Satellites Record Weakening North Atlantic Current
A North Atlantic Ocean circulation system weakened considerably in the late 1990s, compared to the 1970s and 1980s, according to a NASA study.
Source: NASA/Goddard Space Flight Center
Date: 2004-04-16
Sirpa Hakkinen, lead author and researcher at NASA's Goddard Space Flight Center, Greenbelt, Md. and co-author Peter Rhines, an oceanographer at the University of Washington, Seattle, believe slowing of this ocean current is an indication of dramatic changes in the North Atlantic Ocean climate. The study's results about the system that moves water in a counterclockwise pattern from Ireland to Labrador were published on the Internet by the journal Science on the Science Express Web site at: http://www.sciencexpress.org or http://www.aaas.org
The current, known as the subpolar gyre, has weakened in the past in connection with certain phases of a large-scale atmospheric pressure system known as the North Atlantic Oscillation (NAO). But the NAO has switched phases twice in the 1990s, while the subpolar gyre current has continued to weaken. Whether the trend is part of a natural cycle or the result of other factors related to global warming is unknown.
"It is a signal of large climate variability in the high latitudes," Hakkinen said. "If this trend continues, it could indicate reorganization of the ocean climate system, perhaps with changes in the whole climate system, but we need another good five to 10 years to say something like that is happening." Rhines said, "The subpolar zone of the Earth is a key site for studying the climate. It's like Grand Central Station there, as many of the major ocean water masses pass through from the Arctic and from warmer latitudes. They are modified in this basin. Computer models have shown the slowing and speeding up of the subpolar gyre can influence the entire ocean circulation system."
Dominant Pattern of Variability of the Sea-surface Height in the 1990s This image shows the dominant pattern of variability of the sea-surface height in the 1990s. The slope of the sea-surface height is in balance with ocean currents, much in the way weather maps of pressure relate to winds. The large blue region in the northern Atlantic represents a slowing of the counter-clockwise, cyclonically circulating subpolar gyre. For this image, the researchers used TOPEX/Poseidon data, which has been combined with ERS-1/2 data into the NASA Pathfinder data set. The Pathfinder data set also includes the Seasat and Geosat data which are referenced to TOPEX/Poseidon data. The next few years will reveal how sea surface height is going to evolve as the altimetric time series continues with JASON-1 observations. Credit: Sirpa Hakkinen, NASA GSFC
Terra MODIS Sea Surface Temperatures for North Atlantic Ocean This image of North Atlantic Ocean sea surface temperatures represents an eight-day composite from Sept 6 - Sept 13, 2001 from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on Terra. The red and orange colors represent warmer water, while the blue shades represent cold water in the higher latitudes. The Gulf Stream is evident along the U.S. eastern seaboard. The color bar is in units of degrees Celsius. Credit: Ronald Vogel, SAIC for NASA GSFC
Iceberg in North Atlantic Waters An iceberg glides southward along the east coast of Greenland in the Irminger Sea. The tip of this iceberg is about the size of a 2-story house. Credit: C. A. Linder
Trend Velocities in North Atlantic The trend of the velocities (meters per second per decade) derived from NASA Pathfinder altimeter data for the period May 1992 to June 2002. The colored vectors are statistically significant. Note how the vectors trace the following graphic of the subpolar circulation in reverse direction, which denotes a slowing gyre. Credit: Sirpa Hakkinen, NASA GSFC
Satellite data makes it possible to view the gyre over the entire North Atlantic basin. Measurements from deep in the ocean, using buoys, ships and new autonomous "robot" Seagliders, are important for validating and extending the satellite data. Sea-surface height satellite data came from NASA's Seasat (July, August 1978), U.S. Navy's Geosat (1985 to 1988), and the European Space Agency's European Remote Sensing Satellite1/2 and NASA's TOPEX/Poseidon (1992 to present).
Hakkinen and Rhines were able to reference earlier data to TOPEX/Poseidon data, and translate the satellite sea-surface height data to velocities of the subpolar gyre. The subpolar gyre can take 20 years to complete its route. Warm water runs northward through the Gulf Stream, past Ireland, before it turns westward near Iceland and the tip of Greenland.
The current loses heat to the atmosphere as it moves north. Westerly winds pick up that lost heat, creating warmer, milder European winters. After frigid Labrador Sea winters, the water in the current becomes cold, salty and dense, plunges beneath the surface, and heads slowly southward back to the equator. The cycle is sensitive to the paths of winter storms and to the buoyant fresh water from glacial melting and precipitation, all of which are experiencing great change.
While previous studies have proposed winds resulting from the NAO have influenced the subpolar gyre's currents, this study found heat exchanges from the ocean to the atmosphere may be playing a bigger role in the weakening current. Using Topex/Poseidon sea-surface height data, the researchers inferred Labrador Sea water in the core of the gyre warmed during the 1990s. This warming reduces the contrast with water from warmer southern latitudes, which is part of the driving force for ocean circulation.
