When our consumption of a resource (energy, for instance) grows steadily, the doubling time takes on an even scarier meaning: during that time we use up more of the resource than in all of history before that time!

To understand why this is the case, think of the bacteria again. Every minute, there are more of them alive than the sum of all those that lived before that time.

So if we keep increasing our energy consumption like this, we'll use more energy in the next 25 years than we've produced in all of history up to now! Where will we get that much energy? What impact will it have on our environment?