By Richard Black
Environment correspondent, BBC News website, Paris
It was possibly the most eagerly awaited, talked about and leaked environmental report since environmental reports came into existence.
Now the Intergovernmental Panel on Climate Change (IPCC) 2007 report - or at least the executive summary of the first bit of the report - has had its official birth in Paris, it is tempting to ask "so what's new?"
Reading the executive summary, and writing about it, induces a definite sense of deja vu. So do the quotes emerging about what should flow from it - "urgent action needed", "no doubt about the cause", "major impacts ahead", etc.
Indeed, it is easy to say that we have heard it all before, partly because we have; the IPCC is basically a reviewing and collating organisation, so all the evidence it accumulated was already out in the open.
And the scale of the changes it is projecting remains basically unchanged from its last report in 2001; whether the picture is more or less gloomy depends on your interpretation.
Eleven of the last 12 years are among the warmest on record
Oceans have warmed down to 3,000 metres
Mountain glaciers and snow cover have declined
Satellites have seen an acceleration in sea level rise
More intense and longer droughts have been observed
Arctic ice cover is shrinking in depth and in extent
The higher degree of certainty that changes are down to human activities - up from at least 66% in 2001 to at least 90% now - is significant, as is the judgement that human activities are responsible for about 13 times as much of the warming we see as changes in the Sun's output.
As to what all that should mean, Achim Steiner, executive director of the United Nations Environment Programme (Unep), was in little doubt.
"Friday, 2 February 2007 may go down in history as the day when the question mark was removed from the question of whether climate change has anything to do with human activities."
Through the window
These days it is often difficult to separate the words of environmental groups and government ministers on climate change - and you can now throw some business leaders into that mix too.
Hence Britain's Environment Secretary David Miliband could conclude: "The debate over the science of climate change is well and truly over.
"The window of opportunity to avoid dangerous climate change is closing more quickly than previously thought."
And he could find his views echoed by the likes of Greenpeace International, whose climate and energy campaigner, Stephanie Tunmore, declared: "There's a clear message to governments here, and the window for action is narrowing fast.
"If the last IPCC report was a wake-up call, this one is a screaming siren."
The problem out there in the big world, if they are right, is that the window is forcibly being shut, in fact locked, bolted and welded, by the inexorable rise in greenhouse gas emissions.
As the report notes in its dry way: "Annual fossil fuel carbon dioxide emissions increased from an average of 6.4 GtC (billion tonnes of carbon) in the 1990s to 7.2 GtC in 2000-2005."
If Mr Miliband and Ms Tunmore are to entice the global community through the slit in their window that remains, they are going to have to move quickly.
Year of change
Some observers, though, were optimistic that this report will shock the political and business spheres into low-carbon action.
The environmental group WWF is trying to engage business leaders in the process of reducing fossil fuel use; and Hans Verolme, director of its global climate change programme, believes there has been a marked change in attitude.
"In the late 1990s, you had business leaders firmly opposed to taking any action," he said.
"Then the mood started changing. In just the last year we now see business leaders communicating to their customers about new products they're putting on the market which are climate-friendly - of course some of it is 'greenwash' but some of it is real."
Mr Verolme does not believe, however, that everyone will be brought on board by the IPCC report.
"If you want to find an excuse not to act, then because of the nature of the scientific debate and the uncertainties you will find an excuse."
Whether you regard them as people in search of an excuse not to act or as guardians of scientific rigour, the established communities of "climate sceptics" are clearly not accepting this IPCC report.
"Temperatures have risen and fallen significantly over the past two millennia with levels of greenhouse gases being static," commented Martin Livermore of Britain's Scientific Alliance.
"The IPCC continues to blindly follow a single, unproven hypothesis and does not tolerate dissent."
And, of course, the views of Mr Livermore's fellows continue to be heard in some important corridors of power around the globe.
The war of words and impressions has not been won with today's report.
For five minutes on the eve of the report's launch, the Paris authorities switched off lights around the city as a climate call-to-arms, most notably extinguishing its most famous landmark, the Eiffel Tower.
But there was unintended symbolism in this symbolic act. As I went for a late evening jog around the Champ de Mars, the park where the tower sits, the lights were blazing out again, the laser beams scattering prettily through the clouds.
The City of Lights had succeeded in quenching energy consumption which exists totally for recreation. But only temporarily.
The Champ de Mars was originally where French soldiers trained for battles against very tangible enemies.
If climate change is today's enemy, I wondered, does humanity have the knowledge or the will to fight for more than five minutes at a time?