Trump is about to get an earful in Europe for his climate-change denial.

The president left Washington, D.C., for Poland on Wednesday for the annual G-20 summit. This year’s theme is “sustainability,” so, naturally, Trump is expected to be grilled over his controversial decision to leave the Paris climate agreement.

World leaders do not appear to be taking the U.S. decision lightly. Last week, Newsweek reported that German chancellor Angela Merkel “vowed confrontation” with Trump at the G-20 over his refusal to work with other countries to fight global warming. “The differences are obvious and it would be dishonest to try to cover that up. That I won’t do,” she said.

Though the U.S. has contributed more to global warming than any other country, Trump—though his decision to withdraw from the Paris agreement, and his domestic energy agenda—has isolated the U.S. as the only major country not promising to do anything about it. As such, Merkel is emerging as Trump’s most outspoken critic in the international community. Last week, she shamed him for not accepting the science behind the threat. “We can’t wait for the last man on Earth to be convinced by the scientific evidence for climate change,” she said. Trump also spoke with Merkel about “climate issues” over the phone on Monday, according to a White House press release.

Other countries have been speaking out against the president in their own ways. Following Trump’s decision to abandon the Paris agreement, French President Emmanuel Macron offered American climate scientists grant money to come to France, using the cheeky slogan: “Make Our Planet Great Again.” And in a newspaper editorial this week, Japanese Prime Minister Shinzo Abe called on countries to work together on climate change, implicitly calling out the United States.