"Crud - someone's gone and written the post that I was going to write. I've seen very little discussion of leakage issues."
"Well, the author's language really seems overblown."
"Did NRDC really say that? Did Joyce Foundation really fund that?" (Clicks links, reads.) "No they didn't!"
(Reads another link.) "What the hell - IPCC says geological sequestration has a leakage rate of less than 1% per century, maybe less than 1% per 1000 years? This 'issue' just collapses."
So I left a nasty note in the comments. The argument against sequestration claims to be based on the precautionary principle, but you need some actual evidence of risk IMHO before the precautionary principle makes any sense. It doesn't work here, at least for geological sequestration that's properly managed.
I haven't seen much about mid-ocean and deep-ocean sequestration though - leakage and other environmental impacts might be an issue, if anyone's still taking about those ideas.
UPDATE: some good discussion in the comments. I suppose if I were really diligent I could pull out the IPCC cites and read those for flaws, but I'm not that diligent. If the Gristmill author had disclosed the IPCC view and then written an argument for why the leakage rate is wrong, he might have had a better case, but he doesn't really try.