The joint NASA-CNES (French Space Agency) Topex/Poseidon oceanography satellite provides high-precision data on the height of the world's ocean surfaces, a key measure of ocean circulation and heat storage in the ocean.
NASA's Earth Science Enterprise is dedicated to understanding the Earth as an integrated system and applying Earth System Science to improve prediction of climate, weather and natural hazards using the unique vantage point of space. NASA, the National Oceanic and Atmospheric Administration, and the National Science Foundation funded the study.
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For more information and images from the study on the Internet, visit:
Scientists Find That Of Tons Of Carbon Dioxide Get Stored In The Subtropical Oceans
Source: NASA/Goddard Space Flight Center--EOS Project Science Office
Date: 2000-01-31
The cold Southern Ocean surrounding Antarctica soaks up carbon dioxide from the atmosphere like a sponge, but scientists have discovered that the greenhouse gas doesn't stay there. Now researchers have found that the carbon dioxide actually ends up deep in the subtropical ocean and will report their findings in the Jan. 28 issue of the journal Science.
When scientists first started using computer models to see what happens to carbon dioxide added to the atmosphere by humans, the models showed that lots of the greenhouse gas was sponged up from the atmosphere and stored in the cold Southern Ocean, said Kenneth Caldeira, a climate scientist from Lawrence Livermore National Laboratory.
But when scientists tested the water in the Southern Ocean, they didn't find the massive stockpile that would have accumulated if the ocean was storing man-made carbon dioxide. "They found that there was very little anthropogenic carbon in the Southern Ocean, so it seemed that some of the early model results were wrong," said Caldeira.
The ocean absorbs about one-third of all man-made carbon dioxide, said Caldeira, and does it mainly in the cold regions because carbon dioxide dissolves easily into cold water, just like a soda in the refrigerator will stay bubbly a lot longer than a soda sitting in the sun. If the ocean didn't soak up carbon dioxide, the amount in the atmosphere would increase a lot faster.
Caldeira and Philip Duffy, also from Lawrence Livermore, added factors to their computer model that made the global oceans more realistic. "Water in the ocean is layered," said Caldeira. "Warm water sits on the top with colder, dense water below." When the water is very cold, like it is in the Southern Ocean in wintertime, the cold layer of water is very close to the surface and it grabs carbon dioxide out of the atmosphere.
There is a boundary dividing warm surface water and colder waters below. That boundary is very close to the surface in the Southern Ocean, but it becomes deeper and deeper as it runs north into the tropics, where the interface between warm and cold water is as much as a mile deep.
Using their new model, Caldeira and Duffy found that the carbon dioxide that gets absorbed by the Southern Ocean actually ends up in the subtropical latitudes as it slides along base of the cold, dense water layer and sinks into the deep subtropical ocean.
Some scientists expect that global warming will make the Southern Ocean less able to take carbon dioxide out of the air. "The fear is that if you warm things up too much, more precipitation will make the surface of the Southern Ocean less dense," said Caldeira. "You may start shutting off the entrance of carbon dioxide into the ocean, and things would warm up a lot faster," he said. But Caldeira warns that studies also show that if things warm up, more microscopic plants that use carbon dioxide could compensate for a Southern Ocean shutdown.
Although there is plenty of room in the deep tropical ocean to store carbon dioxide, the ocean may not be taking up as much of the greenhouse gas in the future, said Caldeira. "As the ocean absorbs more and more carbon dioxide, it becomes less able to absorb additional carbon dioxide because the water becomes acidic, so the oceans may become less efficient at carbon uptake," said Caldeira. A problem, he said, that could make the climate change more quickly. This study was supported by the NASA Oceanography Program, the Department of Energy Center for Research on Ocean Carbon Sequestration, and the Lawrence Livermore National Laboratory Directed Research and Development Program.
This story has been adapted from a news release issued by NASA/Goddard Space Flight Center--EOS Project Science Office.
Ocean Circulation Shut Down By Melting Glaciers After Last Ice Age
Source: NASA/Goddard Space Flight Center
Date: 2001-11-21
At the end of the last Ice Age 13 to 11.5 thousand years ago, the North Atlantic Deep Water circulation system that drives the Gulf Stream may have shut down because of melting glaciers that added freshwater into the North Atlantic Ocean over several hundred years, NASA and university researchers confirm. Since the Gulf Stream brings warm tropical waters north, Western Europe cooled.
The National Science Foundation (NSF) funded study also finds that if a shutdown persisted for a long enough time, the entire Northern Hemisphere would eventually cool.
The computer model simulations of ocean and atmosphere processes used in this study imply a similar phenomenon has the potential to occur in the future due to freshwater additions from increased rain and snow caused by global climate change.
"For the first time, it is shown that realistic additions of glacial meltwater into the North Atlantic would have shutdown North Atlantic Deep Water production over a period of a few hundred years if the initial ocean circulation was somewhat weaker than that of today," said David Rind, lead author of the study and a senior climate researcher at NASA's Goddard Institute for Space Studies in New York, NY. The study appears in the November 16 issue of Journal of Geophysical Research - Atmospheres.
