The great geological fart

Yes, I know, this is why you read my blog, because I’m informative AND classy.

I’ve finally started doing my initial readings for my grad school project, which I really should have gotten moving on months ago. I don’t know if being out of school for eight months has just destroyed my ability to manage my time, or maybe I lack the sense of urgency that actually being in school and having solid due dates provides. Either way, I’m trying to read a couple per day.

What I’ll be working on in grad school is a project examining the local change in climate in the Bighorn Basin during the Paleocene-Eocene Thermal Maximum. Here’s something of a broad summary at io9 of the PETM and why it’s significant, but if you’re too lazy to read even that extremely conversational post, the one sentence summary is: Temperature went up, a lot of species died, and there are many suspected parallels between those events and the climate change we are facing today. So the PETM is an area of current interest in a lot of fields, because it may further our understanding of current environmental events.

In the io9 article, the emphasis is on the catastrophic event that might have thrown the environment out of whack, either massive volcanic activity or a meteor impact. I think that tends to give the events of the PETM a little less urgency on the surface, since today we’re not facing world-altering volcanic activity OR a meteor strike. Instead, we’re facing whatever threat our own fossil-fuel burning activities might cause. Whatever the ultimate carbon contribution to the atmosphere, billions of humans tooling around in cars is certainly less… well, dramatic than seas of basalt flooding large swathes of the continents.

The articles I’ve read so far have been interesting because the focus hasn’t been on a big, sexy, catastrophic kick-off for all of the carbon that caused the rapid (4-8 degrees C ocean surface temperature rise in a few thousand years) temperature increase, but rather a sort of positive feedback loop from degassing of methane hydrates in continental shelf and deep ocean sediments. This is supported by examining carbon isotope ratios, which show distinct, rapid (geologically speaking) shifts in the ratios that might show multiple pulses of carbon input (Bains et al 1999). This sort of geologically instantaneous is pretty much consistent with either an impact or methane hydrate dissociation. And since we’re looking at possibly several discrete events it’s unlikely that every one of them was an impact.

The most interesting paper I’ve read so far is from 2002; it only looks at a single site, but the isotope data there indicates that there was a brief period of ocean surface warming prior to the massive methane release – the great geological fart, so to speak (Thomas et al). Of course another of the papers suggests that methane hydrate dissociation doesn’t necessarily have to be thermally triggered; a significant amount of methane could be released because of submarine seismic or volcanic activity, or even gravitational slumping (Bains et al).

So the scenario that these papers build up is that something triggered the release of a large amount of methane into the atmosphere. It did what greenhouse gases tend to do, and this might have caused a reinforcing effect that could have lead to more methane getting put into the atmosphere. And then things got hot and uncomfortable. Of course, the initial cause of the methane hydrate dissociation is still a matter of question. Maybe it was seismic activity, or an impact that started this chain reaction, so to speak, and the methane release just added insult to injury. The Thomas et al paper suggests that the dissociation was thermally caused (as indicated by the brief period of surface warming prior to carbon being dumped into the the atmosphere), and that’s really the most worrying scenario. Because if we’re looking at temperature driven methane dissociation, the ultimate source of that temperature change at the end of the Permian wouldn’t be relevant in today’s world – it would be the temperature change happening at all, and driving further warming.

Sea surface temperature already is increasing. At the site in the Thomas paper, they’re estimating about a 2 degree C surface temperature increase before the methane hydrates dissociated and made a beeline for the atmosphere. We’re not really that far off from that sort of increase in some areas of the ocean right now. (Of course, what the surface temperature was at the time is not stated and may not be something we know for certain.) The real take home is that it very well could be a positive feedback situation: you get a little warming, it sets off a big geological fart, that adds up to more greenhouse effect and more warming, and pretty soon the Earth starts sounding like it had the baked bean special at the Chuckwagon last night.

Now, these are of course only a few papers, and this is a complicated subject. The mechanisms for warming in the PETM are still a subject of great debate, and new data is coming in constantly. But it’s certainly something to think about. There very well may be lot more carbon waiting out there than just what we’re burning to run our cars and power our cities, and it could be waiting for a thermal cue to bubble up to the surface and make things quite unpleasant for thousands of years to come.

Silent but deadly, indeed.

ETA: A very nice anonymous commenter pointed me toward a summary of the current research (as of 2008) on the methane hydrate issue. It’s still a very viable hypothesis and the challenge remains figuring out exactly how a massive methane burp would relate to the ocean warming, and exactly how much carbon we’re talking about, here. Also:

…no study has uniquely demonstrated that oxidized CH₄ (or another compound) was the source of the carbon addition. There are also issues regarding the mass of carbon injected during the PETM, and whether gas hydrates at this time could furnish such a quantity.

So there are still questions that need to be answered. But I’d say the three papers I read here are still pretty much in line with the main body of the research, including the questions still remaining to be answered.

Articles:

Warming the fuel for the fire: Evidence for the thermal dissociation of methane hydrate during the Paleocene-Eocene thermal maximum. Deborah Thomas, et al. Geology; December 2002.

A Transient Rise in Tropical Sea Surface Temperature During the Paleocene-Eocene Thermal Maximum. James C. Zachos, et al. Science 302 (2003). DOI: 10.1126/science.1090110

Mechanisms of Climate Warming at the End of the Paleocene. Santo Bains, et al. Science 285 (1999). DOI: 10.1126/science.285.5428.724