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.
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.
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.
Mari N. Jensen | University of Arizona
GPM sees deadly tornadic storms moving through US Southeast
01.12.2016 | NASA/Goddard Space Flight Center
Cyclic change within magma reservoirs significantly affects the explosivity of volcanic eruptions
30.11.2016 | Johannes Gutenberg-Universität Mainz
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy