Environmental science is the key to the survival of both the living and the nonliving parts of Earth; it’s a complex domain of disciplines still in their infancy. Environmental science also opens the door of science to everyone, and especially to young people, whose commitment to science and technology in service to the environment is vital to our species and the rest of life.
I’m going to use this valuable short space to summarize what scientists have learned about biodiversity and extinction during the past twenty years of fast-moving research. Then I’ll suggest what I believe is the only viable solution to halt the continuing and growing rate of species extinction and, thereby, to save the living world.
So, what is biodiversity? What is the living world? It’s the collectivity of all inherited variation in any particular given place, such as a vacant lot in a city, an island in the Pacific, or the entire planet. Biodiversity consists of three cascading levels: an ecosystem such as a pond, forest patch, or coral reef; the species composing each ecosystem; and the genes that prescribe the traits that distinguish the species that compose the living part of the ecosystem.
How much biodiversity exists? How many species are known to science in the whole world? At the present time, it’s almost exactly two million. How many species are there actually still living on Earth, both known and unknown? Excluding bacteria plus the archaea, which I like to call the dark matter of biology because so very little is known of their biodiversity, the best estimate of the number of species of the remaining groups (that is, the fungi, algae, plants, and animals) is about ten million, give or take a million. We know about the big animals—the vertebrates, comprising 63,000 known species collectively of mammals, birds, reptiles, amphibians, and fishes—plus about 270,000 known species of flowering plants. However, next to nothing is known of the millions of kinds of fungi, algae, and invertebrates. These are the foundation of the biosphere. They’re the mostly neglected little things that run Earth.
To put the whole matter in a nutshell, we live on a little-known planet. We really don’t know what we’re doing. At the present rate of elementary exploration, in which about eighteen thousand new species are described and given a Latinized name each year, biologists will complete a census of Earth’s biodiversity only sometime in the twenty-third century.
Next, what is the extinction rate around the world? With the data sets of the best-known vertebrate animal species and with additional information from paleontology and genetics, we can put the extinction rate at the closest power of ten: a thousand times greater than the extinction rate that existed before the coming of humans. For example, from 1895 to the present, human activity has driven to extinction fifty-seven freshwater fish species and distinct geographic subspecies in the United States. These extinctions have removed roughly 10 percent of the total diversity previously alive. This means that the extinction rate of fish species in our country is just under an estimated nine hundred times the level that existed before the coming of humans.
This brings me to the effectiveness of the global conservation movement, a great contribution to world culture pioneered by the United States. The global conservation movement has raised public awareness and stimulated a great deal of research. But what has it accomplished in saving species, hence biodiversity? The answer, from data on the vertebrates, is that it has slowed the rate of species extinction but is still nowhere close to stopping it. An expert study of different groups of land vertebrates around the world, species by species, mammals, birds, reptiles, amphibians, found that the rate of extinction in these most favored groups has been cut by about one-fifth, 20 percent. Furthermore, the Endangered Species Act of 1973, by focusing on recognized endangered vertebrates in the United States, with legal procedures and with actions designed for each species in turn, has brought ten times more species back to health than have been lost to extinction.
Nevertheless, the species, and with them the whole of biodiversity, continue to hemorrhage badly. The prospects for the rest of this century are grim. Almost everyone, I’m sure, knows about the 2°C (3.6°F) threshold, the increase in the ground average temperature above which the planet is going to enter a regime of really dangerous climate changes. What is not well known is that a parallel situation exists in the living world.
Earth is at or very close to an extinction rate of one thousand times prehuman levels, and the rate is accelerating. Repeat: accelerating. Somewhere between one thousand times and ten thousand times, Earth’s natural ecosystems will reach the equivalent of the 2°C global warming threshold and begin to disintegrate, as half or more of the species pass into extinction. We’re in the situation of surgeons in an emergency room who’ve slowed the bleeding of an accident patient by 20 percent. We can say sincerely, “Congratulations! The patient will be dead by morning.”
There is a momentous moral decision confronting humanity today. It can be put in the form of a question: what kind of a species, what kind of an entity, are we, to treat the rest of life so cheaply? What will future generations think of those now alive having made an irreversible decision of this magnitude so carelessly? The five previous such mass extinctions—the last one occurring sixty-five million years ago and ending the Age of Reptiles—required variously five million to forty million years to recover from.
Does any serious person really believe that we can just let the other ten million or so species drain away, and our descendants will somehow be smart enough to take over the planet and ride it like the crew of a real spaceship? That later generations will find the way to equilibrate the land, sea, and air in the biosphere, on which humans absolutely depend, in the absence of most of the natural biosphere?
Most experts understand that only by taking global conservation to a new level can the hemorrhaging of species be brought down to near the original baseline rate, which in prehuman times was one species extinction per one to ten million species per year. Loss of natural habitat is the primary cause of biodiversity extinction—ecosystem, species, and genes, all of it. Only the preservation of much more natural habitat than hitherto envisioned can bring extinction close to a sustainable level. The number of species that can persist in a habitat increases somewhere between the third and fifth roots of the area of the habitat, in most cases close to the fourth root. At the fourth root, a 90 percent loss in area, which is frequent in present-day practice, there will be an automatic drop over time to half the species.
At present, about 15 percent of the global land surface and 3 percent of the global ocean surface are protected in nature reserves. Not only will most of them continue to suffer diminishment of their faunas and floras, but extinction will accelerate overall as the remaining unprotected wildlands and marine habitats shrink because of human activity.
The only way to save the rest of life is to increase the area of protected and inviolable habitat to a safe level. All the signs show that a safe level that can be managed with a stabilized global population of ten billion people is about half Earth’s land surface plus half the surface of the sea.
Now, before you start making a list of why it can’t be done, why half can’t be set aside for the other ten million or so species sharing the planet with us, let me assure you that it most certainly can be done, if enough people wish it so.
Think of humanity in this century, if you will, as passing through a bottleneck of overpopulation and environmental destruction. At the other end, if we pass through safely and bring most of the rest of life with us, human existence could be a paradise compared to today. And a long geologic life-span, essentially immortality, for our species would be possible.