In the lead up to Copenhagen, pressure is mounting on the Untied States to take a stand on global warming instead of doing the usual and digging its heels. Writing in The Guardian, Jeffrey Sachs says US dependence on coal stands in the way of getting any sort of traction at Copenhagen.

"There are several reasons for US inaction – including ideology and scientific ignorance – but a lot comes down to one word: coal. No fewer than 25 states produce coal, which not only generates income, jobs and tax revenue, but also provides a disproportionately large share of their energy,'' Sachs writes. "Per capita carbon emissions in US coal states tend to be much higher than the national average. Since addressing climate change is first and foremost directed at reduced emissions from coal – the most carbon-intensive of all fuels – America's coal states are especially fearful about the economic implications of any controls (though the oil and automobile industries are not far behind)."

Sachs has a point but there is another force that's stopping the US from taking the higher ground, and that's public opinion. According to the latest national survey by the Pew Research Center for the People & the Press, fewer Americans now believe global warming is a problem. Only 35% see global warming as a serious problem, down from 44% in April 2008. That's a massive drop in just over a year. Furthermore, only 57% think there is solid evidence that the average temperature on earth has been getting warmer over the past few decades, compared with 71% 12 months ago. And only 36% say global temperatures are rising as a result of human activity, such as burning fossil fuels, down sharply from 47% last year.

This is not a good sign for Copenhagen. With those sorts of numbers, Obama will struggle to get the US to join the rest of the world on climate change.