Global Sea Levels Likely To Rise Higher In 21st Century Than Previous Predictions

The projected sea-level rise is due to a revised estimate of the ice melt from glaciers, said geological sciences Emeritus Professor Mark Meier.

Meier and CU-Boulder colleague Mark Dyurgerov have collected new data showing the world’s glaciers and ice caps have exhibited significant ice loss in the 20th century, which has accelerated since 1988. That loss has contributed to at least 20 percent of the observed rise in sea level, said Meier.

"Some glaciers around the world now are smaller than they have been in the last several thousand years," he said.

"The rate of ice loss since 1988 has more than doubled," said Meier, a researcher and former director of CU-Boulder’s Institute for Arctic and Alpine Research. Dyurgerov also is an INSTAAR researcher.

Meier said the IPCC report might have underestimated the wastage of glaciers and ice caps around the word -- excluding Greenland and Antarctica -- for several reasons. The IPPC did not include increases in ice wastage since the late 1980s, an apparent increase in the sensitivity of ice wastage to both temperature and precipitation, and a probable increase in melting from small, cold glaciers surrounding the Greenland and Antarctic ice sheets, he said.

In addition, new data from colleagues at the University of Alaska show that huge glaciers on the West Coast of Alaska and northern Canada are wasting rapidly, said Meier. The melting of these large glaciers has contributed roughly 0.14 millimeters per year in sea rise over the long-term, according to calculations by Meier and Dyurgerov, jumping to more than 0.32 millimeters per year during the last decade.

The IPCC, which estimated global ice wastage of only 0.3 millimeters per year, probably underestimated the contribution of glacier disintegration to sea-level rise because little data on the large, maritime glaciers in Alaska was available, said Meier. But this region is the largest contributor to sea-level rise, he said.

"The sensitivity of glacier melt to temperature rise depends largely on precipitation, which in some ‘glaciered’ areas like southern coastal Alaska has been greatly under-measured," said Meier. "The large glaciers of Alaska and adjacent Canada currently are contributing about half of the rate of global ice loss, exclusive of Greenland and Antarctic ice sheets," said Meier. "But they contain only 17 percent of the glacier ice area."

The new data suggests the IPCC calculation for the 21st century -- a total of 0.16 to 0.36 feet -- was an underestimate, said Meier. He calculated that glacier melting could contribute 0.65 feet or more to sea level this century.

The IPCC estimated that other processes such as ocean warming would cause an additional 0.36 feet to 1.4 feet of sea-level rise by the year 2100, Meier said.

"These estimates in sea-level rise may seem small, but a 1-foot rise in sea level typically will cause a retreat of shoreline of 100 feet or more, which would have substantial social and economic impacts," Meier said.

Meier said that in the United States, some large coastal cities like Houston "are not much above sea level now." He also said island nations such as Seychelles off the West Coast of Africa and Kiribati southwest of Hawaii are within a meter of being inundated by sea rise.

In addition, sea rise of only 1 meter in Bangladesh would put one-half of the nation underwater, displacing more than 100 million people.