The US Congress recently began to consider proposals to impose a carbon cap on businesses, at a federal level. There is no guarantee that such proposals will succeed, though there is strong support for them within the Democratic party and some members of the Republican party. They could be mired in the legislative process for months or years.

But the mere fact that a greenhouse gas cap-and-trade system has a serious chance of being adopted denotes a big change in the US attitude towards climate change, and the actions that will be needed to bring down carbon emissions.