Our final warning: degree by degree 03 February 07

As the IPCCs newly-released Fourth Assessment Report raised the worst-case scenario projected warming by 2100 from 5.8 to 6.4 degrees Celsius, the Independent asked me to write a degree-by-degree profile of what the temperature changes would mean. Using material from my upcoming book Six Degrees, the following was published on the Independent’s front page on Saturday 3 February under the dramatic headline ‘FINAL WARNING’.

You can access the original article here – though it may go behind a password at some point…

+2.4°: Coral reefs almost extinct

In North America, a new dust-bowl brings deserts to life in the high plains states, centred on Nebraska, but also wipes out agriculture and cattle ranching as sand dunes appear across five US states, from Texas in the south to Montana in the north. Rising sea levels accelerate as the Greenland ice sheet tips into irreversible melt, submerging atoll nations and low-lying deltas. In Peru, disappearing Andean glaciers mean 10 million people face water shortages. Warming seas wipe out the Great Barrier Reef and make coral reefs virtually extinct throughout the tropics. Worldwide, a third of all species on the planet face extinction

+3.4°: Rainforest turns to desert

The Amazonian rainforest burns in a firestorm of catastrophic ferocity, covering South America with ash and smoke. Once the smoke clears, the interior of Brazil has become desert, and huge amounts of extra carbon have entered the atmosphere, further boosting global warming. The entire Arctic ice-cap disappears in the summer months, leaving the North Pole ice-free for the first time in 3 million years. Polar bears, walruses and ringed seals all go extinct. Water supplies run short in California as the Sierra Nevada snowpack melts away. Tens of millions are displaced as the Kalahari desert expands across southern Africa

+4.4°: Melting ice caps displace millions

Rapidly-rising temperatures in the Arctic put Siberian permafrost in the melt zone, releasing vast quantities of methane and CO2. Global temperatures keep on rising rapidly in consequence. Melting ice-caps and sea level rises displace more than 100 million people, particularly in Bangladesh, the Nile Delta and Shanghai. Heatwaves and drought make much of the sub-tropics uninhabitable: large-scale migration even takes place within Europe, where deserts are growing in southern Spain, Italy and Greece. More than half of wild species are wiped out, in the worst mass extinction since the end of the dinosaurs. Agriculture collapses in Australia

+5.4°: Sea levels rise by five metres

The West Antarctic ice sheet breaks up, eventually adding another five metres to global sea levels. If these temperatures are sustained, the entire planet will become ice-free, and sea levels will be 70 metres higher than today. South Asian society collapses due to the disappearance of glaciers in the Himalayas, drying up the Indus river, while in east India and Bangladesh, monsoon floods threaten millions. Super-El Niños spark global weather chaos. Most of humanity begins to seek refuge away from higher temperatures closer to the poles. Tens of millions of refugees force their way into Scandanavia and the British Isles. World food supplies run out

+6.4°: Most of life is exterminated

Warming seas lead to the possible release of methane hydrates trapped in sub-oceanic sediments: methane fireballs tear across the sky, causing further warming. The oceans lose their oxygen and turn stagnant, releasing poisonous hydrogen sulphide gas and destroying the ozone layer. Deserts extend almost to the Arctic. “Hypercanes” (hurricanes of unimaginable ferocity) circumnavigate the globe, causing flash floods which strip the land of soil. Humanity reduced to a few survivors eking out a living in polar refuges. Most of life on Earth has been snuffed out, as temperatures rise higher than for hundreds of millions of years.