Ground ice and climate change
Ground ice, a type of ice found within the cavities and pores of frozen ground, is a significant feature of permafrost regions, which encompass nearly a quarter of the Northern Hemisphere's landmass. Unlike glaciers formed from compacted snow, ground ice forms when temperatures drop below freezing, leading to the freezing of soil moisture. There are two main types of ground ice: structure-forming ice, which stabilizes sediments, and pure ice, found closer to the surface. As climate change progresses, the melting of ground ice poses serious implications for both the environment and human infrastructure. Even slight temperature increases can lead to significant ground ice thawing, resulting in terrain instability and infrastructure collapse, particularly in vulnerable areas like Alaska and Siberia. As permafrost thaws, it releases stored carbon into the atmosphere, exacerbating global warming and influencing sea levels through increased meltwater runoff. The erosion of coastlines in permafrost regions, such as the island of Shishmaref, highlights the direct impact of climate change on communities that have existed for millennia. Understanding ground ice and its dynamics is crucial for assessing future climate scenarios and the associated risks to natural and human systems.
Subject Terms
Ground ice and climate change
Definition
Ground ice is found in cavities, voids, pores, and other openings in frozen or freezing ground. It is a feature of a region, but the two terms are not interchangeable. A permafrost region is defined as an area where the soil and rocks making up the land remain below the freezing point for two or more consecutive years and can include areas with little or no water content. Permafrost regions account for nearly one-quarter of the landmass of the Northern Hemisphere, and some of these areas have been frozen since the Pleistocene ice age. Ground ice differs from glacier ice as well. Glaciers are created when fallen snow compresses into thick ice masses over long periods of time, and they are capable of riverlike movement, albeit at a pace so slow as to be imperceptible to the human eye.
Ground ice is formed once the temperature drops below 0° Celsius, when most of the moisture in the soil freezes. There are two different types of ground ice: structure-forming ice and pure ice. Structure-forming ice, which holds sediment together, comes in multiple varieties, including ice crystals, intrusive ice, reticulate vein ice, segregated ice, and icy coatings on soil particles. Pure, or massive, ice exists primarily toward the surface and is found as ice wedges, massive icy beds, and pingo cores. Massive ice beds are those with a minimum ice-to-soil ratio of 2.5 to 1.
Ancient ground ice, known as fossil ice, is a valuable source of historical information for geologists, paleontologists, and climatologists. Fossil ice preserves organic material and provides a measurable history of sediment and air quality covering hundreds of thousands of years. Cores drilled from fossil ice are studied to learn about the climates of the distant past.
In 2002, the National Aeronautics and Space Administration reported that the Odyssey orbiter had identified ground ice on Mars, a find that was confirmed by the Phoenix lander in June 2008. The extreme cold and thin atmosphere on Mars would cause to vaporize as dry ice does on Earth, but ground ice buried under the surface remains frozen and should prove invaluable to studies of the planet’s history. NASA started the Subsurface Water Ice Mapping (SWIM) project in 2017 to create detailed maps that astronauts could use when they set foot on Mars. In 2022, NASA used data from the HiRISE (High-Resolution Imaging Science Experiment) to capture a detailed perspective of the ice's boundary line that was close to Mar's equator. Using HiRISE, NASA discovered a 492-foot-wide (150-meter-wide) impact crater that revealed ice beneath the surface.
Significance for Climate Change
Ground ice and permafrost play crucial roles in the industrial development of a region’s energy and mining industries, as well as in the infrastructure needed to support such enterprises. It is possible to build in the presence of ground ice in its structure-forming state, so long as its properties are taken into consideration.
The presence of ground ice is closely linked to a region’s climate, especially to the temperature at ground level. Its impact varies based on a variety of factors, including drainage, snow cover, soil composition, and vegetation. Ground ice affects both topography and vegetation, as well as a region’s response to changes in climate and population.
In regions where the temperature remains close to freezing, a change of only a few degrees can be enough to cause ground ice to start melting. Changes can occur naturally, with normal temperature fluctuations, or as a result of ground clearing through construction or forest fire. When structure-forming ground ice melts, the surrounding terrain is significantly weakened, creating slope instabilities and thaw settlement.
Scientists predict that as much as 90 percent of the permafrost in the Northern Hemisphere could melt by the end of the twenty-first century, with most of the thaw taking place in the top 3 meters of terrain. Some regions in Alaska and Siberia have already experienced collapsed infrastructure and increased rock fall in the high elevations. The resulting meltwater would eventually reach the oceans, causing sea levels to rise around the world. Since the 1930s, Arctic water runoff has increased by 7 percent, and it is projected to reach a 28 percent increase by 2100.
Permafrost traps and holds approximately 30 percent of Earth’s carbon, sequestering it from the atmosphere. Melting ground ice will release the trapped carbon into the atmosphere, contributing to the greenhouse effect, which in turn will cause even more ice to melt. Coastlines in permafrost regions become more vulnerable to erosion as the ice retreats. The Alaskan island of Shishmaref, home to a native population whose ancestors have lived there for more than four thousand years, lost 7 meters of coastline annually between 2001 and 2006.
Bibliography
Alley, Richard B. The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future. Princeton, N.J.: Princeton University Press, 2000.
Davis, Neil. Permafrost: A Guide to Frozen Ground in Transition. Fairbanks: University of Alaska Press, 2001.
Gosnell, Mariana. Ice: The Nature, the History, and the Uses of an Astonishing Substance. Chicago: University of Chicago Press, 2007.
MacDougall, Doug. Frozen Earth: The Once and Future Story of Ice Ages. Berkeley: University of California Press, 2004.
"NASA Is Locating Ice on Mars with This New Map." NASA, 26 Oct. 2023, www.nasa.gov/solar-system/planets/mars/nasa-is-locating-ice-on-mars-with-this-new-map//. Accessed 19 Dec. 2024.
Pielou, E. C. After the Ice Age: The Return of Life to Glaciated North America. Chicago: University of Chicago Press, 1991.