This article was written by a professor from Yale who has been active in environmental issues for many years. He argues that nation states have been disappointing in their efforts to reduce carbon emissions. He cites examples of programs in cities and states that have made an impact at the local level. Many large corporations have also been promoting policies that have been effective.
We should not give up on nation states but it can't hurt to work the issue from both directions. Most large corporations have a long term interest in promoting climate change. We need to figure out how to shift their focus from the current quarter to the perils that they will face from climate change.