"The United States is evaluating its policy with regard to the climate, so the six other G7 countries will reaffirm their commitment (to the global Paris accord) while taking note" of the US position, a French official said at the G7 summit in Sicily.
Other delegates concurred that it was "six against one" at the gathering of leading democracies spanning North America, Europe and Japan.
Under Trump, who once called climate change a "hoax" perpetrated by China, Washington has resisted intense pressure from its partners to commit to respecting the 2015 global accord on curbing carbon emissions.
"His views are evolving, he came here to learn," Cohn said. "His basis for decision ultimately will be what's best for the United States."
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The United States is the world's biggest carbon emitter after China.
Trump has yet to act on his campaign threat to ditch the Paris accord, having said he would listen to what US partners have to say before making a decision on how to proceed after the G7.
Abandoning the Paris agreement would carry a high political cost in Europe and China, where the deal is considered a bedrock for action on climate change, analysts say.
The stalemate on climate change was mirrored by divisions between the US and the other G7 countries over trade and migration at the annual summit, described by officials as the toughest in years.
Delegates worked long into the night in an attempt to reach a compromise on the closing statement which will be issued later today.
But while officials signalled some progress on bridging differences about trade with the protectionist Trump, differences on the climate issue remained irreconcilable.