Mass Extinction from Climate Change
Posted on June 13th, 2012
A “stable state” for our climate is one which remains constant, buffering various forces that would change it. As Goldilocks would have it, the earth’s climate seems to have three stable states: too hot, too cold, and just right. These states may be characterized as follows:
- Too hot. The earth as hot house can occur when a build-up of greenhouse gases occurs. Volcanism releases greenhouse gases and ash; the ash blocks the sun and the earth cools. With enough ash (volcanism lasting tens of thousands of years), global cooling can result, with the rapid formation of polar ice caps and glaciation. When the volcanism subsides, the aerosols settle, the sky becomes clear, and the greenhouse gases take over, rapidly melting the ice and flipping the earth toward hot house.
- Too cold. The earth as ice house occurs on its own, naturally, from a combination of causes. Variations in earth’s orbit can cause more or less heat to fall on the earth. If summers are cool enough that not all of the previous winter’s ice is melted, the planet may become cooler. When continents are located at a pole (as Antactica does today), or a polar sea is almost land-locked (as the Arctic Ocean is today), or the equator is covered by a supercontinent, the flow of warm water from the equator to the poles is blocked, helping polar ice to form.
- Technically, we are living in an “ice age” because extensive ice sheets may be found on earth (in Greenland and Antarctica). The last Glacial Maximum within this ice age took place about 18-20,000 years ago, when a mile-thick glacier stretched across North America. Albedo helped the ice stay cold, reflecting most of the sun’s heat back into space. The low temperature meant that there were few plants, and thus little carbon dioxide available to warm the earth.
- “Too cold” can come about too quickly: about 70,000 years ago, a supervolcano in Indonesia darkened the world’s sky with dust and sulfur, blocking out the sun and causing the world’s temperature to plunge.
- Just right. For the past 8,000 years, this world has had a climate much like that of today, one which favored abundant biodiversity and biomass. But this stable climate is possibly an anomaly in the history of the earth, which is prone to tipping into “too hot” or “too cold” for a prolonged period.
My paper on tipping points argues that one or more tipping points have now “tipped”, and we are uncontrollably, unpreventably, headed toward a world that is too hot.
If that is true, then what is next?
“Extinction” occurs when the last member of a species has died, or perhaps when the species has fallen on such dark times that it is no longer able to produce reproducing offspring.[1. Extinction http://en.wikipedia.org/wiki/Extinction] The average life-span of most species has been about 10 million years, and given the age of life on earth it is estimated that over 99.9% of all species that ever lived are extinct.[1. Extinction http://en.wikipedia.org/wiki/Extinction] A mass extinction is the sum of its parts: many species becoming extinct at the same time.
While extinctions occur “naturally”, our world today can no longer claim to be natural. Humans can cause extinction of a species through overharvesting, pollution, habitat destruction, habitat fragmentation, introduction of new predators and food competitors, overhunting, and other influences.[1. Extinction http://en.wikipedia.org/wiki/Extinction] Explosive, unsustainable human population growth is an essential cause of the extinction crisis.
Current extinction rates are 1,000 times higher than natural rates found in the fossil record.[2. Sebastien Berger. Earth ‘heading towards another mass extinction’ http://www.telegraph.co.uk/education/3347270/Earth-heading-towards-another-mass-extinction.html; Andrew Hough. World’s nature ‘becoming extinct at fastest rate on record’, conservationists warn. http://www.telegraph.co.uk/earth/earthnews/7397420/Worlds-nature-becoming-extinct-at-fastest-rate-on-record-conservationists-warn.http://www.well.com/user/davidu/extinction.html]
We are surely living in the middle of a mass extinction. Our “conversion” of forests to farms and pastures has been rapid. Since 2000, nearly 15 million acres of primary forest have been lost every year. Beachfront living and vacationing has meant that in the Caribbean, average hard coral cover declined from 50% to 10% in the last three decades. 35% of mangroves have been lost in the last two decades.[2. Convention on Biological Diversity. Second Global Biodiversity Outlook http://www.cbd.int/gbo2/] Some scientists, such as Wilson and Leakey, estimate that up to half of presently existing species may become extinct by 2100[1. Wilson, E.O., The Future of Life (2002) (ISBN 0-679-76811-4). See also: Leakey, Richard, The Sixth Extinction : Patterns of Life and the Future of Humankind, ISBN 0-385-46809-1].
Ours is not the first mass extinction on earth. Each geological period has ended with extinctions[3. Wikipedia. Geologic time scale. http://en.wikipedia.org/wiki/Geologic_time_scale]. In the past 540 million years there have been five major events when over 50% of animal species died.[4. Wikipedia. Extinction Event. http://en.wikipedia.org/wiki/Extinction_event]
These extinctions appear to have a variety of causes, including volcanism, falling sea-level, impacts of asteroids or comets, sustained and significant global cooling or warming, etc. Exactly what happens in a mass extinction depends a bit on the triggers.
- For an extinction caused by plume tectonics (a giant pulse of heat rising toward the surface of the planet as a plume), the effect would be sudden cooling as the sky darkened with volcanic ash. “Even a short-lived catastrophe among land plants and surface plankton at sea would drastically affect normal food chains. Large animals would have been vulnerable to food shortage, and their extinction after a catastrophe seems plausible. In the oceans, invertebrates living in shallow water would have suffered greatly from cold or frost, or perhaps from CO2-induced heating. High-latitude faunas and floras in particular were already adapted to winter darkness, though perhaps not to extreme cold. Thus, tropical reef communities could have been devastated, but high-latitude communities could have survived much better. [1. Cowen, Richard. The Permo-Triassic (P-T) Extinction. March, 2002. Online]
- A mass extinction caused by bolide impact would be similar: a cloud of dust would darken the sky, and until it cleared, photosynthesis would stop. Death would roll up the food chain: plants and phytoplankton, herbivores, carnivores.
