The Sixth Extinction: An Unnatural Historyby Elizabeth KolbertHenry Holt, 2014 One of the key terms in Elizabeth Kolbert's relentless, crushing new book The Sixth Extinction, is "Anthropocene" - a fairly new term used to differentiate the age in which we all live from that age's earlier term, the Holocene. The Anthropocene is the Holocene gone hysterical and hyper-accelerated, extending along the axes of several assertions: "human activity has transformed between a third and a half of the land surface of the planet, most of the world's major rivers have been dammed or diverted, fertilizer plants produce more nitrogen than is fixed naturally by all terrestrial ecosystems, fisheries remove more than a third of the primary production of the oceans' costal waters, humans use more than half the world's readily accessible fresh water runoff," and also "people have altered the composition of the atmosphere."And one more extremely distinctive characteristic: the Anthropocene is witnessing the sixth extinction of Kolbert's title, the sixth massive die-off in the history of life on Earth (the last such extinction having happened 66 million years ago, perhaps triggered by the impact of that famous dinosaur-killing asteroid), and as Kolbert reports, biologists like E. O. Wilson have been asserting for decades that the die-off rate of the sixth extinction is astronomically greater than that of any previous mass extinction, and that's a crucial difference:

Roughly one-third of the [carbon dioxide] that humans have so far pumped into the air has been absorbed by the oceans. This comes to a stunning 150 billion metric tons. As with most aspects of the Anthropocene, though, it's not only the scale of the transfer but also the speed that's significant. A useful (though admittedly imperfect) comparison can be made to alcohol. Just as it makes a big difference to your blood chemistry whether you take a month to go through a six-pack or an hour, it makes a big difference to marine chemistry whether carbon dioxide is added over the course of a million years or a hundred. To the oceans, as to the human liver, rate matters.

It's mankind that's causing that accelerated rate, of course - the Anthropocene is entirely humanity's doing, the curse of humanity made manifest on the helpless planet. Kolbert's book has many fascinating digressions and contains some first-rate popular science-writing, but it comes back in the end to the fact that humans are not only radically altering the climate on which they depend for their own survival but also quickly stripping the planet of all life-forms that aren't specifically cultivated and mass-produced for human use ... including the animal family to which humans themselves belong; "with the exception of humans," Kolbert writes, "all the great apes today are facing oblivion":

The number of chimpanzees in the wild has dropped to perhaps half of what it was fifty years ago, and the number of mountain gorillas has followed a similar trajectory. Lowland gorillas have declined even faster; it's estimated the population has shrunk by sixty percent jus in the last two decades. Causes of the crash include poaching, disease, and habitat loss; the last of these has been exacerbated by several wars, which have pushed waves of refugees into the gorillas' limited range. Sumatra orangutans are classified as "critically endangered," meaning they're at 'extremely high risk of extinction in the wild." In this case, the threat is more peace than violence; most of the remaining orangutans live in the province of Aceh, where a recent end to decades of political unrest has led to a surge in logging, both legal and not. One of the many unintended consequences of the Anthropocene has been the pruning of our own family tree. Having cut down our sister species - the Neanderthals and the Denisovans - many generations ago, we're now working on our first n second cousins. By the time we're done, it's quite possible that there will be among the great apes not a single representative left, except, that is, for us.

The central conflict of The Sixth Extinction is Rachel Carson's famous "problem of sharing our earth with other creatures," and although Kolbert's excellent book has received dozens of high-profile reviews that strain at some glimmer of hope, the repeated message in these pages is that Carson's problem now has no solution - other than the obvious. Humanity can't long survive on a planet with no biodiversity, and survival is impossible anyway on a planet constantly ravaged by super-weather of all kinds. And it's too late to avoid either one of those outcomes.So The Sixth Extinction works as the ultimate corrective to environmental optimism. It's the death-knell of an entire epoch of life - and one hell of a good read in the bargain!