I don't. But I've always been a glass-half-empty kinda guy, so I tend to err on the side of caution (or, in this case, catastrophe).

Quite frankly, it doesn't matter to me whether the "real" capacity is 1 billion or 20 billion or 100 billion, as I don't believe we (as a species) have any chance of moderation in the face of opulence. As long as there's any surplus capacity left on this planet, we will find a way to use it. As fast and as wasteful as we can, until it all comes crashing down.