Let's start with the good news: Regardless of what you've heard from grumbling senators here in the United States, the Chinese government is taking global warming seriously. China Daily reports that the country may soon put in place binding rules to regulate its greenhouse-gas emissions, according to a still-circulating draft resolution. Various stage agencies, meanwhile, have been gaming out scenarios in which the country's emissions peak in the next decade or two and then decline. We'll see what comes of all this brainstorming, but these gestures sure beat total intransigence.

But now the not-so-good news. As it turns out, even the most aggressive carbon-cutting scenarios envisioned by China could fall short of what many scientists are saying is needed to avoid climate havoc. Reuters has made a nifty chart based on a recent report by Beijing's National Development and Reform Commission:

Three scenarios here. If China embarks on a "business as usual approach"—polluting as much as it wants from now until 2050—well, we're in for a much, much hotter future. (A future, by the way, in which China suffers immensely—just look at the problems they've already had with widespread drought.) And even that middle, "low carbon" approach would make it nearly impossible for the world to keep atmospheric carbon concentrations below 450 parts per million, which the IPCC has recommended as a way to prevent a 2°C rise in temperatures by 2100 and potentially catastrophic changes. Let alone the 350 ppm target that people like James Hansen are urging.

Now, there is that tantalizing "enhanced low-carbon" scenario, which would entail an extremely sharp push from China to curtail emissions and promote carbon-free power. But as Charles McElwee, who runs the indispensible China Environmental Law blog points out, China's only likely to pursue this scenario if it gets aid from the United States and Europe, in the form of cold hard cash and, more crucially, technology transfers. And, at the moment, no one in the United States seems terribly inclined to fork over aid to China (especially since we're all worried that the country may "win" the clean tech race).

Here's the other catch, though. Even if China does find some way to pursue this "enhanced low-carbon" approach, meeting that 450 ppm target will still be extremely difficult—as this analysis notes, even if the rest of the world cut its emissions to zero by 2050, China's enhanced low-carbon route alone would still nudge us over our carbon budget. Granted, this still leaves the world in a better place than a business-as-usual scenario, in the sense that, say, a 3°C temperature rise by 2100, while likely to be extremely disruptive, beats a 7°C rise, but it's still a huge dice-roll for China—and the world—to take.