When Rind and his colleagues entered realistic estimates of freshwater from melting glaciers into their model, they found the North Atlantic circulation stopped completely after some 300 years. When the model was adjusted to make the circulation weaker than it is today, cessation of the Gulf Stream took only 150-200 years, matching current estimates based on paleo-climate records .
Freshwater additions into the ocean through the St. Lawrence River have a profound effect on the ocean circulation.
"The more freshwater you add, and the longer you add it, the greater reduction in the North Atlantic circulation," Rind said. "According to our model, this is a linear response."
When the Gulf Stream moves warm surface water from the equator north through the Atlantic, the water cools, gets saltier due to evaporation and becomes very dense. By the time it approaches the coast of Newfoundland, or further northeast in the Norwegian Sea, it becomes dense enough to sink. This process is called overturning. The dense water then slowly travels through the deep water southward into the Southern Hemisphere, with the return flow to the north occurring at the surface.
But when freshwater gets mixed with the salty water in the North Atlantic, it makes the water less dense and slows the overturning process and the ocean circulation.
While the study finds that freshwater input could slow and stop overturning, this would not stop the Gulf Stream entirely. That's because the stream is partially pushed by winds. As a result, the model shows the reduced Gulf Stream would only transport about half as much heat northward, thereby cooling Western Europe. Were this to occur in a global warming scenario, it would act to partly counter the effects of projected greenhouse warming in parts of Western Europe.
Many scientists suspect more rainfall in parts of the Northern Hemisphere during this century as a result of greenhouse warming. That's because warmer temperatures increase the atmosphere's capacity to carry water. "The North Atlantic circulation may already be weakening due to freshwater rainfall additions associated with global warming," Rind said.
But the model shows a number of inconsistencies with previous studies on the last ice age. Those studies speculate that once freshwater stopped flowing, the ocean circulation would return within only a few decades, matching a rapid warming seen in the climate record. The model finds that deepwater circulation does not return for at least hundreds of years when the freshwater additions end. Also contrary to observations, the model showed cooling throughout the Northern Hemisphere; during the last ice age, the majority of the United States land mass did not appear to cool.
"It's hard to understand how parts of the Northern Hemisphere might have cooled to the magnitude suggested, but not North America," Rind said. "That seems to imply that either the paleo-records are being misinterpreted, or something else went on, something major that is not being accounted for. This isn't necessarily the end of the story."
This story has been adapted from a news release issued by NASA/Goddard Space Flight Center.
Editor's Note: The original news release can be found here.
Study Of Ice-Age Sediment Cores Hint Climate Change On Earth Could Be Extreme
Source: University Of Colorado At Boulder
Date: 1999-10-25
An analysis of sediments from the subtropical Atlantic Ocean deposited during Earth's last glacial period indicate sudden temperature fluctuations were as large as those seen in the warming at the end of the last ice age, raising concerns about future climate change.
Scott Lehman, a research associate at CU-Boulder's Institute of Arctic and Alpine Research, said the study indicated the temperature of the Sargasso Sea between the West Indies and the Azores fluctuated repeatedly by up to 9 degrees Fahrenheit from 60,000 to 30,000 years ago.
"What is new here is clear evidence that the warm Atlantic, like the polar Atlantic, was undergoing very large and very rapid temperature changes during the last glacial period."
Instrumental climate records and models indicate changes in warm ocean temperatures are likely to produce widespread, global climate impacts, he said. The impacts are due in part to the vast surface area of Earth's warm oceans and the fact that warm oceans create much more water vapor, increasing atmospheric heat trapping.
"The temperature of the warm ocean realm regulates the water vapor content of the atmosphere and its greenhouse capacity," he said. Past temperature records and climate models suggest ocean circulation changes, like those in the last glacial period, can be triggered by human activity, showing that "the impact of possible future circulation changes may be more dramatic and widespread than suspected."
A paper on the subject by Lehman and Julian Sachs, a former CU-Boulder researcher at INSTAAR now at Columbia University's Barnard College, will appear in the Oct. 22 issue of Science, the nation's premier weekly science magazine.
Lehman and Sachs reached their conclusions after studying 50 meters of sediment cores hauled up from several miles deep in the Sargasso Sea near Bermuda by French scientists as part of an international project. The CU researchers analyzed the saturation state of organic molecules from planktonic algae over the past 100,000 years, providing sea-surface temperatures during that period.
"The warming at the end of the last ice age about 10,000 years ago was supported by the disappearance of enormous ice sheets, a one-third increase in atmospheric carbon dioxide levels and changes in the seasonal distribution of the sun's energy," Lehman said. "But the abrupt changes we documented during the last ice age seem to be almost entirely ocean driven."
