¶2 Six thousand years ago, when the world was one degree warmer than it is now, the American agricultural heartland around Nebraska was desert. …
BETWEEN ONE AND TWO DEGREES OF WARMING
¶11 At this level, expected within 40 years, the hot European summer of 2003 will be the annual norm. Anything that could be called a heatwave thereafter will be of Saharan intensity. Even in average years, people will die of heat stress. ...
¶16 In the two-degree world, nobody will think of taking Mediterranean holidays. The movement of people from northern Europe to the Mediterranean is likely to reverse, switching eventually into a mass scramble as Saharan heatwaves sweep across the Med. People everywhere will think twice about moving to the coast. When temperatures were last between 1 and 2C higher than they are now, 125,000 years ago, sea levels were five or six metres higher too. ...
¶18 Everywhere, ecosystems will unravel as species either migrate or fall out of synch with each other. By the time global temperatures reach two degrees of warming in 2050, more than a third of all living species will face extinction.
¶19 Chance of avoiding two degrees of global warming: 93%, but only if emissions of greenhouse gases are reduced by 60% over the next 10 years.
BETWEEN TWO AND THREE DEGREES OF WARMING
¶20 Up to this point, assuming that governments have planned carefully and farmers have converted to more appropriate crops, not too many people outside subtropical Africa need have starved. Beyond two degrees, however, preventing mass starvation will be as easy as halting the cycles of the moon. First millions, then billions, of people will face an increasingly tough battle to survive.
¶21 To find anything comparable we have to go back to the Pliocene – last epoch of the Tertiary period, 3m years ago. There were no continental glaciers in the northern hemisphere (trees grew in the Arctic), and sea levels were 25 metres higher than today’s.
¶23 The end of the world is nigh. A three-degree increase in global temperature – possible as early as 2050 – would throw the carbon cycle into reverse. Instead of absorbing carbon dioxide, vegetation and soils start to release it. So much carbon pours into the atmosphere that it pumps up atmospheric concentrations by 250 parts per million by 2100, boosting global warming by another 1.5C. In other words, the Hadley team had discovered that carbon-cycle feedbacks could tip the planet into runaway global warming by the middle of this century – much earlier than anyone had expected.
¶24 Confirmation came from the land itself. ... All soils will be affected by the rising heat, but none as badly as the Amazon’s. “Catastrophe” is almost too small a word for the loss of the rainforest. Its 7m square kilometres produce 10% of the world’s entire photosynthetic output from plants. Drought and heat will cripple it; fire will finish it off. In human terms, the effect on the planet will be like cutting off oxygen during an asthma attack.
¶32 The summer will get longer still, as soaring temperatures reduce forests to tinderwood and cities to boiling morgues. Temperatures in the Home Counties (UK) could reach 45C – the sort of climate experienced today in Marrakech. ...
¶37 Chance of avoiding four degrees of global warming: poor if the rise reaches three degrees and triggers a runaway thaw of permafrost.
BETWEEN FOUR AND FIVE DEGREES OF WARMING
¶38 We are looking now at an entirely different planet. Ice sheets have vanished from both poles; rainforests have burnt up and turned to desert; the dry and lifeless Alps resemble the High Atlas; rising seas are scouring deep into continental interiors.
¶40 ... Although the total amount of carbon in the atmosphere during the Paleocene-Eocene thermal maximum, or PETM, as scientists call it, was more than today’s, the rate of increase in the 21st century may be 30 times faster. It may well be the fastest increase the world has ever seen – faster even than the episodes that caused catastrophic mass extinctions.
¶43 Chance of avoiding five degrees of global warming: negligible if the rise reaches four degrees and releases trapped methane from the sea bed.
BETWEEN FIVE AND SIX DEGREES OF WARMING
¶44 Although warming on this scale lies within the IPCC’s officially endorsed range of 21st-century possibilities, climate models have little to say about what Lynas, echoing Dante, describes as “the Sixth Circle of Hell”. To see the most recent climatic lookalike, we have to turn the geological clock back between 144m and 65m years, to the Cretaceous, which ended with the extinction of the dinosaurs. There was an even closer fit at the end of the Permian, 251m years ago, when global temperatures rose by – yes – six degrees, and 95% of species were wiped out.
¶49 Then would come hydrogen sulphide from the stagnant oceans. “It would be a silent killer: imagine the scene at Bhopal following the Union Carbide gas release in 1984, replayed first at coastal settlements, then continental interiors across the world. At the same time, as the ozone layer came under assault, we would feel the sun’s rays burning into our skin, and the first cell mutations would be triggering outbreaks of cancer among anyone who survived. Dante’s hell was a place of judgment, where humanity was for ever punished for its sins. With all the remaining forests burning, and the corpses of people, livestock and wildlife piling up in every continent, the six-degree world would be a harsh penalty indeed for the mundane crime of burning fossil energy.