SAN FRANCISCO (CBS SF) — Morning rush hour traffic came to a near halt in San Francisco’s South of Market neighborhood early Thursday as protesters representing a wide variety of environmental causes took to the city streets.

Hundreds of scientists, business leaders and political leaders have gathered in San Francisco for the three-day Global Climate Action Summit hosted by California Gov. Jerry Brown.

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Also in the city were several different environmental groups who were demanding action on a range of issues including offshore oil drilling, timber harvesting and oil pipelines built across Native American lands.

On Thursday, at least two of those groups chose to block streets and the entrance to Moscone Center — the site of the summit — turning the morning commute into a chaotic mess.

Nearly 500 chanting protesters blocked the intersections of 3rd and Howard St. and 3rd and Folsom St. under the watchful eye of a contingent of San Francisco police officers. Many of critical of what they call Brown’s slow response to the threat of increase oil drilling in California.

Inside the event, Brown and former New York Mayor Michael Bloomberg were holding a news conference.

“America’s a wonderful country,” Bloomberg said. “Here we got environmentalists protesting at an environmental conference. It reminds me of people who want to build a wall along the Mexican border to keep people out from a country that we go to for vacations. Something is crazy here.”

Police made two arrests and escorted ten others from the building.

Brown, meanwhile, took aim at President Donald Trump saying: “I think he’ll be remembered, on the path he’s now? I don’t know. Liar, criminal, fool.” He added big challenges were ahead to slow climate change.

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“We are getting it done, but we have a very tall mountain to climb,” he said.

Bloomberg and Brown tried to stay on message during the summit by launching their “America’s Edge” campaign, which circumvents the U.S.’s decision to drop out of the Paris Climate Agreement.

Protesters called the campaign “tone deaf” and called Brown a hypocrite. They said that big oil is Brown’s blind spot; a consumer watchdog report showed that Brown received $9.8 million in campaign contributions from energy companies. Brown didn’t deny the connection.

“You know, politics runs on money, billions and billions of dollars. That’s just what it is. If you want to point to a specific contribution, I’d be glad to comment,” he said.

Brown asserted that the production of crude oil in California is going down, which was confirmed by the Energy Information Administration. He maintained that California is leading the charge on climate change.

“California has the most aggressive green energy plan in the western hemisphere. In fact, the more I keep answering this, the more I’m going to escalate my claim how how much we’re doing. We’re doing a hell of a lot, OK?” said Brown.

When it came to the protesters claims, Brown said he has on a multi-facet global climate plan that includes more than just limits on oil production.

“This is 10 points, 10 dimensions where we are looking. There is no one off here. There’s no one thing,” he said. “California with the leadership of our Air Resources Board has released a scoping plan that covers the whole range of emissions from oil to transportation to trucks to housing…So my plan is an integrated plan built up over time that is subject to review over time.”

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“Our goal is a 45 percent reduction in oil production as well as consumption,” he added. “We have the actual method of getting there.”