Freshening of Earth's oceans is believed to have the ability to trigger abrupt and long-lasting cooling events, including ice ages, by interfering with the conveyor belt of water carrying heat from the tropics to temperate regions. "Numerical modeling studies show that similar changes can be triggered by warming associated with human emissions as well," said Lehman.
"Trapping more heat in the atmosphere has the potential to kill major parts of ocean circulation, with the effects reverberating throughout the world," he said.
A 1999 study by INSTAAR's Don Barber and colleagues showed the collapse of two gigantic glacial lakes near Hudson Bay about 8,000 years ago poured enough fresh water into the Northern Atlantic to shut down the ocean circulation for several centuries, cooling Europe and Greenland by some 6 degrees F.
The last 8,000 years have been remarkably stable in terms of climate, considering the large temperature fluctuations, said Lehman. "By altering the environment through greenhouse gas emissions, we will likely find out how fragile the stability of Earth's climate really is. We may well find out we are dealing with a hair trigger."
The next step is to determine if similar changes occurred in the much larger Pacific Ocean, said Lehman. "If so, any human-induced changes to the ocean's plumbing are likely to affect everyone on Earth, not just Greenlanders and Northern Europeans."
Editor's Note: The original news release can be found here.
This story has been adapted from a news release issued by University Of Colorado At Boulder.
MIT Researcher Finds Evidence Of Ancient Climate Swings
Source: Massachusetts Institute Of Technology
Date: 1998-04-20
CAMBRIDGE, Mass. -- A Massachusetts Institute of Technology researcher has discovered that for at least the last 1.5 million years, the Earth has undergone rapid and dramatic climate changes similar to those observed in ice cores from more recent times. These climate swings are so dramatic that if we lived through one today, it would be like New England taking on Miami-like weather within a 25-year period.
"Ten years ago, we had no idea that climate could change this quickly," said Maureen E. Raymo, associate professor of Earth, Atmospheric and Planetary Sciences at MIT. Publishing their results for the first time in today's (April 16) issue of Nature, Raymo and her colleagues at MIT and at Woods Hole Oceanographic Institute report that millennial-scale climate instabilities--swings of as much as 10 degrees Celsius within a few decades--are not restricted to the large glacial periods of the last 700,000 years but existed much further back in time.
For the last five years, a cutting-edge initiative in climate studies has been the search for understanding of millennial-scale climate instabilities. These rapid, large-amplitude climate fluctuations were first identified in ice cores in Greenland and later in ocean sediment cores around the world.
While other researchers have focused on the geologic record of the past 120,000 years, Raymo and a handful of colleagues have undertaken the far more ambitious effort of looking at climate trends as far back as 1.5 million years ago, at the dawn of mankind.
Their work has turned up some unexpected results. "Our results suggest that such millennial-scale climate instability may be a pervasive and long-term characteristic of Earth's climate, rather than just a feature of the strong glacial-interglacial cycles of the past 800,000 years," the authors wrote.
Raymo and her colleagues, including MIT graduate student Susan Carter and research technician Kristen Ganley, also show that these climate changes are tied to changes in the conveyor-like circulation of ocean waters that delivers tropical heat to the northern Atlantic in surface currents while exporting salt-heavy deep waters cooled by Greenland's winds to the south. But while scientists know that climate changes are linked to the changes in the ocean circulation and heat transfer, they don't know what causes these climate and circulation variations in the first place.
The most dramatic instabilities tend to be triggered during the cooler Ice Age periods, most recently the period from about 100,000 years ago to about 10,000 years ago. "We're living at the end of an unusually stable period," Raymo said. After more than 8,000 years of warmth, we're about due for a cooling phase, "but all bets are off because of global warming from the buildup of carbon dioxide or other greenhouse gases in the atmosphere," she said.
To study these climate changes, Raymo retrieved previously untouched sediments from far below the ocean floor, where deep-water currents sweeping down from Greenland have caused sediment to accumulate at unusually high rates for millions of years. By analyzing the composition and chemical structure of fossils in these sediments, Raymo, a marine geologist and paleoceanographer, reconstructs past conditions on the Earth.
During a 1995 deep-sea drilling expedition--two months at sea aboard the JOIDES Resolution, a former British Petroleum oil-drilling rig--Raymo, leading a team of 24 international scientists, broke the world record for the most sediment recovered in a single ocean-drilling expedition. And although these sediments have provided a multitude of clues about climate variations over the millennia, scientists remain at a loss to explain why parts of the planet have swung from ice age to warm stage and back again. Is it due to external forces such as variations in the output of the sun or internal oscillations caused by instability in the distribution of salt and heat within the ocean?
"What causes climate variations on this time scale is a black box for scientists right now," Raymo said.
This story has been adapted from a news release issued by Massachusetts Institute Of Technology.
CORVALLIS – One of the odd possibilities that could emerge from global warming is that much of Europe, robbed of the ocean current patterns that help keep it warm, could rather abruptly enter a deep freeze and have a climate that more closely resembles Alaska than the modest temperatures it now enjoys.
