Thus came the initial reaction from Todd Stern, the chief US climate envoy, after China's President Hu Jintao told the special session of UN heads of government that he would set mandatory targets for improving "carbon intensity".
(In other words, between now and 2020, Chinese factories and power stations and everything else will become more efficient - making more stuff while producing less and less carbon dioxide per unit of stuff.)
Mr Hu's speech was trailed as potentially ground-breaking by no less a figure than the UN's chief climate official, Yvo de Boer, who said China could "become the front-runner" in climate diplomacy.
Did Mr Hu deliver?
We don't know how big the carbon intensity targets will be, for one thing. Mr Hu described them as "notable"; if they're not notable enough, they will simply be swamped by economic growth.
(The current Five-Year Plan, running from 2006 to 2010, has a goal of improving carbon intensity by 20% during the course of the five years).
Mr Hu also re-affirmed the target of providing 15% of China's primary energy mix by 2020 from non-fossil-fuel sources - renewables and nuclear - and of re-foresting tracts of his country.
And that's about it.
His speech was heard by several key audiences.
One consisted of the other world leaders sitting in the UN chamber - and they seemed appreciative, although the clapometer didn't whizz round as far for him as for Japan's incoming Prime Minister Yukio Hatoyama as he re-affirmed a pledge to slash emissions by about a third over the next 11 years.
An important sub-set of that UN chamber audience was the wider G77 bloc of developing countries with whom China is allied on most issues, and certainly on this one.
Mr Hu made a large nod to them by referencing the needs of least developed countries (LDCs) and African nations for financial and technical support in adopting low-carbon technologies and protecting themselves against impacts of climate change.
Then there was an audience back home - all the technocrats and bureaucrats and other agents of the Chinese government who have been charged over the last few decades with growing the national economy, and who have succeeded in that task very well - perhaps too well for the country's ecological health.
Mr Hu appeared to be telling them that now they have a second key task - de-carbonising the economy while continuing to grow it.
But in the short term, his most important audience lay a few hundred kilometres southwest of UN headquarters, in Washington DC.
Some time this month, the US Senate is due to start debating the Waxman-Markey Bill, which would set emissions caps for various bits of the economy and establish a nationwide carbon market.
Senatorial scepticism on the Kyoto Protocol was a leading reason why the treaty did not deliver what it once promised; the same scepticism in regard of the UN climate process now could substantially scupper the negotiations taking place in Copenhagen in December.
And the main reason for senatorial scepticism this time round - as last - is that leading developing nations such as China aren't "doing enough".
No-one seriously expects developing countries to accept numerical cuts in their greenhouse gas emissions.
But many richer nations believe calculations (stemming from the Intergovernmental Panel on Climate Change) that the more successful ones, including China, must curb the growth in their emissions by about 30% from the "business as usual" trajectory by 2020 or thereabouts.
One senses that anything like 30% would be acceptable to Mr Obama's administration - but the Obama administration is not the US Senate.
If Mr Hu's words are heard in the Senate as a firm commitment to take firm action, swift passage of a strong form of Waxman-Markey becomes more likely, which in turn makes a Copenhagen deal more likely. The reverse is also true.
So how will they regard it? We shall see.
One canard that really has to be slain at some point is the notion that any of these pledges, by China or any other country, are really mandatory in the sense that you or I would understand the word.
It's mandatory that you obey the speed limit when driving, otherwise you'll be up before a judge and might lose your licence. It's mandatory that you fill in a tax return or else you're liable for a fine. It's mandatory that you feed the pet tortoise otherwise it'll die and the kids won't speak to you for a week.
But in all the fine words of the UN climate convention and Kyoto Protocol, in the language likely to come out of Copenhagen, in the UK's "legally-binding" commitment to cut emissions by 80% by 2050 and so far in China's adoption of "notable" carbon intensity targets, there is no sanction - nothing - that compels or even strongly persuades countries to meet their targets.
Mandatory? Not according to the Oxford English Dictionary definition ("binding", "obligatory", "compulsory", "not discretionary"...)
So what has come out of this UN special session, a personal initiative of Secretary-General Ban Ki-moon?
Too soon to tell, perhaps - but I don't think there is any chance that two years ago, you could have had the UN chief, US president, Chinese president, Japanese prime minister and the leader of a low-lying island state such as the Maldives all in the same room and all singing from broadly the same hymnsheet ("vital issue", "time running out", "need to make a deal", etc etc etc).
Whether that's enough to give UN negotiations the kick they appear to need is another matter.
"It depends..." - on a lot of things, including what lies behind the word "notable".