Ok, so maybe "crisis" is too strong a word. But it is true that population is on its way down at a surprising rate in the industrialized world, and birth rate (while still well above replacement level) is falling even among many 3rd-world countries.
This is a dramatic change from the warnings of over-population that I grew up with. It's only been in the past few years that predictions have begun to reverse - global population is on its way down, not up. The birth rates of women in Europe are way below replacement level, and America isn't much better. Two of the worst examples: by 2050, 40% of the people in Italy and Japan will be over 60. How can you sustain an economy when 40% of your population is retired? For that matter, how can you sustain a welfare state?
This is the reason Social Security needs to be reformed. Minor adjustments are not going to allow an increasingly small working class to support an increasingly large number of retired persons forever. It doesn't matter precisely when Social Security will begin to lose money, the point is that it's premised on steady population increase and population is going down.
Of course, the United States is ahead of Europe in birth rate, so we'll be able to see how the European welfate states handle declining populations before it directly affects us. And it's always possible that there will be a dramatic resurgence in birth rates among developed nations. However, I somehow doubt that all those people who said they were "doing their part to control world population" by not having many children will change their reproductive habits because population is on the decline.