Notes on Melting Polar Ice and the Gulf Stream

A large section of stone broke away and tumbled down a famous Swiss Alps mountain Thursday, shrouding a resort in dust but causing no injuries, officials said. Rock on the Eiger had been crumbling in recent days because glacial ice that had been holding it together had melted, geologists said.

Stone from the east face of Eiger mountain fell hundreds of feet in a thundering, 15-minute avalanche, Grindelwald rescue chief Kurt Amacher told TV station SF DRS.

The more than 20 million cubic feet of stone came to rest on a mountainside, sending up a cloud of dust that shrouded nearby Grindelwald resort for hours. Amacher said no one was injured and no buildings were hit in the rock fall.

A 100-foot-high rock formation on the Eiger known as the ''Madonna'' collapsed earlier Thursday. GRINDELWALD, Switzerland (AP) 7/13/06

Greenland's glaciers are melting into the sea twice as fast as previously believed, render(ing) obsolete predictions of how quickly Earth's oceans will rise over the next century, scientists said yesterday.

The new data ... 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....

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... "we are talking of the worst storm settings, the biggest storm surges . . . you are upping the probability major storms will take place."

...(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.
By Shankar Vedantam Washington Post Staff Writer 2/17/06

Glaciers Flow to the Sea at a Faster Pace, Study Says
The amount of ice flowing into the sea from large glaciers in southern Greenland has almost doubled in the last 10 years ... according to a study published in the journal Science ... There is evidence that the rise in flows would soon spread to glaciers farther north. Greenland holds enough water to raise global sea levels 20 feet or more should it all flow into the ocean.

The study compared various satellite measurements of the creeping ice in 1996, 2000 and 2005, and was done by researchers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and the University of Kansas.

...(T)he speedup in Greenland has been detected simultaneously in many glaciers, said Eric J. Rignot, the study's author... "When you have this widespread behavior of the glaciers, where they all speed up, it's clearly a climate signal," he said in an interview. "The fact that this has been going on now over 10 years in southern Greenland suggests this is not a short-lived phenomenon."

Richard B. Alley, an expert on Greenland's ice at Pennsylvania State University who did not participate in the study, agreed that the speedup of glaciers in various places supported the idea that this was an important new trend and not some fluke.

...Julian A. Dowdeswell of the Scott Polar Research Institute in Britain noted that the rising flows could be a result of both the rapid deterioration of the miles of floating "tongues" of ice where the glaciers enter the sea and an increase in water melting on the ice surface and percolating down through crevasses, where it can reduce friction with the underlying rock.
Andrew C. Revkin, New York Times; 2-17-06

Scientists Predict Melting of Ice Cap at Pole
Robert S. Boyd
Knight Ridder 1-13-06

WASHINGTON - Alarmed by an accelerating loss of ice in the Arctic Ocean, scientists are striving to understand why the speedup is happening and what it means for humankind.

If present trends continue, as seems likely, the sea surrounding the North Pole will be completely free of ice in the summertime within the lifetime of a child born today.

The loss could point the way to radical changes in the Earth's climate and weather systems.

Some researchers, such as Ron Lindsay, an Arctic scientist at the University of Washington in Seattle, fear that the polar region already may have passed a "tipping point" from which it can't recover in the foreseeable future.

Others, such as Jonathan Overpeck, the director of the Institute for the Study of Planet Earth at the University of Arizona in Tucson, think the Arctic ice pack is nearing a point of no return but hasn't reached it yet.

The National Science Foundation, a congressionally chartered agency, last month announced an urgent research program to determine what "these changes mean for both the Arctic and the Earth."

"The pace of Arctic change has accelerated," the foundation declared. "Because of the Arctic's pivotal role in the Earth's climate, it is critical -- perhaps urgent -- that we understand this system in light of abundant evidence that a set of linked and pervasive changes are under way."

The concern has heightened because last summer brought a record low in the size of the northern ice pack. "The degree of retreat was greater than ever before," said Ted Scambos, chief scientist at the National Snow and Ice Data Center in Boulder, Colo. Previous lows were set in 2002, 2003 and 2004.

Since 1980, satellite observations taken each September, the warmest month of the year in the Arctic, show that the ice cover has been shrinking by an average of almost 8 percent a year.

During that time, the polar ocean lost 540,000 square miles of ice -- an area twice the size of Texas, Scambos said.

