A Methane Scenario

In reading recent posts about the methane “Arc tic time bomb” on the Neven Arctic blog (neven1.typepad.com), I realized that no one was developing a full-fledged scenario for how a serious methane emissions uptake from Arctic deposits could occur.  So here’s my (amateur) stab at it.

2007-2014

When, around 2007, the Northeast Passage opened up, few worried about the implications for methane emissions.  True, there were 50 Gt of methane locked up in methane clathrates (CH4 in a “water cage”), mostly under the shallow waters of the Arctic above Siberia, but it seemed there were several reasons not to worry:

• ·         Methane has a short half-life, unless it attains a concentration well above its concentration as of now;
• ·         It seemed then that even if the permafrost in which the clathrates resided melted, methane would only be released in a “bursty” manner by landslides caused by the loosening of the icy bonds of the underwater permafrosted land – certainly not in a steady stream such as would be needed to overcome the short half-life;
• ·         It also seemed that even if the methane was released from the clathrates, it would “pop” before reaching the surface, which in turn would mix more carbon with the water and hence put it in the atmosphere, or feed “blooms” which when they died each year would likewise release their carbon in the water and thence to the atmosphere – a fraction of the carbon already being emitted;
• ·         At present, the methane released (if any) was no more than a small fraction of the man-made amount of methane emissions – and that was still not near the danger point.

However, the warming water poured in from the North Atlantic along the western part of the Siberian Sea during the summer, and when Soviet researchers checked during the summer of 2012, methane bubbles hundreds of meters in diameter were coming up.  That meant that both the idea of “bursty” methane and the idea that all the methane would “pop” before reaching the surface were not accurate.  And yet, even during summer, the fluctuations detected amounted to less than 1% of methane emissions measured in the Arctic.  Clearly, some scientists argued, the other two factors (short half-life, small fraction of the total) meant that there was no immediate cause for concern.

And then el Nino arrived.

2015-2023

The splashier effects of el Nino distracted attention from its effects on methane emissions.  While it did indeed raise the temperatures down south significantly, its main effect was to warm the air in the Arctic (already in record-breaking territory) by 3 degrees in summer and by 10 degrees in winter.  The initial effect was to extend summer “insolation” (heating of ice and water from above) and above-freezing average air temperatures for 2 weeks on either end, so that the Arctic water was now just about completely ice-free and accumulating a “storage bank” of heat with which to melt the permafrost.

Now, the period of methane bubbles was lasting twice as long, and the pace of melting was four times as great.  Moreover, towards the end of the period, the small but steady warming of the Beafort Sea from the south was beginning to push into the eastern end of the seas above Siberia.  These, too, began to see bubbles and spikes in methane usage.

At the end of this period, another “distraction” arrived:  adjacent permafrost in Siberia began to thaw.  Although it was not clear in the beginning how much of that thaw would be methane and how much carbon, it turned out to be perhaps a 2/3-1/3 ratio.  Still, compared to human-caused methane emissions (which had gone up another 10% since 2007), the emissions from clathrates and the small contribution from Siberian permafrost were still much less.

2024-2032

Soon after 2025, la Nina arrived; but it had surprisingly little effect.  True, the ascent of temperatures in the Arctic slowed; but the warming water from previous years continued to pour into the Arctic.  That, in turn, extended the iceless Arctic period well into November, and the increasing energy in the air likewise extended the melting-out period over the Siberian seas into June.  And so, having quadrupled the last period, methane clathrate emissions tripled over this period, so that by 2033 worldwide methane emissions were up by 25% compared to 2007 – 15% from humans, 6% from methane clathrates, and 3% from land permafrost melt, which was undergoing its own steep climb.

Still, for a little while, the world could still file methane emissions in the Arctic under “lesser concerns”, at least compared to carbon emissions.  And there, as well, the contributions of carbon from permafrost were still minor compared to human emissions – not to mention the almost full effect of the decreased albedo of the Arctic.

2033-2040

These were the years when things got really serious.  El Nino returned, and the Arctic became ice-free year-round by around 2039.  The warm water year-round plus the increased insolation and the increased energy in the air year-round, transmitted to the water via storms, meant a quintupling of methane clathrate emissions – to a 30% increase over 2007.  Add on 10% from land permafrost and the 20% from human emissions, and methane emissions were up 60% -- an effect of much less than one degree F globally, but nonetheless significant.

And still the worst effects held off, until …

2041-2100

Methane clathrate emissions had reached somewhat of a “steady state”, in which melt reached progressively deeper into the permafrost, but the adjacent melted sediment continued to warm faster, as it penetrated to areas of greater pressure.  However, this “steady state” was adding about 50% more methane emissions than in 2007, at a steady pace.  Meanwhile, the permafrost contribution was steadily climbing, as melted permafrost converted to swamps which produced their own methane.  By about 2060, the result was a 100% increase in methane emissions in total – and that’s when the second shoe dropped.

Doubling methane emissions meant that the methane in the air was now saturated – it was far less likely to decompose into water and/or carbon dioxide.  As a result, the half-life of methane shot up, first to 20 years, and then to 40.  Now the other aspect of methane – that it is 70 times as powerful a greenhouse gas as carbon for the same half-life – began to come into play.  Effectively, the effect was 1 degree F of average global warming; but this was equivalent to the effect of the entire increase in carbon ppm in the atmosphere pre-2007.  To put it another way, methane added perhaps 33% to global warming up to 2070.

In the longer run, of course, carbon emissions continued to dominate for the next thousand years.  However, the land permafrost methane now assumed center stage, continuing the saturation for perhaps 300 of those years.  Global warming baked us; methane clathrates in the Arctic were the trigger to ensure that we were truly well done.