The report came from C40 Cities Climate Leadership, a group whose board is headed by philanthropist and former New York City mayor Michael Bloomberg.
The remarks echoed a pledge the Governor made almost two years ago at a scientific gathering in the face of potential cuts to federal satellite and climate monitoring programs under President Donald Trump, who is skeptical of climate science.
Specifically, some studies suggest that by 2030, global greenhouse gas emissions could be lowered by as much as 1.5 to 2.2 gigatons (CO2e) every year if the commitments from almost 6,000 cities, states, regions and over 2,000 companies are fully implemented.
The Pacific Coast Collaborative (PCC), representing the states of California, Oregon, Washington, the Canadian province of British Columbia and the cities of Los Angeles, Oakland San Francisco, Portland, Seattle and Vancouver, renewed its commitment to working together against climate change and towards a growing renewable energy economy.
Frances Seymour, a senior fellow at the World Resources Institute, a Washington-based think tank, said the gathering marked the start of more united climate action by government bodies and agencies beyond the USA national government, with disparate alliances and initiatives now "gelling".
Many people around the world wrongly concluded that America was "walking away from climate action" when Trump pulled the country out of the Paris climate accord, but "nothing could be further from the truth", he said.
San Franciso is the venue for the Global Climate Action Summit that saw a gathering of over 4,000 delegates from across the globe, mulling ways to step up actions to reduce carbon emissions. He said it reminded him of people "who want to build a wall along the Mexican border to keep people out from a country we go to for vacations".
Trump announced in June 2017 the United States' intention to pull out of the worldwide agreement, which Kerry signed while serving as President Barack Obama's secretary of state.
In response to a question Thursday at a news briefing, Brown said Trump will likely be remembered poorly when it comes to the environment.More news: Christine Blasey Ford, Brett Kavanaugh accuser, details sexual assault allegation
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The goal of the conference is to showcase actions already being taken to prevent climate change and to "inspire deeper commitments" among attendees.
"To me, Gov. Brown is a climate hero", said Todd Stern, the head U.S. climate negotiator in Paris.
President Trump was a popular target Friday at California Gov.
"We have shut this summit down from the outside", demonstrator Dallas Goldtooth of the Indigenous Environmental Network told the crowd.
The bill and a number of others were signed this week in tandem with the Global Climate Action Summit now taking place in San Francisco.
"We are in a fight for our own existence", said Barbados Prime Minister Mia Mottley.
Johan Rockstrom, left, the Executive Director of the Stockholm Resilience Center and Christiana Figueres, Founding Partner, Global Optimism and Convenor, Mission 2020, give a presentation during the opening plenary of the Global Action Climate Summit Thursday, Sept. 13, 2018, in San Francisco.
The legislation also marks the latest conflict between California and President Trump, with the state repeatedly defying the administration's policies on everything from energy to civil rights to immigration.