More on Methane

Real Climate has an analysis of the methane release paper up, which is at least partly reassuring - partly.

CO2 is plenty to be frightened of, while methane is frosting on the cake. Imagine you are in a Toyota on the highway at 60 miles per hour approaching stopped traffic, and you find that the brake pedal is broken. This is CO2. Then you figure out that the accelerator has also jammed, so that by the time you hit the truck in front of you, you will be going 90 miles per hour instead of 60. This is methane. Is now the time to get worried? No, you should already have been worried by the broken brake pedal. Methane sells newspapers, but it's not the big story, nor does it look to be a game changer to the big story, which is CO2.

Actuallly, if you think this is an accurate metaphor, I'd say the answer is...yeah, there's something to worry about. Don't get me wrong, I agree with them that carbon is the central issue, and the shorter lifespan of methane in the atmosphere does mean that it has to be released quite precipitously to cause a major crisis. But think about the analogy - hit another car at 60 miles an hour and it is a disaster - some of the passengers will probably be kiled, but there remains the chance that some will merely survive badly hurt. Do it at 90 and everyone is dead.

This shouldn't take away from our attention on CO2. But that doesn't mean we shouldn't be seriously concerned about this. Real Climate rightly puts this in perspective:

Anyway, so far it is at most a very small feedback. The Siberian Margin might rival the whole rest of the world ocean as a methane source, but the ocean source overall is much smaller than the land source. Most of the methane in the atmosphere comes from wetlands, natural and artificial associated with rice agriculture. The ocean is small potatoes, and there is enough uncertainty in the methane budget to accommodate adjustments in the sources without too much overturning of apple carts.

Could this be the first modest sprout of what will grow into a huge carbon feedback in the future? It is possible, but two things should be kept in mind. One is that there's no reason to fixate on methane in particular. Methane is a transient gas in the atmosphere, while CO2 essentially accumulates in the atmosphere / ocean carbon cycle, so in the end the climate forcing from the accumulating CO2 that methane oxidizes into may be as important as the transient concentration of methane itself. The other thing to remember is that there's no reason to fixate on methane hydrates in particular, as opposed to the carbon stored in peats in Arctic permafrosts for example. Peats take time to degrade but hydrate also takes time to melt, limited by heat transport. They don't generally explode instantaneously.

For methane to be a game-changer in the future of Earth's climate, it would have to degas to the atmosphere catastrophically, on a time scale that is faster than the decadal lifetime of methane in the air. So far no one has seen or proposed a mechanism to make that happen.

We are not seeing evidence that clearly indicates abrupt climate change, and the change in methane concentrations is comparatively small. Nor do we know that this will lead to larger scale feedback mechanisms. That is, people predicting "now is the time to panic" are wrong on several levels - they should have been responding (not panicking) long since and so far, we don't know this will lead to the worst outcomes.

That said, however, the sentence that no one has seen or proposed a mechanism in which this happens doesn't really console me. In models and predictions prior to the revelation that methane levels were increasing, the assumption had been that methane wouldn't rise until fairly late in the game - ie, until recently, no one had expected gradual increases this soon, which suggests that the science still hasn't caught up.

The most likely outcome is that this will lead to a gradual increase in methane (and CO2) as the world warms. This is unhelpful, but only one of many serious feedbacks that make it harder and harder to stop climate change.

But we do know that while we may not have a useful mechanism for describing it, large scale methane releases probably have contributed to abrupt climate change the past, although not in the last 100,000 years, and it would be very much premature to indicate it is happening now.

But what I do think is that this is a useful contribution to the case of the precautionary principle - because what we don't know could very well do us a great deal of harm. As the Real Climate authors imply, carbon dioxide-caused global warming is a plenty good case for precaution, but there are factors that should make us nervous. We know that in historic terms the climate has changed very rapidly, over decades or even a few years. We know that an abrupt climate change would be a world-wide disaster. What we don't know is how likely we are to precipitate one, or even how one might be precipitated. And sometimes to "we don't know" we must add "and we shouldn't wait until we're sure, we should act now."

Sharon