The top and the bottom of the Earth turned sharply warmer at the same time 12,500 years ago, suggesting that some climate change events once thought to be regional may have affected the entire planet.
In a study today in the journal Science, researchers said that climate temperatures climbed by more than 20 degrees, enough to melt sea ice and end the planet's last major ice age.
James White, a climatologist at the University of Colorado, Boulder, said that an analysis of new ice cores from the Antarctica show that the south polar area went through a rapid temperature increase at the same time the north polar region was warming.
White, co-author of the study, said that the Antarctica ice cores show a temperature increase of about 20 degrees Fahrenheit within a very short time.
Ice cores from Greenland, near the Arctic, show that at the same time there was a temperature increase of almost 59 degrees in the north polar region within a 50-year period, White said.
''What we see in Antarctica looks very, very similar to what we see in Greenland,'' said White. ''We used to suspect that some of these big changes that occurred naturally in the past were only local. Since we see the same thing at opposite ends of the Earth, it does imply that the warming was a global phenomena.''
He said the findings ''throw a monkey wrench into paleo-climate research and rearrange our thinking about climate change at that time.''
White said researchers need to look more closely at how the Earth's climate slipped from an ice age that ended about 12,500 years ago and shifted into the current, more temperate climate.
The findings, he said, also increase the urgency for researchers to understand climate shifts because it appears they could be abrupt and happen all over the Earth at the roughly the same time.
''The challenge is to determine if a climate change will be a nice and gradual thing that we can adapt to or will it be a mode shift that happens suddenly,'' said White.
The warming 12,500 years ago came within a typical human lifetime. Such rapid shifts in the climate on a global basis would make it very difficult for humans to adjust, he said. Climate affects agriculture, energy use, transportation and population shifts, and rapid changes would make adjustment in these areas more difficult.
White said the Antarctica ice cores also showed that there was a sudden rise in methane, a major greenhouse gas. Methane, carbon dioxide and some other gases can accumulate in the atmosphere and trap heat from the sun, causing a general warming.
Many scientists now believe that the Earth's climate may be warming because the burning of fossil fuels and other human processes have increased the amount of greenhouse gases in the atmosphere.
White said that global warming caused by man-made greenhouse gases may be similar to warming that may occur naturally.
''What humans are doing is in a way no different than what natural systems do,'' he said. ''Humans add methane to the atmosphere. So does nature. We are simply doing it faster.''
For this reason, said White, studying natural climate change of the past may give a fundamental understanding of how human actions could change the climate in the future.
Thomas F. Stocker of the Physics Institute at the University of Bern, Switzerland, said the research reported by White and his colleagues is surprising. Stocker wrote in Science that the study suggests warming in Antarctica ''may be synchronous with the well-documented abrupt warming 12,500 years ago in the Northern Hemisphere.''
Stocker said more analysis of White's ice core and a comparison with ice cores obtained elsewhere in Antarctica ''are required to get a clearer picture'' of the south polar climate change.
White said that the warming trend detected in his ice core taken from a seaside drill site was not found in ice cores taken from Antarctica drill sites that were farther inland.
The differences, said White, are ''perplexing'', but may be related to the proximity of the ocean.
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