Earth is a water planet. Three-quarters of the planet’s surface covered by ice or oceans,…
Tracking Snow: The Cryosphere in an Era of Climate Change
- Published on Friday, 08 August 2014 16:34
- Osha Gray Davidson
- 1 Comment
Researchers use Earth observation to determine the impact of snow and glacial ice on ecosystems.
On a pleasant summer day, Dan Fagre stands on the shoulder of the only paved route through Glacier National Park and asks no one in particular, “Isn’t this amazing?”
It’s clearly a rhetorical question.
Behind Fagre (a research ecologist with the U.S. Geological Survey), the object of his admiration rises above deep green stands of pines on the slopes of a 10,000-foot mountain: a blinding white swath of snow and ice named Jackson Glacier.
More than 2 million visitors visit these spectacular glaciers every year, icons of the last ice age. Although they’ve been perched here for thousands of years, anyone wanting to see these glaciers may want to do it soon, advises Fagre. The last glacier may be gone by 2030. When this area became a national park a little over a century ago, Jackson Glacier was just one arm of the much larger Blackfoot Glacier, covering 1,875 acres. But a changing climate has separated the mass of frozen water into seven distinct and shrinking glaciers. The two largest — Blackfoot and Jackson — today cover fewer than 700 acres. The pace of the glacial retreat is accelerating; a third of Jackson Glacier vanished between 1966 and 2005 alone.
A Glacier National Park without glaciers will likely put a sizable dent in the area’s tourist industry (which adds $180 million to Montana’s economy annually). But Fagre warns of even more severe consequences for the many species that depend on a steady release of cold glacial melt water. Under the antiseptic-sounding forecast of “climate-induced ecosystem change,” the threatened organisms range from tiny stream insects to bull trout and carnivores that feed on the fish.
Glaciers are retreating worldwide. The Intergovernmental Panel on Climate Change (IPCC), puts annual glacier loss around the globe at 441 gigatons. To get a sense of the magnitude of this change, imagine the world’s largest earthmover, the behemoth LeTourneau L-2350, with a shovel bucket that scoops up 80 tons of material at a time. It would take 100 of these giant machines working non-stop, day and night, a century to move the amount of ice the earth is losing in a single year.
In a 2003 journal article, Fagre and co-author Myrna Hall acknowledged that they had initially thought glacier loss from heating would be mitigated by increased snowfall. That didn’t happen, they discovered, because precipitation fell as rain, not snow. The difference is crucial. When ecologists look at precipitation, Fagre explains, “The form of delivery is as important as the amount.” In an ecosystem shaped by snow and ice, rain is just so much “wasted ecological water.”
Comparing the flora in Fairbanks, Alaska, to that in Tucson, Arizona, illustrates this point. The two cities receive essentially the same amount of precipitation each year, but while Tucson is known for its giant saguaro cactus, Fairbanks has lush stands of birch, white spruce, and aspens. The form of water delivery – snow or rain – accounts for the very different landscapes. Fairbanks, with an average annual temperature of just 27 degrees Fahrenheit, receives 65 inches of snow each year. The amount of snow falling on Tucson (where the average temperature is 68 F) is too small to measure.
Welcome to the Cryosphere
The parts of our planet where water exists in solid form are known, collectively, as the cryosphere, from the Greek word for cold, “kryos.” Dr. Matthew Sturm, a glaciologist at the University of Alaska, Fairbanks, and chair of the NASA Snow Remote Sensing Working Group, is one of the world’s leading authorities on these cold regions. A recent magazine profile praised Sturm’s ability “to read discrete snow crystals as if they were books taken from a library shelf.”
For three decades, Sturm has been honing those skills on more than 30 winter expeditions around the globe, including to the Arctic and Antarctica, monitoring the cryosphere and adding to our understanding of the processes that govern the behavior of snow and its impact on ecosystems. Most recently, Sturm has concentrated on the complex relationship between the cryosphere and the climate.
“If you look at the IPCC report to policymakers,” he says, “you’ll see that some of the main evidence of the Earth’s changing climate is the cryosphere.” Sturm points to changes to glaciers, growth and decay of sea ice, and sea level rise due, in part, to melting ice sheets in Antarctica and Greenland.
The relationship goes both ways, with snow also playing a key role in moderating our climate by reflecting 80 percent of sunlight back into space. Water, trees, and land reflect just 15 percent of solar radiation, which means the other 85 percent is converted into heat. The result: Less snow producing a warmer climate.
“A warmer climate also means winter snow melts more quickly,” Sturm points out. Exposing even more non-reflective surfaces creates a feedback loop that accelerates the rate of warming even more.
Snow cover in the Northern hemisphere has been dropping dramatically since the 1990s, and hasn’t reached the long-term average since 2003.
