Chinese flag against sunLike sparring siblings, China and the United States — the world’s two biggest carbon dioxide emitters — keep passing the climate-action buck back and forth: “Why should I cut emissions if they don’t have to?” Well, China is either the more mature of the pair, or just majorly sucking up to Mama Earth. The country is reportedly gearing up to set firm limits on greenhouse-gas emissions, seriously weakening one of the U.S.’s go-to excuses for climate inaction.

China’s powerful National Development and Reform Commission has proposed an absolute cap on emissions starting in 2016. The proposal still needs to be accepted by the Chinese cabinet, but experts say the commission’s influence makes it likely to pass. China today also announced the details of trial carbon-trading programs that will roll out in seven regions by 2014. In February, the country had said it would implement a carbon tax, but backed off a few weeks later, saying it will wait until early next year to get started on that.

The commission’s carbon-cap proposal calls for Chinese emissions to peak in 2025, five years earlier than previously planned. RenewEconomy explains:

China has already pledged to cut its emissions intensity – the amount of Co2 it emits per economic unit – by up to 45 per cent by 2020. The significance of an absolute cap is that it promises to rein in emissions even if the economy grows faster than expected.

A Chinese carbon cap could shake up future international climate negotiations, The Independent reports:

It marks a dramatic change in China’s approach to climate change that experts say will make countries around the world more likely to agree to stringent cuts to their carbon emissions in a co-ordinated effort to tackle global warming. …

“Such an important move should encourage all countries, and particularly the other large emitters such as the United States, to take stronger action on climate change. And it improves the prospects for a strong international treaty being agreed at the United Nations climate change summit in 2015,” added Lord [Nicholas] Stern, [chair of the Grantham Research Institute on Climate Change at the London School of Economics.]

The 2015 summit will take place in Paris. Previous U.N. climate talks have played out according to a familiar pattern: high hopes giving way to deadlock and failure. When the world’s largest emitters refuse to agree to limits on emissions, it makes the commitments of smaller countries somewhat pointless. U.K. Energy and Climate Change Secretary Ed Davey told The Independent:

I’m really much more confident than many people about our ability to get an ambitious climate change deal done in 2015. Obama in his second term clearly wants to act on this and there has been a fantastic and dramatic change in America’s position. Taken together with China’s change, the tectonic plates of global climate change negotiations are really shifting.