Nearly 400,000 migrants have streamed into Europe this year, setting off the continent’s largest refugee crisis since World War II. But the tide of desperation is nothing compared to the flood of environmental refugees that could be created by unchecked climate change, experts and elected officials warn.

President Obama set the tone in a speech last week in Alaska, where he summoned images of “desperate refugees,” “entire industries of people who can’t practice livelihoods” and “political disruptions that could trigger conflicts around the world.” Secretary of State John Kerry dubbed them “climate refugees,” and warned of a global fight for food, water and “mere survival.”

If we don’t conclude [with a successful agreement],…it won’t be hundreds of thousands of refugees in the next 20 years, it will be millions.

Now, less than 100 days before a major climate change summit in Paris, the president of France is sounding the same alarm.

“There is a risk of failure,” François Hollande said on Monday, following a meeting aimed at securing financial support for poor countries most affected by climate change. “If we don’t conclude [with a successful agreement], and there are no substantial measures to ensure the transition, it won’t be hundreds of thousands of refugees in the next 20 years, it will be millions.”