A chunk of ice shelf nearly the size of Manhattan has broken away from Ellesmere Island in Canada's northern Arctic, another dramatic indication of how warmer temperatures are changing the polar frontier, scientists said Wednesday.

Derek Mueller, an Arctic ice shelf specialist at Trent University in Ontario, told The Associated Press that the 4,500-year-old Markham Ice Shelf separated in early August and the 19-square-mile shelf is now adrift in the Arctic Ocean.

"The Markham Ice Shelf was a big surprise because it suddenly disappeared. We went under cloud for a bit during our research and when the weather cleared up, all of a sudden there was no more ice shelf. It was a shocking event that underscores the rapidity of changes taking place in the Arctic," said Mueller.

Mueller also said that two large sections of ice detached from the Serson Ice Shelf, shrinking that ice feature by 47 square miles — or 60 percent — and that the Ward Hunt Ice Shelf has also continued to break up, losing an additional eight square miles.

Mueller reported last month that seven square miles of the 170-square-mile and 130-feet-thick Ward Hunt shelf had broken off.

This comes on the heels of unusual cracks in a northern Greenland glacier, rapid melting of a southern Greenland glacier, and a near record loss for Arctic sea ice this summer. And earlier this year a 160-square mile chunk of an Antarctic ice shelf disintegrated.

"Reduced sea ice conditions and unusually high air temperatures have facilitated the ice shelf losses this summer," said Luke Copland, director of the Laboratory for Cryospheric Research at the University of Ottawa. "And extensive new cracks across remaining parts of the largest remaining ice shelf, the Ward Hunt, mean that it will continue to disintegrate in the coming years."

Formed by accumulating snow and freezing meltwater, ice shelves are large platforms of thick, ancient sea ice that float on the ocean's surface but are connected to land.

Ellesmere Island was once entirely ringed by a single enormous ice shelf that broke up in the early 1900s. All that is left today are the four much smaller shelves that together cover little more than 299 square miles.

Martin Jeffries of the U.S. National Science Foundation and University of Alaska Fairbanks said in a statement Tuesday that the summer's ice shelf loss is equivalent to over three times the area of Manhattan, totaling 82 square miles — losses that have reduced Arctic Ocean ice cover to its second-biggest retreat since satellite measurements began 30 years ago.

"These changes are irreversible under the present climate and indicate that the environmental conditions that have kept these ice shelves in balance for thousands of years are no longer present," said Mueller.

During the last century, when ice shelves would break off, thick sea ice would eventually reform in their place.

"But today, warmer temperatures and a changing climate means there's no hope for regrowth. A scary scenario," said Mueller.

The loss of these ice shelves means that rare ecosystems that depend on them are on the brink of extinction, said Warwick Vincent, director of Laval University's Centre for Northern Studies and a researcher in the program ArcticNet.

"The Markham Ice Shelf had half the biomass for the entire Canadian Arctic Ice Shelf ecosystem as a habitat for cold, tolerant microbial life; algae that sit on top of the ice shelf and photosynthesis like plants would. Now that it's disappeared, we're looking at ecosystems on the verge of extinction,' said Mueller.

Along with decimating ecosystems, drifting ice shelves and warmer temperatures that will cause further melting ice pose a hazard to populated shipping routes in the Arctic region — a phenomenon that Canada's Prime Minister Stephen Harper seems to welcome.

Harper announced last week that he plans to expand exploration of the region's known oil and mineral deposits, a possibility that has become more evident as a result of melting sea ice. It is the burning of oil and other fossil fuels that scientists say is the chief cause of manmade warming and melting ice.

Harper also said Canada would toughen reporting requirements for ships entering its waters in the Far North, where some of those territorial claims are disputed by the United States and other countries.

CHARMAINE NORONHA

A huge 19 square mile (55 square km) ice shelf in Canada's northern Arctic broke away last month and the remaining shelves have shrunk at a "massive and disturbing" rate, the latest sign of accelerating climate change in the remote region, scientists said on Tuesday.

