Did the Climate do it?

kw: book reviews, nonfiction, extinction, polemics

We've gone from "All mass extinctions are gradual, with many causes" to "All are asteroidal and sudden" to "Maybe some were volcanic (e.g. the Siberian Flood Basalts)", and now to "All but K-T (which we now know was an asteroid) were greenhouse-induced anoxic-ocean transitions".

Peter D. Ward is making his name as a contrarian. He first came to my attention when he and Donald Brownlee published Rare Earth several years ago. I have also read a number of his articles in both scientific and popular organs. In Rare Earth the authors contend that, while microbial life might be common in the Universe, multicellular life, such as the familiar plants and animals we typically mean when we say "life", may be exceedingly rare. In an article in Scientific American a couple years later, they argued that most of the Galaxy (Milky Way) is inimical to life of any kind, and that only a narrow zone, in which our solar system resides, can have life of any kind. I tend to believe that life in high-metal zones of the Galaxy will be more tolerant of "heavy metal toxicity" than we are, and the converse.

In part I agree with the Rare Earth arguments, though one part of the scenario had a big lack. They state that it was primarily a gradually descending CO₂ content in the atmosphere that allowed Earth to remain "friendly" as the sun gradually warmed, by as much as 30% over 4 billion years. I wrote them pointing out that radiogenic heating of Earth was six to seven times as large 4 billion years ago, primarily due to K-40 decay (its half life is about 1.3 billion years; U and Th have much longer half lives). I didn't get a reply. However, my point is relatively minor. I like Dr. Ward's writing, and he brings up issues about which we must think deeply.

In his new book Under a Green Sky: GLOBAL WARMING, the Mass Extinctions of the Past and What They Tell Us About Our Future (emphasis author's), Dr. Ward examines the evidence for mass extinctions, and draws conclusions stated in the title, and in my last blurb above. I could say, one point is that extinctions are typically a series of pulses, what one could call "punctuated equilibrium" if S.J. Gould had not already appropriated the term.

The basic scenario is this: We live with much lower CO₂ than has been usual in the past. Just since the Cambrian, it has been as high as 6,000 ppm (today it is 370 ppm or parts per million). Even during the Ice Ages, it was seldom as low as this. In fact, the longest spell of 400 ppm or less was a 70-million-year period just prior to the great Permian extinction, 251 million years ago. Geologic evidence shows it as a period of ice ages more severe than the more recent ones we're in the midst of. Just prior to that big extinction, CO₂ climbed to 3,000 ppm, probably due to the enormous volcanism going on in Siberia.

OK, so the CO₂ causes warming, which eventually leads to an Earth that is tropical from pole to pole. Reduced contrast between equator and poles leads to reduced storminess except right in the "tropics" (Equator plus and minus 20 degrees). The mixing of the oceans grinds to a halt, O₂-poor water gathers in the deep, then O₂-free water, and most oceanic life vanishes. Bacteria that produce H₂S proliferate, and the gas poisons much life on land. The sky gets greenish (hence the book's title).

The CO₂ doesn't drop until reactions of carbonic acids with rocks begins to deplete it. In the meantime, remaining living creatures are adapting to the new chemistry and begin to use larger amounts of CO₂, and together these eventually cool things down. Oceanic mixing is restored, and thing rock on for another few million or tens of millions of years.

A careful look at the rocks around the ten or so biggest extinctions shows that they tend to occur in pulses (the K-T one excepted) over a few hundred thousand years to a few million. Thus my "punctuated equilibrium" comment above. Also, I am convinced that the proposed mechanism is plausible for a number of the mass extinctions, though not for all.

The author's conclusion is that people are raising CO₂ to the point that endangers the system of ocean mixing. Should things get to that point, we could see a huge extinction, and a great reduction (probably not elimination) of human numbers.

Throughout the book, Dr. Ward uses the term "global warming" for the phenomena caused by elevated CO₂ and other greenhouse gases, mainly methane. While this is scientifically appropriate, in today's political climate it is a loaded term, with the connotation of "human-caused climatic warming". This reveals the polemical intent throughout, and the concluding chapter makes it clear. Dr. Ward thinks we will probably rock right along until it is too late, and that our descendants are in for a really bad century or five...or more.

He may be right. Remember Rachel Carson, and Silent Spring? As it turned out, she may not have been totally right, but she was "right enough" that it soon became apparent her warning was justified, and governments reacted, banning DDT in most places. (Though in the tropics we need more DDT to combat malaria, which is a much greater danger).

Dr. Ward is the first to make this warning this strongly and this convincingly in a public forum. Will we react to his warning?