Kent Garber

U.S. and China both pledged to slow the growth of carbon pollution in advance of Copenhagen

China says that it's getting serious about tackling global warming. After President Obama pledged two weeks ago to cut greenhouse gas emissions in the United States, China came out with its own plan, promising to slow the growth of its fast-rising carbon pollution.

But China's announcement has left many around the world a bit confused about what exactly it means.

Starting this week, world leaders will be gathering in Copenhagen to try to write a new climate treaty by December 19, and much of the meeting's fate will ride on the leadership of the United States and China, the world's two biggest polluters. The recent announcements from the U.S. and China were clearly meant as signals to the world that both countries are taking the issue of emissions seriously.

The question is how seriously. President Obama, in his pledge, said the United States would cut emissions by about 17 percent below 2005 levels by 2020. That's a firm, absolute cut (albeit less than what many scientists recommend). But China said something different. Its goal, the Chinese government said, is to "reduce the intensity of carbon dioxide emissions per unit of GDP in 2020 by 40 to 45 percent" compared with 2005's figures.

If that sounds complicated, don't fret. It is. "A lot of people are trying to understand just what it amounts to," says Elliot Diringer, who oversees international policy at the Pew Center on Global Climate Change.

In theory, what China's leaders are saying is that they will lower the rate at which their country's emissions increase until the emissions level out, and then they'll actually start cutting pollution from there. That approach, experts say, gives China a bit of wiggle room as it tries to expand its economy. "One of the advantages of an intensity target is that you are not tied to an absolute emissions reduction," says Diringer. "Your actual emissions can fluctuate with your level of economic growth." The environmental downside is that there's far less certainty about how much emissions will change compared with business as usual, at least in the next 10 years.

But the bigger point is that China made this pledge at all, and did so very publicly. "If you had asked anybody who's a close China follower as recently as a couple of months ago whether China would, at the highest level, basically signal it's going to curb global warming pollution, you would have been laughed out of the room," says Jake Schmidt, director of international climate policy at the Natural Resources Defense Council.

The pledge, he says, regardless of how ambitious it was, reflects a major change in views that is underway in China. "At the highest level of the Chinese government, it has started to sink in that climate change will hit China hard," he says.

On top of that, China is becoming increasingly concerned about how other countries perceive it. It doesn't want to be viewed as a rogue actor, Schmidt says, especially as it tries to position itself as the world's new leader in clean-energy technologies. One sign that the Chinese leaders are not blowing off Copenhagen, he says, is to read what comes out of the Chinese press, which is strictly censored. By his rough calculation, the number of stories on global warming has "shot up" remarkably in the past few months.