Jan. 31 (UPI) -- A new survey of temperature variability in North America and Europe during the Holocene Epoch suggests the string of record-setting temperatures over the last decade is truly an exception. During the last 11,000 years, it's never been this hot for this many years in a row.
"I would say it is significant that temperatures of the most recent decade exceed the warmest temperatures of our reconstruction by 0.5 degrees Fahrenheit, having few -- if any -- precedents over the last 11,000 years," Jeremiah Marsicek, who recently earned his doctoral graduate in geology and geophysics at the University of Wyoming, said in a news release. "Additionally, we learned that the climate fluctuates naturally over the last 11,000 years and would have led to cooling today in the absence of human activity."
Marsicek and his research partner, Wyoming professor Bryan Shuman, plotted temperature changes since the last major ice age by analyzing ancient fossilized pollen in sediment cores collected from the bottoms of 642 different lakes and ponds in North America and Europe.
"When we collect sediment from the bottom of the lake, we can recognize sequences of plants that grew in a given area based on the shape of the fossil pollen left behind," Shuman said. "Because different plants grow at different temperatures, we can constrain what the temperatures were in a given place at a certain time."
The timeline of temperature variability identified by the pollen analysis revealed fluctuations very similar to those predicted by the long-range climate model built by scientists at the National Oceanic Atmospheric Administration and National Center for Atmospheric Research.
"Our temperature estimates and the NCAR simulations were within one-quarter of one degree Fahrenheit, on average, for the last 11,000 years," said Shuman.
Though warming is the long-term trend during the Holocene Epoch, which began some 11,500 years ago, both the latest analysis and the NCAR model suggest North America and Europe would be experiencing a period of cooling over the last few decades if it weren't for man-made climate change.
There have been brief periods of warmth comparable to today's temperatures during the Holocene, but they're brief and isolated, both temporally and geographically.
"It does show that what has happened in the last 30 years -- a warming trend -- puts us outside of all but the most extreme single years every 500 years since the Ice Age," Shuman said. "The last 10 years have, on average, been as warm as a normal one year in 500 warm spell."
Unlike other climate models, researchers excluded ocean surface and costal temperature data that they believe can skew historic averages and future predictions. They published their results this week in the journal Nature.
"These results help resolve a divergence in climate trends of the past 2,000 years recorded in marine sediments of the North Atlantic Ocean, compared with those recorded in fossil pollen from the continents of North America and Europe," said Jonathan Wynn, earth sciences program director with the National Science Foundation, which provided funding for the research. "These new findings help us understand how the global climate system works over scales of decades to millennia and give us a new perspective from the distant past on recent and future climate changes."