Beto O’Rourke is urging his supporters people to take action to confront climate change.

During his first presidential campaign swing through California on Tuesday, he called climate change the “mother of all challenges.”

Speaking to a crowd in downtown San Diego, the Democratic presidential candidate said that all our current problems would become much worse in the future because of climate change and global warming.

“The places we call home, any city along the coast or on the ocean, will no longer sustain human life going forward on this current trajectory,” he said.

He also said that migration into the U.S. would increase more if we continued down this current path.

The day before, O’Rourke unveiled his first policy proposal–a plan that would see zero carbon emissions in the U.S. by 2050, the re-signing of the Paris Agreement and $5 trillion in spending over 10 years to invest in clean energy and extreme weather preparation.

This plan drew criticism from other Democrats, who pointed to his history of voting for policies on the side of fossil fuel industries rather than renewable energy industries.

O’Rourke responded in an interview with MSNBC, saying that those in the fossil fuel industry must be brought along as partners to ensure a move to greener energy sources.

In his appearance in San Diego, O’Rourke talked about other issues that resonated with Californians, like availability and affordability of housing, urging communities to build more housing units. He also called for “inclusionary zoning” of neighborhoods, meaning that poor and rich people would live next to one another.

The issue of climate change appears to weigh more heavily on the minds of current Democratic voters than it did during the 2016 campaign. In a CNN poll last week, 96 percent of voters said climate change was “very” or “somewhat” important to them. This even topped the issue of healthcare, which came in at 91 percent.