7) COULD THIS BE A NATURAL CYCLE?
Glaciers and ice caps are indeed key indicators and unique demonstration objects of ongoing climate change. Their shrinkage and, in many cases, even complete disappearance leaves no doubt about the fact that the climate is changing at a global scale and at a fast if not accelerating rate. Anyone can see the changes in glacier extent and understand the basic physical principle of snow and ice melting as temperatures continue to rise: as the glaciers and ice caps on earth grow smaller, the energy content in the climate system and in the environment on which we depend becomes greater.
The average annual melting rate of mountain glaciers appears to have doubled after the turn of the millennium in comparison with the already accelerated melting rates observed in the two decades before. The previous record loss in the year 1998 has already been exceeded three times, i.e., in the years 2003, 2004 and 2006, with the losses in 2004 and 2006 being almost twice as high as the previous 1998 record loss.
—Wilfried Haeberli, Director, World Glacier Monitoring Service
Throughout Earth’s history, ice caps and glaciers have grown and melted in response to changes in the Earth’s energy balance. Now, however, the addition of atmospheric greenhouse gases, including carbon dioxide (CO2), methane (CH4) and manmade gases such as nitrogen trifluoride (NF3) is amplifying the natural greenhouse effect, causing intensified warming that international teams of scientists describe as unequivocal, meaning “without doubt.”
In normal circumstances—without human activities influencing the climate and amplifying the greenhouse effect—glaciers and ice caps melt in the summer months, and in the high latitudes when the sun doesn’t set for weeks at a time around the solstice, the melt can be dramatic.
Glaciers that terminate at an ocean also tend to break off—or calve—icebergs faster in summer, causing a seasonal retreat. In the winter months, especially in high latitudes when the sun doesn’t come above the horizon for weeks at a time, the ice grows. On the Greenland ice cap, for instance, there is tremendous melting during the summer, especially on the edges where glaciers meet the sea, but there is also buildup of ice and snow from precipitation during the winter months.
Ocean-ending glaciers slow down their rate of calving in the winter months and recover some or all of their summertime loss. The difference between the summer loss and the winter growth is studied by examining the “mass balance.” Most glaciers in the world have a negative balance and are retreating, and the few that are advancing appear to be close to equilibrium.
What alarms many scientists is not only the extent of retreat but the rapidity of the change and the consistent, worldwide emergence of retreat and volume loss. The EIS time-lapse studies provide evidence not only of the changes that are occurring, but of the processes involved, which have not been well understood.
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