BOULDER—Scientists at the National Center for AtmosphericResearch (NCAR) have created a computer simulation showing Earth'sclimate in unprecedented detail at the time of the greatest massextinction in the planet's history. The work gives support to a theorythat an abrupt and dramatic rise in atmospheric levels of carbondioxide triggered the massive die-off 251 million years ago. Theresearch appears in the September issue of Geology.
"The resultsdemonstrate how rapidly rising temperatures in the atmosphere canaffect ocean circulation, cutting off oxygen to lower depths andextinguishing most life," says NCAR scientist Jeffrey Kiehl, the leadauthor.
Kiehl and coauthor Christine Shields focused on thedramatic events at the end of the Permian Era, when an estimated 90 to95% of all marine species, as well as about 70% of all terrestrialspecies, became extinct. At the time of the event, higher-latitudetemperatures were
18 to 54 degrees Fahrenheit (10 to 30 degreesCelsius) higher than today, and extensive volcanic activity hadreleased large amounts of carbon dioxide and sulfur dioxide into theatmosphere over a 700,000-year period.
To solve the puzzle of howthose conditions may have affected climate and life around the globe,the researchers turned to the Community Climate System Model (CCSM).One of the world's premier climate research tools, the model canintegrate changes in atmospheric temperatures with ocean temperaturesand currents. Research teams had previously studied the Permianextinction with more limited computer models that focused on a singlecomponent of Earth's climate system, such as the ocean.
The CCSMindicated that ocean waters warmed significantly at higher latitudesbecause of rising atmospheric levels of carbon dioxide (CO2), agreenhouse gas. The warming reached a depth of about 10,000 feet (4,000meters), interfering with the normal circulation process in whichcolder surface water descends, taking oxygen and nutrients deep intothe ocean.
As a result, ocean waters became stratified withlittle oxygen, a condition that proved deadly to marine life. This inturn accelerated the warming, since marine organisms were no longerremoving carbon dioxide from the atmosphere.
"The implication ofour study is that elevated CO2 is sufficient to lead to inhospitableconditions for marine life and excessively high temperatures over landwould contribute to the demise of terrestrial life," the authorsconcluded in the article.
The CCSM's simulations showed thatocean circulation was even more stagnant than previously thought. Inaddition, the research demonstrated the extent to which computer modelscan successfully simulate past climate events. The CCSM appeared tocorrectly capture key details of the late Permian, including increasedocean salinity and sea surface temperatures in the high latitudes thatpaleontologists believe were 14 degrees Fahrenheit (8 degrees Celsius)higher than present.
The modeling presented unique challengesbecause of limited data and significant geographic differences betweenthe Permian and present-day Earth. The researchers had to estimate suchvariables as the chemical composition of the atmosphere, the amount ofsunlight reflected by Earth's surface back into the atmosphere, and themovement of heat and salinity in the oceans at a time when all thecontinents were consolidated into the giant land mass known as Pangaea.
"Theseresults demonstrate the importance of treating Earth's climate as asystem involving physical, chemical , and biological processes in theatmosphere, oceans, and land surface, all acting in an interactivemanner," says Jay Fein, director of NSF's climate dynamics program,which funded the research. "Other studies have reached similarconclusions. What's new here is the application of a detailed versionof one of the world's premier climate system models, the CCSM, tounderstand how rising levels of atmospheric carbon dioxide affectedconditions in the world's oceans and land surfaces enough to trigger amassive extinction hundreds of millions of years ago."
The above post is reprinted from materials provided by National Center for Atmospheric Research/University Corporation for Atmospheric Research. Note: Content may be edited for style and length.
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