Russell Roberts, George Mason University econ professor and blogger over at Café Hayek, E-mails me to tell me that my $5 trillion estimate of the cost of Al Gore's 10-year, zero-carbon-emission energy plan could be a bit low.
If 20% of something costs $1 trillion, how much would 40% cost? If it's two trillion, that's linear, and so on so the whole thing would cost $5 trillion. But replacing the first 20% of US energy with wind, solar and a bunch of people pedalling isn't going to be the same as replacing the second 20%. My presumption is that the second fifth is harder than the first fifth. For example, if you replace 20%, you might use solar in the sunniest parts of the country. But what about the non-sunny parts that aren't windy? Those are going to cost more.