"The Sixth Extinction" or how humanity, perching on tree limb, saws it off

Since humans evolved from apes and climbed down from the trees we have altered nature through our activity. This is especially so since the rise of capitalism and its ruthless, destructive global exploitation of nature.

In her book, The Sixth Extinction: An Unnatural History, New Yorker staff writer Elizabeth Kolbert clearly and passionately describes how human destruction of ecological systems is today causing the sixth great mass extinction of biological species, including possibly the human species itself. In the words of scientist Paul Ehrlich, "In pushing other species to extinction, humanity is busy sawing off the limb on which it perches."

Over its 4.5 billion years of existence, the Earth has evolved through many geologic periods. We are now in a new one - what is called the Anthropocene, or human caused, era. Dutch chemist Paul Crutzen, a Nobel Prize winning scientist who helped discover ozone depleting compounds, developed the term.

Crutzen observed human activity has so altered Earth that it constitutes a new geologic age. Humans have transformed land surfaces, soil, rivers, oceans, and most importantly, have altered the atmosphere through a combination of greenhouse gas emission and deforestation.

"Because of these (human caused) emissions," Crutzen said, global climate is likely to "depart significantly from natural behavior for many millennia to come."

In popular language, Kolbert recounts how scientists came to understand extinction and discovered five previous mass extinction events. These include the end-Ordovician extinction caused by an ice age; the end-Permian extinction or Great Dying, which emptied the Earth of 96 percent of species; and the Cretaceous-Tertiary extinction about 65 million years ago that did in the dinosaurs.

A sixth extinction is occurring before our eyes. Species are dying at a rate 1,000 times faster than pre-human habitation. "It is estimated that one-third of all reef-building corals, a third of all freshwater mollusks, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles, and a sixth of all birds are headed toward oblivion," writes Kolbert.

Kolbert documents pioneering scientific research of the current disappearance of species. She trudges through jungles in Panama with scientists studying the mass disappearance of amphibians, in particular the Panamanian golden frog. What's crashing frog populations is fungus called Batrachochytrium dendrobatidis, which spread worldwide. Scientists speculate the fungus migrated through international shipping.

Kolbert accompanies scientists to caves in upstate New York and Vermont in search of what are killing millions of bats. Up to 90 percent of brown bats have succumbed to a cold loving fungus accidentally imported from Europe. The fungus is spreading and causing mass die offs of other varieties of bats.

The author then introduces us to scientists researching the effect of climate change on flora and how slight changes in global temperature can make life inhospitable to plant species.

To illustrate global warming's "equally evil twin," or ocean acidification, we visit Castello Aragonese, a tiny island the product of volcanic activity in the Tyrrhenian Sea near Naples. Underwater vents around the island emit 100 percent carbon dioxide gas, which dissolves in the water.

Scientists clearly see the effects of C02. Approaching the vents, life disappears. This mimics macro changes in the world's oceans. Atmospheric greenhouse gases exchange with ocean water that cover 70 percent of the Earth's surface. Historically, about one third of all greenhouse gases, primarily carbon dioxide, have been dissolved into the vast oceans raising the acidification level.

Atmospheric C02 concentration levels are higher than at anytime in the last 800,000 years. By the end of the century the oceans are projected to be 150 percent more acidic than at the beginning of the industrial revolution. Acidification levels are reaching a "tipping point" where conditions will become inhospitable to most forms of life. Already coral reefs are disappearing.

Kolbert discusses what's called the "New Pangaea." Pangaea is the original global land expanse, when all the present day continents were connected and a single fauna and flora evolved. Plate tectonics caused the landmasses to separate into the present day continents. Fauna and flora evolved separately into unique species.

"Invasive species" are nothing new. Beginning with modern human migration out of Africa, the continents have been exchanging fauna and flora. Many scientists speculate modern humans drove to extinction other archaic human species that existed simultaneously including the Neanderthals, which apparently we Homo sapiens also mated with. With modern trade and transport, species are being exchanged worldwide at an accelerating rate leading to the "New Pangaea."

Kolbert helps us understand that unless we act now, the human species can also be a victim of the sixth extinction. At the very least humanity will deal with the effects of climate change far into the future and many biological species will disappear. Large parts of the human family, mainly the poorest and those living in the most ecologically fragile and vulnerable regions are facing an existential threat by drought and rising sea levels.

Reading the book, one is struck by the ability of humans to grasp their situation and act to change it. Climate awareness is growing and with it action to halt the discharge of greenhouse gas emissions. Also growing is awareness that the capitalist exploitative system and its drive for profits is incompatible with sustainability.

Humanity faces its biggest collective challenge - its very existence. We must not only deal with the impact of the climate crisis on nature and society today, we must be about winning a sustainable society for the future. We must face it with the "fierce urgency of tomorrow."

The Sixth Extinction: An Unnatural History by Elizabeth Kolbert. Henry Holt and Company, 2014, 336 pp (hardcover).