The latest word from the world's climate scientists is both sobering and heartening.
Though it will inevitably be attacked by a sceptical minority, the report of the Intergovernmental Panel on Climate Change will stand as the official word on the subject until it is updated in five or six years.
It is the work of many hundreds of scientists and has been run past more than 2500 expert reviewers.
The panel's best estimate of how much the planet could warm by the end of the century - within the lifetime, in other words, of some children already born - is sobering.
Just what it will mean in terms of environmental and human impacts, and what we can do about it, will be spelled out in later parts of the report due in April and May.
But at the same time it is encouraging that the scientists are now more than 90 per cent sure it is humanity's activities that are responsible for the warming, because it means we can do something about it, provided we don't wait too long.
Not that it will get any easier to design international agreements and national policies that would give new low-emission technologies a fair chance of competing with those - largely inherited from the century before last - that we rely on now.
The political will to accomplish that appears to be building, however.
Even such recalcitrant governments as those of George W. Bush and John Howard are having to make at least token concessions to public concerns about climate change.
The panel's report should reinforce those concerns.
Not that New Zealand can be self-righteous.
Our emissions of greenhouse gases per capita are among the the highest in the world and continue to climb.
But after years of dithering and argument there is now at least the basis for a bipartisan approach and a clear signal to energy users, large and small, that the days of being able to burn what you like with financial impunity are numbered.
Prepare for big changes
The report projects rises of 17cm to 58cm (7 to 23 inches) by the end of the century.
That could be augmented by an additional 10cm to 20cm if polar ice sheet melting continues.
The 2001 report projected a sea level rise of up to 88cm.
Many scientists had warned that this was being too cautious and said sea level rise could be closer to 91cm to 1.52m.
The report predicts a "best estimate" that temperatures would rise by between 1.8C and 4C this century with a likely range from 1.1C to 6.4C.
The best estimate is that, if emissions of the greenhouse gases that are warming the atmosphere go on rising, the global average temperature rise will be 5.4C by 2100.
That level of temperature rise is enough to trigger the start of the melting of land-based ice in Greenland and Antarctica and the dying of the Brazilian rainforest, with severe consequences for sea levels within a century.
Global warming has made stronger hurricanes, including those in the Atlantic such as Katrina.
An increase in hurricane and tropical cyclone strength since 1970 "more likely than not" can be attributed to man-made global warming, the report concludes.
The report is also a marked departure from a November statement by the World Meteorological Organisation which said it could not link past stronger storms to global warming.By Brian Fallow Email Brian