As a result, ships were able to sail freely, without the usual aid of an icebreaker, across the northern rim of Siberia last summer. Polar bears and Inuit natives found it harder to hunt and fish on the dwindling ice.

In addition to covering a smaller area of the ocean, the remaining ice is getting thinner. Submarine measurements indicate that the central ice pack thinned by 40 percent from the 1960s to the 1990s, Lindsay reported in the November issue of the Journal of Climate.

Scientists say the great Arctic thaw will have effects all over the world, not just in the typically frozen north.

It will magnify the global warming trend that's been recorded for the last quarter-century. It'll reshape the Earth's weather systems in unknown ways. It could alter the pattern of ocean circulation, drastically changing Europe's climate.

"Loss of ice on land is also taking place at an accelerating rate, and this means sea levels will rise globally," Lindsay said. "Places like New Orleans will become even less viable."

There are two main reasons for the loss of Arctic sea ice, one external and one internal.

The external cause is the rise in the Earth's temperature, aggravated by increased emissions of carbon dioxide and other "greenhouse" gases, which trap the sun's heat.

Since 1978, the Arctic atmosphere has warmed seven times faster than the average warming trend in the southern two-thirds of the globe, John Christy, the director of the Earth System Science Center at the University of Alabama in Huntsville, reported last week.

Satellite data show that average temperatures over the Arctic spiked upward by 2.1 degrees Fahrenheit over the past 27 years, Christy said, while inching up by less than three-tenths of a degree in southern climes.

"I believe the retreat of sea ice in the Arctic is very likely a manifestation of human-caused global warming," Overpeck said. "Global temperature increases are accelerating, and so is sea-ice retreat. Humans are almost certainly the cause of the change in the Arctic."

The internal cause for the loss of sea ice may be even more alarming. Scientists say the polar ice pack will continue to be in trouble whether or not global temperatures continue to rise.

"Even if temperatures and conditions went flat from this point forward, we anticipate that Arctic ice would eventually disappear," Scambos said.

The reason is that ice and snow, like any light-colored surface, reflect heat from the sun. As the ice shrinks, it leaves more open, darker water to absorb the sun's heat.

More open water slows the formation of fresh ice in the fall and leads to a still earlier, more extensive melt the following summer.

"One of the big factors is the increasing melt in summer and the increasing amount of heat absorbed by the ice-free portions of the Arctic Ocean," Lindsay said. It's a "self-reinforcing feedback process."

Last year's record ice loss "provides further evidence that the system is on a track to this new state," said Jennifer Francis, an Arctic expert at the Institute of Marine and Coastal Sciences at Rutgers University in Highlands, N.J.

The worrisome feedback process is almost certain to continue.

"A large group of Arctic system and climate specialists could not find any natural mechanism that could slow the change," Overpeck said. "To hope for salvation from Mother Nature is to hope on long odds."

"This is a new world for the Arctic," Scambos said.

Hot Past Times hold Few Reasons to Relax about the Present
Andrew Revkin,
NYTimes 12/27/05
Earth scientists with the longest frames of reference, particularly those whose specialties begin with the prefix ''paleo,'' often seem to be the least agitated about human-caused global warming.

This has been true even in 2005, a year that saw the biggest summer retreat of Arctic sea ice ever measured, a new sign that warming seas are rising at an accelerating pace and global temperatures continuing a sharp climb that began around 1990 and appears unmatched in 2,000 years. But these backward-looking experts have seen it all before.

Recent studies have found that 49 million years ago the balmy Arctic Ocean, instead of being covered in ice, was matted with a cousin of the duckweed that cloaks suburban frog ponds. The forests on the continent now called Antarctica and on shores fringing the Arctic were once thick and lush.

And through hundreds of millions of years, concentrations of carbon dioxide and the other trace gases that trap solar energy and prevent the planet from being an ice ball have mostly been far higher than those typical during humankind's short existence.

Compared with that norm, the rapid buildup of carbon dioxide now from a binge of burning forests, coal and oil lasting for centuries (and counting) is but a blip

In fact, the planet has nothing to worry about from global warming. A hot, steamy earth would be fine for most forms of life. Earth and its biological veneer are far more resilient than human societies, particularly those still mired in poverty or pushed to the margins of the livable.

