Glacier Melt Could Signal Faster Rise in Ocean Levels
by: Shankar Vedantam 17 February 2006
Greenland's glaciers are melting into the sea twice as fast as previously believed, the result of a warming trend that renders obsolete predictions of how quickly Earth's oceans will rise over the next century, scientists said yesterday.
The new data come from satellite imagery and give fresh urgency to worries about the role of human activity in global warming. The Greenland data are mirrored by findings from Bolivia to the Himalayas, scientists said, noting that rising sea levels threaten widespread flooding and severe storm damage in low-lying areas worldwide.
The scientists said they do not yet understand the precise mechanism causing glaciers to flow and melt more rapidly, but they said the changes in Greenland were unambiguous -- and accelerating: In 1996, the amount of water produced by melting ice in Greenland was about 90 times the amount consumed by Los Angeles in a year. Last year, the melted ice amounted to 225 times the volume of water that city uses annually.
"We are witnessing enormous changes, and it will take some time before we understand how it happened, although it is clearly a result of warming around the glaciers," said Eric Rignot, a scientist at the California Institute of Technology's Jet Propulsion Laboratory.
The Greenland study is the latest of several in recent months that have found evidence that rising temperatures are affecting not only Earth's ice sheets but also such things as plant and animal habitats, coral reefs' health, hurricane severity, droughts, and globe-girdling currents that drive regional climates.
The ice sheets in Greenland and Antarctica are among the largest reservoirs of fresh water on Earth, and their fate is expected to be a major factor in determining how much the oceans will rise. Rignot and University of Kansas scientist Pannir Kanagaratnam, who published their findings yesterday in the journal Science, declined to guess how much the faster melting would raise sea levels but said current estimates of around 20 inches over the next century are probably too low.
While sea-level increases of a few feet may not sound like very much, they could have profound consequences on flood-prone countries such as Bangladesh and trigger severe weather around the world.
"The implications are global," said Julian Dowdeswell, a glacier expert at the University of Cambridge in England who reviewed the new paper for Science. "We are not talking about walking along the sea front on a nice summer day, we are talking of the worst storm settings, the biggest storm surges . . . you are upping the probability major storms will take place."
The study also highlights how seemingly small changes in temperature can have extensive effects. Where glaciers in Greenland were once traveling around four miles per year, they are now moving twice as fast. While it is possible that increased precipitation in northern Greenland is somehow compensating for the melting in the south, the scientists said that is unlikely.
There are multiple ways warming might be causing glaciers to accelerate. The scientists said increased temperatures may loosen the grip that glaciers have on underlying bedrock, or melt away floating shelves along the shore that can hold ice in place.
Whatever the mechanism, the phenomenon seems widespread. At a news conference organized by the American Association for the Advancement of Science at its annual meeting in St. Louis, glacier scientists Vladimir Aizen from the University of Idaho and Gino Casassa of Chile's Centro de Estudios Cientificos said they were seeing the same thing happen to glaciers in the Himalayas and South America.
"Glaciers have retreated systematically and in an accelerated fashion in the last few decades," Casassa said. One glacier that provided Bolivia with its only ski slope five years ago has splintered into three and cannot be used for skiing, the scientist added.
Rapid melting of Himalayan glaciers also raises concerns for the large portion of humankind that gets its fresh water from glacier-fed rivers in South Asia, Aizen noted.
Most climate scientists believe a major cause for Earth's warming climate is increased emissions of greenhouse gases as a result of burning fossil fuels, largely in the United States and other wealthy, industrialized nations such as those of western Europe but increasingly in rapidly developing nations such as China and India as well. Carbon dioxide and several other gases trap the sun's heat and raise atmospheric temperature.
"This study underscores the need to take swift, meaningful actions at home and abroad to address climate change," said Vicki Arroyo, director of policy analysis at the Pew Center on Global Climate Change.
The data highlight the lack of meaningful U.S. policy, she added: "This is the kind of study that should make people stay awake at night wondering what we're doing to the climate, how we're shaping the planet for future generations and, especially, what we can do about it."