Well, the answer to that question will not doubt depend on how effective the policies are, but as this excellent map from Eric de Place (originally posted at Sightline) illustrates, the climate impacts of various U.S. states are the equivalent of entire nations, and state action is clearly meaningful.
For each state, the above map shows a nation with equivalent greenhouse gas emissions from energy. Click on the image here to see the full map of the United States. How does your state compare?
Eric de Place has this commentary on his map:
When I've shown drafts to people, almost everyone wants to compare populations. The Western states population comparison is after the jump. The full data are here (xls).So bravo to those states who have taken the lead on climate policies. And let's keep the pressure on Congress to step it up and enact comprehensive climate change legislation. It's time to do our part, to lead the nation in enacting solutions to the climate crisis. Several states have shown the way; now Congress must follow the path.
I find the full US map a bit overwhelming. Even more so when I realize that the 2003 population of the US - less than 300 million - has the same climate impact as the more than 1.5 billion people represented by the other countries listed on the map.