Researchers from Oregon State University explored this potential phenomenon, and the fluctuations in "thermohaline circulation" that could trigger it, in an analysis to be published Thursday in Nature, a professional journal. It's by no means certain that climatic changes of this magnitude and speed will come to pass, the scientists say, but even the reasonable possibility that they might are a cause for serious concern.
"To answer difficult questions such as this we depend a lot on our computer models, and in this area different models reach different conclusions," said Peter Clark, an OSU professor of geosciences and one of the world's leading experts on glaciers and prehistoric climate changes.
"What is fairly clear is that if the ocean circulation patterns which now warm much of the North Atlantic were to slow or stop, the consequences could be quite severe," Clark said. "This might also happen much quicker than many people appreciate. At some point the question becomes how much risk do we want to take?"
The big variable in this particular equation, Clark said, is whether or not changes in global temperature and precipitation patterns might affect a gigantic conveyor belt of warm, less-salty surface water that moves from the tropical Atlantic Ocean until it finally becomes so cold and salty in the far north Atlantic that it sinks, moves south and continues the circulation pattern.
This process, called thermohaline circulation, only happens in two regions of the Earth's polar areas. But it is responsible for much ocean circulation, including the critical currents that help keep parts of North America and Europe far warmer than they would otherwise be, considering the far north latitudes at which they lie – most of Great Britain is at the same latitude as central Canada.
This circulation process, researchers say, is not inevitable. Research suggests it may have fluctuated or even stopped numerous times in Earth's distant past, and that it's especially sensitive to moderate increases in temperature or influxes of fresh water. The same very cold, very salty water that sinks in the far North Atlantic Ocean simply won't sink if it's just a little bit warmer or a little bit less salty. And at various times, it appears these changes have happened not in geologic terms of thousands of years, but rather decades.
"This system does not respond in what we call a linear manner," Clark said. "Once you start putting on the brakes, this circulation pattern could slow down faster and faster and eventually stop altogether."
Research has found that some of the Earth's most rapid climatic shifts – up to 15 degrees in decades or less – have in the past occurred during glacial periods, when large ice sheets advanced from the polar regions as far south as New York City, among other places. Some scientists have even theorized that the wild temperature fluctuations of the last ice age may have retarded the evolution and development of humans as a species, as they struggled to cope with rapidly changing conditions.
We are now in an "interglacial" period that, in theory, may have less volatility, but could also be coming to an end.
Global warming will simply delay the inevitable, Clark said, because it actually should be about time for Earth to enter its next ice age. There's a fairly well defined pattern of about 10,000-year-long interglacial periods followed by 90,000-year-long ice ages, and the current interglacial period is already more than 10,000 years old.
"At this point we just aren't sure what to expect in terms of climatic volatility," Clark said. "But the more we learn about them, it becomes clear that these thermohaline circulation patterns are quite sensitive to temperature and influxes of fresh water, such as you might get with changing precipitation patterns triggered by global warming, not to mention melting ice caps or glaciers."
So the paradox, the scientists say, is that the same greenhouse effect which might make the Earth warmer, overall, could have the opposite effect on much of Europe by slowing or shutting down the warm ocean circulation patterns on which it depends.
"Most, but not all, coupled general circulation model projections of the 21st century climate show a reduction in the strength of the Atlantic overturning circulation with increasing concentrations of greenhouse gases," the researchers said in their report in Nature. "If the warming is strong enough and sustained long enough, a complete collapse cannot be excluded." This prospect – the collapse of the thermohaline circulation patterns that dictate its climate - has raised enough concern, Clark said, that Great Britain recently launched a $40 million research program to analyze this phenomena and its possible implications. And the National Academy of Sciences recently issued a report that made reference to an "inevitable surprise" of "climate changes with startling speed."
At this time, Clark said, some of the best potential to improve the ocean and atmospheric computer models that could help resolve some of these questions about future climate lie in studies of the distant past. Ice cores from Greenland glaciers have been instrumental in this work, he said, providing a look backwards at climatic conditions more than 100,000 years into the past, and work in that area will continue.
This story has been adapted from a news release issued by Oregon State University.
Global Sea Levels Likely To Rise Higher In 21st Century Than Previous Predictions
Source: University Of Colorado At Boulder
Date: 2002-02-20
New calculations by a University of Colorado at Boulder researcher indicate global sea levels likely will rise more by the end of this century than predictions made by the Intergovernmental Panel on Climate Change in 2001.
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.
This story has been adapted from a news release issued by University Of Colorado At Boulder.
ANCHORAGE, Alaska (Reuters) - Anyone who doubts the gravity of global warming should ask Alaska's Eskimo, Indian and Aleut elders about the dramatic changes to their land and the animals on which they depend.
Native leaders say that salmon are increasingly susceptible to warm-water parasites and suffer from lesions and strange behavior. Salmon and moose meat have developed odd tastes and the marrow in moose bones is weirdly runny, they say.
