Under a Green Sky

Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us about Our Future

How’s this for a writer’s motivation? “I am as scared as hell, and I am not going to be silent anymore!…Thus this book, words tumbling out powered by rage and sorrow but mostly fear, not for us but for our children – and theirs.” The book is Under a Green Sky: Global Warming, the Mass Extinctions of the Past and What They Can Tell Us About our Future, first published  in 2007 with a paperback version in 2008.  The scared as hell author is Peter D. Ward, a paleontologist and and professor of Biology and of Earth and Space Sciences at the University of Washington, Seattle.

The book certainly shows why the author has reason to be scared, but he lets us know gently, with a mixture of patient explanation and lively narrative.  He has worked at many interesting sites and he knows how to bring his visits back to life for the reader, whether gently chipping at cliffs on a heavily populated French beach or spending a week of 18-hour days in unceasing rain with a small group of colleagues on a remote Queen Charlotte Islands beach and running out of food the day before weather permitted the helicopter to return.

Mass extinctions in the past are his focus.  His work helped to confirm the 1980 hypotheses of the Alvarez team that the extinction which saw the end of the dinosaurs some 65 million years ago was catastrophic and caused by an asteroid striking the earth.

There have been other sometimes greater extinction events in the past, especially the “Great Dying” at the end of the Permian period some 250 million years ago.  Were they too the result of asteroid impact?  If it could happen once, why not other times as well? Ward explains the investigations that lead to the conclusion that only the one extinction  was the result of impact.  The rest were different.

He takes the reader carefully through the discoveries which point to the proposal that they were greenhouse extinctions, the result of complex processes which began with releases of carbon dioxide and methane (sophisticated estimates of past carbon dioxide levels show sharp increases at the time of each extinction), caused initially by volcanic activity on a large scale. This meant a warmer world which affected the ocean circulation systems and disrupted the conveyor currents. The oceans were a key factor. Bottom waters started to have warm, low-oxygen water dumped into them, ocean winds and surface currents came to a near standstill so that there was less mixing of oxygenated surface water with the deeper waters and, gradually, ever-shallower water changed from oxygenated to anoxic.  When it moved high enough for light to penetrate, green sulphur bacteria expanded in numbers and filled the low-oxygen shallows.  Accompanying them were other bacteria which produced toxic amounts of hydrogen sulphide which rose into the atmosphere.  There it broke down the ozone layer and the subsequent increase in ultraviolet radiation killed much of the green plant phytoplankton.  As the hydrogen sulphide moved up into the sky it also killed some plant and animal life and its combination with high heat increased its toxicity.

This summary conclusion is supported by a wealth of careful detail.  Like most climate history it is based on a great variety of evidence from people working in many fields of study.  Much of the work and hypothesising is quite recent, and will no doubt be put to much examination  before it can be regarded as established.  In the meantime it’s a fascinating read, fully accessible to the non-scientist. (It helps to have a chart of the geological periods alongside though if, like me, you’re a bit hazy about them.)

But the book doesn’t finish there.  Ward is all too aware that we also are living in a time of rapidly rising carbon dioxide levels – not from volcanic sources this time but from burning fossil fuels.  The question he addresses is whether the rate of increase today is on a par with the rate during those times when greenhouse extinctions occurred. He concludes that the present rise seems to eclipse any other rate of increase in the past. Oceanic acidification is an indication of this, since the natural buffering systems need time to strip the carbon dioxide out of the water. We are “hurtling towards carbon dioxide levels not seen since the Eocene epoch of 60 million years ago, which, important enough, occurred right after a greenhouse extinction.”

Would it matter if human civilisation was transported to the Eocene world?  New Caledonia everyone?  Any apparent attractions are rapidly punctured.  He instances the harshness of tropical life, the catastrophe of sea level rise, high mortality rates, widespread infectious diseases, famine and war.

If we can sharply curtail emissions in the 21st century we have a chance of getting carbon dioxide levels down to 400 ppm, even if we overshoot it briefly, and hence have some chance of limiting temperature rise to 2 degrees.  If not we are heading for an ice-free world, a change in the thermohaline conveyor belt currents and a new greenhouse extinction. “The past tells us that this is so.”

Towards the end of the book he records a memorable interview with David Battisti of the University of Washington, a notable climate scientist, one of whose lectures stimulated Ward to write this book. He asks Battisti to describe verbally the world we are headed for on our current trajectory. It’s a very different world and it’s not nice, though Battisti still hopes that under the pressures of climate change we will put into place a political structure able to implement the global regulations and incentives that might rescue us.

Ward concludes with three possible scenarios based on what he has written in his book and the “massive scientific literature” dealing with global warming and climate change.  The first is the only one I can bear to contemplate.  It’s bad enough, but the sea level will have risen by ‘only’ a metre, the conveyor belt current system will not have stopped, the ocean will stay mixed.

The political solution is out of the hands of the scientists.  But the policy makers can’t say they aren’t being warned. “This book is my scream”, Ward writes. It’s a very civilised scream, like that of many other scientists, but we must hope like hell enough politicians have ears to hear it.