Only we humans have to be concerned, and species like polar bears that, like the poorest people, are pushed to an edge -- in the bear's case the tenuous ecosystem built around coastal sea ice.

Henk Brinkhuis, a paleoecologist and botanist at Utrecht University in the Netherlands, said it might be hard to get used to the idea, but the Arctic as we have known it for centuries ''is history.''

He said this may spell doom for polar bears, a species that branched off from brown bears only about 250,000 years ago -- an evolutionary blink of the eye.

Still, this is a special case, not necessarily a blow to the prospects of mammals in general.

The world's last huge warm spike, the Paleocene Eocene Thermal Maximum some 55 million years ago, preceded ''the biggest radiation in mammals ever,'' Dr. Brinkhuis said.

''The first horses, cows, the first primates had their origin right around then,'' Dr. Brinkhuis said. ''It may be that the extinction of the polar bear would be followed by all kinds of new species in return.''

None of this means that humans should simply embrace their fossil-fueled potency without regard to the effects. In fact, many scientists say, if we value the world as it is, there are still strong, and purely self-serving, reasons to start curbing releases of carbon dioxide and the other greenhouse gases.

That long-scale earth history, while speaking of nature's vagaries, holds supporting evidence. It is rife with thresholds, points at which a little warming turns into a lot in a hurry. Avoiding such thresholds could forestall things that societies decide matter, like rapidly rising seas or a farewell to cherished Arctic icons.

The Arctic, particularly, is filled with what amount to flippable climate switches, including natural repositories of carbon, like boggy tundra, that could emit vast amounts of greenhouse gases should the current warming trend pass certain points, said Jonathan T. Overpeck, the director of the Institute for the Study of Planet Earth at the University of Arizona.

This could amplify warming and take the climate into a realm beyond anything experienced through human evolution.

Another lesson of deep planetary history, Dr. Overpeck said, is that, once set in motion, such warm-ups can happen fast and then last a very, very long time.

''That's a condition that might be really hard to get out of for tens of thousands of years,'' he said.

Studies of the past also show that pace matters. The rise in temperature and greenhouse gases during the great heat wave 55 million years ago, while instantaneous on a geological time scale, took thousands of years to unfold.

But the pace of the recent rise in carbon dioxide is as much as 200 times as fast as what has been estimated in past rapid climate transitions.

Slowing that pace would help human endeavors as much as ecosystems, said David G. Barber, who holds the Canada research chair in Arctic systems science at the University of Manitoba.

Those who speak of the potential benefits of warming, he noted, forget that a thawing, greening Arctic, for example, will not suddenly transform from spongy tundra to wheat-friendly farmland.

''You have to generate soil,'' Dr. Barber said. ''It takes a long time to generate this kind of stuff. So it's not going to be an instantaneous sort of thing. There's going to be a lot of messiness in between.''

Even for polar bears, there are reasons to think the end is not necessarily nigh. There was at least one significant period -- the last gap between ice ages 120,000 years ago -- when the global climate was several degrees warmer than it is today and they clearly squeaked through.

So at least slowing or blunting the warming might allow them to squeak through once again. Dr. Barber said he was confident that biology would endure much of what humans throw at it. His concern is for the effects on people and the things they rely on or cherish.

''All of global warming has nothing to do with the planet,'' Dr. Barber said. ''The planet will go on through its normal cycles, and it'll do its own thing.

''It only has to do with us -- as people. Our economic side of things and our political side of things are really what are being affected by climate change. The planet could care less.''

Rethinking Warming and Hurricanes
An Interview with Kerry Emanuel by Claudia Dreifus
For decades, Kerry Emanuel, the meteorologist and hurricane specialist from the Massachusetts Institute of Technology, was known as a cautious centrist on questions of global warming and hurricane ferocity.

Professor Emanuel asserted often that no firm link had been established between warming and the intensity and frequency of hurricanes.

But in August, two weeks before Hurricane Katrina struck the Gulf Coast, Professor Emanuel wrote in the journal Nature that he had discovered statistical evidence that hurricanes were indeed affected by global warming. He linked the increased intensity of storms to the heating of the oceans.

''His paper has had a fantastic impact on the policy debate,'' said Stephen Schneider, a climatologist at Stanford. ''Emanuel's this conservative, apolitical guy, and he's saying, 'Global warming is real.' ''

On a recent visit to New York, Professor Emanuel, who is 50, said, ''It's been quite a ride since the Nature article.'' He added, ''But it's a really bad thing for a scientist to have an immovable, intractable position.''

