Methane: The Final Shoe

Recently, Neven’s blog on Arctic sea ice (neven1.typepad.com) featured a new post on recent scientific observations of methane – observations that Neven said made him “sick to my stomach.” I am not as easily panicked – I reserved my stomach sickness for a recent British report about how most life in the oceans, except jellyfish, will be dead within the century unless we do far more than we are doing. However, I do understand his reaction. Effectively, these reports indicate that the dreaded “final shoe” of global warming, the one reinforcing side-effect of global warming that we hoped against hope would not happen, appears to be partially beginning to drop. Moreover, it seems clear to me that most if not all folks, even those who are aware of methane’s role in climate, are underestimating its potential impact in causing additional and more rapid murder, disaster, and then catastrophe.

So here is my understanding of methane’s role in our tragedy – for yes, some small tragedy is unavoidable now, even without methane’s impact and even if we do everything we can from now on. I am sure that as an amateur I am missing or misrepresenting some points. I am also pretty sure that most amateur commentators are doing far worse. If I were you, I would not take comfort from any of this post’s stumbles or missteps.

How It Works

Methane is CH4, or a carbon atom with four hydrogen atoms. It is, imho, the second most important “greenhouse gas”, and to understand its effects it is best to compare it with carbon tossed into the atmosphere and combined with oxygen to form CO2, or carbon dioxide.

Here’s how carbon emissions that form carbon dioxide work (excess detail stripped away). As they ascend in the air they combine with the oxygen to form carbon dioxide. Most of that carbon dioxide sits in the atmosphere for perhaps 150 years, and most of the carbon has fallen to earth again within 250 years. While it is up there, doubling the amount of carbon (in CO2 form) in the atmosphere adds about 3 degrees C to global temperatures, and double that in the far north and south, especially in the winter. The “normal” rate of carbon in the atmosphere is 250-280 ppm (parts per million), and we are presently somewhere around 395 ppm.

Methane emissions work in a similar fashion, but with some important differences. In the first place, methane is typically stored in the earth and emitted as a gas – i.e., not as carbon but as CH4. Once it gets into the air, it can either split the carbon atom to form carbon dioxide – hence increasing that greenhouse gas – or remain as methane. If it stays methane, most of it stays in the atmosphere for 10 years, and most is gone after 15 years. So what’s the problem?

Well, the problem is that while methane is in the atmosphere it has up to 70 times the impact on global warming of comparable amounts of carbon dioxide. I find it useful here to imagine the old image of keeping a ping-pong ball in the air with jets blowing from beneath. If I toss a ball of carbon dioxide in the air, it stays up there for 200 years. With methane, I have to keep blowing like crazy – or, if you like, adding the same number of new balls of methane every 12 years. But if I keep an amount of methane in the atmosphere comparable to doubling carbon dioxide, then I drive up temps not by 3 degrees C, but by 100 degrees C. No, we haven’t gotten to the worrisome part yet.

In other words, the effects of increased amounts of atmospheric methane, piled on top of increasing carbon dioxide from other sources, fall somewhere in between two extremes. At one extreme, all the methane turns into carbon dioxide, and hangs there for 150-250 years. As we will see, that means that carbon dioxide may double or quadruple compared to global warming without intervention by methane, for an additional 3-6 degree C global warming. At the other extreme, all the methane stays methane. As we will see, a reasonable guess for its effects then is a 12-18 degree C additional increase starting somewhere around 20 years from now and going for 120 years, and then fading out. To put it bluntly: we roast more now (stays methane) or we fry more later (changes to carbon dioxide).

The Real Worry

So where are these new methane emissions coming from? Mainly, there are two potential types of source. The first is human-caused activity: just as we emit more carbon by burning fossil fuels as our population and industry grows, so emissions of methane for industry and personal tasks and by increasing populations of farm animals like cows increases accordingly. The second is methane frozen in the earth between periods of unusual global warming. That methane lies in three main places:

i. The shallow Arctic seas, especially the shallow Siberian sea north of Russia, where it is frozen not in ice but in a comparable substance known as a clathrate;

ii. The permafrost of Siberia and northern Canada/Alaska, where it is locked in frozen ground tens of meters deep on top of unfrozen earth;

iii. The peat bogs further south, where it is often mixed with water.

