\Scott Pruitt, a friend of the oil industry who is sceptical about man-made climate change and was Trump's controversial choice to head the US Environmental Protection Agency, will represent Washington's interests at the two-day meeting.
Up against him will be the likes of Barbara Hendricks, the German environment minister who once tried to ban meat from her ministry's catering on the grounds it was bad for the planet.
And France is deploying prominent Green campaigner Nicolas Hulot, new President Emmanuel Macron's high-profile pick for the environment brief.
Italy's large environmentalist movement has also vowed to make its voice heard. A major demonstration against Trump's decision is planned for Sunday afternoon in Bologna, an ancient university city and bastion of progressive activism.
"We are expecting a good turnout. A lot of people are very upset about Trump's decision and it has started a new debate," Giacomo Cossu, one of the organisers of the demonstration, told AFP.
Trump announced at the start of this month that the US would not abide by the 2015 Paris agreement and would seek to renegotiate terms he denounced as unfairly damaging to the American economy and overly generous to India and China.
A spokesman for Hendricks said Germany would be looking for "something more concrete" from Pruitt in terms of what the US was going to do.
Trump has said Washington will not be bound by the targets on reducing emissions of greenhouse gases set down in Paris, and will cut funding for developing countries affected by climate change.
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