Climate Change Book Review

Peter D. Ward, Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us About Our Future (Smithsonian Books: Collins, 2007)

Ward is a paleontologist writing about his career in paleontology, with a focus on mass extinction events. The book features some of Ward's field expeditions and the debates among paleontogists on the causes of various extinctions.

Ward cites a 1997 study that of 14 recognized mass extinctions, 12 involved poor oxygenated oceans. Many of these mass extinctions were also associated with high levels of atmospheric carbon dioxide. Some of these extinctions were also associated with hydrogen sulphide production in the oceans. Ocean circulation models for the period suggest that conditions of those times may have caused a change in ocean circulation patterns. Putting these pieces together, Ward hypothesizes the following sequence of events:

1. High levels of carbon dioxide through natural processes lead to a warming of the atmosphere and oceans.
2. With warmer oceans, the ocean conveyor systems which move warm oxygenated water on the surface to the bottom layers, shifts position from the high latitude regions to the lower latitudes. Bottom waters become warm and without oxygen.
3. With continued warming, the difference in temperature between the poles and the equator reduce ocean winds and surfac currents.
4. The volume of warm but low oxygen waters in the ocean increases, eventually reaching the shallow areas accessible to light
5. In these waters, green sulphur producing bacteria expand and fill the shallow waters. They live among other bacteria producing hydrogen sulphide.
6. The hydrogen sulphide percolates into the atmosphere.
7. The gas rises to the high atmosphere, killing some living plants and causing the ozone layer to breakdown.
8. As a result, ultraviolet solar radiation kills much of the photoplankton.
9. Oxygen-based life on the land diminishes in the parched and polluted environment. Oxygen-based life in the sea has already disappeared. The disappearance of oxygen-based life on land and in the sea is the mass extinction.
10. The shallow oceans turn purple from a vast floating one hundred foot mat of green and purple bacteria that bubbles hydrogen sulphide into the atmosphere.
11. The sky is green, hence the title for his book.

Ward's look back in the history of Earth provides an important lesson in the potential consequences if humans insist on combusting all available fossil fuels.

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