A Deep Thaw: How Much Will Vanishing Glaciers Raise Sea Levels?

GLACIAL SPEED: Greenland may get much of the scientific
attention but it is smaller glaciers such as the Columbia Glacier
in Alaska pictured here that are already contributing to sea level
rise--and will continue to do so in future.

Greenland, the world's largest island, holds enough ice to raise global sea levels by 23 feet (seven meters). Add the ice sheets of Antarctica and the oceans would deepen more than 200 feet (60 meters). Satellite measurements from space and speed measurements on land confirm that Greenland's glaciers are melting and on the move. And although the picture is less clear in Antarctica, the global warming seems to be having an impact there, too.

New research from glaciologist Tad Pfeffer of the University of Colorado at Boulder and colleagues published in Science attempts to better estimate the possible sea level rise over the next century by measuring the speed at which the world's glaciers—in Greenland and Antarctica but also the many mountain ice sheets throughout the globe—are actually speeding to the sea as well as how swiftly they may melt.

"What would the flow velocities of the ocean-ending outlet glaciers have to be," if Greenland alone was to raise sea level by just six feet (two meters)? "The answer turned out to be huge: about 49 kilometers [30 miles] per year, 70 times faster than those glaciers move today," Pfeffer says, "and three times faster than we've ever observed an outlet glacier to move."

Given that Greenland's glaciers are not presently moving anywhere close to that pace—Kangerdlugssuaq Glacier, the fastest, reached speeds above nine miles (14 kilometers) per year in 2005—the researchers also looked at ice that could contribute from the rest of the world. Assuming that the largest remaining ice shelves in East Antarctica—Filchner-Ronne and Ross—will remain intact, sea level rise from all other melting ice and the expansion of seawater as the weather gets warmer over the next century would be somewhere between 2.6 feet (0.8 meter) and six feet (two meters)—or nearly twice as much as projected last year by the U.N. Intergovernmental Panel on Climate Change (IPCC).

This does not take into account how much sea level might swell from the metldown of the numerous small glaciers in Alaska, Argentina, Canada and Russia, which already contribute 60 percent of sea level rise from glacial melt. (In fact, Pfeffer notes that they are melting faster and therefore adding to sea levels more rapidly than Greenland and Antarctica combined currently do.) Nor is it clear whether something might suddenly occur to change that upper estimate. "If those two big ice shelves [in Antarctica] go out, then it's an entirely different situation," Pfeffer says. "But there's no good evidence that that's going to happen over the next century."

Ancient melting events suggest that glaciers can disappear in a hurry, however, and raise sea levels by more than half an inch a year.

The Laurentide ice sheet that stretched as far south as New York State and Ohio some 20,000 years ago had retreated to eastern Canada, just across the water from Greenland, by roughly 11,000 years ago thanks to increased sunlight (due to the periodic wobble in Earth's axis known as precession). It then completely disappeared by 6,800 years ago in two geologically rapid bursts, shedding enough ice to raise sea levels by as much as four feet (1.3 meters) per century, according to research published this week in Nature Geoscience.

"The inspiration came from the IPCC report stating that we don't know how fast ice sheets will retreat and raise sea level in the future," says Anders Carlson, a paleoclimatologist at the University of Wisconsin–Madison and lead author of that study. "Well, we do have past records of ice sheet retreat under climates warmer than present so we decided to determine what those rates of retreat were."

At the same time, Greenland's glaciers were also smaller, though they persisted because of snowfall generated from the ocean. "More snow can partially offset the greater melting, helping the Greenland Ice Sheet to survive this interval," Carlson says. "But note it did retreat and this is what we are predicting for the future."

Based on this historical record and the fact that the Laurentide melted away under summertime temperatures similar to those expected in Greenland by the end of this century, Carlson and his colleagues forecast glacial melting that contributes somewhere between 2.8 inches (seven centimeters) and 5.1 inches (13 centimeters) of sea level rise per year, or as much as a 4.3-foot (1.3-meter) increase by 2100. Current rates are just 0.1 inch (3 millimeter) per year—and Greenland is contributing roughly 0.02 inches (0.4 millimeters) of that rise annually.

Pfeffer notes that the Laurentide and other ice sheets that disappeared in the past had an easier path to the sea than the glaciers in Greenland or Antarctica. "The analogies between those past climates and today aren't strong enough to say anything specific about the rate of sea level rise in the next century," he says.

The bottom line: sea levels will rise much more than predicted by the IPCC, based on both present understanding of current glacial melt as well as evidence from the geologic record. "The IPCC noted that their estimates should be seen as minimum estimates," Carlson notes, "and they are right."

