View of rapidly darkening region in SW Greenland, settled on ice sheet surface.
According to the results of a new study reported in the journal, The Cryosphere on March 3rd, see e.g. http://bit.ly/Cryo-Dark
the ongoing warming of Greenland is speeding changes to the crystalline structure of fallen snow in such a way that snow pack more readily absorbs solar energy. This has resulted in a change in albedo (surface reflectivity) which in turn has further propelled the transformation to more heat absorbent snow and more melting. This has led to a vicious cycle currently playing a role in the growing losses of snow and ice from the region.
This according to Sarah Doherty a co-author of the journal article and atmospheric scientist at the University of Washington.
The process basically entails the subtle alteration of the shape of snowflakes, which then tend to become more rounded, enabling them to more easily merge with others to form larger grains once they've landed. Doherty explains that as Greenland warms the merging occurs more rapidly. She adds that because larger grains don't have as many crystal boundaries or as rough textures, they tend to reflect sunlight back into space less effectively than finer-grained snow. This results in a lower of albedo. The process is especially pronounced at near infrared wavelengths (700- 2500 nm) that make up half the solar energy the Earth receives.
According to Doherty, quoted in Eos - Earth & Space Science News (March, p. 5):
"You have a self-reinforcing mechanism. When you have larger snow grains you end up with a darker snow pack. It is actually absorbing more sunlight which accelerates melting."
This new phenomenon pointed out by Doherty and her team is interesting because atmospheric scientists previously thought the more rapid rates of melting of Greenland's ice sheet were due to black carbon settling on the snow. This carbon -mainly as aerosolized pollution and soot from wildfires - would limit snow's ability to reflect sunlight causing melting.
In fact, the latest research shows the amount of black carbon in the air has been slowly declining after peaking around 1920, according to an article published in Science, e..g.
http://bit.ly/Blk-Carbon
Note, however, that diminished particulates (as black carbon) reaching Greenland doesn't mean they don't play a role, as Doherty et al noted. They point out, in fact, that as the top layer of snow melts it leaves behind a deposit of tiny particles trapped inside it. These dark particulates further reduce the reflectivity of the ice, increasing warming and causing more melting.
Doherty explains (ibid.) that the melting snow exposes more dirt which can then be picked up by the wind and deposited on the ice - in other areas- which also makes it melt faster
This study and others related to it are of immediate import to the welfare of coastal cities - like Miami Beach - currently coping with different degrees of flooding due to rising sea levels. In fact, any major melting of Greenland's ice sheet could threaten many coastal cities because of the sea level rise caused globally. In addition, the influx of fresh melt-water entering the sea could also disrupt ocean circulation patterns and harm marine organisms, the Doherty team concluded.
It bears noting that we need to carefully monitor albedo changes occurring. Already, researchers based at the National Oceanic and Atmospheric Administration (NOAA) using the NASA Moderate Resolution imaging Spectro-radiometer (MODRIS) and an advanced, high resolution NOAA radiometer, have found that between 1996 and 2012 Greenland's summertime reflectivity if the ice sheet has decreased by about 2 percent per decade.
In contrast to the nonsense about claims of "global warming" on Mars - for which there is no hard evidence of any albedo change- we do have hard evidence of such changes here on Earth. If we know what's good for us we will pay attention to them and cease making excuses to ignore them. Which we do at our own peril, and this is no "global warming alarmist conspiracy" as computer techie Kort Patterson seems to believe.
See also:
http://brane-space.blogspot.com/2011/05/greenland-arctic-ice-acceleratingso-why.html
No comments:
Post a Comment