PARIS – In 2040/2050, will demographers speak of "the white man’s loneliness” in the way historians once referred to "the white man’s burden” to describe the so-called "imperial responsibilities” of some European nations?

Demography is not an exact science. Countless dire predictions, from that of Malthus to that of the Club of Rome, have been proven wrong. But, according to a recent and very convincing essay published in the magazine Foreign Affairs, a dual demographic and economic trend is taking place that will result in spectacular shifts by the middle of this century.

The Western world will represent only 12% of the world’s population, with Europeans reduced to 6%. (In 1913, a year before the outbreak of World War I, Europe was slightly more populated than China.)

Economically, the West will account for around 30% of global output – a level that corresponds to Europe’s share in the eighteenth century and down from 68% in 1950.

What we are witnessing can be seen is a return to the past, with the West returning to its old place in the world before the start of China’s long process of historical decline at the beginning of the nineteenth century.

The West’s long period of global dominance is ending, encouraged and accelerated by its own mistakes and irresponsible behavior. We are entering a new historical cycle, in which there will be proportionally fewer Westerners, more Africans and Middle Easterners, and – with greater relevance economically and strategically – many more Asians.

It is with these figures in mind that one must consider Barack Obama’s decision not to attend the next European-American summit that was due to take place in Madrid in May.

It would be tempting to use a formula coined during the Cold War to describe the comparative evolution of the United States and the Soviet Union and to apply the notion of "competitive decline” to the relationship between the US and Europe.

An America that may be undergoing a process of relative if not absolute decline chooses to ignore a Europe that in US eyes is no longer a problem compared with Asia or the Middle East, and that offers little help in finding solutions to the problems that most vex Americans.

In a hasty and excessively provocative manner, some in the American media are starting to speak of Obama as "a second Jimmy Carter” and predict that he will serve only one term.

What is more serious is the impression that the American political system, with its inability to transcend party divisions and forge national consensus, is increasingly sclerotic.

America’s political institutions have aged like the country’s infrastructure. They were devised more than two centuries ago for a mostly agrarian world. Today, they need to be amended and rejuvenated. But that may not be possible, given the sacrosanctity with which many Americans regard the US Constitution.

As for the European Union, the problem is not what will not happen in Madrid. The EU’s problem is much more what happened in Copenhagen last December at the summit to "save the planet,” or what is taking place before our eyes with the challenge to the euro posed by the weakness of some of its member states, most prominently Greece.

In Copenhagen, Europe came with a common and responsible position. The EU was "showing the way” to other great actors and behaved as the "good pupil” of the world class.

The Union was ignored, with the US and China choosing to disagree over its head. Europe must realize that it cannot be seen as a model for anyone if no one any longer takes it seriously as a global actor.

But how can you be taken seriously by others if you do not take yourself seriously? The EU’s new High Representative for external affairs, Baroness Catherine Ashton, tried to justify her failure to go to Haiti in the immediate aftermath of its terrible earthquake by saying, "I am neither a nurse nor a fire person.”

Lack of such skills did not keep US Secretary of State Hillary Clinton from traveling to the scene of the devastation to show here support and concern.

Confronted with revolutionary demographic and economic transformations, Americans and Europeans should behave in a much more responsible manner.

Instead of ignoring the other (the American way) or lamenting a wounded ego (the European way), they should confront the common challenges they face as a result of a globalization process that they are no longer able to master.

Dominique Moisi is a Visiting Professor at Harvard University and the author of The Geopolitics of Emotion.