Re: Ch. 9: Arctic methane, a catastrophe in the making
Chapter Nine: Arctic Methane: A Catastrophe in the Making
The Arctic Ocean has three temperature levels. Down to depth of 150 metres, the surface water is close to freezing point. Below that, a layer of warmer Atlantic water extends down to about 1km. Then the cold bottom water layer goes to the sea bed, in places more than 5km deep.
Much of the Arctic Ocean is very shallow, with most of the East Siberian Continental Shelf less than 40 metres deep. The retreat of sea ice means that these large shallow sea areas are exposed to sunlight through the summer and autumn, without the previous protective ice cover. As well, wave action caused by the lack of ice mixes the solar warming down to the sea bed on the shelves. These large areas, shown in light blue on this map
have none of the second level warmer Atlantic water. But now, for the first time in thousands or possibly even several million years, ocean warming and mixing due to ice melt means the continental shelves have water well above freezing point.
This is dangerous for global warming. The Arctic continental shelves have solid methane compounds called clathrates on the sea floor. Worldwide, these clathrates hold over ten trillion tonnes of carbon, over ten times more carbon than all the CO2 in the air. The clathrates are held in place by water pressure, and in the shallow Arctic by frozen sediment. But now that sediment is melting as the shallow water warms. The clathrates are disintegrating, and methane is bubbling up to the surface, even in winter, working its way up through fissures deep in the sediment of coastal seas. This is a factor in the acceleration of the methane increase in recent years
, tripling from its Holocene level of 772 parts per billion to 1900 ppb today.
Methane causes one quarter of greenhouse gas radiative forcing. Per molecule its global warming effect is more than 100 times as bad as CO2, but its short lifetime means that over decades this falls to about 20 times CO2.
Wadhams calculated that releasing 10% of the methane locked in the East Siberian Sea over ten years would increase world temperature by 0.6°C and speed up other feedbacks, causing economic damage estimated at $60 trillion over a century under a business as usual scenario, with global effects mainly impacting the poor.
The precautionary principle requires risk analysis based on probability and impact. Wadhams contends that the likelihood and effect of a large Arctic methane pulse are both huge, making it one of the greatest immediate risks facing the human race. That makes it a puzzle why it is so comprehensively ignored, including by climate policy makers. He suggests the failure of nerve arises from the problem that the loss of ice has only started since 2005, but there appears to be a psychology of denial.
As I mentioned earlier, Wadhams published his book in 2016, and since then the ice loss has not maintained the same rapid decline that occurred from 2002 to 2012. But that only means the likelihood of such a methane pulse is deferred, not prevented.
The challenge is to prevent the methane escaping, and that is where there is a lack of solutions. Wadhams asks if fracking the Siberian shelf might be a way to prevent methane escape.
This is a problem that I have been studying. I had a conversation about this yesterday with Peter Wadhams and some other leading polar scientists. The idea I suggested was that finding the most efficient ways to thicken sea ice in winter could have significant cooling effects by slowing the melting of ice and snow in summer. My idea is to pump sea water up through the sea ice in winter so it will freeze and thicken the ice sheet from above, slowing summer melt and albedo loss, and delivering regional cooling and prevention of methane loss.
Three possible energy sources to pump sea water onto ice are wind, tide and current. Each of these could be tested where it is optimal. An array of mobile windpumps could be installed for winter on areas of sea ice that melt in summer. Worldwide use of wind pumps is explained at https://en.wikipedia.org/wiki/Windpump
. Tidal pumps could be tested in locations such as Hudson Bay and current powered pumps in Baffin Bay. I am not aware of either tide or current being previously used for pumping. Gas and shipping industries might not welcome such tests in view of their commercial interests in an ice-free Arctic.
Increasing the ice thickness in the sea between Greenland and Canada may have a significant regional cooling effect for Canada and the US. Slowing the Greenland glacial summer ice melt would require deployment to the northeast to catch the prevailing winds from the pole.
Cooling energy used to freeze sea water on the ice surface will equal the warming energy going into the air. Targeted geographical application would prevent the sea surface turning from icy white to near black in summer. If this idea gets any serious study, it would require modelling of the albedo increase of longer seasonal ice cover, and its ability to prevent a methane pulse. The cooling effects would need to outweigh the increased radiative forcing of the warmer air caused by the additional winter freezing.