- Global Temperatures
- Northern Hemisphere Snow
- Mountain Glaciers
- Permafrost and Frozen Ground
- Sea Ice
- Ice Shelves
- Ice Sheets
- Sea Level
SOTC: Mountain Glaciers
Because they are so sensitive to temperature fluctuations, glaciers provide clues about the effects of global warming (Oerlemans, J. 2001). The 1991 discovery of the 5,000 year-old "ice man" preserved in a glacier in the European Alps fascinated the world, yet the discovery meant that this glacier had reached a 5,000-year minimum. With few exceptions, glaciers around the world have retreated at unprecedented rates over the last century. Some ice caps, glaciers, and ice shelves have disappeared altogether. Many more are retreating so rapidly that they may vanish within decades. Some scientists attribute this retreat to the Industrial Revolution; burning fossil fuels releases greenhouse gases into the atmosphere and affects our environment in ways we did not understand before.
Over long periods, glacial response to climate change becomes obvious.
Glaciers and ice caps, except for those next to the large ice sheets of Greenland and Antarctica, occur on all continents except Australia. Collectively, these glaciers have an estimated total area of about 525,000 square kilometers. Although large collections of aerial and ground photographs can be used to study historic changes in glaciers (see Repeat Photography of Glaciers in the Glacier Photograph Collection), only in the last few decades has satellite imagery provided a means to monitor glacier extent changes worldwide. The Global Land Ice Measurements from Space (GLIMS) project, with participation from more than 60 institutions in 28 nations, is now working on a baseline study to quantify the areal extent of existing glaciers (Raup et al. 2007).
Scientists can study short-term changes in the extent of snow cover and sea ice to gauge climatic conditions, but glaciers are different. Glaciers continually move, carrying mass downhill somewhat like a conveyor belt. If the combination of climate and ice dynamics determines that the glacier is advancing as well as moving, the advance of the terminus increases the overall glacier area. Because glaciers move slowly, however, a significant time lag occurs between the changing climatic conditions and the resulting glacier advance or retreat. This time lag may last several decades or longer, and is determined by complicated processes that control how fast the glacier moves. Not all of these processes are fully understood.
More direct methods have been developed to determine the year-to-year mass balance, or "health," of a glacier. During winter, a glacier gains mass from accumulating snow. During the following summer, some or all of that winter accumulation is lost to ablation. The difference between the accumulation and ablation for a given year describes the annual net mass balance, which corresponds to the change in glacier thickness and volume.
For glaciers outside Antarctica or Greenland—referred to here as subpolar and mountain glaciers—researchers have compiled and analyzed numerous measurements of existing mass balance (Dyurgerov and Meier 1997, Cogley and Adams 1998, Dyurgerov 2002, Cogley 2002, Dyurgerov and Meier 2005, Kaser et al. 2006). Glaciers involved in mass balance studies are sparsely distributed over all mountain and subpolar regions, with about 70 percent of the observations coming from the mountains of Europe, North America, and the former Soviet Union.
Since 1946 researchers have measured mass balance on more than 300 glaciers, although we only have continuous records for about 40 glaciers since the early 1960s. These results indicate that, in most regions of the world, glaciers are shrinking in mass. From 1961 to 2005, the thickness of "small" glaciers decreased approximately 12 meters, or the equivalent of more than 9,000 cubic kilometers of water.
Last updated: 4 June 2008
NSIDC's Glacier Glossary: General and scientific terms related to glaciers
GLIMS at NSIDC: Global Land Ice Measurements from Space
All About Glaciers: A glacier site with something for everyone from glaciologists to grade school students
Glacier Photograph Collection: Photographs from "then" and "now"
World Glacier Inventory: Information on more than 100,000 glaciers