Green sky at morning, humans take warning
01/12/2007 . Source: Mark R. Leeper 
When Mark was a teenager he read science fiction with its stories like When Worlds Collide. In those days it was not quite respectable to read science fiction. But he thought we really did live in a world where some of these things really could happen and by the time he became an adult some of this science fiction would have become reality and science fiction would be more respectable. Perhaps both have happened but they are not as tightly bound together as he would have thought. Nobody respects the old science fiction because of its accuracy. Nobody has come back to me to say I was right about that science fiction. Yes, we now accept that when worlds collide it is really, really bad. And it maybe can happen. In fact, when a world collides with a piece of stone very much smaller than another world would be, that can still be a catastrophe. In fact, it can be an extinction level event.
The real monsters of the past were not the dinosaurs. The dinosaurs were small and puny. The real monsters of the past were the great extinctions. And the great extinctions are not dead. They still hang over us.
With celestial collisions we might be headed for an extinction level event, but the smart money doesn't bet that way. There are two reasons for this. One is that the smart money knows that if there is an extinction level event it won't be around to collect. That observation is not very comforting. What is a little more comforting is that celestial collisions are random events that are no more likely to occur now than they were a millennium ago. And we got through the last millennium all right. But there are other extinction events that do not need a collision to create. With these smaller changes in the environment can lead non- linearly to very big watersheds that can cause extinction. If we are going to live to see a major extinction happen--and we will only see the early parts--it will be this sort of extinction we will see.
The great extinctions of the past are the subject of Under A Green Sky by Peter D. Ward. Ward is primarily a professor of biology and earth and space sciences at the University of Washington in Seattle. The subject that fascinates Ward is the great extinctions of the past. He has specialized in the Cretaceous-Tertiary extinction event--the one that supposedly killed off the dinosaurs. And much of his book is about his work there. As interesting at that part is, it is really just a long prologue to the important parts of his book.
His real subject is the Permian-Triassic extinction event 251 million years ago. In this event 96% of all known marine species died off. The surface had it slightly better with only 70% of all vertebrate species going extinct. And there is no evidence that this, the greatest of the extinction, was caused by a meteor impact. In fact, Ward finds chemical evidence that what killed so many species off (and turned the sky a light shade of green) was a super-abundance of hydrogen sulfide gas.
What causes so much hydrogen sulfide gas to be created? Well, the fossil record says that it was anoxic bacteria in deep water. These are bacteria that, as the name implies, do not need oxygen. They grow when there is less oxygen in the deep oceans, beating out the oxygen-needing bacteria. They get their energy converting sulfur to hydrogen sulfide. It is produced on the ocean floor and rises to the surface in huge, foul-smelling, poisonous bubbles of yellow gas. This was what Ward thinks caused the great extinction at the end of the Permian Age.
Why is there less oxygen in the deep oceans? Where do the deep oceans get their oxygen? Well, the waters of the ocean flow in a cycle powered by the heat of the sun. What is deep water in the more temperate regions is really toward the top in arctic regions and that is where it gets oxygenated. Life on Earth is very dependent on that cycle. Interrupting that cycle probably does not cause the quick freeze that the film The Day After Tomorrow suggested. (No, we are not just talking about the Permian- Triassic extinction here.) It takes longer than a few days and the results are not as optimistic (?) as that film painted them. But the film did get one thing right. Global warming for carbon dioxide in the atmosphere definitely has a big impact on that cycle of water and can easily redirect it.
Let us get down to some numbers. The change is not linearly proportional to the amount of carbon dioxide in the air. You hit a point where the flow is disrupted and the deep ocean gets most of its water from someplace else where there is less oxygenation. It is a watershed event--no pun intended. You reach a point where change starts coming very quickly.
Carbon dioxide content is measured in PPM (or parts per million). Ward believes that a watershed point is estimated at 450 PPM. That is when you start seeing really major changes in the environment. OK it is not that simple, but that is where Ward concludes the effect really starts kicking in. Right now the level is at 360 PPM. That means we have a margin of 90 PPM. That does not mean we will not have other very bad things happening at even these levels. It is suggesting that redirecting the cycle of water will not happen to a great degree until that point.
The watershed point does seem to depend on other factors also. There have been times in our planet's past when carbon dioxide was much higher without causing an extinction, but the mass extinctions that do not involve impacts have occurred at times of accelerated growth of carbon dioxide in the atmosphere. The source could be volcanic. That level of 450 PPM is not the absolute level or even the rate of growth, but they seem to be correlated to times that the rate of increase is itself increasing.
As the world industrializes and automobilizes and who knows what else-izes, the carbon dioxide levels rise about 2 PPM each year. But the industrialization is increasing as places like India and particularly China get into the act, it is expected to rise about 4 PPM per year. Remember we have a margin between us and the cliff of maybe 90 PPM and we lose from that margin maybe 2 PPM a year. It probably will not hit the environment like the hydrogen sulfide extinction. That may be up around 1000 PPM, but 450 is enough to make major changes in the balance of bacteria on the ocean floor. This is a much more immediate threat than a celestial collision.
Ward's book goes into possible alternate futures where it is different levels. I will not go into that here. Right now these predictions may seem a little science fictional. That is mostly because they are quite frightening. But we are doing little but some international wrangling as to who should be cutting back. That is only natural because nobody wants to be the one to make the sacrifice. Unfortunately, doing the natural may no longer be working in unnatural times.
There is an exchange from my favourite science fiction film, Quatermass And The Pit:
Professor Bernard Quatermass: The will to survive is an odd phenomenon. Roney, if we found out our own world was doomed, say by climatic changes, what would we do about it?
Dr. Mathew Roney: Nothing, just go on squabbling like usual.
That may be the most prophetic observation of all.
Mark R. Leeper
Copyright 2007 Mark R. Leeper |
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