Reflections on a hugely changed climate
It's hard to overstate how much the events of the last two months have altered the global picture of climate politics.
Picture the scene you'd have found on any day towards the end of last year: more prime ministers and presidents talking publicly about climate change than ever before; the vast majority of the world's governments apparently committed to making some kind of agreement that would restrain the growth in greenhouse gas emissions sufficiently to avoid "dangerous" climate change; the world's two biggest emitters - China and the US - announcing targets to take into the maelstrom of Copenhagen; rafts of mayors and business leaders and activists straining every sinew to encourage everyone across the finishing line.
How different things look now.
Out of Copenhagen came a piece of paper agreeing that limiting the global temperature rise to 2C was indicated by the science, but not agreeing to set 2C or any other temperature figure as a firm target, and not containing anything that would commit governments to policy measures that could achieve such a target.
Meanwhile, the prospective US climate legislation encounters new hurdles, the latest being the election of Republican Scott Brown to succeed Democrat Edward Kennedy as Massachusetts Senator.
That pushes the Democrats below the majority they need to prevent long discussions on the healthcare bill that, it's generally assumed, must go through before the climate wrangles begin in earnest.
It also could be interpreted as indicating that Mr Obama's raft of policies is proving less palatable to the electorate - and with campaigning for mid-term elections due to begin in just half a year's time, one possible consequence would be to push Democrats and Republicans alike away from the camp supporting climate legislation.
Other interpretations and other projections of the US scene are possible, of course. But it's hard to avoid the conclusion that passage of the American legislation looks less likely than it did two months ago.
Internationally, this is hugely significant. If the big developing countries do not see action from the US, they will be even more reluctant to curb their own emissions - that's abundantly clear.
Perhaps because the Copenhagen summit ended at a time when much of the world was preparing for Christmas and New Year revelries, I'm not sure that news organisations - including ourselves - have adequately reflected how momentous a shift it signalled.
Before Copenhagen, most of the building blocks appeared to be in place for some kind of global, negotiated, and possibly even effective deal - if not in Copenhagen itself, then within a further year.
Would anyone now make that assessment?
The travails of the Intergovernmental Panel on Climate Change (IPCC), too, may be affecting politicians' views - it's impossible to make a broad judgement on that, despite the protestations of many players in Copenhagen that the basics of the IPCC's scientific argument remained sound.
Anyway, we discussed at the tail end of last year some of the reasons why the summit did not produce a solid deal, and the point of this post isn't to re-tread that ground.
It's simply to reflect, with the benefit of a bit of distance, just how far the world of climate politics has shifted.
Without US legislation, without a willing China and India, it is hard to see how anything more significant than the Copenhagen Accord can come later this year or in the next few years - despite continued European protestations of support, despite the demands of small island states, and despite the judgement of many of the accord's architects (from Barack Obama to Indian Prime Minister Manmohan Singh) that it falls short.
Depending on your views on man-made global warming, you might find the mood-shift encouraging or disappointing. But it's hard to argue, I think, that it isn't significant - perhaps the most significant change in international environmental governance since the Rio Earth Summit.
And the question that not even the most clued-up observers know how to answer at the moment is: "what happens next?"