[Complex and controversial international accords usually take several years to enter into legal force. But the haste on the Paris accord was driven at least in part by the looming American election. Donald J. Trump, the Republican candidate, has vowed to pull the United States out of the accord if he is elected. If the deal comes into legal force before the presidential inauguration, it will take four years under the accord’s rules for the United States to legally withdraw. That would keep the country bound to the measure through the first term of the next administration.]
By Coral Davenport
Ban Ki-moon, the United Nations secretary general, backstage on Tuesday
at the annual session of the General Assembly. Credit Sam
Hodgson for The New York Times
UNITED NATIONS — The United Nations secretary general, Ban Ki-moon, is expected to announce on Wednesday that he has secured enough commitments from world leaders to ensure that the 2015 Paris climate accord will enter into legal force this year, binding the next American president, whoever it is.
The milestone is in reach in large part because Mr. Ban, who sees the climate deal as a centerpiece of his legacy, began a sustained push to win the formal approval of 55 countries representing 55 percent of global emissions — the threshold needed to put the accord into force. He pressed the issue personally with dozens of world leaders and with legislative bodies, including those in Russia and his native South Korea.
“We are absolutely certain that we will have the Paris agreement entering into force by the end of 2016,” said David Nabarro, a special adviser to Mr. Ban.
Complex and controversial international accords usually take several years to enter into legal force. But the haste on the Paris accord was driven at least in part by the looming American election. Donald J. Trump, the Republican candidate, has vowed to pull the United States out of the accord if he is elected. If the deal comes into legal force before the presidential inauguration, it will take four years under the accord’s rules for the United States to legally withdraw. That would keep the country bound to the measure through the first term of the next administration.
“We have no time,” Mr. Ban said, addressing the General Assembly on Tuesday. “I urge you to bring the Paris agreement into force this year.”
Nearly 400 of the world’s top scientists, including 30 Nobel laureates, on Tuesday condemned Mr. Trump’s pledge to withdraw the United States from the Paris agreement. A decision to withdraw could fatally undermine the accord and send a message to the rest of the world that “you are on your own,” declared 375 members of the National Academy of Sciences, as well as foreign affiliates of the academy. They included Stephen Hawking of the University of Cambridge in Britain, who is perhaps the world’s most famous living scientist; Neil deGrasse Tyson, the renowned astrophysicist and science communicator; and the physicist Steven Chu, the Nobel laureate and former United States energy secretary.
“The consequences of opting out of the global community would be severe and long-lasting — for our planet’s climate and for the international credibility of the United States,” the scientists added.
A breakthrough in the quest for quick ratification came this month when the European Union, which represents about 10 percent of global warming emissions, set an Oct. 9 vote to join the agreement, with or without action by its member states. The bloc has pledged under the Paris agreement to cut its emissions 40 percent from 1990 levels by 2030, but not all of its 28 member states are yet prepared to approve their individual climate pledges.
That push gained unexpected momentum on Tuesday when President Andrzej Duda of Poland declared before the General Assembly that he expected his government to legally join the deal this year. It had been widely expected that Poland, one of Europe’s heaviest coal polluters, would object to the broader European body’s effort to move forward without all of its member states.
“What is important is the heritage that we leave to our children and grandchildren — how they will remember us, and how they will write about us in the history books,” Mr. Duda said.
Another concern had been Britain’s vote to leave the European Union, which advocates of the Paris deal feared would complicate the bloc’s ratification process and raise questions about Britain’s own climate policy. But Theresa May, the new British prime minister, pledged before the General Assembly on Tuesday that her government too would legally join the Paris agreement this year.
“The Parliament of Europe,” said Ségolène Royal, the French environment minister who presided over the Paris climate summit meeting and has taken a leading role in pushing for ratification of the deal this year, “will be able to do it even without agreement of all 28 countries.”
At the ceremony on Wednesday, it is expected that at least 20 other countries — including Albania, Argentina, Bolivia, Brazil, Canada, Costa Rica, Indonesia, Iran, Mexico, New Zealand and Saudi Arabia, which together represent about 8 percent of total world emissions — will submit their legal paperwork or pledge to do so by the end of the year, United Nations officials said.
The governments of Chad, Egypt, Ethiopia, Ghana, Honduras, Kuwait, Madagascar, Mali, Niger, Rwanda and Ukraine, which together represent roughly 2 percent of global emissions, are expected to pledge to submit their legal documentation of commitment to the Paris accord by the end of the year.
“The Paris agreement gives a framework to act, but there must be a sense of urgency about bringing the agreement into force,” President Obama said on Tuesday in his last address as head of state to the General Assembly.
The accord approached its legally binding threshold this month after the United States and China, which together account for nearly 40 percent of emissions, jointly announced that they would legally join the deal. About two dozen other countries, collectively representing about 2 percent to 3 percent of global emissions, have also legally joined it.
But many of the largest polluters have not signed on. In an interview, Ms. Royal conceded that the European Union’s power move would inflame opposition from some member countries. “Three or four countries will be very difficult,” she said. “But it will pass.”
Still an open question are the timetables of the world’s three other major polluters: India, which accounts for about 7 percent of emissions, Russia, which produces about 5 percent, and Japan, which produces about 3 percent.
Prime Minister Narendra Modi of India has worked closely with Mr. Obama and Mr. Ban on the issue of climate change, but members of his Parliament remain wary of a deal that would require emissions cuts as the country seeks to supply cheap electricity to millions of impoverished people.
Japanese officials say there is a good chance that Tokyo will pass the deal in the autumn session of the Diet.
Russian officials did not respond to emailed questions about their plans, but United Nations officials said they were optimistic that Moscow might sign on by year’s end. President Vladimir V. Putin, who has mocked the science of climate change, surprised many when he showed up at the Paris accord negotiations and promised to prioritize the deal.
“Putin is having a conversation with the Russian government,” said Robert Orr, the dean of the University of Maryland School of Public Policy and a special adviser to Mr. Ban. “It’s one of the governments that has surprised many with how forward-leaning they are on this. That’s the kind of situation we would like to see.”
Mr. Orr and others noted that Russia’s commitment under the Paris deal would not be difficult to meet — it is one of the weakest pledges and is unlikely to do much to significantly reduce pollution. But they said Mr. Putin’s legal acceptance of the deal would still be valuable.
Follow Coral Davenport on Twitter @CoralMDavenport.
Justin Gillis contributed reporting.