Arctic pack ice is disappearing, making food scarce for sea animals and causing difficulties for the Natives who hunt them. It is feared that polar bears, to name one species, may disappear from the Northern hemisphere by mid-century.
As trees and bushes march north over what was once tundra, so do beavers, and they are damming new rivers and lakes to the detriment of water quality and possibly salmon eggs.
Still, to the frustration of Alaska Natives, many politicians in the lower 48 U.S. states deny that global warming is occurring or that a warmer climate could cause problems.
"They obviously don't live in the Arctic," said Patricia Cochran, executive director of the Alaska Native Science Commission. The Anchorage-based commission, funded by the National Science Foundation, has been gathering information for years on Alaska's thawing conditions.
The climate changes are disrupting traditional food gathering and cultures, said Larry Merculieff, an Aleut leader from the Pribilof Islands in the Bering Sea.
Indigenous residents of the far north are finding it increasingly difficult to explain the natural world to younger generations. "As species go down, the levels of connection between older and younger go down along with that," Merculieff said at a recent Anchorage conference.
SAFETY AFFECTED
Climate and weather changes even affect human safety, said Orville Huntington, vice chairman of the Alaska Native Science Commission.
"It looks like winter out there, but if you've really been around a long time like me, it's not winter," said Huntington, an Athabascan Indian from the interior Alaska village of Huslia. "If you travel that ice, it's not the ice that we traveled 40 years ago."
River ice, long used for travel in enterior Alaska, is thinner and less dependable than it used to be.
Global warming is believed to result from pollutants emitted into the atmosphere, which trap the Earth's radiant heat and create a greenhouse effect. The warming is more dramatic in polar latitudes because cold air is dry, allowing greenhouse gases to trap more solar radiation. Even a modest rise in temperature can thaw the glaciers and permafrost that cover much of Alaska.
There is no question that global warming is having pronounced effects in Alaska, said Gunter Weller, director of the University of Alaska Fairbanks' Center for Global Change and Arctic System Research.
Average temperatures in Alaska are up about 5 degrees Fahrenheit from three decades ago, and about twice that during winter, said Weller, who also heads the Cooperative Institute for Arctic Research established by the National Oceanic and Atmospheric Administration (NOAA) and the university.
That causes serious problems not only for rural Natives who live off the land but for major industries and for public structures, he said.
Most of Alaska's highways run over permafrost that is now rapidly thawing, meaning maintenance headaches for state officials. The thaw has already caused increased maintenance costs for the trans-Alaska oil pipeline, which uses special vertical supports for suspension over the tundra.
If the plight of Alaska Natives does not get politicians' attention, then the economic toll should, Weller said.
He cited the cost -- estimated at over $100 million -- of moving Shishmaref, an Inupiat Eskimo village on Alaska's northwestern coastline, to more stable ground. The village of 600 is on the verge of tumbling into the Bering Sea because of severe erosion resulting from thawed permafrost and the absence of sea ice to protect the coastline from high storm waves.
Along with Shishmaref, there are about 20 Alaska villages that are candidates for relocation because of severe erosion, with similar costs, Weller said.
Alaska's economy has already suffered from the permafrost thaw, said Robert Corell, chairman of the international Arctic Climate Impact Assessment committee.
The hard-frozen conditions needed to support ice roads around the North Slope oil fields now exist for only about 100 days a year, he pointed out. Thirty years ago, oil companies could use ice roads for about 200 days of the year, he said.
Antarctica Key To Sudden Sea Level Rise In The Past
Source: Oregon State University
Date: 2002-04-01
CORVALLIS, Ore. – A massive and unusually abrupt rise in sea level about 14,200 years ago was caused by the partial collapse of ice sheets in Antarctica, a new study has shown, in research that solves a mystery scientists have been heatedly debating for more than a decade.
In less than 500 years at the end of the last Ice Age, this event caused the Earth's sea level to rise about 70 feet. That's about four times faster than sea levels were rising most of the time during this period, and at least 20 times faster than the sea level is currently rising.
The findings were reported today in the journal Science by researchers from Oregon State University, the University of Toronto and the University of Durham in the United Kingdom.
The cause of this event, called the "global meltwater pulse 1A" since it was first identified in 1989, has until now been unknown. This study not only pinpoints the source of the meltwater pulse, but it also makes clear that significant climatic events can occur very rapidly and unpredictably.
This type of melting event thousands of years ago is different from the more recent events in Antarctica, researchers say, such as the breakup of a large percentage of the Larsen ice shelf earlier this month. But the dramatic melting illustrates the pressing need for a better understanding of Antarctica's huge ice sheets and their stability.
"We can't say at this point whether the recent breakup of part of an ice shelf in Antarctica has any relevance to this type of huge meltwater event that originated from Antarctica thousands of years ago," said Peter Clark, a professor of geosciences at OSU and one of the world's leading experts on glaciers. "We don't know yet how important these ice shelves are to stabilizing the larger ice sheets of the continent."
