All 195 nations in Paris agreed to the deal except Nicaragua, which objected that it demanded too little of the rich.

Many nations are pushing for swift ratification of a Paris agreement to slow climate change and lock it in place for four years before a change in the White House next year that might bring a weakening of Washington’s long-term commitment.

More than 130 nations with 60 leaders including French President Francois Hollande are due to sign December’s pact at a U.N. ceremony in New York on April 22, the most ever for a U.N. agreement on an opening day, the United Nations said.

Both China and the United States, the world’s top emitters accounting together for 38 percent of emissions, have promised to sign then. U.S. Secretary of State John Kerry is expected to attend.

But signing is only a step in a tortuous U.N. process for the deal to enter into force, which requires formal approval by at least 55 nations representing 55 percent of man-made greenhouse gas emissions.

In many countries, that needs a parliamentary vote.

Some experts predict the 55 percent thresholds can be reached this year, before President Barack Obama leaves office in January 2017.

But many developing nations want the Paris agreement to move forward as rapidly as possible on ratification, partly to lock in the United States if Republican candidates Donald Trump or Ted Cruz, who do not think that climate change is man-made, win the U.S. presidency.

Once the Paris accord enters into force, a little-noted Article 28 says any nation wanting to withdraw will first have to wait four years – the length of a U.S. presidential term.

“I would expect non-compliance, but not necessarily a formal withdrawal,” under a Republican president, said Oliver Geden, of the German Institute for International and Security Affairs.

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