Q. Let's go back to late August. What were your feelings as you watched television and saw Hurricane Katrina heading toward New Orleans?

A. I'll go back to a few days before that. As Katrina was making up off the coast of Florida, it was already an interesting storm. Though she was weak, the prediction was she was going to hit Florida.

But when Katrina came off the west coast of Florida, there were new predictions taking it into the central gulf and then up toward New Orleans, and I became concerned.

Many people in my profession had been worried about New Orleans for a very long time. And we had always envisioned these worst-case scenarios, and this was beginning to look like one of those. And so I plotted out the position of the ''loop current,'' which is this warm current of water in the Gulf of Mexico, and the forecast had the hurricane going right up the axis of this loop current.

I remember looking at that, and alarms went off. I had this terrible feeling of dread, which deepened when the hurricane was elevated to a Category 5. We all knew that the pumps that kept New Orleans dry wouldn't be able to handle more than about a Category 3.

My mother has an elderly friend in New Orleans, and I did something I never do. I sent her a message: ''You ought to get out, now!'' In retrospect, I will say that had Katrina been 30 miles further west, the death toll could have been much worse. New Orleans would have flooded more rapidly and to deeper levels.

Q. Because last year's hurricane season was so intense, many people declared: ''Ah, ha! Global warming!'' Were they right?

A. My answer is, Not so fast. That may have been a contributor. But the fact we had such a bad season was mostly a matter of chance. On the other hand, though the number of storms globally remained nearly constant, the frequency of Atlantic storms has been rising in concert with tropical ocean temperature, probably because of global warming.

There is no doubt that in the last 20 years, the earth has been warming up. And it's warming up much too fast to ascribe to any natural process we know about.

We still don't have a good grasp of how clouds and water vapor, the two big feedbacks in the climate system, will respond to global warming. What we are seeing is a modest increase in the intensity of hurricanes.

I predicted years ago that if you warmed the tropical oceans by a degree Centigrade, you should see something on the order of a 5 percent increase in the wind speed during hurricanes. We've seen a larger increase, more like 10 percent, for an ocean temperature increase of only one-half degree Centigrade.

Q. So what are the implications of increased ocean temperatures?

A. Not much for storms at the time of landfall. But if you look at the whole life of storms in large ocean basins, we are seeing changes. And even if that doesn't have an immediate effect, people ought to be concerned about this because it is a large change in a natural phenomenon.

Q. There are scientists who say of fossil fuel consumption and global warming, We may not have all the evidence yet, but we ought to be acting as if the worst could happen. Do you agree?

A. It's always struck me as odd that this country hasn't put far more resources into research on alternative energy. Europeans are. France has managed to go 85 percent nuclear in its electrical generation. And the Europeans have gotten together to fund a major nuclear fusion project. It almost offends my pride as a U.S. scientist that we've fallen down so badly in this competition.

Q. How did hurricanes become your specialty?

A. When I was a child, we lived in Florida for three years, and I went through of a couple of hurricanes and was very impressed by them. Later, at M.I.T., I was asked to teach a course in tropical meteorology, which included hurricanes.

As I started preparing, I realized I didn't understand what I'd been taught on the subject. As with many things, you think you understand something until you try to teach it. After some reading, I realized that the reigning theory had to be wrong.

This theory held that the main thing that drives a hurricane is just ingestion of enormous quantities of water vapor from the atmospheric environment. It made predictions that weren't true. So it became a very big intellectual challenge to me. The more I got into it, the more interesting it became.

Q. Given what you know about hurricanes, should we be building beachfront housing on the Atlantic and Gulf Coasts?

A. Disaster specialists will tell you that part of the increasing lethality of land-falling hurricanes isn't related to nature. A lot of it has to do with human activity. We're moving to the coasts in droves, like lemmings.

We're building waterfront structures there that aren't necessarily strong. We're taxing the infrastructure and paying a big price for doing that.

Q. Would you ever buy a house on the beach?

A. I'd love to! But if I could do that, I'd insist on paying for my risk. And I'd do what is now being called ''the Fire Island option,'' which involves putting up flimsy houses that you don't mind losing to a storm. You don't insure them.

