Shrinking Glaciers Evidence of Global Warming: Differences Seen by Looking at Photos From 100 Years Ago
"Shrinking Glaciers Evidence of Global Warming: Differences Seen by Looking at Photos From 100 Years Ago"
By: David Perlman
Date: December 17, 2004
Source: Perlman, David. "Shrinking Glaciers Evidence of Global Warming: Differences Seen by Looking at Photos From 100 Years Ago." San Francisco Chronicle (December 17, 2004).
About the Author: David Perlman reports on all areas of science for the San Francisco Chronicle, where he has been the science editor since 1960. Perlman attended Columbia University, where he edited the college newspaper. He also served as a foreign correspondent in Europe after World War II. Perlman has served as the president of the National Association of Science Writers and received the Sustained Achievement Award in Science Journalism from the American Geophysical Union in 1997.
Global warming refers to an increase in temperature throughout the Earth's atmosphere. The term is usually used in connection with an accumulation of certain gases in the atmosphere. These gases, which result from the combustion of fossil fuels, are able to hold heat, much as a greenhouse collects heat within its glass walls. Global warming is of particular interest in the polar regions, where ice, some of which is in the form of glaciers, covers a substantial part of the land. Glaciers act as sensitive indicators of temperature change.
Scientists know that temperature variability is a fundamental part of the Earth's climate. About one thousand years ago during a warming period known as the Medieval Warm, glaciers retreated greatly. Greenland, which is covered in ice today, was able to support an agricultural economy. The global temperature then cooled during the Little Ice Age, approximately four hundred years ago. Glaciers expanded in all of the temperate regions of the world. Following the Little Ice Age, a warming period began and continues through the present.
One of the most significant features of the current warming period is that temperatures are rising more quickly during the last fifty years than they have during the prior 250 years. A variety of reports have also shown that glaciers are melting more quickly than they have in any of the past 250 years. However, some of the information in the reports has been contradictory and temperature information is poor prior to about 1800. In addition, measurements of the size of glaciers was difficult before technological advances like satellite remote sensing.
Two geophysicists, Bruce Molnia and Ken Tape, collected thousands of photographs taken between thirty and 110 years ago in Alaska. They then returned to the same locations where the photos were taken and took pictures of the same scenes. Visual comparisons between the photographs showed that glaciers had retreated greatly and that the landscape had become much more vegetated. Both of these results indicate that, at the very least, a regional increase in temperature is having significant effects on the landscape and further suggests that more global temperature change is affecting the polar regions.
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Molnia and Tape's work received considerable interest from the scientific community and generated a continuing dialog on the effects of global warming on the landscape and glaciers in the polar region of the northern hemisphere.
Tape, along with colleagues Matthew Sturm and Charles Racine, found that the types of vegetation that were found in increased abundance in Alaska were alder, birch, and willow. All three of these species grow more quickly in warmer environments. Because the locations where the comparative photographs were taken are remote and free from human interference, the researchers believe that the reason that the changes to the landscape are occurring is because of a warming climate.
By 2005, Molnia surveyed approximately two thousand of the largest glaciers in every part of Alaska that contained glacier ice. He found that at least 95 percent of the glaciers were retreating, thinning or stagnating. Glacier National Park in Montana contained approximately fifty glaciers in the mid 1800s. In 2005, only twenty remain and all of them are decreasing in size. Similar losses of glaciers have been documented in North Dakota, Wyoming, Colorado, Oregon, and Idaho, indicating that the warming climate has a significant impact on the landscape of the northern polar region.
Molnia found a dependence on the rate of retreat on altitude. Those glaciers at higher altitudes were not melting as rapidly. In fact, there is evidence that the additional melting of glaciers at low altitudes is feeding precipitation at higher altitudes. As a result some of the higher-altitude glaciers are actually increasing in size. Molnia expects that a similar trend will continue throughout the next fifty years. In particular, glaciers at altitudes lower than 8,000 feet will continue to shrink or disappear and those at higher altitudes will not change significantly.
The melting of glaciers increases the amount of freshwater in the regions where glaciers are found. This can cause localized flooding, the effects of which have been observed. In Italy, a glacial lake was preemptively drained to decrease the risk of flooding. In Peru, overflowing glacial lakes have resulted in flooding and deaths.
The impact of the current rate of glacial melt on sea level is not enormous. However, if all of the temperate glaciers were to melt, the result would be a sea level rise of about nine inches. Global warming has a second impact on sea level rise. As water warms, it expands, causing an additional rise in sea level. Such a sea-level rise would affect low-lying regions of the world like Bangladesh, the Netherlands and South Florida, as well as island nations such as the Marshall Islands. In particular, storm surge could be extremely damaging to property in these areas given a rise in sea level.
Sturm, Matthew, Charles Racine, and Kenneth Tape. "Climate Change: Increasing Shrub Abundance in the Arctic." Nature 411 (May 31, 2001): 546-547.
Alaska Science Forum. "Melting Alaska Makes the Front Page." 〈http://www.gi.alaska.edu/ScienceForum/ASF17/1731.html〉 (accessed January 6, 2006).
PBS's Journey to Planet Earth. "The State of the Planet: Global Warming." 〈http://www.pbs.org/journeyto-planetearth/stateoftheplanet/index_globwarming.html〉 (accessed January 6, 2006).
SeaGrant: Alaska Arctic Science Journeys. "Alaska Getting Shrubbier." 〈http://www.uaf.edu/seagrant/NewsMedia/01ASJ/06.01.01shrubs.html〉 (accessed January 6, 2006).