A new kind of nerd waits for a perfect snow day to study one of the feedback mechanisms driving climate change
On a cold February morning at a cabin near Hanover, New Hampshire, Adam Schneider rises early, straps on his snowshoes and heads to a clearing to find a patch of freshly fallen snow. Methodically, he marks out a precise square metre of snow and sprinkles it with what looks like soot. At 7am, he places a small, lightweight dome-shaped instrument on the snow’s surface and takes the first measurement of the day. The instrument has been specially designed to record the size of snow grains without disturbing the snow’s surface.
The sooty snow begins to melt as the day gets warmer. Schneider, a PhD student in Climate and Space Sciences and Engineering at the University of Michigan, continues to collect data, noting changes in snow grain size. Although the link might not be immediately obvious, this experiment seeks to better understand an important element in scientists’ predictions of global climate change: the Earth’s energy budget. This is the total amount of energy from sunlight that the planet’s surface absorbs without reflecting.
Currently, uncertainties in the future of the Earth’s energy budget cause climate models to project different scenarios. The energy budget depends strongly on the outcomes of a number of highly sensitive positive feedback effects, which influence the reflectivity, or albedo, of the Earth’s surface.
“One of the challenges in this community is to constrain these feedbacks, because they can really diverge model output,” Schneider says.
One of the more prominent effects is known as snow albedo feedback. This concerns the portion of the Earth’s surface covered with snow and ice — the cryosphere. Because snow is very reflective, snow cover plays a crucial role in determining the Earth’s albedo. As the cryosphere melts, the Earth’s energy budget increases, which causes further melting.
To shed new light on the magnitude of this accelerating effect, scientists are focusing on understanding the micro-processes that influence the macro-process of snow albedo feedback.
Schneider’s new dome-shaped instrument, which he designed and built himself, is called the NERD (Near-Infrared Emitting and Reflectance Monitoring Dome). It allows Schneider to observe one of the micro-processes: the connections between snow’s melting rate, grain size, and reflectivity. As freshly fallen snow ages and melts, the average size of snow grains tends to increase through a process known as snow metamorphosis. As snow grains grow, they become much less reflective.
Previously, the effects of snow metamorphosis on snow albedo feedback were hard to study because existing instruments that measured snow grain size, such as the DUFISSS instrument, disturbed snow surfaces too much to observe changes in grain size.
“You take a scoop of snow and you put it into the instrument, so you can’t monitor it over time,” Schneider says.
“The NERD, which is my instrument, sits on top of the snow. This allows for quick, repeatable, reliable measurements in cold conditions, and it doesn’t destroy the snow surface.”
Schneider was inspired to build the NERD by an instrumentation class he took.
“I was enthralled!” he says. “I had to build that into my PhD somehow.”
The homemade nature of the instrument has led to several of its design elements being improvised on the fly. For example, when the surfaces of the plastic domes Schneider ordered off the internet were too reflective, he painted them matte black.
His previous work focused on computer simulations of climate processes. When his advisor, Mark Flanner, won a National Science Foundation Career Award, funding was freed up for Schneider to build a new instrument and take a more hands-on approach to studying climate processes.
The capabilities of the NERD have opened up new areas of study, such as the rate of snow metamorphosis when there is soot on the surface of the snow. This is important because, all over the world, microscopic soot particles are released into the atmosphere. This can be from naturally occurring events such as forest fires, as well as through human activity such as fossil fuel burning. Some of these tiny particles are carried by winds to the polar regions of the Earth and eventually come to their final resting place on the surface of snow and ice.
These particles, which include black carbon and brown carbon, are known as Light Absorbing Impurities (LAIs) because their presence causes snow surfaces to darken and absorb more sunlight than usual. As humanity continues to burn fossil fuels such as coal and diesel, levels of LAIs in the cryosphere are increasing.
Previous laboratory measurements carried out by researchers, such as Hadley and Kirchstetter, have shown how black carbon reduces snow albedo. Making use of his new instrument, Schneider has been able to demonstrate in nature that this reduction in albedo accelerates snow metamorphosis. He chose New Hampshire for the location of the experiment because it’s known to have relatively clean naturally occurring snow.
The particles that Schneider uses are designed to mimic the LAIs that are being released into the atmosphere. He uses a mix of hydrophilic and hydrophobic black carbon particles purchased from a lab, as well as sand to simulate dust. The sand and black carbon particles are sifted multiple times to filter out coarser particles, which are too heavy to be carried by winds and transported to the Arctic.
However, this process is not without its flaws. The blend differs from naturally occurring LAIs in the cryosphere, most notably because it doesn’t replicate the size distributions of the particles. According to Schneider, other studies have used more elaborate strategies in an attempt to address this issue — for example, burning wood in a chimney and using a system of fans to blow particles onto snow.
The optical technique Schneider developed to measure snow grain size will soon be published in a journal, and he’s also applied for a patent for the electronics processing idea. Schneider hopes that the NERD will then become more widely adopted by the scientific community.
“Ultimately what we’re after is better representations of snow albedo feedback and internal feedback mechanisms, to better constrain future climate projections,” he says. “But it’s hard to measure and there’s a lack of data. The future direction is to do more similar experiments.”
Schneider is currently working on his thesis and will graduate this spring. He hopes to continue studying snow as a postdoctoral researcher, possibly back out in the field studying pond snow.
“I’m going to look at light interaction with snow. What happens when you start melting snow on top of ice on top of water? There’s a lot of questions to be answered.”
Edited by Lauren Fuge and Ivy Shih.