They said the Markham Ice Shelf, one of just five remaining ice shelves in the Canadian Arctic, split away from Ellesmere Island in early August. They also said two large chunks totaling 47 square miles had broken off the nearby Serson Ice Shelf, reducing it in size by 60 percent.

"The changes ... were massive and disturbing," said Warwick Vincent, director of the Centre for Northern Studies at Laval University in Quebec.

Temperatures in large parts of the Arctic have risen far faster than the global average in recent decades, a development that experts say is linked to global warming.

"These substantial calving events underscore the rapidity of changes taking place in the Arctic," said Derek Mueller, an Arctic ice shelf specialist at Trent University in Ontario.

"These changes are irreversible under the present climate and indicate that the environmental conditions that have kept these ice shelves in balance for thousands of years are no longer present," he said in an e-mailed statement from the research team sent late on Tuesday.

Mueller said the total amount of ice lost from the shelves along Ellesmere Island this summer totaled 83 square miles -- more than three times the area of Manhattan island.

The figure is more than 10 times the amount of ice shelf cover that scientists estimated on July 30 would vanish from around the island this summer.

"Reduced sea ice conditions and unusually high air temperatures have facilitated the ice shelf losses," said Luke Copland of the University of Ottawa.

BLEAK FUTURE

"Extensive new cracks across remaining parts of the largest remaining ice shelf, the Ward Hunt, mean that it will continue to disintegrate in the coming years," he said.

The first sign of serious recent erosion in the five shelves came in late July, when sheets of ice totaling almost eight square miles broke off the Ward Hunt shelf. Since then that shelf has lost another 8.5 square miles

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Ellesmere Island was once home to a single enormous ice shelf totaling around 3,500 square miles. All that is left of that shelf today are the four much smaller shelves that together cover little more than 300 square miles

.

Scientists say the ice shelves, which contain unique ecosystems that had yet to be studied, will not be replaced because they took so long to form.

The rapid melting of ice in the Canadian Arctic archipelago worries Ottawa, which fears foreign ships might try to sail through the waters without seeking permission first.

Last week Prime Minister Stephen Harper said Canada would toughen reporting requirements for ships entering its waters in the Far North, where some of those territorial claims are disputed by the United States and other countries.

David Ljunggren

More ominous signs Wednesday have scientists saying that a global warming "tipping point" in the Arctic seems to be happening before their eyes: Sea ice in the Arctic Ocean is at its second lowest level in about 30 years.

The National Snow and Ice Data Center reported that sea ice in the Arctic now covers about 2.03 million square miles. The lowest point since satellite measurements began in 1979 was 1.65 million square miles set last September.

With about three weeks left in the Arctic summer, this year could wind up breaking that previous record, scientists said.

Arctic ice always melts in summer and refreezes in winter. But over the years, more of the ice is lost to the sea with less of it recovered in winter. While ice reflects the sun's heat, the open ocean absorbs more heat and the melting accelerates warming in other parts of the world.

Sea ice also serves as primary habitat for threatened polar bears.

"We could very well be in that quick slide downward in terms of passing a tipping point," said senior scientist Mark Serreze at the data center in Boulder, Colo. "It's tipping now. We're seeing it happen now."

Within "five to less than 10 years," the Arctic could be free of sea ice in the summer, said NASA ice scientist Jay Zwally.

"It also means that climate warming is also coming larger and faster than the models are predicting and nobody's really taken into account that change yet," he said.

Five climate scientists, four of them specialists on the Arctic, told The Associated Press that it is fair to call what is happening in the Arctic a "tipping point." NASA scientist James Hansen, who sounded the alarm about global warming 20 years ago before Congress, said the sea ice melt "is the best current example" of that.

Last year was an unusual year when wind currents and other weather conditions coincided with global warming to worsen sea ice melt, Serreze said. Scientists wondered if last year was an unusual event or the start of a new and disturbing trend.

