I was fortunate enough last night to hear Tim Flannery — he of The Weathermakers — speak here in Toronto to a crowd of businessmen and lawyers. Favorite moment:

Questioner: Mr. Flannery, do you think or wish that Al Gore should run for President?

Flannery: He’s already done it, and what’s more, he won!

Levity aside, Flannery delivered an excellent talk and specifically explained why, exactly, the atmosphere is so much more vulnerable to human disruption than something like the ocean.

When it comes to human impact on a system like the atmosphere, the important variable isn’t volume, but mass. More simply, it’s not the size of the sky, but the amount of stuff in it.

This is important, because the atmosphere’s actual mass is less than impressive. Rather than a "great aerial ocean,” the atmosphere that surrounds us is in fact rather insubstantial. Flannery said that if you liquefied it, the atmosphere would be 1/500th the volume of the earth’s oceans. Some quick Wikipedia searches later, and we see that this corresponds roughly to the volume of the Gulf of Mexico.

That would be this Gulf of Mexico. And this one. Clearly, humanity has the ability to alter systems as massive as the earth’s atmosphere, in extremely harmful ways.

There is hope, of course. Flannery is extremely optimistic about our ability to pull carbon back out of the sky by reforesting tropical rainforests. This will, however, be problematic so long as we’re deforesting them to make biofuels.

One area where I disagree with Flannery: he supports nuclear (in a lukewarm sort of way) because not all regions have the same renewable opportunities and uranium is a carbon-free, portable source of energy. I’m not sure he’s necessarily correct about that — electricity can be moved thousands of kilometers by HVDC cables with low losses (PDF). Moving solar and wind electricity from places that have it to places that don’t shouldn’t be overly taxing to the economy.

Oh, and this one’s for you Dave: Flannery says coal is the enemy of the human race.