That brings me to the extinction rate of species around the world. With data on the best known vertebrate species, and a lot of additional information from fossil studies and genetics, we can put the fraction of species disappearing each year at upward of a 1,000 times the rate that existed before the coming of humans.

Most of this loss is occurring in tropical countries, and especially tropical forests on islands. But to bring it home to the United States, consider that from 1895 to 2006, 57 species and distinct geographic races of freshwater fishes were driven to extinction, which is 10 percent of the total previously alive; hence the rate of extinction was just under 900 times that which existed before the coming of humans.

The global conservation movement, pioneered by the United States, has raised awareness of nature’s plight, and stimulated a great deal of excellent research. It has slowed the hemorrhaging of species, but is still a long way from stopping it. Conservation efforts are concentrated on the roughly one-fifth of vertebrate species worldwide that are ranked as endangered to some degree. We have managed to stabilize or reverse the decline of one-fifth of the species in this group. A better record has been achieved within the United States by the Endangered Species Act of 1973, which has brought 10 times more species back to health than have been lost in the same time period to extinction.

All this is progress, but the prospects for the rest of the century remain grim. The global conservation movement is like a surgeon in an emergency room treating an accident victim: He has slowed the bleeding by half. Congratulations, we might say — even though the patient will be dead by morning.

Unless we wish to pauperize the natural world drastically and permanently, believing that later generations will be smart enough to find a way to bring equilibrium to the land, seas and air, then we, the current inheritors of this beautiful world, must take more serious action to preserve the rest of life.

There is only one rational way to accomplish this goal, and that is to bring the extinction rate back to the level that existed before the worldwide expansion of human populations. The disappearance of natural habitat is the primary cause of biological diversity loss at every level — ecosystems, species and genes, all of them. Only by the preservation of much more natural habitat than previously envisioned can extinction be brought close to a sustainable level.

The only way to save upward of 90 percent of the rest of life is to vastly increase the area of refuges, from their current 15 percent of the land and 3 percent of the sea to half of the land and half of the sea. That amount, as I and others have shown, can be put together from large and small fragments around the world to remain relatively natural, without removing people living there or changing property rights. This method has been tested on a much smaller scale at the national and state park levels within the United States.