|The Week That Was
Jan 8, 2000 NEW ON THE SEPP WEB:
This is our week for science. We kept hearing stories that global warming would produce more El Ninos, so we looked at the data. And it's not true. We have had a genuine global warming between about 1900 and 1940, most likely all natural. And what happened to sea-surface temperatures (SST)in the Eastern Tropical Pacific (a sure indicator of El Nino)? They trended downward!
The Week That Was January 8, 2000 brought to you by SEPP
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The world's climate can change in just a few decades-without any human intervention. Jeffrey P. Severinghaus of the Scripps Institution of Oceanography, using a new method of analyzing gases trapped in Greenland ice, showed air temperatures warming rapidly at the end of the last ice age about 15,000 years ago.
The study is based on a new technique that analyzes the isotopic chemistry of argon and nitrogen in the ice cores and allows the detection of temperature change with unprecedented precision.
"There was a 16degree F abrupt warming at the end of the last ice age," said Severinghaus, lead author of a study in the journal Science [Science 1999 October 29; 286: 930-934]. "It happened within just a couple of decades. The old idea was that the temperature would change over a thousand years." The rapid temperature increase may have been touched off by a surge in warm currents in the Atlantic Ocean that brought a melting trend to the vast ice sheet covering the Northern Hemisphere. It still took hundreds of years for the ice to recede, but the start of the great thaw was much more sudden than scientists had once thought.
Pieter P. Tans, a scientist at the National Oceanographic and Atmospheric Administration, said that "both the rapidity and the magnitude of the temperature change is surprising." But scientific caution demands "another piece of evidence to support it." Climate models, such as used by the UN-IPCC had predicted that an increase in greenhouse gases, such as carbon dioxide, would cause a gradual global warming, with temperatures rising slowly over many decades.
A quite different study supports the story, however. Scott Lehman and Julian Sachs report (in Science, Oct. 22, 1999) that temperatures in the Sargasso Sea (between the West Indies and the Azores) fluctuated repeatedly by up to 9 degrees Fahrenheit from 60,000 to 30,000 years ago. (The last ice age occurred between 110,000 and 10,000 years ago.)
After analyzing sediment deposited during the last ice age, they discovered that extreme temperature fluctuations occurred during and at the end of the period. Even during an ice age, warm oceans can heat up. "What is new here is clear evidence that the warm Atlantic, like the polar Atlantic, was undergoing very large and very rapid temperature changes during the last glacial period," said Scott Lehman, a research associate at the University of Colorado Institute of Arctic and Alpine Research. The researchers next hope to determine if similar changes occurred in the much larger Pacific Ocean.
Lehman and Sachs reached their conclusions after studying 50 meters of sediment cores hauled up from several miles deep in the Sargasso Sea near Bermuda by French scientists as part of an international project. They analyzed the saturation state of organic molecules from planktonic algae over the past 100,000 years, revealing sea-surface temperatures during that period.
"The warming at the end of the last ice age, about 10,000 years ago, was supported by the disappearance of enormous ice sheets, a one-third increase in atmospheric carbon dioxide levels and changes in the seasonal distribution of the sun's energy," said Lehman. "But the abrupt changes we documented during the last ice age seem to be almost entirely ocean driven."
BUT CLIMATE MODELS ARE SHAKY
James E. Hansen, who coined the term 'global warming', recently stated in the Proceedings of the National Academy of Sciences (95, 12753, 1998) that "The forcings that drive long-term climate change are not known with an accuracy sufficient to define future climate change." He added: "The summary implication is a paradigm change for long-term climate projections: uncertainties in climate forcings have supplanted global climate sensitivity as the predominant issue ... The natural forcing due to solar irradiance changes may play a larger role in long-term climate change than inferred from comparison with anthropogenic greenhouse gases alone."
In "Physics of Climate" J. P. Peixoto and A. H. Oort, aptly remark: "The integration of a fully coupled model including the atmosphere, oceans, land, and cryosphere with very different internal time scales poses almost insurmountable difficulties in reaching a final solution, even if all interacting processes were completely understood."
And Myles Allen from the Rutherford Appleton Laboratory in the United Kingdom explains in Nature (14 October 1999) that the state-of the-art climate model developed by the UK Meteorological Office can be used to forecast climate change for the next 50 years only if the hundreds of undetermined parameters in this model are first tested exhaustively. This requires running hundreds of thousands of different simulations of the past 50 years of climate, using all the possible combinations of parameters. The hundreds of thousands of different combinations that need to be tested, however, would take up resources far beyond any officially available.
This is why Allen suggests to recruit an army of home PCs to do the job. Any volunteers out there?