President Biden’s climate czar, John Kerry, said that while the Ukraine refugee crisis is a “problem” amid Russia’s invasion, it pales in comparison to the wave of migration that will come if climate change is not addressed.

Kerry, the U.S. special presidential envoy for climate, said during the annual CERAWeek conference in Houston Monday that the U.S. must not lose sight of its path toward clean energy now that the Russia-Ukraine war has accelerated the global energy crisis.

“We’re already seeing climate refugees around the world,” he said. “If you think migration has been a problem in Europe in the Syrian War or even from what we see now, wait until you see 100 million people for whom the entire food production capacity has collapsed.”