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In 1844, the last remaining living pair of great auks – the "penguins of the north", as they have been called – were killed by three local fishermen on the small skerry Eldey, off the coast of Iceland. The skins were sold to collectors. Some two hundred years earlier, no one could have foreseen their extinction. In fact, the very existence of the extinction of species was heavily debated at the time. Great auks lived in colonies tens of thousands strong, scattered around remote islands in the north Atlantic. Whenever a boat-crew needed to stock up with some fresh meat, they anchored off one such island and simply caught and boiled hundreds of auks. Since all such islands were treeless, they even fueled the fires beneath the pots with the fatty birds themselves. The stench must have been awful.
Extinctions are quick events. The death of the last individual in a species can pass in half a minute – it's the prior death of all its conspecifics that takes time. Seen with an evolutionary perspective, extinctions tend to be fairly undramatic events, threatening only a small proportion of the species in existence at any one point in time. But there have been five remarkable exceptions: mass extinctions. It's as if long periods of ennui are occasionally interrupted by extreme panic. During these terrible periods, whole groups of once-dominant organisms can disappear or be relegated to secondary roles. Evolution lacking foresight of course, there is limited scope for organisms to guard themselves against such times, to preadapt. Mass extinctions strike hard and seemingly random.
But in a stroke of irony of global proportions, the relatively recent human discovery of mass extinctions in the history of life on earth coincides with what seems to be becoming the sixth mass extinction. And this time the blame is not on some hard-hitting heavyweight comet, giant volcanic eruption or unhappy configurations of continents. This time the blame is on us. Oh, the humanity. In her book The Sixth Extinction (Henry Holt, 2014), Elizabeth Kolbert reports from the front line of extinction on our planet, giving an account as personal and readable as it is scientifically correct and thoroughly documented.
This is not the first time Elizabeth Kolbert writes about big problems. In her 2006 book Field Notes from a Catastrophe, she reported on the cause and effect of climate change from various locations around the world. Her long experience of science journalism is evident in her punchy prose. As she puts it, "the notion that a sixth such event [mass extinction] would be taking place right now, more or less in front of our eyes, struck me as, to use the technical term, mind-boggling".
Facing reality can be hard. We humans tend to build a mental block against catastrophes.But major changes to the world's fauna are happening more or less under our noses right now. Here's one local example of a global problem concerning one of our few great groups of backboned animals. In a village in Peru, local people started asking visiting researchers in the nineties about what had happened to all their frogs. They could hardly fail to notice the great concert that the frogs used to give during their mating season. But they don't hear it anymore.
The seminal paper, "Are We in the Midst of the Sixth Mass Extinction? A View from the World of Amphibians" by Wake and Vredenburg did receive a lot of attention in the scientific world when it was published in 2008, and it's easy to understand why. Amphibians are among the planet's great survivors. Their first ancestors crawled out of the water 400 million years ago and the earliest representatives of amphibians as we know them today emerged some 250 million years ago – before mammals even existed. Their disappearance would be, to put it mildly, an event of historic magnitude. At this very moment more than one-third of the 6,300 known species of amphibians are threatened with extinction. Disease, pollution, introduced predators and habitat destruction seems to be the major causes for this drastic decline.
But are we humans always to blame when species go extinct? Concerning the extincion of the mammoth, the mastodont and other so-called mega-fauna of the ice-age, debate among scientists is ongoing. Kolbert, not unexpectedly, argues for humans as the ultimate cause of the extinction of the megafauna. Two Swedish researchers, Love Dahlén and Lars Werner at the Museum of Natural History in Stockholm would argue otherwise, but the co-occurrence of a massive die-off and the introduction of our own species is compelling evidence. Still, as scientists always say, correlation does not equal causation. I guess this debate might still roam back-and-forth for some time.
There is no single cause or mechanism explaining all the mass extinctions in the record, but changes in ocean chemistry seems to be a good predictor. If so, we're in trouble. The amount of carbon dioxide and other greenhouse gases present in the atmosphere today is, in fact, not extraordinary from a historical perspective. It is the speed at which it is released that is important. We humans are on the way to cause a cataclysmic event in the history of our planet. The coming centuries may see more ocean acidification than the past 300 million years.
It's hard to comprehend, and easy to stop easyreading about all the disasters that we seem to be piling up for the future. But Elizabeth Kolbert managed to keep me reading her book. She spiced more analytical scientific reportage with first-hand reports from all over the world in a way that gripped my attention, even when it was over thirty degrees outside and the biggest wild-fire in swedish history was turning trees to ash just a hundred kilometers away. That's good science writing!