Warming may have caused the mass extinctions at the end of the Triassic and the Permian periods.[5.Knoll, A. H.; Bambach, Canfield, Grotzinger (26 July 1996). “Fossil record supports evidence of impending mass extinction”. Science 273 (5274): 452–457. Bibcode 1996Sci…273..452K. DOI:10.1126/science.273.5274.452. PMID 8662528. Ward, Peter D.; Jennifer Botha, Roger Buick, Michiel O. De Kock, Douglas H. Erwin, Geoffrey H. Garrison, Joseph L. Kirschvink, Roger Smith (4 February 2005). “Abrupt and Gradual Extinction Among Late Permian Land Vertebrates in the Karoo Basin, South Africa”. Science 307 (5710): 709–714. Bibcode 2005Sci…307..709W. DOI:10.1126/science.1107068. PMID 15661973. Kiehl, Jeffrey T.; Christine A. Shields (September 2005). “Climate simulation of the latest Permian: Implications for mass extinction”. Geology 33 (9): 757–760. Bibcode 2005Geo….33..757K. DOI:10.1130/G21654.1.]
Climate Change as Contributor to this Mass Extinction
Of the various ways that humans contribute to Mother Nature’s demise, climate change may prove to be the most severe and irreversible. Our planet may have been on its leisurely way toward another ice age when man’s agricultural age began 8,000 years ago. Such a prediction comes from an understanding that the earth’s orbit around the sun changes at regular intervals — Milankovitch cycles — and that these changes impact the intensity of the sun on the earth, in turn impacting plant growth, CO2 production, and the greenhouse effect. So if the earth was moving toward an ice age when our species came along, we’ve have certainly reversed that trend — at least temporarily. But the stored carbon is finite, and sometime not too long from now, we will run out of oil, out of coal, and out of wood. When we are out of wood, the current mass extinction will already be quite advanced.
Some computer models predict that human-generated greenhouse gases will heat the earth, postponing the next glaciation by as much as 50,000 years. Other computer models predict that such warming will, paradoxically, trigger global cooling and increased glaciation. I think it likely that we are in store for both heating and cooling, in that order. But I don’t think any of us will live to see the cooling. Here’s what is most likely:
- As we release greenhouse gases, the arctic will warm, and the polar ice will melt. This fresh water will block the flow of the Gulf Stream, eventually causing it to come to a stop.
- Once the ocean conveyer belt has come to a halt, the impacts on land will vary. The rainforest, western U.S., and Mediterranean will begin to dry, and be consumed by forest fires, releasing vast amounts of CO2 — These areas will become uninhabitable. The British Isles will lose the moderation of weather that the ocean conveyer delivered, and suffer hot summers and cold winters. Throughout the east coast of the U.S., weather patterns will stall for longer periods, bringing alternations from flood to drought.
- The new warmth in the arctic will melt the permafrost, releasing huge amounts of CO2 and methane.
- The release of CO2 and methane from forest fires, burning peat swamps in Indonesia, and melting permafrost will act as a positive feedback loop, producing runaway warming.
- Throughout the world, storms will become unimaginably intense.
- With all ice melted, our oceans will rise, drowning all coastal cities. Low-lying areas like Bangladesh and Holland and Florida will be gone.
- Our oceans will become far too acidic for corals or phytoplankton, and the bottom of the ocean’s food chain will be gone.
- Almost equally quickly, our oceans will become anoxic, and nearly all life in them will die.
- On the land, the heat and fires will reduce most areas to a look now found in parts of central Australia: near lifeless desert.
- Unknown, but likely, are three final blows:
- stored methane in the oceans will be released in giant bubbles, increasing the greenhouse effect.
- Sulfur-based bacteria, that don’t need oxygen, will begin to rule the seas, producing upwellings of poisonous hydrogen sulfide, killing everything in their path, and serving as still another greenhouse gas.
- The hydrogen sulfide will destroy the ozone layer. Without an ozone layer, only those animals that live in burrows and are active at night will have a chance to survive mutations triggered by the ultraviolet penetrating the atmosphere. As in parts of central Australia, our new life may be rats, snakes, and flies.
- Eventually, most of the stored carbon on earth will have been released as CO2, and no further warming will occur. The planet will be stable — and remarkably unpleasant — for many million years, until the natural effects of the earth’s wobbly orbit finally begin to create seasons again.
Of course, there will be smaller scale events along the way. The polar bears will die. The penguins will die. The sea birds will die. But there will be some more unpleasantness involving humans:
- In less than 50 years, Pakistan will have a doubled population and no water. The glaciers that feed the Indus River will be gone, the Indus will be dry, and Pakistanis will look to India for water. This will not be a comfortable situation for either nuclear power.
- The water tables in the Middle East will have dropped too far to be usable, and water will come only from expensive desalinization processes. Agriculture will nearly cease, and populations will be on the move.
- In 100 years, much of the populations of Florida and the U.S. west of the Mississippi will have moved to the east, to avoid the fires and flooding. In the east, population will far outstrip the water supply, and rivers like the Potomac and Hudson won’t reach the sea.
Many forces may be conspiring behind the mass extinction that may have begun a decade or more ago, but the human role in climate change may prove to be the most robust, the most inexorable. The future is certain: it will not be pleasant for most species, including our own.