Researchers have pinpointed the timing of the start of an ancient global warming episode known as the Paleocene-Eocene thermal maximum (PETM).
The early part of the Cenozoic era witnessed a series of transit global warming events called hyperthermals. The most severe of these was the PETM at the Paleocene-Eocene boundary, which took place around 56 million years ago. Over a 20,000-year period, ocean temperatures rose globally by about 41 degrees Fahrenheit.
The team said one possibility of this temperature rise is that these hyperthermals were driven by cyclic variations in the eccentricity of the Earth's orbit around the sun. Increased temperatures at the cycle peaks could have caused methane hydrate deposits in the deep sea to release large amounts of methane.
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Their analyses indicated that the onset of the PETM did not occur at the peak of a 400 thousand year cycle in the Earth's orbital eccentricity. "Compared to other early Eocene hyperthermals, it appears that the PETM was triggered by a different mechanism, and thus may have involved volcanism. However, a thorough test of this hypothesis will require further detailed dating studies," Adam said in a statement.
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http://www.redorbit.com/news/science/2064800/researchers_pinpoint_start_of_ancient_global_warming_episode/index.html?source=r_science