Unknowns behind climate chief's resignation
Rumours that Yvo de Boer, the UN's top climate official, would be leaving his post well before the end of this year were rife even during the Copenhagen summit.
The theory went like this. If Copenhagen turned out to be a "failure" - however you want to define that - then someone would have to take the blame.
The two candidates mentioned most often for that role were Danish climate minister Connie Hedegaard, who chaired most of the conference, and Mr de Boer.
Blaming Ms Hedegaard would divert ordure from the head of her boss, Prime Minister Lars Lokke Rasmussen, according to this thesis, while pointing the finger at Mr de Boer would divert responsibility away from the chain of senior UN officials right up to Secretary-General Ban Ki-moon who had invested large amounts of prestige in moves to "seal the deal".
It would also assuage the anger said to be felt in governments of some rich countries, notably the US, at how far Mr de Boer had gone in public in saying that they had to demonstrate more ambition if there were to be a deal in Copenhagen.
The fact that he signed only a one-year contract extension last year rather than the three years that is normal in UN circles was cited by some as an indication that not all governments were happy to see him continue. In Copenhagen itself, some delegates appeared only too happy to lay blame for some of the summit's logistical fiascos - notably the repeated barring by security forces of a senior Chinese negotiator - at his door.
It's important to say at this juncture that rumours of many hues were woven into a rich tapestry during the Copenhagen fortnight, and which of them contained a germ of truth was a matter of usually-inconclusive debate.
Now that Mr de Boer has announced his departure from the post of UN climate convention (UNFCCC) executive secretary, you might expect matters to have become somewhat clearer, especially to those who follow the process closely; but there still appears to be a pretty dense cloud surrounding the issue.
Ms Hedegaard has moved on to become the EU's climate commissioner - a job for which she had been nominated before the summit - and what blame there is within Denmark has fallen principally on Mr Rasmussen.
But the questions concerning Mr de Boer are still very much live, and his official comments about his departure - that he believes "the time is ripe for me to take on new challenge" - give nothing away.
If he has decided that the prices paid in stress, abuse and time away from home for doing such an onerous job are no longer worthwhile, who could find anything surprising in that?
In public, he backs the accord approved by most governments on the summit's final day - "the political commitment and sense of direction toward a low-emissions world are overwhelming".
But if in private he has concluded that the job is no longer worth doing, given that Copenhagen's central message is that powerful governments in what we are accustomed to call the developed and developing worlds do not want to tackle climate change through the UN process, who would blame him?
While Copenhagen remains fertile ground for those of a forensic disposition, the more important question for the wider world is: what happens now?
Greenpeace - whose campaigners were among the more successful in prising out what was going on behind closed doors during the summit - comments that Mr de Boer "injected much-needed dynamism and straight-talking into the role of executive secretary to the UN climate convention".
Are the most important governments prepared to tolerate a straight-talking boss any more?
It's worth recalling in this context how a previous US administration engineered the departure of another senior UN climate official, Intergovernmental Panel on Climate Change (IPCC) chief Bob Watson, because his talk was seen as too straight for their interests.
"The job is to make sure that countries and world leaders not only turn up (to the next UN climate summit in Mexico) but do so with the intention of agreeing a fair, ambitious and legally binding deal to avert climate chaos."
In reality, is it within the gift of anyone in or outside the UN system to do that, however campaigners and governments of nations projected to be especially vulnerable to climate effects might wish it?
Mr de Boer leaves behind a string of memories that I am sure are emblazoned on his brain cells even more strongly than they are on mine: the collected calm under the tropical downpours of the 2006 UNFCCC summit in Nairobi; the extraordinary work rate during the Bali summit; the tearful breakdown as an oversight threatened to derail negotiations at the end of that meeting; the quick-fire capital-to-capital diplomacy last year as Copenhagen loomed; the measured-yet-wry replies to the sometimes inane questioning of journalists; the past-midnight revelations in Copenhagen of how Barack Obama and Wen Jiabao - arguably two of the three most powerful people on the planet - had personally sat down to write a climate non-treaty together.
These are among the memories that Yvo de Boer leaves with as he trades the UN climate convention for life as a climate advisor to business and as an academic.
In public, it's entirely his decision to leave a process that in public he says has many more miles to run.
In private? We can only guess.