Author Mark Lynas explains how the high end of global warming could well lead to mass die-offs -- including humans.
Buried within the newly released IPCC report is an apocalyptic warning: if greenhouse gas emissions continue to rise at current rates, global warming by the end of the century could total 6.4C. The scientists don't say so explicitly, but 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. 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.
An eco-alarmist fantasy? Unfortunately not - having spent the past three years combing the scientific literature for clues to how life will change as the planet heats up, I know that life on a 6C-warmer globe would be almost unimaginably hellish. A clue to just how unpleasant things can get is contained within a narrow layer of strata recently exposed at a rock quarry in China, dating from the end of the Permian period, 251 million years ago. For reasons that are still not properly understood, temperatures rose by 6C over just a few thousand years, dramatically changing the climate and wiping out up to 95 per cent of species alive at the time. The end-Permian mass extinction was the worst ever: the closest that this planet has ever come to becoming just another lifeless rock orbiting the sun. Only one large land animal survived the bottleneck: the pig-like Lystrosaurus, which for millions of years after the disaster had the globe pretty much to itself.
Clues as to how the world looks in a long-term extreme greenhouse state also come from the Cretaceous period, 144 to 65 million years ago, when there was no ice on either pole and much of Europe and North America was flooded by the higher seas. Tropical crocodiles swam in the Canadian high Arctic, whilst breadfruit trees grew in Greenland. The oceans were incredibly hot: in the tropical Atlantic they may have reached 42C, whilst at the North Pole itself, the oceans were as warm as the Mediterranean is today. The tropics and sub-tropics were so hot that no forests grew, and desert belts probably extended into the heart of modern-day Europe.
During the Cretaceous, of course, species evolved over millions of years to be able to survive on a much hotter planet. Nowadays very few species could survive such a sudden transition. Cold-adapted species like polar bears would obviously be an early casualty, and coral reefs will also disappear from the tropics. The Met Office's Hadley Centre has predicted that the Amazonian rainforest could start to burn as early as 2050, gradually transforming towards desert as temperatures soar in the interior of South America. Ash and smoke would blanket much of the southern hemisphere, and nearly half of the world's terrestrial biodiversity would be wiped out at a stroke.
How people might fare is anyone's guess. 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.
The Independent also offered up this cheery bit of news:
According to yesterday's UN report, the world will be a much hotter place by 2100. This will be the impact ...
Published: 03 February 2007
+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.