The average American emits 20 tons of CO2 every year. Scientists estimate that the world average will have to drop to 2 tons a year by 2050 to avoid the worst effects of global warming. Right there, we already have a problem - there's no way to avoid global warming effects completely.
The US and China are the world's two problems. China wants the living standards of the US. They will need to rely on coal for a large part of the energy mix necessary to sustain those living standards, which will be disastrous. If the US, which is the world's current largest energy hog, doesn't show any leadership, then the Chinese will do nothing. They will probably continue doing nothing when they're the world's largest energy hog, and then the US cutting its emissions won't have the same weight.
So, the US has to cut emissions now. However, there might not be the political will to do so.
But Frances Beinecke, the head of New York City-based environmental group the National Resources Defense Council, threw some cold water on Stern's optimism, pointing out the economic crisis in America has made any sort of climate change agreement in the U.S. - at least for the time being - politically untenable. "Americans don't want to hear about climate change," says Beinecke, "they want to hear about jobs."
The American coal industry, one of the biggest contributors to greenhouse gas emissions, has been lobbying hard on Capital Hill for more coal mining and coal plants as a way to create jobs. Beinecke says that the coal industry has the ear of a powerful group of senators from coal producing states, and without their support, the passage of any climate treaty coming out of Copenhagen seems nearly impossible - at least until the economy turns around.
America, please prove me wrong.