Global sea levels are likely to rise higher this century than previously predicted according to calculations made by glaciologists at the University of Colorado at Boulder.
No one factor can account for the nine-inch increase caused by glacial melt, said Mark Dyurgerov, one of the researchers, but warmer temperatures are partly responsible. “Glaciers immediately respond to this climatic change,” he said.
Nine inches may seem insignificant when ocean depth is measured in thousands of feet. But a few inches’ rise in sea level could mean considerable damage for coastal areas, such as cities and ports, wetlands and beach areas.
“A one-foot rise in sea level typically will cause a retreat of shoreline of 100 feet more,” said UC-Boulder glaciologist Mark Meier, “which would have substantial social and economic impacts.” This is particularly threatening for small nation islands that are only a few feet above sea level to begin with, he said. A sea level rise could engulf them entirely.
The Intergovernmental Panel on Climate Change made the earlier prediction in a 2001 report. The IPCC comprises the world’s top climate scientists and is the leading scientific body for assessing the consequences of climate change. The 2001 report presents the most current research in related fields, such as biology, glaciology and environmental science.
The new figures on glacial melt, combined with the rise in sea level for other processes, such as ocean warming, could mean sea levels will rise by as much as three feet by the end of the century.
A rise in sea level alone could have devastating effects. But the world’s oceans don’t exist in isolation. They are part of an integrated ecosystem system, said Ted Sambos, an UC-Bolder researcher. Scientists have no way to predict every consequence of a major climate disruption, even with the best climate models.
The IPCC reported in September that the expected rise in sea level due to glacial melt was between a fraction of an inch and nine inches. Dr. Meier and Dr. Dyurgerov have calculated a range between eight and eighteen inches.
Dr. Meier said at a recent meeting of the American Association for the Advancement of Science that the panel’s estimates needed revision because data from some regions were unavailable at the time of the September report.
As a result, the September report underestimated the influence of large glaciers in Alaska, smaller glaciers around Antarctica and Greenland, and left out data on increases in ice melt since the late 1980s. Glacial melt has accelerated since then, according to Dr. Meier.
“The rate of ice loss has more than doubled since 1988,” said Dr. Meier. “Some glaciers are smaller than they’ve been in the last 1,000 years.”
At the time of its report, the panel was unable to consider data from difficult to measure glaciers in Alaska and the West Coast of Canada. These glaciers are isolated and tricky to measure. The combination of the glacier’s size and snow or rainy weather makes flying a helicopter over them nearly impossible. However, in the early 1990s, the University Alaska at Fairbanks developed new surveillance techniques using light airplanes and a laser altimeter system. This enabled better measurements of glacier elevation and as a result, changes in glacier volume. The details of the study will be submitted for publication, said Craig Lingle, a geophysicist at the UAF, but early analysis indicate a trend.
“Glaciers and ice fields of Alaska, Yukon, and Northwestern British Columbia are melting more rapidly than previously assumed,” said Lingle. “They’re making a contribution to rising sea level that is significantly larger than previously estimated.”
Dr. Meier agreed. “The large glaciers of Alaska and adjacent Canada currently are contributing to about one-half the rate of global ice loss,” excluding the Greenland and Antarctica ice sheets, which are the largest in the world, he said.
The revisions on glacial melt do not discredit the panel’s climate model, said Sambos. Climate models are complex, he said, and, by nature, present a general trend of the changing environment. The panel created a model with the best data available at the time. As monitoring technologies improve and more data from regional areas become available, he said, the picture would become more refined. He says that he and his colleagues support the panel’s other predictions.
“That the glaciers will continue to retreat world-wide, we are very confident,” he said. That climate will continue to warm - very confident. Whether sea level will rise exactly seven inches or eleven inches, it’s a much tougher call. But no doubt, sea level will rise.”