Three million cubic kilometers of ice won’t wash into the ocean overnight, but researchers have been tracking increasing melt rates since at least 1979. Last summer, however, the melt was so large that similar events show up in ice core records only once every 150 years or so over the last four millennia.
“In July 2012, a historically rare period of extended surface melting raised questions about the frequency and extent of such events,” says Ralf Bennartz, professor of atmospheric and oceanic sciences and scientist at the University of Wisconsin–Madison‘s Space Science and Engineering Center. “Of course, there is more than one cause for such widespread change. We focused our study on certain kinds of low-level clouds.”
In a study to be published in the April 4 issue of the journal Nature, Bennartz and collaborators describe the moving parts that led to the melt, which was observed from the ICECAPS experiment funded by the National Science Foundation and run by UW–Madison and several partners atop the Greenland ice sheet.
“The July 2012 event was triggered by an influx of unusually warm air, but that was only one factor,” says Dave Turner, physical scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory. “In our paper we show that low-level clouds were instrumental in pushing temperatures up above freezing.”
Low-level clouds typically reflect solar energy back into space, and snow cover also tends to bounce energy from the sun back from the Earth’s surface.
Under particular temperature conditions, however, clouds can be both thin enough to allow solar energy to pass through to the surface and thick enough to “trap” some of that heat even if it is turned back by snow and ice on the ground.
While low, thin cloud cover is just one element within a complex interaction of wind speed, turbulence and humidity, the extra heat energy trapped close to the surface can push temperatures above freezing.
That is exactly what happened in July 2012 over large parts of the Greenland ice sheet, and similar conditions may help answer climate conundrums elsewhere.
“We know that these thin, low-level clouds occur frequently,” Bennartz says. “Our results may help to explain some of the difficulties that current global climate models have in simulating the Arctic surface energy budget.”
Current climate models tend to underestimate the occurrence of the clouds ICECAPS researchers found, limiting those models’ ability to predict cloud response to Arctic climate change and possible feedback like spiking rates of ice melt.
By using a combination of surface-based observations, remote sensing data, and surface energy-balance models, the study not only delineates the effect of clouds on ice melting, but also shows that this type of cloud is common over both Greenland and across the Arctic, according to Bennartz.
“Above all, this study highlights the importance of continuous and detailed ground-based observations over the Greenland ice sheet and elsewhere,” he says. “Only such detailed observations will lead to a better understanding of the processes that drive Arctic climate. ”
NOAA’s Earth System Research Laboratory and the Department of Energy’s Atmospheric Radiation Measurement program contributed to the work at NSF’s Summit Station, supporting collaborating scientists Matt Shupe of the University of Colorado Boulder, ICECAPS principal investigator Von Walden of the University of Idaho, Konrad Steffen of the Swiss Federal Institute for Forest, Snow and Landscape Research, UW–Madison’s Nate Miller and Mark Kulie, and graduate students Claire Pettersen (UW-Madison) and Chris Cox (Idaho).
— Mark Hobson, 608-263-3373, firstname.lastname@example.org
Mark Hobson | Newswise
Water - as the underlying driver of the Earth’s carbon cycle
17.01.2017 | Max-Planck-Institut für Biogeochemie
Modeling magma to find copper
13.01.2017 | Université de Genève
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
18.01.2017 | Power and Electrical Engineering
18.01.2017 | Materials Sciences
18.01.2017 | Life Sciences