German Chancellor Angela Merkel is gearing up to defend global action on climate change at the upcoming G20 leaders’ summit in Hamburg, with at least one United States cabinet secretary already downplaying the prospects for open conflict between Merkel and Donald Trump.

“These will not be easy talks,” Merkel said, in what Reuters styled as a “defiant” speech to the German parliament. Though she didn’t refer to Trump by name, she affirmed that “the differences are obvious and it would be wrong to pretend they aren’t there. I simply won’t do this.”

“Of course there are going to be differences in relations with any country, and we’ll talk frankly about those differences,” responded U.S. National Security Advisor H.R. McMaster, adding that Trump “enjoys those conversations”.

Reuters recalls that the G7 summit in Sicily a few months ago “exposed deep divisions between other western countries and Trump on climate change, trade, and migration,” and that Trump announced the U.S. exit from the Paris agreement shortly afterwards. As the G20 gather, “the German hosts face a difficult challenge. Along with Trump, Russia’s Vladimir Putin and Turkey’s Tayyip Erdogan will be attending. All have strained relations with Merkel and other European leaders.”

But Merkel, who’s said to be in no mood to compromise, described climate change as an “existential challenge” and declared herself “more determined than ever” to make Paris work. “We cannot wait until every last person on Earth has been convinced of the scientific proof,” she said. “Anybody who believes the problems of the world can be solved with isolationism and protectionism is making a big mistake.”