Global warming boosts century-to-century variability, study finds

As Earth gets hotter, century-to-century climate variability increases, according to a new study.

When scientists compared the century-scale climate variability during the last interglacial period, between 130,000 and 115,000 years ago, with variability during the last 11,700 years, they found a significant correlation between warming and variability.

During the last interglacial, or Eemian stage, the planet experienced significant Arctic warming. The average global temperature was between 3 and 11 degrees Celsius warmer than the pre-industrial average.

In other words, Earth was about as warm as climate scientists expect the planet to get by the end of the century -- should global warming continue unabated.

Earth not only experienced higher temperatures during the last interglacial period; the planet also experienced century-scale climate patterns, including arid events in southern Europe and cold water-mass expansions across the North Atlantic.

Several previous studies have detailed dramatic climatic changes during the last interglacial period. One survey of coral fossils showed sea levels rose as much as 20 feet.

Most previous analyses of climatic shifts in the last interglacial relied on localized evidence. For the new study, scientists compiled a comprehensive survey of relative geologic evidence from around the world. Researchers coupled the evidence with advanced climate models to created a detailed timeline of ocean and atmospheric changes during the period.

To normalize evidence from different environments, scientists created a key of sorts by comparing different fossils collected from the same sediment cores in Portugal.

"The marine core also contained pollen transported from the Tagus river into the deep sea, thus enabling a direct comparison of vegetation and North Atlantic ocean changes," Vasiliki Margari, a geographer at University College London, said in a news release.

Scientists also compared precipitation shifts revealed by changes in vegetation with those demonstrated by stalagmites in the Corchia Cave in northern Italy.

"The Corchia record is particularly important because it is supported by very detailed radiometric dating using the decay of uranium isotopes, producing one of the best chronologies for this period available," said UCL researcher Russell Drysdale.

Scientists found agreement between their datasets and climate simulations, which found warming during the period likely disrupted the Atlantic meridional overturning circulation, in turn increasing century-scale climate variability.

Researchers published their findings Friday in the journal Nature Communications.

"Although not a strict analogue for future anthropogenically-driven changes, the profile of the last interglacial that emerges is one of enhanced century-scale climate instability, with implications for ice-sheet and ocean dynamics," said Andrea Taschetto of the University of New South Wales. "Future research efforts should focus on constraining further the extent of melting and runoff from the Greenland ice-sheet and its effects on ocean circulation during the last interglacial."

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