Under the gun

While the nations of the world, Australia included, continue to dawdle on greenhouse mitigation policy they appear blithely unaware there is a gun pointed at their collective heads - a gun that, potentially, can take out the whole of humanity and, possibly, most life on Earth. The clathrate gun.

Locked in the deep ocean sediments are an estimated three trillion tonnes of methane hydrates - methane gas trapped under immense pressure in water ice. Methane is a gas with about 70 times the global warming potential of CO2 and if a significant amount of it were to escape it could trigger runaway global warming, raising Earth’s temperature by 10 degrees or more in a matter of decades. If ignited, the gas could create gigantic explosive airbursts, and it may also toxify vast expanses of the ocean.

Some palaeontologists are of a view that it was a catastrophic clathrate eruption that brought about the “Great Death” at the end of the Permian era (251my), which took out 96 per cent of ocean species and 70 per cent of land vertebrates - a view advanced by Gregory Ryskin in 2003. According to Jim Kennett (2004) a more recent eruption may have caused the loss of the megafauna and ended the last ice age with a warming episode.

The trigger that fires the gun is ocean warming, but to do so apparently requires quite high temperatures - of the order of 18C, and it will take a very long time before the deep oceans are warmed up that much. Or will it? The subtlety is that the clathrate gun is a machine gun, not a pistol - small shallow clathrates release methane and this warms the planet, which releases more methane, which melts more clathrates, and so on.

In an ingenious piece of reasoning, Geoff Hudson (ABC Ockham’s Razor, May 24, 2009) argued that the observed weakening of the Gulf Stream and other warm polewards currents would trap enormous heat in the low latitudes, sufficient to melt out the clathrates in equatorial regions where only a 3 degree rise is required. Other researchers have warned that the melting of polar sea ice and warmer ocean temperatures may release shallow seabed clathrates in the Arctic. Others still fear that huge undersea mudslides on the continental margins will liberate the gas.

Another doomsday scenario, the sceptics will cry. Ignore it and it will go away. Do nothing. It may cost jobs. It may inconvenience certain businesses and upset investors.

But realistically, who is willing to take such a risk with their children? And why?

Important scientific theories have been advanced before and rejected because people at the time could not imagine them. Alfred Wegener’s theory of plate tectonics is one such case, ridiculed for half a century before coming to be generally accepted. But this did not imperil life on Earth.

Frozen methane being disgorged into the atmosphere with lethal consequences for many of Earth’s species including ourselves is not a trivial risk, even if at this stage the possibility appears small. Yet if there was even one chance in a thousand of the gun firing, should we ignore it? We find similar risks completely unacceptable in connection with air travel and most other human activities.

The point is that, for the average citizen and nation, the impacts of global warming until now have seemed minor and remote - a metre or so of sea level rise over a century, a degree or two more warmth at night, a few more droughts, floods and hurricanes in foreign countries but nothing humanity can’t cope with, on the whole, seems to be the general attitude.

The clathrate gun is in a different category. On a large enough scale it would probably eliminate most agriculture and fishing as sources of food production and return the Earth to one of its earlier desert states - a blistering, wind-scoured landscape of barren rock and sand. Whether a handful of humans might cling on amid the wreckage is unknowable - but if the Permian is anything to go by, then we’d have about three chances in ten of doing so.

This requires urgent and worldwide scientific investigation. It also requires all governments and political parties to observe the precautionary principle and take urgent action to curb emissions. To do otherwise is to gamble with the future lives of our children in a way that is completely unacceptable.