I recently received a letter from reader Jane Rectenwald in Missoula, Montana asking a good question: What do the melting glaciers in Glacier Park indicate about global warming?
Rectenwald had heard me speaking on a local radio station after she read quite a long article in a recent issue of the Missoulian showing pictures of the glaciers.
I’m glad she asked the question. Receding glaciers in Glacier National Park are not necessarily evidence of a global warming crisis—or of anything other than natural fluctuations. Glaciers advance and recede for many reasons, of which temperature change is just one.
Kilimanjaro Is Example
The alpine glacier atop East Africa’s Mt. Kilimanjaro, for example, is shrinking, yet scientific measurements show the mountain has been cooling for decades, and the temperature virtually never rises above freezing.
So why are Kilimanjaro’s glaciers melting? There are two main factors. Recent deforestation at the base of the mountain means wind updrafts are drier than they have been in the past, resulting in less mountaintop snowfall to sustain the glacier.
Moreover, even though temperatures have been cooling for several decades, they rose dramatically as the Earth emerged from the Little Ice Age 100 to 200 years ago. Kilimanjaro temperatures are still much warmer than during the Little Ice Age, and the large mountaintop glacier has yet to find its equilibrium since the Little Ice Age ended. Kilimanjaro’s glacier has been receding since the 1800s, long before humans were emitting significant amounts of carbon dioxide.
Temps Now Below Average
Something very similar is happening at Glacier National Park. The National Climatic Data Center has an official weather station very close to the park, at Kalispell, Montana.
The accompanying figure shows the temperature history for Kalispell, dating back to 1896. Typical of the trend throughout the United States, temperatures peaked in the 1930s (before humans were emitting significant amounts of carbon dioxide) and have been in a long-term cooling trend since then. As the figure shows, temperatures today are below the 100-year average.
Regional land use changes may be affecting the glaciers at Glacier National Park. Almost certainly the “rebound effect” is occurring as the glaciers move toward a new equilibrium in our post-Little Ice Age era.
Receding though Temps Fall
Patrick Michaels, Ph.D., a professor of climate science at the University of Virginia and a past president of the American Association of State Climatologists, uses the following example to describe how this rebound effect can occur with temperatures in a modest long-term decline:
If you take an ice cube out of a freezer at 0 degrees and put it in a refrigerator at 40 degrees, the ice cube will begin to melt. If you then turn the refrigerator down to 34 degrees and check the ice cube an hour later, it will have melted still further, even though the refrigerator temperature has declined. The declining size of the ice cube in the last hour is not an indication that temperatures rose during that hour, but simply reflects that the lower temperature of the last hour was still warmer than the temperature that existed when the ice cube formed.
Similarly, even though temperatures in the Glacier National Park region have been modestly cooling since human activities began emitting significant amounts of carbon dioxide (approximately 1940), temperatures are still warmer than they were during the prolonged Little Ice Age (approximately 1300-1875), when the Glacier National Park glaciers formed.
Thus, like the ice cube in our example, the glaciers continue to recede in response to the natural rapid warming of the late nineteenth and early twentieth centuries, even though regional temperatures have cooled during the past several decades.
James M. Taylor ([email protected]) is a senior fellow of The Heartland Institute and managing editor of Environment & Climate News.