This year's results suggest the latter because the ice had recovered a bit more than usual thanks to a somewhat cooler winter, Serreze said. Then this month, when the melting rate usually slows, it sped up instead, he said.

The most recent ice retreat primarily reflects melt in the Chukchi Sea off Alaska's northwest coast and the East Siberian Sea off the coast of eastern Russia, according to the center.

The Chukchi Sea is home to one of two populations of Alaska polar bears.

Federal observers flying for a whale survey on Aug. 16 spotted nine polar bears swimming in open ocean in the Chukchi. The bears were 15 to 65 miles off the Alaska shore. Some were swimming north, apparently trying to reach the polar ice edge, which on that day was 400 miles away.

Polar bears are powerful swimmers and have been recorded on swims of 100 miles but the ordeal can leave them exhausted and susceptible to drowning.

And the melt in sea ice has kicked in another effect, long predicted, called "Arctic amplification," Serreze said.

That's when the warming up north is increased in a feedback mechanism and the effects spill southward starting in autumn, he said. Over the last few years, the bigger melt has meant more warm water that releases more heat into the air during fall cooling, making the atmosphere warmer than normal.

On top of that, researchers were investigating "alarming" reports in the last few days of the release of methane from long frozen Arctic waters, possibly from the warming of the sea, said Greenpeace climate scientist Bill Hare, who was attending a climate conference in Ghana. Giant burps of methane, which is a potent greenhouse gas, is a long feared effect of warming in the Arctic that would accelerate warming even more, according to scientists.

Overall, the picture of what's happening in the Arctic is getting worse, said Bob Corell, who headed a multinational scientific assessment of Arctic conditions a few years ago: "We're moving beyond a point of no return."

SETH BORENSTEIN and DAN JOLING

In northern Greenland, a part of the Arctic that had seemed immune from global warming, new satellite images show a growing giant crack and an 11-square-mile chunk of ice hemorrhaging off a major glacier, scientists said Thursday.

And that's led the university professor who spotted the wounds in the massive Petermann glacier to predict disintegration of a major portion of the Northern Hemisphere's largest floating glacier within the year.

If it does worsen and other northern Greenland glaciers melt faster, then it could speed up sea level rise, already increasing because of melt in sourthern Greenland.

The crack is 7 miles long and about half a mile wide. It is about half the width of the 500 square mile floating part of the glacier. Other smaller fractures can be seen in images of the ice tongue, a long narrow sliver of the glacier.

"The pictures speak for themselves," said Jason Box, a glacier expert at the Byrd Polar Research Center at Ohio State University who spotted the changes while studying new satellite images. "This crack is moving, and moving closer and closer to the front. It's just a matter of time till a much larger piece is going to break off.... It is imminent."

The chunk that came off the glacier between July 10 and July 24 is about half the size of Manhattan and doesn't worry Box as much as the cracks. The Petermann glacier had a larger breakaway ice chunk in 2000. But the overall picture worries some scientists.

"As we see this phenomenon occurring further and further north — and Petermann is as far north as you can get — it certainly adds to the concern," said Waleed Abdalati, director of the Center for the Study of Earth from Space at the University of Colorado.

The question that now faces scientists is: Are the fractures part of normal glacier stress or are they the beginning of the effects of global warming?

"It certainly is a major event," said NASA ice scientist Jay Zwally in a telephone interview from a conference on glaciers in Ireland. "It's a signal but we don't know what it means."

It is too early to say it is clearly global warming, Zwally said. Scientists don't like to attribute single events to global warming, but often say such events fit a pattern.

University of Colorado professor Konrad Steffen, who returned from Greenland Wednesday and has studied the Petermann glacier in the past, said that what Box saw is not too different from what he saw in the 1990s: "The crack is not alarming... I would say it is normal."

However, scientists note that it fits with the trend of melting glacial ice they first saw in the southern part of the massive island and seems to be marching north with time. Big cracks and breakaway pieces are foreboding signs of what's ahead.

