350.org. This organization has branches throughout the US and internationally, including 6 branches in the Bay Area alone. They are committed to mass actions to reject new fossil fuel projects, divest from polluting industries, and transfer to a clean energy economy as soon as possible.
Citizens Climate Lobby. Another grassroots organization with branches across the US and internationally. They are focused on building relationships with citizens and their elected officials, in order to influence climate policy. Notably, they are a bipartisan group that works with both Democratic and Republican legislators, to find climate change solutions that can be supported across the political spectrum.
Extinction Rebellion: A global movement to coerce governmental climate action through the use of civil disobedience.
The Climate Reality Project. Founded by Al Gore, this organization is focused on education and advocacy.