From the Preface, How Civilizations Die: (And Why Islam Is Dying Too), by David P. Goldman. Quoted in the Asia Times Online.
Population decline is the elephant in the world's living room. As a matter of arithmetic, we know that the social life of most developed countries will break down within two generations. Two out of three Italians and three of four Japanese will be elderly dependents by 2050.  If present fertility rates hold, the number of Germans will fall by 98% over the next two centuries. No pension and health care system can support such an inverted population pyramid. Nor is the problem limited to the industrial nations. Fertility is falling at even faster rates - indeed, at rates never before registered anywhere - in the Muslim world. The world's population will fall by as much as a fifth between the middle and the end of the 21st century, by far the worst decline in human history.
The world faces a danger more terrible than the worst Green imaginings. The European environmentalist who wants to shrink the world's population to reduce carbon emissions will spend her declining years in misery, for there will not be enough Europeans alive a generation from now to pay for her pension and medical care.  For the first time in world history, the birth rate of the whole developed world is well below replacement, and a significant part of it has passed the demographic point of no return.
But Islamic society is even more fragile. As Muslim fertility shrinks at a rate demographers have never seen before, it is converging on Europe's catastrophically low fertility as if in time-lapse photography. The average 30-year-old Iranian woman comes from a family of six children, but she will bear only one or two children during her lifetime. Turkey and Algeria are just behind Iran on the way down, and most of the other Muslim countries are catching up quickly. By the middle of this century, the belt of Muslim countries from Morocco to Iran will become as gray as depopulating Europe. The Islamic world will have the same proportion of dependent elderly as the industrial countries - but one-tenth the productivity. A time bomb that cannot be defused is ticking in the Muslim world.
HT: Craig L. Adams