"The relative importance of solar radiation in the summer is changing," says Jennifer Kay of the National Center for Atmospheric Research (NCAR) in Boulder, Colo., who is lead author of the study. "The amount of sunshine reaching the Arctic is increasingly influential, as there is less ice to reflect it back into space," she says.
"A single unusually clear summer can now have a dramatic impact," Kay says.
A report on the new results will be published tomorrow 22 April 2008 in Geophysical Research Letters, a journal of the American Geophysical Union (AGU).
Last summer's loss of Arctic sea ice set a modern-day record, with the ice extent shrinking in September to a minimum of about 4.1 million square kilometers (1.6 million square miles). That was 43 percent less ice coverage than in 1979, when accurate satellite observations began.The soon-to-be-published study draws on observations from new NASA satellite radar and lidar instruments. Lidar devices make measurements using lasers.
Looking at the first two years of satellite data from those sensors, Kay and her colleagues found that total 2007 summertime cloud cover was 16 percent less than the year before, largely because of a strong high-pressure system centered north of Alaska that kept skies clear.
Over a three-month period in the summer, the increased sunshine was strong enough to melt about a foot of surface ice. Over open water, it was sufficient to increase sea-surface temperatures by 2.4 degrees Celsius (4.3 degrees Fahrenheit).
Warmer ocean waters can contribute to sea ice loss by melting the ice from the bottom, thereby thinning it and making it more susceptible to future melt.
"Satellite radar and lidar measurements allow us to observe Arctic clouds in a new way," says CSU's Tristan L'Ecuyer, a co-author of the study. "These new instruments not only provide a very precise view of where clouds exist but also tell us their height and thickness, which are key properties that determine the amount of sunlight clouds reflect back to space."
The research team also examined longer-term records of Arctic cloud and weather patterns, including a 62-year-long record of cloudiness from surface observations at Barrow, Alaska. The scientists found that the 2007 weather and cloud pattern was unusual but not unprecedented. Five other years--1968, 1971, 1976, 1977, and 1991--appeared to have lower summertime cloud cover than 2007, but without the same impact on sea ice.
"In a warmer world, the thinner sea ice is becoming increasingly sensitive to year- to-year variations in weather and cloud patterns," Kay says.The research suggests that warmth from the sun will increasingly affect Arctic climate in the summer. As the ice shrinks, incoming sunshine triggers a feedback
mechanism: the newly exposed dark ocean waters, much darker than the ice, absorb the sun's radiation instead of reflecting it. This warms the water and melts more ice, which in turn leads to more absorption of radiation and still more warming.
The authors note that, in addition to solar radiation, other factors such as changes in wind patterns and, possibly, shifts in ocean circulation patterns also influence sea ice loss. In particular, strong winds along regions of sea ice retreat were important to last year's loss of ice. The relative importance of these factors, and the precise extent to which global climate change is driving them, are not yet known.
This study was funded by NASA and by the National Science Foundation.Title:
Tristan L'Ecuyer, Graeme Stephens, and Chris O'Dell: Department of Atmospheric Sciences, Colorado State University, Fort Collins, Colorado, USA.Citation:
More than 100 years of flooding and erosion in 1 event
28.03.2017 | Geological Society of America
Satellites reveal bird habitat loss in California
28.03.2017 | Duke University
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
28.03.2017 | Life Sciences
28.03.2017 | Information Technology
28.03.2017 | Physics and Astronomy