Friday, April 11, 2008
Prehistoric Global Warming
I haven't read this book yet, but it sounds quite plausible... and very frightening. Here's a review from Amazon.com
Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell us About Our Future
"Mass extinctions periodically reshape life on Earth. The best known, the Cretaceous - Tertiary (K-T) boundary, ended the reign of the non-avian dinosaurs approximately 65 MYA when an asteroid roughly 10 kilometers wide gouged the Chicxulub crater near the Yucatan Peninsula, setting the stage for mammals, including Homo sapiens, to become the dominant terrestrial vertebrates.
Another extinction event, the Permian - Triassic (P-Tr), some 251 MYA, is informally known as 'the Great Dying.' Up to 96 percent of all marine species and 70 percent of terrestrial species were erased as global ecosystems crumbled. Life itself nearly died - and Peter Ward makes a compelling case in "Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us About Our Future" that global warming was the primary culprit.
The occurrence of mass extinction events is not open to debate - the data is in the strata - available to any researcher diligent enough to decode the physical evidence. Unlike some global warming books "Under a Green Sky" carefully examines the fossil and climate record to justify models and simulations designed to predict future events. Ward, a paleontology professor at the University of Washington, and a NASA staff astrobiologist, invokes runaway global warming as the primary driver of the P-Tr extinction - and convincingly demonstrates that an anthropogenic (human-caused) encore is the obscene outcome of business as usual energy policies.
"Under a Green Sky" recounts how scientists examine mass extinctions and determine plausible causes based on paleontological and geological evidence. After the K-T event was convincingly attributed to an asteroid strike, extraterrestrial (ET) impacts because the default explanation for other mass extinctions. Ward avoided the ET impact bandwagon and pursued a more nuanced approach by examining the fossil record in painstaking detail to determine if extinctions happened slowly, in phases, or all at once - only the last option favors an impact hypothesis.
If the pace of extinction rules out an impact event, what other agent could kill so indiscriminately across land and sea on a global scale? Scientists can measure past atmospheric concentrations of greenhouse gases such as carbon dioxide or methane by analyzing isotope ratios in rocks and counting stomata, the microscopic pores found on the under side of leaves. Both methods show that a major greenhouse episode took place at the end of the Permian and continued into the early Triassic. On land Therapsids (mammal-like reptiles) made way for the dinosaurs - a topic covered in Ward and Ehlert's superb Out of Thin Air: Dinosaurs, Birds, And Earth's Ancient Atmosphere.
Life's nemesis was ultimately found on the P-Tr ocean floor. ET impact events like the K-T extinction kill ocean life from the surface down - and most losses take place in the upper half of the ocean. Surprisingly, to impact partisans, the P-Tr killer struck first in the ocean depths and moved upward. Dark bands in P-Tr strata signal the presence of anoxic (without-oxygen) archaea and bacteria - potent producers of greenhouse accelerating methane or deadly hydrogen sulfide gas. How did these usually innocuous and ancient organisms devastate life on Earth?
The Pangean supercontinent formed halfway through the Permian. Availability of shallow aquatic environments diminished, ocean currents and weather patterns were radically altered, and seasonal monsoons lashed coasts separated by a vast interior desert. These changes stressed the global ecosystem - much as humanity does today - then global warming triggered by the Siberian Traps, the largest known volcanic eruption in Earth history, initiated the coup de grace by delivering massive amounts of carbon dioxide and sulfur dioxide into the atmosphere over a 700,000 year period as the Permian drew to a close.
Temperatures soared 10 - 30 degrees Celsius (18 - 54 degrees Fahrenheit) as sulfur dioxide combined with water vapor to form acid rain. The ocean conveyor which carries warm and poorly oxygenated surface water toward the poles where it cools and is re-oxygenated before sinking and making its way back to the equator shut down.
The collapse of the ocean conveyer was catastrophic. Aerobic (with-oxygen) life in the deep sea suffocated as oxygen disappeared. Anoxic replacements quickly filled the vacant niche until the killing zone reached the surface of the global Panthalassic Ocean. Methanogenic archaea and bacteria produced prodigious amounts of methane - a far more efficient greenhouse gas than carbon dioxide - while sulfate-reducing microorganisms released unprecedented amounts of deadly hydrogen sulfide (rotten egg gas) into the ocean and atmosphere. The sky literally turned green as oxygen levels dwindled, the ozone layer disappeared, and hydrogen sulfide poisoned animals and plants. Pangaea, already arid, approached desiccation - more than enough to drive the mother of all mass extinctions.
Fast forward 251 million years to the present. Ward presents three possible Anthropocene scenarios:
1. Humanity manages to keep atmospheric carbon dioxide levels below 450 ppm (parts per million) by the year 2100. Earth warms somewhat, additional ice melts, but sea level rise is manageable and life goes on much as it has in the past - but any pending ice age will be indefinitely postponed. This outcome, as Ward notes, is hopelessly optimistic unless a massive initiative to limit or sequester greenhouse gas emissions is successfully implemented within this decade.
2. Greenhouse gas emissions accelerate as China and India continue to industrialize; carbon dioxide levels reach 700 ppm by the year 2100. Rising seas have forced countries to relocate some essential coastal infrastructure and deal with regional population displacements. Scientists note that the ocean conveyor recently shut down - triggering climate and weather pattern changes that even politicians can't ignore. Famine and scarcity replace consumer culture as societal norms. The future is bleak but technological civilization may continue to exist if it adapts quickly enough.
3. Carbon dioxide levels hit 1,100 ppm by 2100. The result resembles the worst parts of the bible - no adequate secular alternative is available. Earth is 10 degrees Celsius warmer. All of the world's ice is melting. Sea level rise is measured in meters. Much of the world's population is displaced by rising waters and vital infrastructure losses cannot be replaced. Polar bears are long gone, Homo sapiens is the latest endangered species. The ocean conveyor shut down decades ago. Signs of deep ocean anoxia are increasingly apparent and appalling - the sky turns a sickly shade of green. The sixth great mass extinction is underway. Remaining governments fight savage wars over scarce resources as entire ecosystems collapse. Natural selection and humankind are brutally reacquainted when medicine reverts to pre-industrial norms. Rampant famine and disease causes a global population implosion. Humanity will probably survive but a second stone age is the most likely outcome.
Those who forget the lessons of history - majestically inscribed into the paleontological and geological record - are doomed to repeat it. Educate yourself, become politically active, and force our leaders to change course before an anthropogenic apocalypse devours us all."
by Carl Flygare
If you read this book, please let me know what you think.