Probably the biggest, nastiest monster under my bed for some time has been the possibility of a massive methane release from the Arctic region kicking global warming into warp speed. To people who don’t follow this stuff as obsessively as I do, this probably sounds like I’ve suddenly enlisted in the tinfoil hat brigade. Let me explain, as it’s sadly nowhere near that nutty a concept.

First, consider that methane is a much more powerful greenhouse gas than CO2. It doesn’t hang around in the atmosphere nearly as long as does CO2, but the net effect, once you take that timing into account, is usually quoted as roughly 20 times more greenhouse forcing than an equivalent amount of CO2. That’s a scary-big number. (To be more precise, the effect is estimated to be 62 times higher over the first 20 years, and “only” 21 times higher over a century.)

Second, there are two main stores of methane: Methane hydrates (a.k.a. methane ice or methane clathrates) in oceans and methane trapped in permafrost in places like Siberia.

How much of this stuff are talking about? A lot:

Recent estimates constrained by direct sampling suggest the global inventory lies between 1×10**15 and 5×10**15 m³ (1 quadrillion to 5 quadrillion). This estimate, corresponding to 500-2500 gigatonnes carbon (Gt C), is smaller than the 5000 Gt C estimated for all other fossil fuel reserves but substantially larger than the ~230 Gt C estimated for other natural gas sources. The permafrost reservoir has been estimated at about 400 Gt C in the Arctic, but no estimates have been made of possible Antarctic reservoirs. These are large amounts. For comparison the total carbon in the atmosphere is around 700 gigatons.

So , for the oceans and the Arctic permafrost combined we have 900 to 2,900 billion metric tons of carbon, roughly 1.3 to 4 times as much carbon as is already in the atmosphere.

Third, is there any real threat that this stuff will wind up in the atmosphere? Actually, there is, as relatively small amounts have been measured bubbling out of Siberia thaw lakes for at least a couple of years. That same article states that Siberian methane releases are about 3.8 Tg/year, compared to IPCC’s estimates of 600 Tg/year for all methane emissions, so from just the permafrost the current methane releases seem to be pretty small compared to other sources, such as the one US government reports delicately refer to as “enteric fermentation” in livestock, a.k.a. cow farts.

But there’s more evidence than that:

Higher atmospheric levels of the greenhouse gas methane noted last year are probably related to emissions from wetlands, especially around the Arctic.

…

Indications that methane levels might be rising after almost a decade of stability came last month, when the US National Oceanic and Atmospheric Administration (Noaa) released a preliminary analysis of readings taken at monitoring stations worldwide.

Noaa suggested that 2007 had seen a global rise of about 0.5%.

…

Ed Dlugokencky, the scientist at Noaa’s Earth System Research Laboratory (ESRL) who collates and analyses data from atmospheric monitoring stations, agrees that the 2007 rise has a biological cause.

“We’re pretty sure it’s not biomass burning; and I think 2007 is probably down to wetland emissions,” he said.

“In boreal regions it was warmer and wetter than usual, and microbes there produce methane faster at higher temperatures.”

Dr Dlugokencky also suggested that the drastic reduction in summer sea ice around the Arctic between 2006 and 2007 could have increased release of methane from seawater into the atmosphere.

A further possibility is that the gas is being released in increasing amounts from permafrost as temperatures rise.

Researchers will be keeping a close eye on this year’s data which will indicate whether 2007 was just a blip or the beginning of a sustained rise.

Methane concentrations had been more or less stable since about 1999 following years of rapid increases, with industrial reform in the former Soviet bloc, changes to rice farming methods and the capture of methane from landfill sites all contributing to the levelling off.

In the recent past, concentrations have risen during El Nino events, whereas the world is currently amid the opposite climatic pattern, La Nina.

…

A sustained release from Arctic regions or tropical wetlands could drive a feedback mechanism, whereby higher temperatures liberate more of the greenhouse gas which in turn forces temperatures still higher.

A particularly pertinent question is whether methane is being released from hydrates on the ocean floor.

These solids are formed from water and methane under high pressure, and may begin to give off methane as water temperatures rise.

See that link for a graph of methane emissions as measure by NOAA.