Further south in Greenland, Box's satellite images show that the Jakobshavn glacier, the fastest retreating glacier in the world, set new records for how far it has moved inland.

That concerns Colorado's Abdalati: "It could go back for miles and miles and there's no real mechanism to stop it."

SETH BORENSTEIN

Climate change could release unexpectedly huge stores of carbon dioxide from Arctic soils, which would in turn fuel a vicious circle of global warming, a new study warned Sunday.

And according to one commentary on the research, current models of climate change have not taken this extra source of greenhouse gas into account.

Scientists have long known that organic carbon trapped inside a blanket of frozen permafrost covering one fifth of the world's land mass would, if thawed, release greenhouse gases into the atmosphere.

But until now they simply did not have a good idea of how much carbon is actually locked inside this Arctic freezer.

To find out, a team of American researchers led by Chien-Lu Ping of the University of Alaska Fairbanks examined a wide range of landscapes across North America.

They took soil samples from 117 sites, each to a depth of at least one metre, in order to provide a full assessment of the region's so-called "carbon pool."

Previous estimates of the Arctic carbon pool relied heavily on a relative handful of measurements conducted outside of the Arctic, and only to a depth of 40 centimetres (15.5 inches).

The study, published in the British journal Nature Geoscience, found that the stock of organic carbon "is considerably higher than previously thought" -- 60 percent more than the previously estimated.

This is roughly equivalent of one sixth of the entire carbon content in the atmosphere.

And that is just for North America. The size and mix of landscapes in the northern reaches of Europe and Russia are about the same, and probably contain a comparable amount of carbon-dioxide producing matter currently held in check only by the cold, the study said.

And the danger of a thaw is real, note climate scientists.

The Nobel Prize-winning UN panel of climate change scientists project temperature increases by century's end of up to six degrees Celsius (10.8 degrees Fahrenheit) in the Arctic region, which is more sensitive to global warming than any other part of the planet.

Commenting on the research, Christian Beer of the Max Planck Institute in Jena, Germany, pointed out that the climate change models upon which future projections are based, do not include the potential impact of the gases trapped frozen Arctic soils.

"Releasing even a portion of this carbon into the atmosphere, in the form of methane or carbon dioxide, would have an significant impact on Earth's climate," he noted in his commentary, also published in Nature Geoscience.

Methane, another greenhouse gas, is less abundant than carbon dioxide but several times more potent as a driver of global warming. >>>>

US and British researchers have confirmed the link between warmer climate and an increase in powerful rainstorms, according to a study released Thursday that underscores one of the challenges of global warming.

The researchers even found that the increase of extreme rainfall was higher than what has been predicted in current computer models, according to the study published in the journal Science.

The scientists pointed out that one of the biggest concerns regarding climate change is that heavy rainstorms will become more common and intense in a warmer climate due to the higher moisture available for condensation.

The more powerful rains also increase the risk of flooding that could have substantial impacts on societies and economies, they said.

To understand the link between warmer climate, the researchers used naturally-driven changes associated with the El Nino weather system as a laboratory for testing their hypotheses.

El Nino is an occasional seasonal warming of the central and eastern Pacific Ocean that upsets normal weather patterns from the western seaboard of Latin America to East Africa, and potentially has a global impact on climate.

Studying satellite observations from the past 20 years, the experts found that heavy rain events increased during warm periods and decreased during cold times.

"A warmer atmosphere contains larger amounts of moisture which boosts the intensity of heavy downpours," said Brian Soden, associate professor at the University of Miami Rosenstiel School of Marine & Atmospheric Science.

"Comparing observations with results from computer models improves understanding of how rainfall responds to a warming world" said Richard Allan, of the University of Reading's Environmental Systems Science Centre. >>>>

During the European heat wave of 2003 that killed tens of thousands, the temperature in parts of France hit 104 degrees. Nearly 15,000 people died in that country alone. During the Chicago heat wave of 1995, the mercury spiked at 106 and about 600 people died.

