As the US Population reaches toward the astronomical total of 40 million persons, we are reaching the limits of the number of people this earth can support. If one were to extrapolate current population growth rates, this country in a hundred years could have over 250 million people in it! Now of course, that figure is impossible - the farmland of this country couldn't possibly support even half this number. But it is interesting to consider the environmental consequences.
It's a crisis, I tell you.