These changes in the cryosphere, unprecedented in modern times, have impacts far beyond harming creatures that live in cold streams in Glacier National Park.
In Asia alone, melt water from the mass of ice contained in some 15,000 Himalayan glaciers flows into three major rivers (the Indus, Ganges, and Brahmaputra) that half a billion people in Tibet, China, India, Bangladesh and Pakistan, depend on for water.
In the Western U.S., about 60 million people rely on snow melt for water, says Sturm. The region has been suffering through a multi-year drought, making the shrinking snowpack all the more problematic, especially because the population in the Intermountain West is expected to add 13 million people by 2040. That makes it the fastest growing region in the country, according to a study by the Brookings Institution. Large eastern cities aren’t immune from the problem, either, with largest metropolitan areas like New York City depending partially on snow melt for their drinking water.
It’s not just drinking water that’s at issue, adds Sturm. “If one plots where people live and conduct agriculture,” he explains, “it rims the large mountain ranges. The fertile plains are irrigated with snow melt water.”
In an Earthzine article published in October 2013, a team of researchers led by Andrew Ngueyn and supported by the NASA DEVELOP National Program, also found a strong relationship between the amount of water from snow and wildfire.
“As the climate warms,” they determined, “increasing amounts of Sierra Nevada precipitation will turn from snow to rain, effectively lengthening and intensifying the fire season.” Better monitoring of the area’s snowpack, they reasoned, will help forest managers assess fire risk and manage lands accordingly.
“Given this huge impact,” says Sturm, “you’d think we can track snow well. But we can’t.”
Satellites began mapping snow in 1962 with the launch of NASA’s TIROS 6 (Television InfraRed Observation Satellite). The series of 10 increasingly sophisticated experimental weather satellites proved that monitoring from space could aid in tracking and predicting weather events like hurricanes. TIROS 10, the last in the series, produced 400 images a day, with a top resolution of two miles. Between 1978 and 1986, the next generation of weather satellites used an Advanced Very High Resolution Radiometer (AVHRR) and other sensors to obtain more accurate information on additional parameters, including day and night readings of ice and snow. Still, what these satellites did best was simply show where snow was and wasn’t.
The harder part, says Sturm, is determining the volume of water contained in an area of snowpack – what’s known as the Snow Water Equivalent (SWE). Rainfall easily converts into volume. A $10 gauge from a local hardware store can do the basic job. But the amount of water contained in an inch of snow varies depending on the crystal structure, wind speed, temperature, and other natural conditions present at the time the crystals were formed in the atmosphere.
How long snow has been on the ground also makes a big difference in its SWE. Because there is so much air in and between ice crystals in newly fallen snow, 10 inches of hours-old snow can produce as little as a tenth of an inch of water when melted. The ratio of air to water in snow drops quickly as the crystals settle. The average density of snow worldwide is about 30 percent, which means that 70 percent of snow’s volume is actually air. But averages can be misleading. The actual percentage of air in a given area of snow can range from 40 to 90 percent.
“That’s a big difference,” Sturm stresses, “especially when you need to determine how much drinking water people can count on from snow melt.”
Over the last several decades, researchers have used a variety of technologies to better understand snow’s nuances. These include microwave radar to measure snow depth, and air- and ground-based Lidar systems, which use lasers to analyze snow properties based on reflected light.
A New Era in Precipitation Research
Experts call the Global Precipitation Measurement (GPM) Core Observatory, launched this February, “revolutionary.” In addition to gathering its own information, unifies data from a constellation of weather satellites launched by the U.S., Japan, France, India, and the European Union. The GPM Core Observatory, a joint mission by NASA and the Japan Aerospace Exploration Agency (JAXA), finished its check-out period on May 29 and now provides information on rain and snow anywhere on the planet with unprecedented accuracy every three hours.
Dual-frequency Precipitation Radar (DPR) aboard the GPM can actually image ice and light rain inside of clouds, producing 3-D profiles of structures in and below storms. A GPM Microwave Imager (GMI) also measures total precipitation within all cloud layers, and is especially sensitive to light rain and snowfall. Working in tandem, the two instruments collect information on the size, intensity, and distribution of individual raindrops and snowflakes.
GPM will continue to improve its coverage of the cryosphere as future satellites are added to the constellation. Sturm says he’s eager to use these new capabilities in a mission that will only become more important on a warming planet.
“Snow is a crucial part of life as we know it on Earth,” he says. “It’s also a part that’s changing and we need to track it better and more closely.”
For more information on snow, snow monitoring, and cryospheric research:
– Additional research for this article was made possible by a fellowship from the Institute for Journalism and Natural Resources.