In a few decades, people will look back at those heat waves "and we will laugh," said Andreas Sterl, author of a new study. "We will find (those temperatures) lovely and cool."

Sterl's computer model shows that by the end of the century, high temperatures for once-in-a-generation heat waves will rise twice as fast as everyday average temperatures. Chicago, for example, would reach 115 degrees in such an event by 2100. Paris heat waves could near 109 with Lyon coming closer to 114.

Sterl, who is with the Royal Netherlands Meteorological Institute, projects temperatures for rare heat waves around the world in a study soon to be published in the journal Geophysical Research Letters.

His numbers are blistering because of the drying-out effect of a warming world. Most global warming research focuses on average daily temperatures instead of these extremes, which cause greater damage.

His study projects a peak of 117 for Los Angeles and 110 for Atlanta by 2100; that's 5 degrees higher than the current records for those cities. Kansas City faces the prospect of a 116-degree heat wave, with its current all-time high at 109, according to the National Climactic Data Center.

A few cities, such as Phoenix, which once hit 122 degrees and is projected to have heat waves of 120, have already reached these extreme temperatures once or twice. But they would be hitting those numbers a little more often as the world heats up over time. For New York, it would only be a slight jump from the all-time record of 104 at John F. Kennedy Airport to the projected 106.

It could be worse. Delhi, India is expected to hit 120 degrees; Belem, Brazil, 121, and Baghdad, 122.

Those figures make sense, Ken Kunkel, a top Midwestern climate scientist and interim director of the Illinois Water Survey.

These are temperatures that are dangerous, said University of Wisconsin environmental health professor Dr. Jonathan Patz.

"Extreme temperature puts a huge demand on the body, especially anyone with heart problems," Patz said. "The elderly are the most vulnerable because they don't sense temperature as well."

And it's not just at the end of the century. By 2050, heat waves will be 3 to 5 degrees hotter than now "and probably be longer-lasting," Sterl said.

By mid-century, southern France's extreme heat waves should be around 111 degrees and then near 118 by the end of the century, Sterl's climate models predict. In the 1990s, that region's extreme heat wave peaked at 104 degrees; in the 1950s, the worst heat wave peaked around 91 degrees, according to Sterl.

SETH BORENSTEIN

Hurricane Bertha strengthened to a Category 3 storm Monday as it swirled in the central Atlantic, but it posed no immediate threat to land.

Forecasters expect the Atlantic season's first hurricane to head toward Bermuda. It was too early to tell whether the storm would hit the island, but residents were urged to monitor Bertha's progress.

At 5 p.m. Monday, the hurricane was located 730 miles east-northeast of the Northern Leeward Islands and about 1,150 miles southeast of Bermuda. It was moving west-northwest at about 12 mph. Maximum sustained winds were measured at 115 mph.

Daniel Brown, a forecaster at the National Hurricane Center, said Bertha was expected to stay at roughly the same intensity.

"It looks like it will remain over warm enough waters for the next couple of days," Brown said. "Conditions aren't going to change too much over the next couple days, so it will likely remain a strong hurricane."

The hurricane center has projected 12 to 16 named storms in the Atlantic this season, with six to nine of them hurricanes.

The U.S. has not been hit by a major hurricane since 2005, the busiest season on record, which brought a destructive triple-punch of Katrina, Wilma and Rita ashore.

The Atlantic hurricane season runs through Nov. 30. >>>>

Experts Worry About a Disturbing Trend at the North Pole

The distinct possibility that the North Pole could be free of sea ice -- for the first time in recorded history -- may become a cold reality this summer.

The Arctic's thick, resilient multiyear sea ice (frozen sea surface), which usually accumulates and lasts through the annual melting season, has started to give way to thinner, vulnerable first-year ice.

Satellite data gathered by the University of Colorado's National Snow and Ice Data Center showed that young sea ice, which is no more than about 60 inches deep and much more susceptible to melting away, now makes up only 72 percent of the Arctic ice sheet. Using that estimate, scientists at the center see a 50 percent chance that ice at the highest point in the Arctic will melt by the summer's end.

