Written by Melissa Christensen, ASD
Case
Study: Is Greenland Getting Darker?: National Science Foundation-Sponsored
Research Project Uses ASD Instruments to Measure Climate Change
Challenge:
The Greenland ice sheet has
experienced a recent period (since ~1990) of accelerating glacier melting,
causing global sea level rise. Along with warming Arctic temperatures,
Greenland’s melting may have been enhanced by a darkening snow surface, but
scientists haven’t been able to determine if, and why, Greenland’s snow is
getting darker due to the expense and difficulty of getting researchers out in
the field. A darker snow surface absorbs solar radiation more quickly, warms
up, and causes melting. The necessary research would focus not only on how much
snow is falling, but also where it’s snowing, how much snow is melting, and
whether and why the snow surface is darkening. The end goal is to determine how
far sea level will rise in the next few decades to centuries, threatening many
of America’s major coastal cities.
Solution:
In 2016, a collaborative research
group from Dartmouth College, The University of Maine and Boise State
University, Idaho, sponsored by the National Science Foundation (NSF), began
studying the recent changes in surface mass balance on the western Greenland
ice sheet percolation zone. The research project includes two field seasons snowmobiling
~3000 km across Greenland to investigate how the massive ice sheet is changing
and why.
In order to gather crucial data,
Gabriel Lewis, Dartmouth College Ph.D. candidate, wrote a NSF Graduate Research
Fellowship grant, as well as a Goetz Fellowship Grant from ASD, to borrow an ASD FieldSpec® 4 spectroradiometer
and was awarded temporary use of the instrument for both field seasons.
“We knew we needed to measure albedo
to find out if Greenland is getting darker as a result of more impurities from
fossil fuel pollution in the snow, or if the darkening is from larger snow
grain sizes from warmer temperatures, or if the satellite measurements are
falsely indicating a darkening ice sheet,” said Lewis.
Lewis chose the ASD FieldSpec 4
because:
･ Unlike
other spectroradiometers, the FieldSpec 4 can measure albedo (the ratio of
incoming and outgoing radiation of the snow) at multiple frequencies (in this
case, 350-2500 nanometers with high resolution and accuracy) for a more
complete picture.
･ The
FieldSpec 4 can also be used with a contact probe to measure the optical grain
size of snow grains – a vital piece of information to determine if the snow has
darkened.
･ The
instrument is portable, making it easy to transport and use in the field.
･ The
instrument came highly recommended by engineering colleagues at Dartmouth
College.
The FieldSpec 4 instrument was used
to measure albedo, as well as the optical grain size of the snow. Additionally,
samples of snow were collected and analyzed to measure their dust and soot
impurities. Through laboratory analysis back at Dartmouth, the group was able
to measure the quantity of impurities, their origin and whether their creation
was natural or man-made.
Results:
Though the research project has yet
to be completed, the preliminary results exhibit a statistically significant
correlation between the snow grain size and albedo, and no statistically
significant correlation between the impurities and albedo. There is great
agreement between the NSF-sponsored research project’s measurements and both
NASA satellites and computer climate models. Most of the measurements fall
within the expected uncertainty from the samples and locations processed so far
and the team is eager to collect more data.
“It’s great to know we are on the
right track. I am very excited to take the FieldSpec 4 back into the field this
spring and expand on some of the correlations we’ve already noticed,” commented
Lewis. “From my work last summer, it is clear the ASD FieldSpec 4 albedo
measurements in Greenland agree nicely with many of the satellite and climate
model measurements -which is wonderful.”
In April 2017, Lewis and his team
will return to Greenland to gather additional measurements over the course of
eight weeks. From there, the final research data will be compiled to determine
whether or not current climate models need to be altered to better predict the
future of the Greenland ice sheet, including what is specifically causing the
snow to melt or become darker (e.g. grain size, pollution, warmth, etc.).
Lewis concludes, “climate change is
not up for discussion. It is real. It is happening, and we have all the data to
prove it. The data I am helping to gather and analyze will help us understand
the impact of climate change on Greenland, and what it means for the future of
the planet.”
No comments:
Post a Comment