Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Recent Arctic Warming Reverses Millennia-long Cooling Trend

04.09.2009
UA scientists and colleagues link reversal to increases in greenhouse gases

Warming from greenhouse gases has trumped the Arctic's millennia-long natural cooling cycle, suggests new research. Although the Arctic has been receiving less energy from the summer sun for the past 8,000 years, Arctic summer temperatures began climbing in 1900 and accelerated after 1950.

The decade from 1999 to 2008 was the warmest in the Arctic in two millennia.
Arctic temperatures are now 2.2 F (1.2 C) warmer than in 1900, reports an interdisciplinary team of scientists that includes two geoscientists at The University of Arizona in Tucson.

To track Arctic temperatures 2,000 years into the past, the research team analyzed natural signals recorded in lake sediments, tree rings and ice cores. The natural archives are so detailed the team was able to reconstruct past Arctic temperatures decade by decade.

As part of a 21,000-year cycle, the Arctic has been getting progressively less summertime energy from the sun for the last 8,000 years. That decline won't reverse for another 4,000 years.

The new research shows the Arctic was cooling from A.D. 1 until 1900, as expected. However, the Arctic began warming around 1900, according to both the natural archives and the instrumental records.

"The amount of energy we're getting from the sun in the 20th century continued to go down, but the temperature went up higher than anything we've seen in the last 2,000 years," said team member Nicholas P. McKay, a doctoral candidate in UA's department of geosciences.

"The 20th century is the first century for which how much energy we're getting from the sun is no longer the most important thing governing the temperature of the Arctic," McKay said.

Greenhouse gases are the most likely cause of the recent rise in Arctic temperatures, said McKay and his co-author Jonathan T. Overpeck, a UA professor of geosciences and atmospheric sciences and director of UA's Institute of the Environment.

Overpeck said, "The Arctic should be very sensitive to human-caused climate change, and our results suggest that indeed it is."

As the Arctic warms, the warming accelerates, he said, because there is less snow and ice to reflect solar energy back into space. Instead, the newly exposed dark soil and dark ocean surfaces absorb solar energy and warm further.

McKay, Overpeck, lead author Darrell S. Kaufman of Northern Arizona University in Flagstaff and their colleagues will publish their findings in the September 4 issue of the journal Science. The paper's title and a complete list of authors are at the bottom of this release. The National Science Foundation funded the research.

Overpeck and his colleagues have been working in the Arctic for about 20 years to understand the region's ancient climate. Until recently, the group had been able to peer back in time only 400 years.

About five years ago, Kaufman, Overpeck and their colleagues began a multi-institution project to analyze sediment cores from more than two dozen Arctic lakes. Lake sediments are often laid down in distinct yearly layers, much like the rings of a tree.

As part of the research for his master's degree at NAU, McKay collected and analyzed sediment cores from Hallet Lake in south-central Alaska.

The annual sediment layers contain indicators of temperature and climate.
The changes in the abundance of algae remnants reflect the length of the growing season. In addition, warmer summers result in a thicker annual sediment layer because as glacial meltwater increases, more sediment is deposited.

For the new climate reconstruction, the researchers compared the information from lake sediments with previously published climate reconstructions of the Arctic based on glacial ice cores and tree rings. The data from the natural archives were calibrated against the instrumental temperature record.

The analysis shows that summer temperatures in the Arctic, in step with reduced energy from the sun, cooled at an average rate of about 0.36 F (0.2

C) per thousand years -- until the 20th century.

"The data tell a remarkably clear and consistent story," McKay said.

UA Regents' Professor Malcolm Hughes of UA's Laboratory of Tree-Ring Research and colleagues published research in 1999 documenting that temperatures in the Northern Hemisphere "were on a long, slow, natural decline until the late 19th century."

The new findings strongly support the previous finding and extend it into the Arctic, Hughes said, adding, "Only human influence, in particular the increased concentration of greenhouse gases in our atmosphere, can account for the strong reversal of that natural trend."

Overpeck, McKay and their colleagues also compared their new work with climate reconstructions from a computer model of global climate based at the National Center for Atmospheric Research (NCAR) in Boulder, Colo.

The model's estimate of the reduction of seasonal sunlight in the Arctic and the resulting cooling was consistent with the analysis from natural archives. The finding gives scientists more confidence in computer projections of future Arctic temperatures.

The new study follows previous work showing that temperatures over the last century warmed almost three times faster in the Arctic than elsewhere in the Northern Hemisphere.

The finding has implications far beyond the Arctic, McKay and Overpeck said.

Warming in the Arctic may affect sea level rise, primarily from the melting of the great ice sheets, Overpeck said.

A warming Arctic affects weather in the southwestern U.S., McKay said.
"Winter storms in the western U.S. are going further north than they used to
-- and these are the same storms that bring our rain and snowfall."
Kaufman, McKay and Overpeck's co-authors on the paper, "Recent Warming Reverses Long-Term Arctic Cooling," are David P. Schneider, Caspar M. Ammann and Bette L. Otto-Bliesner of NCAR in Boulder, Colo.; Raymond S. Bradley of the University of Massachusetts, Amherst; Keith R. Briffa of the University of East Anglia in Norwich, UK; Gifford H. Miller of the University of Colorado in Boulder; Bo M. Vinther of the University of Copenhagen in Denmark; and the NSF Arctic System Science Program in Fairbanks, Alaska.
Researcher Contact Information:
Nick McKay
nmckay@email.arizona.edu
Jonathan Overpeck
520-622-9065
jto@u.arizona.edu
Media contact:
Mari N. Jensen
520-626-9635
mnjensen@email.arizona.edu
Related Web sites:
Overpeck lab
http://www.geo.arizona.edu/dgesl/
UA Dept. of Geosciences
http://www.geo.arizona.edu
UA Institute of the Environment
http://www.environment.arizona.edu/

Mari N. Jensen | University of Arizona
Further information:
http://www.arizona.edu

More articles from Earth Sciences:

nachricht New research calculates capacity of North American forests to sequester carbon
16.07.2018 | University of California - Santa Cruz

nachricht Scientists discover Earth's youngest banded iron formation in western China
12.07.2018 | University of Alberta

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Barium ruthenate: A high-yield, easy-to-handle perovskite catalyst for the oxidation of sulfides

16.07.2018 | Life Sciences

New research calculates capacity of North American forests to sequester carbon

16.07.2018 | Earth Sciences

Nano-kirigami: 'Paper-cut' provides model for 3D intelligent nanofabrication

16.07.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>