The new bad boy on the block
Arctic stores of methane have the potential to dramatically accelerate warming.
Move over CO2. Methane is emerging as the bad boy on the block. Until now, emissions of this gas, which weight for weight is 25 times more potent at warming the planet than carbon dioxide, have largely been due to belching cows and sheep. In Australia, some 10% of greenhouse gas emissions come from the farmyard. But that’s nothing compared to the mighty methane burp that the planet itself looks set to release.
The source is the frozen Arctic seabed. It contains loads of methane in the bizarre form of methane clathrate, where each methane molecule is trapped in a cage of frozen water molecules. These in turn are frozen in with the sand and ice, creating a sort of methane clathrate granita.
But this granita is no treat. Methane clathrate goes by the sobriquet “ice that burns”. But until now the granita has stayed frozen, locking in the methane.
That’s changing. As the Arctic warms, the blanket of sea ice is melting. The shallow seas along Russia’s northern shores, for instance, were once permanently covered, but each summer the ice now retreats a little further. Without this protective ice cap, the frozen seabed a few hundred metres below is beginning to thaw. Methane made by microbes or leaking from deeper natural gas deposits, accumulating and forming clathrates there since the last ice age, is beginning to bubble out.
The melting in Russia’s shallow northern seas, is bad enough. But our deep ocean floors contain thousands of gigatonnes of methane clathrate. Thankfully, methane eruptions from the deep ocean are highly unlikely anytime soon. Even under the most pessimistic of global warming scenarios, the deep oceans would take centuries to warm sufficiently to melt those clathrates.
Until recently the best we could do was worry about the problem.
So how bad could the emissions from Russia’s northern seas be? In 2010, Natalia Shakhova and colleagues at the International Arctic Research Center in Fairbanks, Alaska, predicted 50 gigatonnes of methane could be released from the East Siberian Shelf in the next 50 years, either as a steady leak or a dramatic belch over just a year or two. A 50 gigatonne methane belch is equivalent to around 25 times the entire world’s current annual greenhouse gas emissions – an event researchers think could bring us closer to the date at which global temperature rise exceeds the two degree threshold beyond which dangerous climate changes take effect.
Until recently the best we could do was worry about the problem. Now scientists are putting a price on it and at least trying to think up solutions to nibble at the edges.
This July, University of Cambridge ocean physicist Peter Wadhams and his colleagues calculated that the economic cost of the environmental impact of this methane release was $60 trillion, as reported in Nature.
It’s a figure that others have criticised. No one knows just how much methane is stored in these shallow oceans. And some of it would be consumed by microbes before it could reach the atmosphere.
But Wadhams counters that his figure is based on the lower estimate of how much methane is being released. The reality could be worse. “Each year, the methane plumes bubbling up to the surface are bigger, it really is suggestive of a big release of methane over a few years,” he says. “That would really be a catastrophic acceleration of global warming, so we ought to be taking urgent precautions, which we’re not.”
Roger Bodman, a climate scientist at Victoria University in Melbourne, agrees. “Lab experiments and modelling suggest a wide range of possible outcomes. By continuing to emit carbon we are running an experiment where we’re not sure what will happen.” If results don’t go our way, methane leaks could soon tip our atmosphere into faster warming. Sudden methane emissions, albeit on a far larger scale than predicted from Arctic thaw, have had devastating impacts in the past, causing mass extinctions (see Beware the M-bomb, opposite).
So what can we do? Collecting and burning the methane (aka natural gas) for energy would help a bit, giving us the lesser of two evils. Burning methane converts it into CO2, which has 1/25 the greenhouse gas effect of methane. Plus burning it would reduce our need for coal, which generates about double the CO2 as methane for the same energy output.
In March this year, the Japanese energy agency JOCMEG announced the first successful use of an offshore rig to extract methane from stable deep-sea clathrates. But capturing the methane from the melting clathrates off Russia, where it is already bubbling out across the entire seabed, is a different matter altogether. “I’ve only ever seen one paper that looks a little bit hopeful for capturing this methane,” Wadhams says. The proposal is to drill down under the clathrate layer in the seabed and draw out the methane from below, so that the gas released by melting clathrates might diffuse downward into the collecting pipe rather than upward into the atmosphere. “It might be an answer, but this needs pursuing very quickly.”