Andy Mahoney, a center researcher, has pinpointed this year in particular as having the "greatest chance" of being ice-free.

Such a scenario, however, will depend on the weather during the next couple of months. "It will probably come down to how cloudy it is this summer," Mahoney says. "If there's clear skies and if atmospheric patterns resemble last year's, you're going to see a lot more melt."

Increased rates of Arctic melt have altered the region in unprecedented ways. Arctic sea ice dwindled to a record low in September, clearing a route through the fabled Northwest Passage that runs from Greenland to Alaska. Opening of the path has provided ships a shorter, more direct route between Asia and Europe.

"It's got a shock level for people because there's always ice at the North Pole, but there are also real implications," Mahoney said. "If the North Pole melted out, the shipping industry would be paying very close attention to that."

Wieslaw Maslowski, who conducts Arctic ice research from his base at the Naval Postgraduate School in Monterey, Calif., told ABC News last summer that there was a chance that the Arctic's entire ice sheet could vanish for the first time in just four or five years.

Such a statement was considered a daring projection at the time, given that climate prediction models estimated a few years before that it would take at least another 40 or 50 years before such a scenario is likely to occur.

But now, Maslowski says that "whether the Arctic sea ice disappears for the first time this summer or four or eight summers from now may be beside the point."

"The point," he noted, "is that we may well be passing through the sea-ice tipping point now. We'll just have to see what July and August weather have in store for the ice this summer."

The disappearance of Arctic sea ice may mean an even hotter planet, since the region's ice pack helps cool the earth by bouncing the sun's rays back into outer space. This reflective property, known as albedo, also prevents the rays from reaching the ocean, where heat is absorbed.

Less sea ice means more dark open water to absorb the heat, which melts the sea ice even further.

"Losing the ice sheet means losing an important way of cooling down," Mahoney said. "As a result, global warming would accelerate as the ice retreats."

BILL BLAKEMORE and TUAN C. NGUYEN

This month's flooding in the Midwest is reminiscent of the Great Flood of 1993, weather officials now say. But while a repeat of 1993 can't be ruled out, they say, this year is unlikely to match that colossal disaster.

Several of the 1993 records have already been broken this year and flooding is forecasted to last for weeks more. Preliminary estimates put damage into the billions of dollars with overall storm deaths put at 24 since late May.

But barring unexpected summer rains, National Weather Service officials do not expect a repeat of the incredible intensity and duration of the tremendous flood 15 years ago.

Regardless, history is repeating itself as some residents who moved into the floodplain since 1993, with assurances from FEMA and other officials that they would be safe, have seen their towns submerged this month, creating personal financial disasters for people who in many cases have no flood insurance.

Looking back

Few disasters in U.S. history match the devastation of 1993, when hundreds of levees along the Mississippi and Missouri Rivers failed, killing 50 people and causing more than $15 billion in damage.

One of the most remarkable aspects of the 1993 flood was its duration. From May through September, major flooding occurred across North Dakota, South Dakota, Nebraska, Kansas, Minnesota, Iowa, Missouri, Wisconsin, and Illinois.

Some 50,000 homes were destroyed or damaged. And 75 towns were "totally and completely under flood waters," according to an account by Lee W. Larson, Chief of the Hydrologic Research Laboratory at NOAA's National Weather Service.

"It was certainly the largest and most significant flood event ever to occur in the United States," Larson said.

There were plenty of lessons to learn.

Levees inadequate

According to the U.S. Army Corps of Engineers, water overtopped or damaged 40 of 229 federal levees and 1,043 of 1,347 non-federal levees.

Among the other monumental effects in 1993:

• Barge traffic on both mighty rivers halted for almost 2 months.
• Bridges were out or not accessible on the Mississippi River from Davenport, Iowa to St. Louis, Missouri.
• Ten commercial airports were flooded.
• All railroad traffic in the Midwest was halted.
• The 1993 and 1994 harvests were lost.
• Numerous sewage treatment plants were destroyed.

