SAN DIEGO ― Beto O’Rourke urged ambitious action to confront climate change ― what he called the “mother of all challenges” ― during his first presidential campaign swing through California, a state hit hard by drought and wildfires in recent years.

On Tuesday, speaking to a packed crowd at a community center near downtown San Diego, the former Democratic congressman argued that nearly all of the problems facing the U.S. will become exponentially worse in the future if the world does not address the threat of 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,” O’Rourke said.

He also warned that the levels of migration to the U.S. will become much greater if the average global temperature rises by three to four degrees Celsius as projected.

The day before, O’Rourke unveiled his first substantive policy proposal, a sweeping new plan that would see net-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.