Sure, here are ten of the most prominent grassroots organizations working on climate action in the United States, ordered by prominence… :

1. Sunrise Movement: A youth-led organiz...ation that focuses on pushing for a Green New Deal to address the climate crisis, they have been successful in bringing the Green New Deal to the forefront of the national conversation and pushing for a transition to 100% clean energy and a just transition for workers.
2. Extinction Rebellion: A movement that uses non-violent direct action to demand immediate action on the climate crisis, they have played a critical role in raising awareness on the issue and pushing for more aggressive policy solutions.
3. 350.org: A global grassroots organization that works to address the climate crisis and promote clean energy solutions, they are known for their campaigns and mass mobilization events on climate change and environmental issues.
4. Citizens' Climate Lobby: A non-profit, non-partisan, grassroots advocacy organization focused on national policies to address climate change, they have been active in lobbying for carbon fee and dividend legislation.
5. Climate Strike: A youth-led movement that began with the strikes of Greta Thunberg, the strikes are a way for young people to speak out against government inaction on climate change and demand urgent action.
6. Zero Hour: A youth-led movement dedicated to addressing the climate crisis and promoting environmental justice, they have been active in advocating for climate policies and raising awareness on the issue.
7. The Climate Mobilization: A grassroots organization that advocates for a WWII-scale mobilization to rapidly transition to a sustainable economy and stabilize the climate, they have been active in promoting the idea of a "Climate Emergency" and pushing for immediate action.
8. The Climate Justice Alliance: A national alliance of organizations working on the intersection of climate change and social and economic justice, they have been active in promoting solutions that address both climate change and social inequality.
9. Earth Guardians: A youth-led organization that empowers young people to be leaders in the environmental movement, they have been active in promoting the rights of nature and advocating for climate policies.
10. Mothers Out Front: A grassroots organization that aims to mobilize mothers and caregivers to take action to address climate change and promote clean energy solutions, they have been active in advocating for policies that promote clean energy and reduce carbon emissions.

This list is not exhaustive, but it gives a good overview of the most prominent grassroots organizations working on climate action in the United States. These groups are known for their grassroots mobilization, activism, and their role in raising awareness on the issue and pushing for policy solutions.