In the Deccan

Every once in a great while the earth's surface receives, in one relatively continuous belch, an outpouring of lava millions of times greater in volume than any human has ever witnessed a volcano release. Here in India for a wedding this week, I got to spend a little time in the Deccan -- a plateau created ~65 million years ago in just such an immense burp of volcanic gas (including our friend CO2) and magma. The pore spaces in the resulting rocks (namely basalts) are incredible! This was clearly a magma packed with volatiles such as carbon dioxide.

I wasn't able to photograph any fresh surfaces, but I plan on posting a photo of a hand sample, at least. For now, here's a link to a page about flood basalts and their consequences for the earth system: http://www.geolsoc.org.uk/template.cfm?name=fbasalts

Methane Catastrophe

Another issue that comes up when you pump gases into the seafloor is the danger of catastrophic degassing. One of all the predictable effects of global warming, probably the most cataclysmic -- and least talked about -- is the release of naturally occurring methane ice currently lying bound in cold seafloor sediments. In what is colloquially referred to as the "clathrate gun hypothesis," all that needs to happen is for seabottom water temperatures to rise a few degrees, and this ice would begin to release methane gas bubbles into the water. Once they float to the surface, they would join the atmosphere, where they would act with a greenhouse effect ~20 times more powerful than the equivalent amount of carbon dioxide. This increased greenhouse effect would further warm the atmosphere and oceans, causing further release of methane, causing further warming.....it's a runaway positive feedback loop. And it wouldn't stop until huge amounts of methane -- somewhere between 500 billion and 2500 billion tons of carbon equivalent -- have been released into the atmosphere. In terms of greenhouse effect, that's like burning all known conventional fossil fuels on the entire planet in one gasp. Twice. So do I think it makes sense to bury billions of tons of greenhouse gases (or anything else) in the seafloor, where their destabilizing effects could initiate a deadly runaway release of greenhouse gases? Hmmmm.

As if all that weren't bad enough, we might consider the much more horrible additional side effects of the large-scale methane release.

• Initially some of the methane gas being released would spontaneously oxidize, transforming it into CO2. Sounds great in terms of reducing methane's greenhouse effect, but in fact that very oxidation would rob the oceans of their small amount of dissolved oxygen. This dissolved oxygen is what all fish, shellfish, and ocean life (excepting higher vertebrates and some bacteria) breathe! We would witness mass deaths of fish as never before seen -- right on the continental shelves, where the methane release would be most strongly felt. Entire fisheries would be eliminated, and the oceans would go dead over large areas. The only winners would be methane-eating bacteria, which would cover the continental shelves in layers meters thick. Yukk.
  
• Next the methane would reach the atmosphere. The impact on atmospheric oxygen supplies would be less profound than in the ocean, so there's little need to fear death by asphyxiation. However, once the methane collecting in the atmosphere came into contact with clouds of water vapor (which are nearly everywhere), the clouds of saturated methane/water vapor would be denser than air, and would therefore settle close to the ground -- like a fog. Except......this fog would be highly flammable. Ever hear about the wildfire that covered the entire earth following the extinction of the dinosaurs? No doubt the conflagration was fuelled, at least in part, by global methane degassing.
  

So, yeah. I'm not so hot on burying anything in the seabed. Let's hope we can do better, eh? Otherwise.....things may not end up looking so rosy here in the biosphere.

Here's a link to a longish summary of scientific work on methane catastrophes in earth history: http://www.killerinourmidst.com/methane%20catastrophe.html

And here's a pretty comprehensive list of scientific articles regarding the end-Cretaceous extinction and associated events, like global wildfires: http://www.scn.org/~bh162/extinction_refs.html