We always hear things like "Coal will last 500 years at today's rate of
consumption" or "We have enough oil for 30 years [at today's rate of
consumption]". Of course, they're also telling you we have to start
using the resource in question at a higher rate of consumption. So what
happens to a resource base when you increase the rate of consumption?
Here's a little calculator to figure it out: Just enter the number of
years they say it will last, and press enter