I wasn't able to actually find this 17-scientist study at Nature Geoscience mentioned in the article. The debate to date has been about the relationship between reduction of GHGs and mitigation strategies in the context of a 2°. This article suggests that the discussion is shifting to mitigation versus utter disaster.
World on course for catastrophic 6° rise, reveal scientists - The Independent
The world is now firmly on course for the worst-case scenario in terms of climate change, with average global temperatures rising by up to 6C by the end of the century, leading scientists said yesterday. Such a rise – which would be much higher nearer the poles – would have cataclysmic and irreversible consequences for the Earth, making large parts of the planet uninhabitable and threatening the basis of human civilisation...
Meanwhile, the scientists have for the first time detected a failure of the Earth's natural ability to absorb man-made carbon dioxide released into the air.
They found significant evidence that more man-made CO2 is staying in the atmosphere to exacerbate the greenhouse effect because the natural "carbon sinks" that have absorbed it over previous decades on land and sea are beginning to fail, possibly as a result of rising global temperatures.
6C rise: The consequences
If two degrees is generally accepted as the threshold of dangerous climate change, it is clear that a rise of six degrees in global average temperatures must be very dangerous indeed, writes Michael McCarthy. Just how dangerous was signalled in 2007 by the science writer Mark Lynas, who combed all the available scientific research to construct a picture of a world with temperatures three times higher than the danger limit.
His verdict was that a rise in temperatures of this magnitude "would catapult the planet into an extreme greenhouse state not seen for nearly 100 million years, when dinosaurs grazed on polar rainforests and deserts reached into the heart of Europe".
He said: "It would cause a mass extinction of almost all life and probably reduce humanity to a few struggling groups of embattled survivors clinging to life near the poles."
Very few species could adapt in time to the abruptness of the transition, he suggested. "With the tropics too hot to grow crops, and the sub-tropics too dry, billions of people would find themselves in areas of the planet which are essentially uninhabitable. This would probably even include southern Europe, as the Sahara desert crosses the Mediterranean.
"As the ice-caps melt, hundreds of millions will also be forced to move inland due to rapidly-rising seas. As world food supplies crash, the higher mid-latitude and sub-polar regions would become fiercely-contested refuges.
"The British Isles, indeed, might become one of the most desirable pieces of real estate on the planet. But, with a couple of billion people knocking on our door, things might quickly turn rather ugly."
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