For the fourth day running, France has been crippled by strikes. Airlines are canceling flights. Travelers making their way to Paris from DeGaulle and Orly face long delays.

Tourists are stranded. The Eiffel Tower was closed. Rail and subway traffic into the city has been curtailed. By shutting down refineries, French oil workers may cause a shutdown of gas stations and force the government to raid the strategic petroleum reserve.

Millions have gone on strike. One in 10 high schools has been closed. Students at secondary schools and universities march beside workers and block entrances to paralyze the educational system.

And what is the cause of this national tantrum?

President Nicolas Sarkozy has moved through the National Assembly and is pushing through the Senate a measure raising the retirement age for state pensions from 60 to 62.

For if France does not raise that retirement age, its social security system will face a $58 billion deficit by 2018. Sarkozy’s reform follows his victory in repealing a decade-old Socialist law that mandated the 35-hour workweek in France.

What world, one wonders, are these French living in?

Around 2050, those high school and college students will be near or above today’s retirement age of 60. Who do they think is going to pony up for their pensions? Are they not aware of what is coming for France and Europe?

Today, 23 percent of French men and women are 60 or older. That will rise to 33 percent by 2050, when there will be one French worker for each French retiree, if 60 is retained as the age of retirement.

Today, 5.5 percent of French men and women are 80 or older. By 2050, that doubles to 11 percent.

Who do the French strikers think is going to pay the taxes for the medical expenses of this infirm and aged ninth of a nation?

Where the median age of the French is 40, in 2050 it will be 45. But that number disguises a far drearier reality.

Since 1970, the fertility rate of French women has been below the 2.1 children needed to sustain France’s population, what demographers call zero population growth. For the next four decades until 2050, the fertility level of French women is projected to remain roughly 15 percent below ZPG.

Yet France’s population of 62.6 million is projected to make a healthy leap to 67.7 million. How can a population continue to grow when the birth rate for almost 80 years running to 2050 is below replacement level?

Answer: As the French retire, age and die, France is filling up with immigrants coming to replace the departed and departing French, and the millions of French children who were never born because their potential parents did not want them.

Where are the immigrants coming from?

Some come from Eastern Europe. But more are arriving from Morocco, Algeria, Tunisia and the former French colonies of the sub-Sahara. Arabs and Africans are populating cities like Marseilles and Grenoble, and filling up the burgeoning banlieues around Paris, where every few years, they go on a tear and burn thousands of cars. For Paris police, the banlieues are off-limits, except when traveling in platoons.