The vote today on whether to give another decade of life to California's cap-and-trade program has global implications as the largest US state moves to be a leader in reducing carbon emissions at a time when President Donald Trump is pulling back from fighting global warming.
Brown portrays the initiative as essential for the survival of civilisation, but critics say it fails to aggressively combat pollution.
The program expires in 2020 if lawmakers don't renew it. Brown sounded an apocalyptic tone in a rare personal appeal before a Senate committee last week, telling lawmakers that failing to pass his bill would lead to fires, disease and mass migration, not to mention higher costs for food and gasoline.
The idea is supported by national environmental groups and business interests, which echo Brown's refrain that cap and trade is the most affordable way for California to meet its ambitious climate goals.
Cap and trade puts a limit on carbon emissions and requires polluters to obtain permits to release greenhouse gases. Some permits, known as allowances, are given away while others are auctioned, generating billions of dollars in revenue for the state.