Here is a fuller explanation.
BETWEEN FIVE AND SIX DEGREES OF WARMING
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.
That episode was the worst ever endured by life on Earth, the closest the planet has come to ending up a dead and desolate rock in space.” On land, the only winners were fungi that flourished on dying trees and shrubs. At sea there were only losers. Warm water is a killer. Less oxygen can dissolve, so conditions become stagnant and anoxic. Oxygen-breathing water-dwellers – all the higher forms of life from plankton to sharks – face suffocation. Warm water also expands, and sea levels rose by 20 metres.” The resulting “super-hurricanes” hitting the coasts would have triggered flash floods that no living thing could have survived.
There are aspects of the so-called “end-Permian extinction” that are unlikely to recur – most importantly, the vast volcanic eruption in Siberia that spread magma hundreds of metres thick over an area bigger than western Europe and shot billions of tonnes of CO2 into the atmosphere. That is small comfort, however, for beneath the oceans, another monster stirred – the same that would bring a devastating end to the Palaeocene nearly 200m years later, and that still lies in wait today. Methane hydrate.
What happens when warming water releases pent-up gas from the sea bed: First, a small disturbance drives a gas-saturated parcel of water upwards. As it rises, bubbles begin to appear, as dissolved gas fizzles out with reducing pressure – just as a bottle of lemonade overflows if the top is taken off too quickly. These bubbles make the parcel of water still more buoyant, accelerating its rise through the water. As it surges upwards, reaching explosive force, it drags surrounding water up with it. At the surface, water is shot hundreds of metres into the air as the released gas blasts into the atmosphere. Shockwaves propagate outwards in all directions, triggering more eruptions nearby.
The eruption is more than just another positive feedback in the quickening process of global warming. Unlike CO2, methane is flammable. Even in air-methane concentrations as low as 5%, the mixture could ignite from lightning or some other spark and send fireballs tearing across the sky. The effect would be much like that of the fuel-air explosives used by the US and Russian armies – so-called “vacuum bombs” that ignite fuel droplets above a target. According to the CIA, those near the ignition point are obliterated. Those at the fringes are likely to suffer many internal injuries, including burst eardrums, severe concussion, ruptured lungs and internal organs, and possibly blindness.” Such tactical weapons, however, are squibs when set against methane-air clouds from oceanic eruptions. Scientists calculate that they could “destroy terrestrial life almost entirely (251m years ago, only one large land animal, the pig-like lystrosaurus, survived). It has been estimated that a large eruption in future could release energy equivalent to 108 megatonnes of TNT – 100,000 times more than the world’s entire stockpile of nuclear weapons. Not even Lynas, for all his scientific propriety, can avoid the Hollywood ending. “It is not too difficult to imagine the ultimate nightmare, with oceanic methane eruptions near large population centres wiping out billions of people – perhaps in days. Imagine a ‘fuel-air explosive’ fireball racing towards a city – London, say, or Tokyo – the blast wave spreading out from the explosive centre with the speed and force of an atomic bomb. Buildings are flattened, people are incinerated where they stand, or left blind and deaf by the force of the explosion. Mix Hiroshima with post-Katrina New Orleans to get some idea of what such a catastrophe might look like: burnt survivors battling over food, wandering far and wide from empty cities.
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.