Q. Almost concurrent to Hurricane Katrina, you published a beautifully packaged book, ''Divine Wind: The History and Science of Hurricanes.'' How did you feel about the timing of its publication?

A. Not terribly good. If one is just interested in sales, I suppose it was fortuitous. But I was trying to convey a sense of hurricanes as not just things of scientific interest, but as beautiful. A leopard is a very beautiful animal. But if you took it out of its cage, it would go for your jugular. Anyone can understand that neither a leopard nor a hurricane is a willful killer.

Claudia Dreifus, NY Times, 1-10-06

MANAQUIRI, Brazil - The Amazon River basin, the world's largest rain forest, is grappling with a devastating drought that in some areas is the worst since record keeping began a century ago. It has evaporated whole lagoons and kindled forest fires, killed off fish and crops, stranded boats and the villagers who travel by them, brought disease and wreaked economic havoc.
In mid-October, the governor of Amazonas State, Eduardo Braga, decreed a ''state of public calamity,'' which remains in effect as the drought's impact on the economy, public health and food and fuel supplies deepens. But other Brazilian states have also been severely affected, as have Amazon regions in neighboring countries like Peru, Bolivia and Colombia.

With hundreds of riverside settlements cut off from the outside world, the Brazilian Armed Forces have for three months mounted what officials describe as the biggest relief operation that they and civil defense agencies have carried out together. Nearly 2,000 tons of food and 30 tons of medicine have already been airlifted by plane and helicopter to affected communities just in Amazonas State, the region's largest.

''There have been years before in which we've had a deficit of rainfall, but we've never experienced drops in the water levels of rivers like those we have seen in 2005,'' said Everaldo Souza, a meteorologist at the Amazon Protection System, a Brazilian government agency in Manaus, the nine-state region's main city. ''It has truly been without precedent, and it looks like it is only going to be December or January, if then, that things return to normal.''

Scientists say the drought is most likely a result of the same rise in water temperatures in the tropical Atlantic Ocean that unleashed Hurricane Katrina. They also worry that if global warming is involved, as some of them suspect, it may be the beginning of a new era of more severe and frequent droughts in the region that accounts for nearly a quarter of the world's fresh water.

''The Amazon is a kind of canary-in-a-coal-mine situation,'' said Daniel C. Nepstad, a senior scientist at the Woods Hole Research Center in Massachusetts and the Amazon Institute of Ecological Research in Belém.

''We have no idea of the game we have played into by running this worldwide experiment of pumping so much greenhouse gases into the atmosphere,'' Mr. Nepstad said. Even more than in other parts of the world, people who live in the world's largest rain forest depend on water for transportation, food, sewage removal -- in short, just about everything, so the drought has touched nearly every aspect of their lives.

''I am very frightened,'' said Jair Souto, the mayor of a sleepy market town, Manaquiri, that started seeing signs of drought in September. ''One thing goes wrong, and the entire system follows.''

In Acre State in western Brazil, parched trees turned to tinder, and the number of forest fires recorded tripled to nearly 1,500 at its peak in September compared with a year earlier. The resulting smoke, which may itself have intensified the drought by impeding the formation of storm clouds, was so thick on some days that residents took to wearing masks when they went outdoors.

On the Madeira River, a main trade artery for products including soybeans and diesel oil, navigation had to be suspended when water levels fell to barely one-tenth of their rainy season level. Peasant farmers have watched their crops rot because they cannot ship them to market, and schools have shut down now that students can no longer get to class even in small boats.

''The water level wasn't but two fingers high, and the channel was choked in the grass that sprang up, so you couldn't even paddle a canoe,'' Rivaldo Castro Serrão, a peasant farmer in a hamlet on the Purus River, São Lázaro, said in late November as an army helicopter was delivering supplies to the 41 families living there. ''With the fish all dead and our watermelon and banana crop all rotted, we'd be starving if it weren't for the food packages the government brings.''

As water levels dropped, areas where the river normally flowed free instead became stagnant pools, the ideal breeding ground for mosquitoes. As a result, malaria, always a problem in the region, has become more prevalent and has further strained limited health care resources.

