Why? Because, for all its flaws, this bill is the first comprehensive attempt by America to mitigate climate change by putting a price on carbon emissions. Rejecting this bill would have been read in the world as America voting against the reality and urgency of climate change and would have undermined clean energy initiatives everywhere.

More important, my gut tells me that if the U.S. government puts a price on carbon, even a weak one, it will usher in a new mind-set among consumers, investors, farmers, innovators and entrepreneurs that in time will make a big difference — much like the first warnings that cigarettes could cause cancer. The morning after that warning no one ever looked at smoking the same again.