Obviously statements about the future can't be about knowing, robomatic. They are about predicting, on the basis of information about the present and past. I don't know the sun will rise tomorrow - after all, it might go supernova in the night. But it's a reasonable prediction to make.

As for the six months figure, that's the estimate of the Alaska project director of the Natural Resources Defence Council. Maybe it's an underestimate - on the basis of 20,000,000 barrels used up by the USA every day, and the US Geological Survey estimate of about 10 billion available barrels, there might be enough for 18 months supply. Wow! ( "Senate backs exploitation of Alaskan wildlife refuge" )

In terms of meeting the US appetite for oil, this is pretty marginal. But of course, in terms of making money for friends and colleagues of people in high places, it's not at all marginal, and pretty evidently that is what it is actually all about.