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Irreversable climate change within ten years, says report.

And it breaks new ground by putting a figure – for the first time in such a high-level document – on the danger point of global warming, that is, the temperature rise beyond which the world would be irretrievably committed to disastrous changes. These could include widespread agricultural failure, water shortages and major droughts, increased disease, sea-level rise and the death of forests – with the added possibility of abrupt catastrophic events such as “runaway” global warming, the melting of the Greenland ice sheet, or the switching-off of the Gulf Stream.

The report says this point will be two degrees centigrade above the average world temperature prevailing in 1750 before the industrial revolution, when human activities – mainly the production of waste gases such as carbon dioxide (CO2), which retain the sun’s heat in the atmosphere – first started to affect the climate. But it points out that global average temperature has already risen by 0.8 degrees since then, with more rises already in the pipeline – so the world has little more than a single degree of temperature latitude before the crucial point is reached.

More ominously still, it assesses the concentration of carbon dioxide in the atmosphere after which the two-degree rise will become inevitable, and says it will be 400 parts per million by volume (ppm) of CO2.

The current level is 379ppm, and rising by more than 2ppm annually – so it is likely that the vital 400ppm threshold will be crossed in just 10 years’ time, or even less (although the two-degree temperature rise might take longer to come into effect).

http://www.climatehotmap.org