A vast majority of communities rely on the river to carry away human waste. With sewage now accumulating near the settlements, the risk of cholera and other diseases is expected to rise with water levels when the rainy season, which is starting in some parts of the basin, finally arrives in earnest. Around larger towns like Manaquiri, peasants who fled the drought looking for aid and still cannot return home have formed floating slums. Horácio de Almeida Ramos, for example, has been marooned in Manaquiri since September, when river levels began falling as much as 20 inches a day. In October, the teeming schools of fish in the lagoon suddenly died off, and by November, the entire lagoon had dried up, leaving boats here stranded and outlying communities isolated.

So Mr. Ramos lives, with his wife and their seven children, ranging in age from 2 to 15, in the canoe that brought them here and is now beached beside the pier. ''We're stuck here until the lagoon fills up again, living off charity and whatever make-work I can find,'' he said resignedly. ''We had to abandon all our crops, so I don't know what it's going to be like when we eventually go back.''

Even as the drought begins to subside, scientists are still debating what caused it. The explanation accepted most widely pins primary responsibility on higher water temperatures in tropical regions of the Atlantic Ocean, the same phenomenon being blamed for the increase in the number of hurricanes forming in the Northern Hemisphere this year.

''A warmer Atlantic not only helps give more energy to hurricanes, it also aids in evaporating air,'' said Luiz Gylvan Meira, a climate specialist at the Institute for Advanced Studies at the University of São Paulo. ''But when that air rises over the oceans in one region, it eventually has to come down somewhere else, thousands of miles away. In this case, it came down in the western Amazon, blocking the formation of clouds that would bring rain to the headwaters of the rivers that feed the Amazon.''

Whether the increases in deforestation registered in the Amazon in recent years have also played a role is less clear. The Brazilian government, often criticized for not doing enough to stop the depredations of loggers and ranchers, argues there is no direct connection, attributing the drought to larger external forces beyond the country's control.

''There are a lot of peculiar things happening on a large scale, like the tsunami, hurricanes and now this drought without precedent,'' Ciro Gomes, the minister of national integration, said in October, during a tour of the affected region. ''We should all be concerned and launch an alert to the world that irresponsible management of natural resources needs to cease, the sooner the better.''

In fact, some of the areas hardest hit by the drought are those that have done the most to limit or control deforestation. Here in Amazonas, which is larger than France, Germany, Britain and Italy combined, officials say that 98 percent of their forest remains intact but that they are suffering more than neighboring states where deforestation has been rampant.

But river-dwellers old enough to remember the era before deforestation began on a large scale say that the cutting down of trees along rivers and lakes has aided in the accumulation of silt. As a result, they say, navigation channels that remained open even in the most severe of previous dry seasons are now blocked and choked.

Research also suggests that the forest itself, and consequently the entire ecosystem, has been made more vulnerable by the drought. When deprived of an adequate ration of rainfall, trees instead drain water from the soil and curb the growth of their trunks, which are vital to their role in pulling immense quantities of carbon dioxide out of the air.

''Because droughts remain registered in the soil for up to four years, the situation is still very critical and precarious, and will remain so,'' Mr. Nepstad said. Where there are ''forests already teetering on the edge,'' he added, the prospect of ''massive tree mortality and greater susceptibility to fire'' must be considered.

While scientists largely agree that higher temperatures in the Atlantic are responsible for the severity of this year's drought, they are still searching for an explanation for that phenomenon. It could be just a one-time disturbance, or it could be more permanent, perhaps brought on by greenhouse gas emissions.

''Yes, a global warming effect would explain increases in ocean temperatures, but no one is saying that yet, because it is still very early, and we don't yet have enough data,'' said Carlos Nobre, director of Brazil's National Institute of Space Research, which monitors climatic patterns in the Amazon. ''Droughts like this one are very rare, but one consequence of a warmer planet would be that they occur with more frequency, which is something we are going to have to be watching for.''

Local governments in the Amazon do not have the luxury of awaiting the results of that research, and they fear that the drought this year may not be an aberration. So they have already begun taking as many steps as their limited budgets will permit to prepare for a recurrence.

In a region where water has always been abundant and taken for granted, programs are under way to build wells and cisterns. Warehouses to stock food, medicine and fuel are being built, in anticipation that communities may again be left isolated in the near future.

''We have become the victims of a phenomenon we did not provoke,'' said Mr. Braga, the governor of Amazonas. ''What is happening is not our fault. We didn't heat up the atmosphere or chop down our trees. But we are paying the price with the suffering of our people.''

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