The 1993 flood was not entirely unexpected. NOAA hydrologists had warned that a wet fall in 1992 and normal or above normal snowpack in the central United States meant flooding could be serious when things began to thaw in 1993.

"I think everyone was ready for some short-term heavy rain and serious flooding, but nobody thought it would last all summer," recalled Kenneth D. King, chief of hydrologic services at the NOAA National Weather Service Central Region Headquarters in Kansas City, Mo.

Nonstop rain

The rains were unrelenting.

In a five-month stretch starting April 1, 1993, nearly 48 inches fell in east-central Iowa, where an average of 33 inches of precipitation normally falls in an entire year.

By mid-June, soil throughout the entire region was saturated, so additional rains brought heavy runoff. In many locations within the nine-state area hardest hit by the flooding, it rained for 20 or more days in July; normally it rains eight or nine days during that month.

An unusual climate setup fueled the rains. A high pressure system known as the Bermuda High, which typically sits out in the Atlantic Ocean during summer and steers hurricanes toward the United States, was stronger than normal and moved farther to the north and west. This created a dam of air that stopped storms in their tracks over the Midwest, preventing them from sliding to the East Coast as they normally would.

The Missouri River crested at a record 48.9 feet at Kansas City on July 27, 1993. This water joined the already full Mississippi River and pushed the Mississippi to a record crest of 49.47 feet at St. Louis in Aug. 1.

Some locations on the Mississippi River were in continuous flood for six months.

Lessons learned?

One might assume some lessons had been learned. In fact, the NOAA administrator at the time, Dr. James (Jim) Baker, assumed so, too:

"Although the Great Flood of 1993 has caused devastating human, environmental and economic impacts, the lessons learned will guide us in providing improved services and benefits to the nation in the future," Baker wrote then.

But 15 years later, more homes than ever exist in the Midwest floodplains, and few projects to improve levees have been undertaken.

As an example of lessons not learned, the town of Gulfport, Illinois was inundated by 10 feet of water this month when a levee failed. That levee had been deemed safe by local officials and FEMA. Only 28 of the town's 750 residents had flood insurance, the Associated Press reports.

As Gerald Galloway, a professor of engineering at the University of Maryland, put it a few months after Hurricane Katrina: "The half-life of the memory of a flood is very short."

Repeat of 1993?

Already, several 1993 records have fallen.

"Major and record flooding continues at numerous points from Iowa to Missouri," according to NOAA. So far 31 levees have been overtopped or breached on the Mississippi between southern Iowa and St. Louis, with additional levees threatened through the weekend, the agency said in a statement. The breached levees actually reduce flooding downstream, officials note.

The Mississippi is not expected to rise above 40 feet this week at St. Louis. That's nearly 10 feet lower than in 1993.

Rivers across Iowa are generally falling, while record and major flooding continues on several rivers in Wisconsin, NOAA states.

Preliminary indications are that new records have been set at 21 National Weather Service river forecast locations on tributaries to Mississippi and Missouri Rivers.

Flooding will continue for weeks, forecasters say.

"If we compare 1993 and 2008 for the same time periods - through mid-June - we cannot rule out 2008 flooding could become comparable to 1993 if we have similar storms during the summer of 2008," the agency stated.

Bright future

The summer outlook appears sunny, however:

"As the upcoming weather pattern is expected to change and favor drier weather for the central plains in mid-late June, the chance of repeating 1993 appears to be low at this time," NOAA states. "The critical unknown elements are the pattern of future rainfall ... and the timing and frequency of any future rainfall."

Predicting the future is of course tricky. And it's liable to get trickier.

Last week, NOAA released a report detailing how the agency expects global warming to affect the United States. The bottom line: "Droughts, heavy downpours, excessive heat, and intense hurricanes are likely to become more commonplace."

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Robert Roy Britt