There's a lot of deja vu all over again in the fourth assessment by the Intergovernmental Panel on Climate Change, but what it has done is remove the question mark about human influence on climate change, writes the BBC's Richard Black.
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.
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." ...
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.
The war of words and impressions has not been won with today's 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.
