This is a developing story and may be updated.

Sen. Bernie Sanders was joined at a Climate Crisis Summit in Des Moines Saturday afternoon by author Naomi Klein, Rep. Alexandria Ocasio-Cortez, and other influential figures in the grassroots effort to pass a Green New Deal and achieve environmental justice for all.

Ahead of the summit, Klein said on Twitter that she was planning at the event to announce her endorsement of the senator's 2020 presidential campaign.

"The world is on fire and our most credible hope of beating the arsonists is Bernie Sanders," Klein tweeted.

I’ve written about my preferences but I have never formally endorsed a candidate for President in my life - never mind spoken at a campaign rally. That ends today in #Iowa. The world is on fire and our most credible hope of beating the arsonists is #Bernie2020 #NotMeUs — Naomi Klein (@NaomiAKlein) November 9, 2019

The Sanders campaign sent an email to supporters on Friday highlighting a number of polls showing that the Vermont independent senator is seen as a climate leader in the Democratic primary.

"Bernie's leadership on climate is set to be particularly critical to his Iowa campaign, because the state has already been so battered by climate change," wrote the campaign. "Climate-intensified flooding in Iowa has caused billions of dollars of damage and bludgeoned the state’s agriculture sector—all while fossil fuel corporations have polluted the state with pipeline leaks and oil spills."

Also joining Sanders at Drake University on Saturday was Isra Hirsi, a leader of the U.S. Climate Strike movement; Zina Precht-Rodriguez of the Sunrise Movement, and Sanders's Iowa campaign co-chair, Stacey Walker.

The summit was scheduled to begin at 12:00pm central time/1:00pm Eastern.

Watch the summit below: