A senior adviser to the Chinese government said he was urging China to put a cap on its own carbon-dioxide emissions in the years ahead.*

As with many of China's climate pledges, it's worth being a bit skeptical

If that actually happened, it would be a significant boost to international efforts to tackle global warming. But it's hardly guaranteed. As with many of China's announcements on energy and climate, it's worth parsing the details here and remaining skeptical.

First, the news: On Tuesday, a senior climate advisor to the Chinese government told a conference in Beijing that he and other experts were urging China to include some sort of cap on carbon emissions in its next Five-Year Plan, which starts in 2016.

Now the caveats: This is only an advisor talking, and the Chinese government certainly hasn't made anything official yet.** It's also not clear what the proposed cap would look like or how enforceable it would be — and those details are utterly crucial.

Perhaps even more tellingly, the adviser also predicted that China's greenhouse-gas emissions would nonetheless keep growing for years to come until they peaked in 2030 — a trend that would make it difficult for the world to avoid significant climate change. (Some analyses have suggested that China's emissions need to peak in 2025 or earlier for the world to meet its goal of preventing more than 2°C of global warming.)

A few general points here:

1) If China ever did put a cap on its absolute carbon emissions, that would mark a big policy shift. For now, China has only aimed to restrict its "carbon intensity" — the amount of carbon-dioxide it produces per unit of economic output. That means China's overall emissions keep growing as the nation's economy expands. A cap on emissions, by contrast, would require overall emissions to peak.

2) China's moves on climate will get particular scrutiny after the Obama administration announced its own new rules to cut emissions from US power plants. The implicit hope of Obama's climate plan was that it would spur countries like China into doing more on global warming. After all, it's extremely difficult to mitigate global warming without dealing with China's fast-rising emissions:

3) Still, skepticism is warranted: It's far from guaranteed that China will actually enact a cap. The man who made the announcement — He Jiankun, chairman of China's Advisory Committee on Climate Change — is thought to be an influential adviser to the government, but he's not a government official. So it remains to be seen whether the Chinese government adopts these recommendations or not.

The fact that China's emissions won't peak until 2030 is also important

4) What's more, we don't yet know any of the details of this supposed cap. What emissions would get capped? All of them? Some? How stringent would the cap be? Would it be enforceable?

5) Those pesky details matter. Back in 2011, China introduced a cap on overall energy consumption. But that "cap" was more a set of guidelines than a binding limit. And, as a result, many of China's provinces continued to consume more energy than was allowed by the cap — in part because they still had plenty of incentives to keep using coal and boost economic activity.

6) The fact that the adviser predicted that China's emissions wouldn't peak until 2030 is also noteworthy. Various analyses have suggested that China's emissions would need to peak by 2025 (or earlier) if the world wants a decent shot at limiting global warming to below 2°C.

7) That said, way back in 2009, some officials were predicting that China's emissions wouldn't peak until 2050 or later. So clearly predictions about peak emissions can change over time. (And for an analysis of how China's emissions could actually peak by 2030, see this study by researchers at Lawrence Berkeley National Laboratory.)

8) One important dynamic here: China's decades-long boom in coal consumption appears to be slowing lately. That may help China's emissions peak sooner than expected. That said, most of China's coal power plants will also stick around for decades, which means that reducing China's emissions will be arguably even more difficult.

9) China is already experimenting with carbon caps right now at the local level. Seven Chinese provinces and cities already have their own local cap-and-trade schemes intent on putting a ceiling on total emissions. Those programs have experienced glitches early on — in part due to a lack of trading. But there's at least a model here if they want to expand those programs further.

* Update: My lead sentence here originally said that the adviser was "hinting" that China might adopt an emissions cap (based on earlier reporting from Reuters). But the the Financial Times later got additional clarification from the adviser in question: "This is our experts' advice and suggestion," he said. "The government has not decided on this policy yet." I've updated the first sentence and the headline to reflect this.

** Update: Here's even more skepticism and reporting from Andrew Revkin about this development.

Further reading: China's coal boom is slowing — that's a big deal for climate change