TWO elements, air and water, are essential to life as we know it. They are fragile and at our mercy: Toxic products dumped in the North Sea end up in the liver of penguins; the destruction of tropical forests speeds up the melting of glaciers.
Our planet is a delicate thermal machine in which the Antarctic ice cap plays an essential role. The most basic prudence dictates that we jealously protect this reserve of coldness and of fresh water, the Antarctic, to avoid the worst climatic catastrophies.
Despite appearances, water is rare on our planet. The immensity of the sea, the impetuousness of the great rivers, the majesty of ice floes, and the violence of rainstorms have given us a false perspective. In fact, if we imagine our Earth reduced to the size of an egg, all the water it possesses would be contained in a single drop.
Humanity has available to it about 300 times less air than it does water. And the atmosphere is in a much more worrisome situation than the hydrosphere. The air will become unbreathable long before the water becomes undrinkable.
The air and water constantly react with each other: The increase in the percentage of carbon dioxide gas is causing the planet to heat up. As a consequence, glaciers are melting and ocean levels are rising.
Today, 1.7 million human beings have no access to potable water. This is monstrous.
Can things get better while during my lifetime - in about 80 years - the world's population has more than tripled? Every six months, the equivalent of France appears on Earth; and every 10 years, a China.
Let us be realistic: It does not matter whether the population peaks at 18 billion, 16 billion, 14 billion, or even 12 billion; these numbers are unacceptable. Even if we succeed in feeding this tide of humanity, it would be impossible to obtain decent living conditions for such a multitude.
It is generally accepted that the principal obstacles to family planning are religious and spiritual, thus insurmountable.
But the facts prove the contrary. It is Italy, the closest possible country to the Vatican, that has the lowest birth rate in Europe. Catholic Spain is in the same situation. And the largest Muslim country in the world, Indonesia, has put in place an effective plan to limit its birth rate.
The true obstacles are not spiritual. But the condition of women is a measuring stick. In all countries with high fertility, girls and women are the victims of discrimination. Young girls are often deprived of elementary hygienic care, and their illiteracy rate is one-third higher than that of boys.
In Africa, it has broken my heart to see young girls walk 10 kilometers [6.2 miles] to fetch a little bucketful of water instead of going to school. In Haiti, the residents of overpopulated shantytowns wait for hours, then fight mercilessly to get a miserly portion.
In poor countries, millions of girls exhaust themselves in fatiguing walks to procure the potable water their family needs. Instead of spending hours each day looking for water - the water that we use to clean our toilets - they could be going to school.
Let's start with that: Let us drill wells. The education of girls and women first of all, and the assurance of a small pension in our later years, are fundamental to halting the population explosion. Let us give dignity to all those who live like animals and they will be able to take charge of their own destiny.
I have tried to make an informal estimate of the cost of the education of women and the old-age pensions for all human beings on the planet who do not benefit from either: $400 billion a year; or one-third of the military expenditures of all nations.
Such a program will no doubt seem Utopian in a world shaken by economic crisis and armed conflict. But the meter is running, and future generations will not forgive us for deliberately wasting this last chance to save the planet.