What is very clear, however, is the importance of Antarctica's huge ice sheets remaining stable. The West Antarctic ice sheet is thought to be potentially unstable, and if it collapsed sea levels around the world would rise almost 20 feet. The melting of the larger and more stable East Antarctic ice sheet would raise Earth's sea levels another 200 feet.
And during this comparatively short period thousands of years ago, it is now known that these two huge ice sheets were anything but stable. One or the other, or some combination of the two, melted at a surprisingly rapid rate and caused a 70-foot surge in sea levels in just a few hundred years.
"This event happened near the end of the last Ice Age, a period of de-glaciation that lasted from about 21,000 years ago to 12,000 years ago," Clark said. "The average sea level rise during that period was about eight millimeters per year. But during this meltwater pulse there was an extremely rapid disintegration of an ice sheet and sea levels rose much faster than average."
The amount of sea level rise that occurred during a single year of that period, Clark said, is more than the total sea level rise that has occurred in the past 100 years.
For some time, researchers had speculated that the cause might have been the partial melting of a major ice sheet in North America. But the OSU and other university scientists were able to develop a method that "fingerprinted" each of the possible melting scenarios from known ice sheets in the world at that time, and found that a source from Antarctica most closely matched data about sea level rise available from fossil shoreline deposits.
Using this approach, it became clear that the melting of the North American ice sheet could not have been the sole source for the meltwater pulse, and some combination of ice sheet melting in Antarctica was the more likely culprit for the sudden spurt in sea level rise.
This period thousands of years ago, Clark said, was also a time of increasing temperature, sea level and atmospheric carbon dioxide that is conceptually similar to the present day.
Prior to the partial collapse of the Antarctic ice sheets 14,200 years ago, carbon dioxide levels had risen about 50 parts-per-million in the atmosphere. In the past 150 years, since the beginning of the Industrial Revolution, carbon dioxide levels in Earth's atmosphere have risen 85 parts-per-million.
But in comparing these two eras there were differences in Earth's overall temperature, atmosphere and location of ice sheets, so it's not possible to use the events that happened then as any certain predictor of what might happen to Earth today, Clark said. What is clear is that large ice sheets of the past were vulnerable to global warming.
This meltwater event thousands of years ago not only caused the sea level to rise, the researchers said in their report, but also may have affected the atmosphere, ocean circulation and global climate.
This story has been adapted from a news release issued by Oregon State University.
Global Warming Could Trigger Cascade Of Climatic Changes
Source: Oregon State University
Date: 2003-03-14
CORVALLIS, Ore. - Global warming and the partial melting of polar ice sheets can dramatically affect not only sea levels but also Earth's climate, in ways that may be complex, rapid and difficult to adjust to, scientists say in a new study to be published Friday in the journal Science.
Sea level and climatic changes in Earth's distant past, near the end of the last Ice Age about 14,600 years ago, offer significant clues to some phenomena that Earth may experience in the near future, possibly in coming decades or centuries, the study found.
The research was done by scientists at the University of Victoria, Oregon State University, and the University of Toronto. It revealed changes in global temperature, sea level and ocean currents that can occur with surprising rapidity.
"With the advent of global warming, we're trying to identify the climatic surprises that may be in store for us, the events that we really aren't expecting," said Peter Clark, a professor of geosciences at OSU and a co-author of the study. "The more we look at this, the more it appears there have been large and abrupt changes in climate and sea level that are interconnected. If these changes were to happen in the future, they could cause huge societal disruptions."
About a year ago, Clark and his colleagues outlined in a publication in Nature how one of the unanticipated outcomes of global warming could be disruption of a "thermohaline circulation" pattern in currents of the North Atlantic Ocean, robbing Europe of the influence of warm ocean currents and causing widespread cooling. This could happen when additional rainfall or melting glaciers in the Northern Hemisphere inject more fresh water into the North Atlantic and make the ocean less salty.
Scientists now believe this current may have slowed or stopped altogether many times in Earth's past. The shutdown of this current was one prominent feature of the last Ice Age.
In the new study, the researchers found that an Antarctic melting event called "Meltwater Pulse 1A," which occurred near the end of the last Ice Age about 14,600 years ago, raised Earth's sea levels about 70 feet in less than 500 years. The melting event simultaneously caused the North Atlantic circulation to turn on, causing widespread warming of the Northern Hemisphere.
The melting event occurred following a time of increasing temperature, sea level and carbon dioxide that had some similarities - and key differences - to the present day, Clark said.
"These past events provide important clues as to how the climate system may change as the Earth warms," Clark said.
"Global warming might cause a shutdown of currents in the North Atlantic and cause Europe to cool," he said. "But just as people are trying to adjust to that event, the same warming might also help melt an Antarctic ice sheet which would tend to start the current in the North Atlantic moving again. And that might be considered a good thing, unless you live in a coastal area which is now going to be flooded by rising sea levels."
