Under a Green Sky

by Peter D. Ward

I bought this book because I had read that it predicts that anthropogenic climate change (ACC – what most people call “global warming”) will trigger a mass extinction. The book starts off with an explanation of mass extinctions and the history of paleontologists’ understanding of their causes. Up until 1980 the common view was that these were things that just kinda happened. Then Luis and Walter Alvarez came up with the hypothesis that the KT extinction (the one that killed the dinosaurs) was caused by the impact of a 10-mile meteor. The evidence in support of the hypothesis came pouring in, Alvarez got the Nobel Prize, and pretty soon everybody was assuming that each of the five known mass extinction events was caused by a big meteor impact.

But then other people started coming up with research results that contradicted the application of the impact hypothesis to other mass extinctions, especially the mother of all mass extinctions at the end of the Permian 250 million years ago. So everybody was confused. But they are now piecing together some hypotheses that better fit the data. Mr. Ward suggests that a major factor in those other extinctions was abrupt climate change. There may well have been other factors, such as the eruptions of the Siberian Traps (a huge series of lava flows that covered an immense area and released enormous amounts of carbon dioxide into the atmosphere). But Mr. Ward points out that these other events may have been the triggers for runaway climate change. We know that there are some strong positive feedback mechanisms in climate change. For example, as temperatures rise, sea ice melts. Sea ice reflects sunlight, which cools the earth; water absorbs sunlight, which warms the earth. So, if the temperature starts rising, the melting of sea ice accelerates the process. So too does permafrost melting. There are stupendous amounts of methane trapped in the permafrosts of the extreme north. If the permafrost starts to melt, than methane is released into the atmosphere. Methane is a powerful greenhouse gas. Fortunately, it decays after a decade or so. Unfortunately, it decays into carbon dioxide.

There are some other positive feedbacks, all of which suggest that the earth’s climate is unstable, bouncing between extremes. One extreme is what we had during the Ice Ages, when ice covered much of the Northern Hemisphere down to about 50º latitude. The other extreme is the tropical earth, when there were no polar caps, sea level was about 200 feet higher than today, and the entire earth was hot and humid, covered with jungle.

Mr. Ward also points out that the circulation of the oceans is fundamental to the climate, and the current circulation system is vulnerable to a rapid shift due to the generation of large amounts of fresh water in the Arctic from the melting of ice. That fresh water changes the vertical motions of the circulation pattern, forcing a shift. Such a shift would surely change global climate.

I think that Mr. Ward pulled his punch at the end of the book. He had spent most of the book marshaling evidence to show that climate change is a major factor in past mass extinctions, but he stops short of predicting such a mass extinction due to ACC. I can’t understand why he stopped short of the obvious conclusion of his book.

Stylistically, I have mixed feelings about the book. Each chapter starts with a few pages describing some field experience he had while looking for fossils all over the world. It adds a human touch but I’m not sure that it helps the book; the field experiences are mostly irrelevant to the book’s thesis.

What I definitely didn’t like was the overblown prose. Here’s a sample:

“We rocket out of the parking lot, screaming through Reno on the freeway east, passing quickly into the empty rat lands of the sorely missed Hunter S. Thompson, tripping out at the absolute ugliness of a landscape repellant to begin with that has had twisted, rusting metal hulks of unknown ancestry sprinkled among the itinerant whorehouses and casinos in a random pattern across its waterless salt flats and outcrops.”

This becomes tiresome; happily, the author seems to back off from such prose as the book proceeds.

All in all, I can’t quite recommend the book. It’s good, and I suppose somebody genuinely interested in mass extinctions might enjoy it, but I’ve read better books on mass extinctions – which I can’t recall just now. Sorry.