The geothermal gradient is usually quoted as 25–50 degrees Celsius per mile of depth in normal terrain (not, e.g., in the crater of Kilauea). Two kilometers down, therefore, (that's a mile and a quarter if you're not as science-y as Al) you'll have an average gain of 30–60 degrees — exploitable for things like home heating, though not hot enough to make a nice pot of tea. The temperature at the earth's core, 4,000 miles down, is usually quoted as 5,000 degrees Celsius, though these guys claim it's much less, while some contrarian geophysicists have posted claims up to 9,000 degrees. The temperature at the surface of the Sun is around 6,000 degrees Celsius, while at the center, where nuclear fusion is going on bigtime, things get up over 10 million degrees.Mark Steyn piles on,
If the temperature anywhere inside the earth was "several million degrees," we'd be a star. (Links in the original)
Al Gore's being a little more than merely innumerate when he breezily asserts that the temperature of the earth's interior is "several million degrees". His entire, highly lucrative shtick rests on the proposition that a one-degree increase in surface temperature in the course of a century imperils not merely the poor old polar bear, not merely the planet itself, but is "altering the balance of energy between our planet and the rest of the universe". But he's so insouciant about "several million degrees" boiling away a couple of miles under his loafers that he can't even be bothered getting it right to within three figures.Yup, this is the guy whose movie should be required viewing in all schools. Sheesh!
It makes you wonder whether even he believes any of this stuff.