The "Grim Realities" of Global COOLING

"The central fact is that after three quarters of a century of extraordinarily mild conditions, the earth's climate seems to be cooling down. Meteorologists disagree about the cause and extent of the cooling trend, as well as over its specific impact on local weather conditions. But they are almost unanimous in the view that the trend will reduce agricultural productivity for the rest of the century. If the climatic change is as profound as some of the pessimists fear, the resulting famines could be catastrophic."

The Cooling World
Newsweek, April 28, 1975

There are ominous signs that the Earth's weather patterns have begun to change dramatically and that these changes may portend a drastic decline in food production– with serious political implications for just about every nation on Earth. The drop in food output could begin quite soon, perhaps only 10 years from now. The regions destined to feel its impact are the great wheat-producing lands of Canada and the U.S.S.R. in the North, along with a number of marginally self- sufficient tropical areas – parts of India, Pakistan, Bangladesh, Indochina and Indonesia – where the growing season is dependent upon the rains brought by the monsoon.

The evidence in support of these predictions has now begun to accumulate so massively that meteorologists are hard-pressed to keep up with it. In England, farmers have seen their growing season decline by about two weeks since 1950, with a resultant overall loss in grain production estimated at up to 100,000 tons annually. During the same time, the average temperature around the equator has risen by a fraction of a degree – a fraction that in some areas can mean drought and desolation. Last April, in the most devastating outbreak of tornadoes ever recorded, 148 twisters killed more than 300 people and caused half a billion dollars' worth of damage in 13 U.S. states.

To scientists, these seemingly disparate incidents represent the advance signs of fundamental changes in the world's weather. The central fact is that after three quarters of a century of extraordinarily mild conditions, the earth's climate seems to be cooling down. Meteorologists disagree about the cause and extent of the cooling trend, as well as over its specific impact on local weather conditions. But they are almost unanimous in the view that the trend will reduce agricultural productivity for the rest of the century. If the climatic change is as profound as some of the pessimists fear, the resulting famines could be catastrophic.

"A major climatic change would force economic and social adjustments on a worldwide scale," warns a recent report by the National Academy of Sciences, "because the global patterns of food production and population that have evolved are implicitly dependent on the climate of the present century."

A survey completed last year by Dr. Murray Mitchell of the National Oceanic and Atmospheric Administration reveals a drop of half a degree in average ground temperatures in the Northern Hemisphere between 1945 and 1968. According to George Kukla of Columbia University, satellite photos indicated a sudden, large increase in Northern Hemisphere snow cover in the winter of 1971-72. And a study released last month by two NOAA scientists notes that the amount of sunshine reaching the ground in the continental U.S. diminished by 1.3% between 1964 and 1972.

To the layman, the relatively small changes in temperature and sunshine can be highly misleading. Reid Bryson of the University of Wisconsin points out that the Earth's average temperature during the great Ice Ages was only about seven degrees lower than during its warmest eras – and that the present decline has taken the planet about a sixth of the way toward the Ice Age average. Others regard the cooling as a reversion to the "little ice age" conditions that brought bitter winters to much of Europe and northern America between 1600 and 1900 – years when the Thames used to freeze so solidly that Londoners roasted oxen on the ice and when iceboats sailed the Hudson River almost as far south as New York City.

Just what causes the onset of major and minor ice ages remains a mystery. "Our knowledge of the mechanisms of climatic change is at least as fragmentary as our data," concedes the National Academy of Sciences report. "Not only are the basic scientific questions largely unanswered, but in many cases we do not yet know enough to pose the key questions."

Meteorologists think that they can forecast the short-term results of the return to the norm of the last century. They begin by noting the slight drop in overall temperature that produces large numbers of pressure centers in the upper atmosphere. These break up the smooth flow of westerly winds over temperate areas. The stagnant air produced in this way causes an increase in extremes of local weather such as droughts, floods, extended dry spells, long freezes, delayed monsoons and even local temperature increases – all of which have a direct impact on food supplies.

"The world's food-producing system," warns Dr. James D. McQuigg of NOAA's Center for Climatic and Environmental Assessment, "is much more sensitive to the weather variable than it was even five years ago." Furthermore, the growth of world population and creation of new national boundaries make it impossible for starving peoples to migrate from their devastated fields, as they did during past famines.

Climatologists are pessimistic that political leaders will take any positive action to compensate for the climatic change, or even to allay its effects. They concede that some of the more spectacular solutions proposed, such as melting the Arctic ice cap by covering it with black soot or diverting arctic rivers, might create problems far greater than those they solve. But the scientists see few signs that government leaders anywhere are even prepared to take the simple measures of stockpiling food or of introducing the variables of climatic uncertainty into economic projections of future food supplies. The longer the planners delay, the more difficult will they find it to cope with climatic change once the results become grim reality.

[end]

The Cooling World:
http://denisdutton.com/cooling_world.htm

Original Newsweek article with scary maps and graphs:
http://denisdutton.com/newsweek_coolingworld.pdf

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