Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us about Our Future by Peter D Ward, is a chronology of the paleontological research linking mass extinction events with prehistoric episodes of global warming caused by high atmospheric concentrations of carbon dioxide (CO2) and methane. Ward explores the likelihood that current, unprecedented increases in both greenhouse gasses will lead to a new mass extinction.
The dinosaurs were wiped out by a mass extinction 144 million years ago at the end of the Cretaceous era. Most evidence suggests it was triggered by a massive asteroid striking the Earth. This collision produced massive quantities of dust that blanketed the earth, significantly reducing the solar radiation reaching the surface of the Earth. This, in turn, led a planet with a universally tropical climate to experience a decade or more of freezing temperatures. Most of Earth’s plant species were killed off, along with the animal life that relied on them.
Accord to Ward, fossil evidence suggests that this K-T (Cretaceous-Tertiary) extinction was only one of multiple extinction events occurring when adverse living conditions developed that didn’t support complex plant and animal life. Fossil remains suggest that smaller extinction events occurred every 26 million years, triggered by massive increases in volcanic activity, leading to high atmospheric concentrations of CO2 and methane.
Under a Green Sky details Ward’s role in the excavations that support this conclusion, as well as the specific scientific methodology used to determine prehistoric CO2 levels; e.g., the size of plant soma1 and differential ratios of carbon and oxygen isotopes.2
The book concludes by outlining the mass extinction event Ward predicts for the 22nd century if we continue our reckless burn-off of fossil fuels. Based on past extinction events, this is the scenario he predicts:
1) A decrease in equator/polar temperature differences leads to total disruption of the thermohalene conveyer currents3 responsible for oxygenating the ocean depths. Cold oxygenated water is steadily replaced with warm oxygen-poor water.
2) Sulfur bacteria proliferate in the anoxic water (termed a Canfield Ocean) and release toxic hydrogen sulfide (the rotten egg smell associated with thermal hot springs).
3) Hydrogen sulfide rises into the upper atmosphere where it breaks down the ozone layer blocking ultraviolet radiation. A massive increase in UV radiation kills off the phytoplankton, the ultimate food source of all ocean swelling animals.
4) A combination of intense heat and toxic hydrogen sulfide kills off many land based higher plants and animals.
5) The ocean turns purple, due to green and purple sulfur bacteria. The sky turns green, owing to the proliferation of yellow dust from drought-stricken continents in the mid-latitudes.
Ward offers the following timeline for the coming mass extinction:
Antarctica’s ice sheet will have totally melted by 2200 and Greenland’s by 2300. By 2050, a steady rise in sea levels will have flooded all the world’s coastal cities and the deltas responsible for a significant proportion of global food production. Millions of people will die from famine (due to drastically reduced agricultural yields), extreme weather events and resource wars.
Human beings, however, will fare somewhat better than lower species, many of which will become extinct.
- The soma are tiny organs which enable plants to capture sunlight and combine CO2 and water to produce sugar. They become more numerous as atmospheric CO2 concentrations increase. [↩]
- Plant fossils contain varying concentrations of carbon-13 and carbon-14 isotopes and oxygen-16 and oxygen-18 isotopes (the number varies according to the number of neutrons in the atom’s nucleus) depending on the relative atmospheric concentration of CO2 and oxygen when the plant was alive. [↩]
- Thermohaline circulation is an ocean conveyor belt that moves a massive current of water around the globe, from northern oceans to southern oceans, and back again. See Ocean Conveyer Belt [↩]