Massive climate change is expected in a century from now, inflicted by a fast-warming atmosphere, according to a report by the UN's Inter-governmental Panel on Climate Change.
Experts confirm that the worst environmental crisis in human history is being caused by mankind itself, not by a quirk of the planet or a solar hiccup.
Worse, the warming is accelerating faster than anyone expected, as more and more carbon dioxide (CO2) is disgorged into the air from burning oil, gas and coal, they add.
What makes them so confident in this conclusion is new evidence culled from weather records that go back about a century and a half, or from ice cores, coral and tree rings, which indicate changes in rainfall, temperature and CO 2 levels sometimes millions of years ago. Powerful supercomputers have processed this data.
The report says:
CO2 volumes have increased by 31 per cent over the past 250 years, reaching the highest levels in 420,000 years and possibly as far back as 20 million years.
The Earth's average surface air temperature rose about 0.6 degrees in the 20th century. The warming began to speed up 3550 years ago. The 1990s were the warmest decade and 1998 the warmest year since reliable records were first kept, back in 1861.
The atmosphere is likely to warm by 1.4 to 5.8 degrees from 1990 to 2100. This is much higher than the previous top estimate, five years ago, of 3.5 degrees, ironically because efforts to curb the air pollutant, sulphur dioxide, will reduce the amount of particles that help to reflect back the Sun's rays.
The biggest effects so far have been seen in the northern hemisphere. Its temperature rise in the 20th century was probably the largest of any recorded century.