UNITED NATIONS (AP) — Monaco’s Prince Albert II, a life-long environmental campaigner, has a message for President Donald Trump after his withdrawal from the Paris climate accord: Listen “a little more carefully” to scientists and scientific evidence on the impact of climate change.

The ruler of the tiny city-state on the Mediterranean Sea told reporters Wednesday that if he met the U.S. leader he would also tell him to “look at the tremendous implications that go along with having the U.S. withdraw from the Paris agreement.”

Albert, son of the late Prince Rainier and American actress Grace Kelly, said that while Trump’s withdrawal “is catastrophic,” the reaction from U.S. mayors, governors and many in the corporate world has been “wonderful.”

“So I think there’ll be a tremendous movement to … keep the fight against climate change alive around the world and in this country,” he said.

Albert noted that it will be at least three years before the United States can withdraw from the Paris agreement, which aims to reduce carbon emissions and keep global warming below 2 degrees Celsius (3.6 degrees Fahrenheit) compared with pre-industrial times.

“So there might still be hope,” he said. “I think everybody’s crossing their fingers for that – that there might be a reversal of that decision.”

Even without the United States, the global movement to combat climate change remains strong, Albert said.

“We’re not doing this just for ourselves, not for now, but for future generations, and I think that should resonate in most people’s minds and hearts,” he said.

Albert spoke at the first-ever U.N. conference on oceans and announced that Monaco Explorations will send the transoceanic exploration vessel Yersin on a three-year trip starting in July with scientific teams to conduct research in nine remote locations. The 250-foot ship with six laboratories has technology to prevent any waste entering the sea or the atmosphere.

Monaco faces the sea, Albert said, and that’s why its rulers have always worked to protect the oceans.

“More than anything else, they are suffering from our ignorance and our indifference,” he said.