In the history of life on earth, there have been five great extinctions, when a substantial fraction of the life on the planet has suddenly died. The causes have varied and some are poorly understood. But the events are unambiguously present in the fossil record. The last was the Dinosaur Killer, the asteroid that plowed into the present-day Yucatan, some 65 million years ago.
Kolbert offers a lay treatment of the emerging scientific consensus that humankind is causing a sixth great extinction event in the present, one that rivals the Dinosaur Killer in its scope and impact.
It’s not just the increasing level of CO2 in the atmosphere, now past 400 parts per billion and still climbing. Certainly the elevated CO2 levels are lowering the pH of the oceans, killing coral and other forms of life evolved to extract calcium carbonate from seawater. As the oceans become more acidic, that process becomes impossible. The base of the ocean’s food chain is built on plankton that use calcium carbonate for their skeletons. We’re running an uncontrolled experiment on our oceans, finding out what happens when the base of that food chain vanishes.
But as Kolbert documents, the Anthropocene Extinction goes far beyond CO2. The mobility that our technology has given us, beginning with the great migrations of early humans and continuing through the age of jet travel, has brought humankind and its fellow travellers – ranging from rats to pigs to mosquitoes to viruses, fungi and bacteria – to areas that had evolved without them. Rats unintentionally brought by the Polynesians to the Pacific Islands; pigs brought intentionally. They have damaged each island colonized by the Polynesians. The megafauna of ice age North America; the the large, flightless moas of New Zealand; the unique animals of Madagascar. What happened to them was us. Humans.
And the process seems to be accelerating. Chestnut blight, Dutch Elm disease, white nose fungal infections in bats, avian malaria in the Hawaiian Islands, fungal infections in amphibians; we have spread diseases to areas where the animals have no resistance.
Humans also bring technologically-leveraged hunting pressure. The list of victims is depressingly long. Whether the technology is throwing weapons among early migrants to the Americas (mastodons, mammoths), the telegraph and shotguns (Passenger Pigeons) or AK-47s and cell phones (elephants, rhinos), our technology has enabled us to kill populations far faster than they can reproduce. Kolbert points out there is only one possible outcome.
Humans are also the most effective animal in history at altering the environment. And the result has been habitat loss. Much of the Amazon basin, for example, has been destroyed to permit oil palm plantations. Animals evolved for the Amazon ecosystem disappear with the jungle that nurtured them. Habitat loss, across the planet, is yet another great cause of the Anthropocene Extinction.
The total effect is an extinction event unmatched since the arrival of the Dinosaur Killer at the end of the Cretaceous. Caused by us, by humans.
All of this is meticulously documented by Kolbert. It fascinating and terrifying. And cannot answer the critical question: how much longer can this go on before the planet is so badly damaged that humankind, too, joins the list of extinct species. With the dubious distinction of having exterminated itself.
Not an easy or fun read, although quite well written. Recommended, but be prepared to be depressed.