The methane emissions from our first type of source have caused methane in the atmosphere to shoot up fairly steadily over the last 100-odd years, so that methane is now a significant contributor to today’s global warming. It would be a really excellent idea to cut down on it. However, to some extent that increase has apparently leveled off. No, what really scares us over the next 200 years is the second set of sources.

The last time the globe apparently became (not when it was, when it became) this warm or warmer – maybe 55 million years ago, in what is called the Paleocene-Eocene Thermal Maximum, or PETM for short – it seems very likely that methane from the second source type was indeed emitted in quantity as methane, as that is a very good explanation for why temps actually went a little higher than the amount of carbon dioxide in the air would seem to dictate. However, that should not give us comfort. Ken Caldeira in Nature notes that methane of this type was stored in much smaller quantities then. That would mean that methane from sources i-iii emitted now would either (a) have similar effects over a much longer period of time or (b) would have much greater effects over the same period of time. So which is it, (a) or (b)?

Well, one obvious factor in deciding between (a) and (b) is how fast our global temps are going up already, before we start emitting i-iii. Once we start that faster rate of emissions, of course, that will speed up global warming even further, so we can bet that a faster initial rate of global-temp increase will keep methane emissions higher right throughout the process. And every available bit of evidence points to the fact that we are warming already much faster than in the PETM – because we humans are emitting carbon stored in the earth as “fossil fuels” (really, mostly decayed vegetable matter) much faster.

All right, so it’s faster. Is it fast enough to worry about? Here we have to consider sources i, ii, and iii separately. Methane clathrates are apparently a big honking source of methane, according to scientific estimates. No one is entirely sure about how fast these clathrates will “melt” and methane bubbles will rise to the surface, once they start melting. However, they are sitting in shallow seas and they start right at the surface of the sea-floor. We know what it takes: warming of the water above the clathrates. And that has been happening, as the Arctic sea ice in that area at the top of the water melts in the summer where it hasn’t before, the sun beats down on the newly-exposed water to heat it, and warmer water from the south moves in.

Now let’s consider ii. Joe Romm at www.thinkprogress.com has an extended post focusing on this source. The net of what he has to say is: Methane stored in permafrost is comparable in amount to methane stored in clathrates – big and honking. Permafrost melting is already underway at a brisk pace. Projections that are unrealistically conservative about how fast global warming will occur project that methane/carbon dioxide emissions from that permafrost will reach a high level about 20 years from now and continue at that level or somewhat higher for 120 years, at which point most of the permafrost will be gone. Make your own adjustments – however you adjust, it’s going to reach a higher level than that sooner, and stay there for a shorter period of time. Is that enough, by itself, to worry about? You betcha.

Then there’s iii – peat bogs and wetlands, even in the tropics. It’s not clear that there is as much methane there, or that it will be released as quickly. Remember, the further south (north, for the Southern Hemisphere) you go, the slower the rate of global warming. But it’s very clear that it’s happening. That was what the Russian summer fires were all about: global warming led to warmer temperatures that dried up the peat bogs and they went up in smoke, releasing methane. My totally random guesstimate is that peat bog methane emissions will follow much the same trajectory as those in i and ii, and will therefore have ½ to ¼ the impact at any one time or overall of either i or ii.

Now let’s reach ahead and note that things get drastically worse if all of these emissions increases happen over the same period of time – somewhere around 2-2.5 times worse. Luckily, so far emissions source i has not yet kicked in. Scientists report that as of 2010, there were no atmospheric signs of unusual methane or CO2 from Arctic sea sources. Be careful. There’s a trick in that statement.

Doing the Math

Before we hurry on to our conclusion, let’s pause and see if we can nail down a little better what those effects are likely to be if all three sources of the second type fire off fast at the same time. In particular, let’s assume a scenario like that predicted for source ii, only this time with all three sources emitting like crazy.

