The international study, led by Northern Arizona University and the National Center for Atmospheric Research (NCAR), will be published in the September 4 edition of Science. It was primarily funded by the National Science Foundation, NCAR's sponsor.
The scientists reconstructed summer temperatures across the Arctic over the last 2,000 years by decade, extending a view of climate far beyond the 400 years of Arctic-wide records previously available at that level of detail. They found that thousands of years of gradual Arctic cooling, related to natural changes in Earth's orbit, would continue today if not for emissions of carbon dioxide and other greenhouse gases.
"This result is particularly important because the Arctic, perhaps more than any other region on Earth, is facing dramatic impacts from climate change," says NCAR scientist David Schneider, one of the co-authors. "This study provides us with a long-term record that reveals how greenhouse gases from human activities are overwhelming the Arctic's natural climate system."
Darrell Kaufman of Northern Arizona University, the lead author and head of the synthesis project, says the results indicate that recent warming is more anomalous than previously documented.
"Scientists have known for a while that the current period of warming was preceded by a long-term cooling trend," says Kaufman. "But our reconstruction quantifies the cooling with greater certainty than before."
Greenhouse gases overtake a natural cycle
The new study is the first to quantify a pervasive cooling across the Arctic on a decade-by-decade basis that is related to an approximately 21,000-year cyclical wobble in Earth's tilt relative to the Sun. Over the last 7,000 years, the timing of Earth's closest pass by the Sun has shifted from September to January. This has gradually reduced the intensity of sunlight reaching the Arctic in summertime, when Earth is farther from the Sun.
The research team's temperature analysis shows that summer temperatures in the Arctic, in step with the reduced energy from the Sun, cooled at an average rate of about 0.2 degrees Celsius (about .36 degrees Fahrenheit) per thousand years. The temperatures eventually bottomed out during the "Little Ice Age," a period of widespread cooling that lasted roughly from the 16th to the mid-19th centuries.
Even though the orbital cycle that produced the cooling continued, it was overwhelmed in the 20th century by human-induced warming. The result was summer temperatures in the Arctic by the year 2000 that were about 1.4 degrees C (2.5 degrees F) higher than would have been expected from the continued cyclical cooling alone.
"If it hadn't been for the increase in human-produced greenhouse gases, summer temperatures in the Arctic should have cooled gradually over the last century," says Bette Otto-Bliesner, an NCAR scientist who participated in the study.
Natural archives of Arctic climate
To reconstruct Arctic temperatures over the last 2,000 years, the study team incorporated three types of field-based data, each of which captured the response of a different component of the Arctic's climate system to changes in temperature.
These data included temperature reconstructions published by the study team earlier this year. The reconstructions were based on evidence provided by sediments from Arctic lakes, which yielded two kinds of clues: changes in the abundance of silica remnants left behind by algae, which reflect the length of the growing season, and the thickness of annually deposited sediment layers, which increases during warmer summers as deposits from glacial meltwater increase.
The research also incorporated previously published data from glacial ice and tree rings that were calibrated against the instrumental temperature record.
The scientists compared the temperatures inferred from the field-based data with simulations run with the Community Climate System Model, a computer model of global climate based at NCAR. The model's estimate of the reduction of seasonal sunlight in the Arctic and the resulting cooling was consistent with the analysis of the lake sediments and other natural archives. These results give scientists more confidence in computer projections of future Arctic temperatures.
"This study provides a clear example of how increased greenhouse gases are now changing our climate, ending at least 2,000 years of Arctic cooling," says NCAR scientist Caspar Ammann, a co-author.
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. This phenomenon, called Arctic amplification, occurs as highly reflective Arctic ice and snow melt away, allowing dark land and exposed ocean to absorb more sunlight.
"Because we know that the processes responsible for past Arctic amplification are still operating, we can anticipate that it will continue into the next century," says Gifford Miller of the University of Colorado at Boulder, a member of the study team. "Consequently, Arctic warming will continue to exceed temperature increases in the rest of the Northern Hemisphere, resulting in accelerated loss of land ice and an increased rate of sea level rise, with global consequences."
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Title: "Recent Warming Reverses Long-Term Arctic Cooling"
Authors: Darrell S. Kaufman, David P. Schneider, Nicholas P. McKay, Caspar M. Ammann, Raymond S. Bradley, Keith R. Briffa, Gifford H. Miller, Bette L. Otto-Bliesner, Jonathan T. Overpeck, Bo M. Vinther, and Journal of Paleolimnology special issue authors.
On the Web:
More on this research www.arcus.org/synthesis2k/
Resources for journalists: www.ucar.edu/news/journalists.jsp
Read this and past releases or sign up for e-mail delivery: www.ucar.edu/news/releases
David Hosansky | EurekAlert!
Further reports about: > Arctic > Arctic's natural climate system > Arizona > Atmospheric > Atmospheric Research > Earth's magnetic field > Hemisphere > Little Ice Age > NCAR > Science TV > climate system > emissions of carbon dioxide > greenhouse gas > greenhouse gases > summer temperatures > widespread cooling
Better model of water under extreme conditions could aid understanding of Earth's mantle
21.06.2018 | University of Chicago
The Janus head of the South Asian monsoon
21.06.2018 | Max-Planck-Institut für Chemie
In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.
Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...
Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...
Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.
Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...
The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.
Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.
An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.
Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...
13.06.2018 | Event News
08.06.2018 | Event News
05.06.2018 | Event News
21.06.2018 | Earth Sciences
21.06.2018 | Life Sciences
21.06.2018 | Earth Sciences