It's actually on a site called gizmodo but I got to it through Huffington Post under the "Green" tab.
This is obviously not definitive but if the debate is how the output of the volcano stacks up against the output of the planes it is grounding, it seems pretty likely that the amounts don't equate to decades of output from Europe's airlines industry let alone all human activity over decades.
I don't know for sure whether human activity is currently causing irreversible global warming over and above natural cycles but I do no we are polluting in greater and greater volumes and if we don't get a handle on it, it will eventually have an impact on our health or our survival.
Dick Cheney put fort the 1% doctrine, It went like this (I'm paraphrasing so if I've got it wrong feel free to correct me). If there is a 1% chance that terrorists will get a nuclear weapon we have to act as though it is a certainty. I don't know whether I agree with that threshold but I have a hard time understanding how the same people who buy into that, can react to an indisputably much higher chance of irreversible global warming by saying we should ignore that risk because the evidence only supports a 70% likelihood. Not the first time, ideology and an industries' self interest has trumped science. Just look at how long the tobacco industry was able to avoid admitting that smoking caused cancer on the back of a handful of paid scientists who provided plausible denial.