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There have been five great extinctions in our planet’s history. We are causing the sixth one.
I wanted to get some context before reading Elizabeth Kolbert’s book The Sixth Extinction and turned to Peter D. Ward’s Under a Green Sky for the historical context of previous extinction events. It was quite an interesting What-Did-It that covers what we know about the past extinction events and how scientists gathered evidence of their causes. It was written in 2006 and as such doesn’t include many of the Greenland and Antarctic science that has scientists even more alarmed.
Much of the early science weighed toward asteroids slamming into the earth, which in turn obscured the sun, killed plants and then the dinosaurs. With thorough examination of the geological fossil record in places across the globe where the extinction boundary is accessible, the state of our known science has evolved.
It turns out only one of the great five extinction events involved a 6-mile wide asteroid impact; the K-T impact that cause the Cretaceous-Tertiary mass extinction event 65 million years ago.
The rest were caused by massive volcanism events altering the composition of our atmosphere with massive influxes of carbon dioxide.
The extinction process starts with a sudden increase of carbon dioxide and methane. In the case of past extinction events this comes from the formation of vast volcanic provinces called flood basalts. Our current extinction era is driven by industrialization, fossil fuels, industrial farming practices and deforestation.
The warming world causes glacial meltwater runoff that affects the ocean circulation systems and disturbs the position of the global ocean conveyor currents.
Bottom waters begin to have warm, low-oxygen water dumped into them.
As the continued warming reduces the difference in equator-to-pole temperatures, this brings ocean winds and surface currents to a near standstill.
The mixing of oxygenated surface waters with the low-oxygen bottom waters decreases, which causes ever more shallow water to change from oxygenated to anoxic.
The shallow low oxygen surface waters and light produces a prime environment for green sulfur bacteria to bloom amid other bacteria to produce toxic amounts of hydrogen sulfide.
The flux of hydrogen sulfide into our atmosphere increases 2,000-fold and breaks down the ozone layer which kills much of the photosynthetic green plant phytoplankton.
On its way up into the sky the hydrogen sulfide and high heat kills plant and animal life to continue the mass extinction event on land.
So are global warming changes to the ocean conveyer visible in our current warming planet? In 2006 a paper in Nature reported just that.
Alarmingly these extinction events are now happening in our own world. In 2005 in the Arctic, John Raven from the University of Dundee in Scotland discovered that pteropods, a type of mollusks that are important to the food chain are going extinct as their shells dissolve of their backs in increasingly acidic waters.
By 2050 it is estimated that over that over 1 million species will be extinct or on the route to extinction from climate change. This level of extinction is second only to the Permian extinction event.
In island nations like Vanuatu and Fiji, where temperatures continually hover near 100 degrees F, the citizens use drugs like khat to cope with extreme heat. Intellectual development takes sweater weather as our brain does not do well under continuous heat. Intellectual insights, Nobel Prizes and contributions from the tropics are few and far between.
The stress of feeding 7 billion people means that neither hemisphere cannot have widespread crop failure for even one year without consequences of famine. We have seen this already in the Arab Spring as countries are destabilized over lack of food. This will be challenged as global warming continues and arable land turns to desert. As the tropics spread towards the poles diseases like malaria will follow.
As our planet continues to heat, migration, starvation and war will become commonplace as the communal order of our civilization breaks down.
Can we avoid our own extinction? In 2000 the level of carbon dioxide was 370 parts per million. Last year we passed 400 parts per million, which gives us roughly a two parts per million per year increase of carbon dioxide. A 2006 article from Meinshausen, Knutti and Frame point to the need to peak somewhere between 450 and 475 parts per million and level back off at 400 parts per million to avoid the 2 degree Celsius danger point. Above 2 degrees we are in danger of turning off our ocean conveyors and lurching through the mass extinction process listed above.
This gives us conservatively 25 years or so to wean ourselves from fossil fuels, change our farming practices to burn carbon and work together to build a low-carbon society. Our future depends on it.
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