By Paul Reynolds
World affairs correspondent, BBC News website
Mega-conferences like Copenhagen have proved to be very difficult to handle
He came. He did a quick deal. He left.
That was how US President Barack Obama intervened in the global warming conference in Copenhagen and whether he saved it from total deadlock or condemned it to issuing a powerless piece of paper depends on your point of view.
The result was a political commitment not a treaty.
And it was worked out by the United States with China and a handful of others. The rest of the conference simply "took note of it", most with resignation, many with anger,
The words sound fine enough. "We emphasise our strong political will to urgently combat climate change."
And: "We shall, recognising the scientific view that the increase in global temperature should be below 2C, on the basis of equity and in the context of sustainable development, enhance our long-term co-operative action to combat climate change."
But where's the beef? That apparently has to be added to this sandwich later.
The deal - done between President Obama and Chinese Prime Minister Wen Jiabao, along with India, Brazil and South Africa - tells you a lot about how diplomacy will happen in future.
US-LED COPENHAGEN DEAL
No reference to legally binding agreement
Recognises the need to limit global temperatures rising no more than 2C above pre-industrial levels
Developed countries to "set a goal of mobilising jointly $100bn a year by 2020 to address the needs of developing
On transparency: Emerging nations monitor own efforts and report to UN every two years. Some international checks
No detailed framework on carbon markets - "various approaches" will be pursued
The US and China had to work with each other on this. They will have to deal with each other on other issues. It is at least encouraging that they are talking.
New players are coming onto the stage. Russia was absent. The EU was nowhere. It has already made its commitments and did not need to be brought on board.
The rest had to go along.
A difficult period lies ahead as governments have to sign up to making cuts and everyone will be watching to see who does something and who does nothing.
Perhaps there was just too much to bite off. It is often the case in international diplomacy that tackling problems salami-style is more effective than trying to digest them all at once.
It is also true that mega-conferences are very difficult to handle. Even European summits, still small by Copenhagen standards, almost always come down to what happened there - a small number of countries take control and impose their will.
It is a toss-up however as to why Copenhagen did not get further - was it the format or the decisions? Were too many governments trying to negotiate at too late a stage or was the reality that they simply did not want to compromise or commit, with some of them not even believing that the world needs saving?
It's probably a mixture of the two.
And perhaps more time would have helped. But time is not available to statesmen and women these days. They have to be on the move all the time.
President Obama even had to rush back to Washington to avoid the worst of a snow storm.
The pace used to be more leisurely.
The Congress of Vienna, which divided Europe up after the Napoleonic wars, lasted from November 1814 to June 1815. All the deals were done informally. And there was no 24-hour television to ask why progress had not been made.
The Congress of Berlin, which tried to sort out the Balkans, lasted a month in the summer of 1878.
The Versailles Treaty followed negotiations that lasted from January to June 1919.
It is proper to compare Copenhagen with these meetings if only because the agenda was even more momentous in the eyes of many - the saving not of continents but of the planet.
In the absence of such a timeframe, there were pre-negotiations, such as they were, and these were left to lower level ministers and delegations.
But it is always the same - nobody wants to back down until the very last minute and the decisions had to come from the very top.
A similar process has been going on in world trade talks, in the so-called Doha Round, which seeks to lower tariffs and other barriers to trade. Admittedly time has not been a problem there. The talks started in 2001 and are still staggering on.
Maybe a better formula might be to have a series of meetings at the top level - so governments could make progress bit-by-bit.
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