Finally, we have the issue of just how bad a big methane emission could be, in terms of global warming. As it turns out, we may have a truly hair-raising historical precedent:

Melting of methane ice unleashed runaway global warming some 635 million years ago, according to a study released Wednesday that has implications for today’s climate-change crisis.

Release of the potent greenhouse-gas, at first in small amounts and then in massive volumes, brought a sudden end to the planet’s longest Ice Age, its authors believe.

During the “Snowball Earth” era, Earth froze over completely, with glaciers that crept down into the tropics and possibly even reached the equator.

The chill was self-sustaining, because the ice formed a brilliant white shell that reflected the Sun’s rays, preventing the surface from warming.

After a frozen slumber lasting 155 million years, Earth warmed dramatically.

How this happened has been fiercely disputed, although all agree that the event changed the planet’s climate system and ocean chemistry forever.

Publishing in the weekly British journal Nature, scientists in the United States and Australia point the finger at methane clathrates — methane-rich ice that forms under ice sheets at specific temperatures and pressures.

The researchers believe that the ice sheets on Snowball Earth became unstable, which released pressure on the clathrates.

They began to evaporate, releasing the methane, which helped to warm the planet slightly. This thawed more clathrates and fuelled the warming and so on, creating a vicious circle or “positive feedback” in scientific parlance.

…

Billions of tonnes of methane are locked up in these reservoirs, and the big worry is that it could take a relative small rise in temperature to start unleashing the gas, which would then trigger an unstoppable warming cycle.

“One way to look at the present human influence on global warming is that we are conducting a global-scale experiment with Earth’s climate system,” said Kennedy.

“We are witnessing an unprecedented rate of warming, with little or no knowledge of what instabilities lurk in the climate system and how they can influence life on Earth.”

If the end of Snowball Earth is a guide, positive feedbacks, “once initiated, change the climate to a wholly different state,” he observed.

If the mechanism for clathrates’ feedback is now clearer, the scientists have still to explain how much forcing was needed for the vicious circle to set in motion — and whether we are approaching any similar threshold today with the CO2 from fossil fuels.

All this means… what, exactly?

Let me be as clear as possible about this: I’m not saying that we’re definitely on track for a rendezvous with a methane burp (or clathrate gun, as some call it) scenario. As the last bit of text quoted above points out, we don’t know where the tipping point is, even if we assume that these latest findings hold up to scientific scrutiny. And to be completely objective, they might not, although that’s not how I would bet my Internet connection right now.

For me, there are two factors that elevate the methane apocalypse from “dumb thing I read on the Internet and can now ignore” to “something I really hope we’re spending a lot of money researching, right now“. The first is the rate at which climate change is happening, not least of all in the Arctic ice situation, as shown on the home page of the NSIDC (National Snow and Ice Data Center). I’ve pointed out numerous times on this site that the worldwide climate is changing much quicker than we expected, which means that despite the best efforts of a lot of extremely smart and dedicated people we still don’t understand what’s going on as well as we’d prefer. Will the changes we’re seeing level off or even decline over the next few years? Or will feedback effects, from albedo flip (reflective ice being replaced by less reflective water or ground) to methane releases accelerate change, possibly to the point where no reduction in our CO2 emissions will save the day?

The other factor is the similarity of the scenario outlined in the last article I quoted from above to our current situation. The critical difference is that in 2008 we’re changing the CO2 level in the atmosphere at a lightning fast pace, by geologic standards, and with virtually no hope of reducing that buildup this century. We could very well be running, at full-speed and blindfolded, into the mother of all tipping points and triggering catastrophic effects in a few decades instead of hundreds or thousands of years.

Maybe the situation isn’t that dire. Maybe this is all a lot of worry over nothing, and there are negative feedbacks we either haven’t discovered or grossly underestimate that will buy us considerable time to reduce our CO2 emissions and then the level of CO2 in the atmosphere. But right now, it feels more like we’re playing Russian roulette with the biosphere instead of being prudent and applying the precautionary principle.

See also Joe Romm’s take on this:

The permafrost won’t be perma for long, Part 1

Tundra, Part 2: The point of no return