taking, we'll have to be very pro-active for France to be the homeland of the (fight against) climate change," the spokesman said.
Macron had "asked his ministers to take a number of initiatives, with our European partners or directly in France".
European Commission Vice-President Maros Sefcovic said of a U.S. pullout: "It would be disappointing but I really do not think this would change the course of mankind.
"There is a much stronger expectation from our partners across the world from Africa, Asia and China that Europe should assume leadership in this effort and we are ready to do that," Sefcovic said.
Guy Verhofstadt, leader of the liberal group in the European Parliament, sent a tweet in the literary style of the U.S. president: “Trump puts his ego ahead of the future of our planet - sad! Let's double down on our efforts to make the #ParisAgreement a success.”
Johan Rockstrom, director of the Stockholm Resilience Centre, called Trump's decision "irresponsible and egoistic".
"It's now up to the European Union, India and China to take the lead" on climate change, he said.
"The U.S. is going from being a global leader to putting itself in a very destructive minority position." But he predicted the deal would survive without Washington.
Denmark's energy and climate minister Lars Christian Lilleholt told Reuters: "It will be necessary for the EU to show leadership if the U.S. should pull out of the deal."
Judy Wakhungu, Kenya's cabinet secretary for environment and natural resources, said her government would be "very disappointed" by a U.S. withdrawal and hoped it could be reversed.
"We all live on the same Earth and face the same challenges," she added.
Friends of the Earth's U.S. president Erich Pica said: "By pulling out of the Paris Agreement, Trump will make the United States the world's foremost climate villain."
Some observers saw chances that Washington would not, in the end, pull out.
"I hope that the president will be swayed instead by the rather sensible advice he is receiving from his Secretary of State, his Secretary of Defense and his Chief Economic Adviser, who have all recommended against withdrawal," said Bob Ward of the Grantham Research Institute on Climate Change at the London School of Economics.
By reporters in Reuters bureaux; editing by Peter Millership