The United States could influence or disrupt work by other nations to combat climate change until late 2020 if it quits Paris Agreement
* Trump to honour pledge to quit Paris deal - source
* U.N. rules say formalities to leave last four years
* Trump could obstruct work on Paris rule book
By Alister Doyle Environment Correspondent
OSLO, May 31 (Reuters) - The United States could influence or even disrupt work by other nations to combat climate change until late 2020 even if President Donald Trump quits a global agreement, legal scholars said on Wednesday.
Trump will honour a campaign pledge to pull out of the 195-nation Paris Agreement, a source briefed on the decision told Reuters on Tuesday. Trump tweeted he would announce his formal decision "over the next few days".
U.N. rules for the 2015 pact, which seeks to shift the world economy from fossil fuels this century, say Washington would formally have to wait until November 2020 to withdraw. Trump could shorten the formalities to just one year by exiting Paris' 1992 parent treaty.
Quitting the Paris Agreement would leave Trump in a legal grey zone until the next U.S. presidential election in 2020, retaining a vote as other nations work on detailed rules on issues such as how to monitor greenhouse gas emissions.
In the worst case "the U.S. could make it more difficult to adopt the Paris rules", said Daniel Bodansky, a law professor at Arizona State University.
"To the extent that (withdrawal from Paris) is already going to harm relations with our allies, staying in and being obstructionist would be even more harmful," he said. Trump has promised to promote the coal industry over renewables.
Bodansky noted, however, that Washington did not try to obstruct other nations' work on the 1997 Kyoto Protocol, which obliged rich nations to cut emissions, after President George W. Bush angered U.S. allies by deciding in 2001 not to take part.
Megan Bowman, a law lecturer at King's College, London, said the four-year waiting period was partly intended to insulate the agreement from a shift to a Republican presidency after Democratic President Barack Obama.
"The downside ... is that if they (the United States) are recalcitrant they are sitting at the table, able to obstruct or stall the process," she said. Paris imposes few legal obligations before 2020 and has no sanctions for non-compliance.
The Paris Agreement's Article 28 says any nation wanting to pull out has to wait three years from the date the agreement gained legal force, which was Nov. 4, 2016, before seeking to leave. It then has to wait another year.
In Berlin, European Commission President Jean-Claude Juncker stressed that withdrawal would take years. "The Americans can't just leave the climate protection agreement. Mr. Trump believes that because he doesn't know the details."
Trump would be taking a riskier step by withdrawing from Paris' parent treaty, the 1992 Climate Convention, even though it would require only a year's notice and void U.S. commitments under Paris.
That Convention, seeking voluntary actions to rein in greenhouse gas emissions and a landmark in cooperation between rich and poor nations, has had bipartisan U.S. support. It was signed by Republican President George Bush.
Paris goes one step further by obliging all nations to set domestic targets to curb emissions to limit a creeping rise in temperatures blamed for more heat waves, downpours and rising sea levels.
Leaving the Convention would make the United States an "international pariah on global climate change", said Robert Stavins, director of Harvard University's environmental economics program.
Johan Rockstrom, director of the Stockholm Resilience Centre, said a U.S. presence in the Paris negotiations until 2020 would be "the most negative thing ... they would still be allowed to vote in the room".
But he said a quick, clean break by the United States from the 1992 Convention might be best for other nations which could then work without risks of obstruction. (Reporting By Alister Doyle; Editing by Andrew Bolton)
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