One estimate has the amount of stored methane, converted to carbon dioxide, at about 7 times the amount in the atmosphere right now. Let’s assume that, starting 20 years from now, this emits about 1/3 of itself at a fairly steady rate over the course of the following 160 years. So, 2.3 times 400 ppm or 920 ppm is the amount added to the atmosphere by 2170, on top of the existing amount (400 ppm) and the amount estimated to be added to the atmosphere by 2100 under “business as usual” (900 ppm). We’re up to about 7-9 degrees C global warming somewhere between 2100 and 2150. Even if we cut our emissions to zero today (totally unrealistic), we’re up to 5-7 degrees Celsius.

If you want to be gloomy, you can assume almost all the methane, turned to carbon dioxide, vents in the same time period. Add on another 1800 ppm, and then add on another 500 ppm for continuing “business as usual” between 2100 and 2170. Now we’re talking 12 degrees C.

OK, same thing, but it all stays methane. If you remember, this is over 160 years, but methane falls from the sky after about 12 years, so we’re talking about 12/160 = 1/12.33 of the equivalent amount of carbon dioxide on an ongoing basis over that 160 years. However, that methane has perhaps 33 times the effect on temps while it’s up there. So starting 20 years from now, there is an overall jump of about 8 degrees C on top of the effect from carbon dioxide noted above – and that effect lasts for 160-odd years. That baked-in non-methane carbon dioxide effect is going to be around 3 degrees C under the most optimistic of assumptions, and could go as high as 9 degrees C. And remember, if you want to be gloomy, tack on an additional 6 degrees C from emitting almost all the methane.

So here’s your two extremes. If you’re lucky, it’ll all go up as methane, and fall right down again. Now we’re talking 11-23 degrees C global warming between 2030 and 2190, and we fall down to a nice comfortable 6 degrees C after that. If you’re unlucky, it’ll all go up as carbon dioxide, in which case we’ll see maybe 8 degrees C of global warming from 2050 to about 2330. By the way, initial estimates are that more of it will rise as carbon dioxide.

The best part of this analysis is that I left out other “positive forcings.” In particular, I left out the fact that all this warming is going to turn part of the ocean (The Arctic and Antarctic) and part of the land (all those nasty glaciers) darker, from white (snow) and off-white (ice) to dark brown and green (land) and dark blue (ocean). Darker colors store heat. I’m not sure what how much warming effect that will have, but scientific estimates suggest indirectly (it’s included in some scientific estimates suggesting 3-6 degrees additional warming beyond that due to carbon dioxide in the atmosphere) that it’s likely to be at least an additional 1 degree C. Icing on the cake. Or not icing.

The Best Part

Now back to that trick. You noticed, didn’t you, that I said “as of 2010.” Well, the recent article cited by Neven said that a Russian scientist reported that in their annual sample of Siberian Sea methane emissions, which they had been doing for 20 years, for the first time ever they were seeing, not “funnels” of tens of meters across from which methane was bubbling up, but lots of funnels “more than a thousand meters across”. Do the math: that’s between 1000 and 10,000 times the rate they had ever seen before. He was very confident that results across much of the Siberian Sea would be similar. Is that enough to signal the start of Arctic sea methane emissions on the scale we’ve been talking about? How can it not be enough?

Now let’s add the usual caveats: wide variance inherent in the estimates, lack of confirming evidence in some areas, uncertainties in data collection, blah, blah. The scientist’s reaction to these is to minimize the impact by stating the most likely impact of which he or she can be certain. The realistic reaction is to ask what is the impact of median likelihood, with equal likelihood of a lesser or greater impact – and, as far as I can tell, that’s what I’ve given you.

And, by the way, don’t bother to object that present projections don’t show this. Guess what – most models don’t consider the impact of even one natural methane source behaving this way, and the rest (only recently) of just one (permafrost).
Like I said, I don’t get sick to my stomach about this – because I did my own guesstimates more than a year ago and got my puking done then. I’m still hoping that the methane shoe will drop more slowly; and also that I’ll win the lottery. Right now, the latter seems more likely. Happy holidays, all.