This story has been adapted from a news release issued by Oregon State University.
Climate Change Will Affect Carbon Sequestration In Oceans, Scientists Say
Source: University Of Illinois At Urbana-Champaign
Date: 2002-12-04
CHAMPAIGN, Ill. -- The direct injection of unwanted carbon dioxide deep into the ocean is one suggested strategy to help control rising atmospheric carbon dioxide levels and mitigate the effects of global warming. But, like the problems associated with the long-term storage of nuclear waste, finding a safe place to sequester the carbon may be more difficult than scientists first anticipated.
Because the atmosphere interacts with the oceans, the net uptake of carbon dioxide and the oceans' sequestration capacity would be affected by a change in climate. Just how effective carbon sequestration would be, in light of projected climate change, has not been studied before. Indeed, estimating the impact of carbon injection is complicated because of a limited understanding of climate and oceanic carbon cycle feedback mechanisms.
"Through various feedback mechanisms, the ocean circulation could change and affect the retention time of carbon dioxide injected into the deep ocean, thereby indirectly altering oceanic carbon storage and atmospheric carbon dioxide concentration," said Atul Jain, a professor of atmospheric sciences at the University of Illinois at Urbana-Champaign. "Where you inject the carbon dioxide turns out to be a very important issue."
To investigate the possible effects of feedbacks between global climate change, the ocean carbon cycle and oceanic carbon sequestration, Jain and graduate student Long Cao developed an atmosphere-ocean, climate-carbon cycle model of intermediate complexity. The researchers then used the model to study the effectiveness of oceanic carbon sequestration by the direct injection of carbon dioxide at different locations and ocean depths.
Jain and Cao found that climate change has a big impact on the oceans' ability to store carbon dioxide. The effect was most pronounced in the Atlantic Ocean.
"When we ran the model without the climate feedback mechanisms, the Pacific Ocean held more carbon dioxide for a longer period of time," Cao said. "But when we added the feedback mechanisms, the retention time in the Atlantic Ocean proved far superior. Based on our initial results, injecting carbon dioxide into the Atlantic Ocean would be more effective than injecting it at the same depth in either the Pacific Ocean or the Indian Ocean."
Future climate change could affect both the uptake of carbon dioxide in the ocean basins and the ocean circulation patterns themselves, Jain said. "As sea-surface temperatures increase, the density of the water decreases and thus slows down the ocean thermohaline circulation, so the ocean's ability to absorb carbon dioxide also decreases. This leaves more carbon dioxide in the atmosphere, exacerbating the problem. At the same time, the reduced ocean circulation will decrease the ocean mixing, which decreases the ventilation to the atmosphere of carbon injected into the deep ocean. Our model results show that this effect is more dominating in the Atlantic Ocean."
Tucking away excess carbon dioxide in Davy Jones's locker is not a permanent solution for reducing the amount of carbon dioxide in the atmosphere. "Sequestering carbon in the deep ocean is, at best, a technique to buy time," Jain said.
"Carbon dioxide dumped in the oceans won't stay there forever. Eventually it will percolate to the surface and into the atmosphere."
To buy as much time as possible, the carbon dioxide must remain trapped for as long as possible. "The big question is in what region of which ocean will future climate change have the least effect," Jain said. "That's where we will want to store the carbon dioxide."
Jain and Cao will present their latest findings at the American Geophysical Union meeting in San Francisco, Dec. 6-10. The U.S. Department of Energy funded the work.
This story has been adapted from a news release issued by University Of Illinois At Urbana-Champaign.
New Climate Model Predicts Greater 21st Century Warming
Source: American Geophysical Union
Date: 2003-05-21
WASHINGTON - For the first time, scientists have incorporated multiple human and natural factors into a climate projection model. They predict that increased carbon dioxide in the atmosphere, due to changes in the carbon cycle, combined with a decrease in human-produced sulphates, may cause accelerated global warming during the 21st century, as compared with simulations without these feedback effects.
Results of the study, completed by Chris D. Jones and colleagues at the Met Office's Hadley Centre for Climate Prediction and Research in Bracknell, United Kingdom, appear in the journal Geophysical Research Letters, published by the American Geophysical Union.
Previous studies have indicated that human activities, such as carbon dioxide and sulphate emissions, as well as natural factors, such as changes in solar radiation, emissions from volcanic eruptions and interactions between climate and the carbon cycle, are important mechanisms for causing climate change. No previous climate studies have, however, integrated all of these factors into a single climate experiment.
The climate-carbon cycle experiment completed by Jones and his colleagues is the first to take a more comprehensive Earth-systems approach to climate modeling. This "all-forcings experiment," or ALL, incorporates carbon dioxide emissions, non-carbon dioxide greenhouse gases, human-produced sulphate aerosol levels, the reflection of solar radiation associated with sulphate in the atmosphere (the "albedo effect"), atmospheric ozone levels, levels of solar radiation, the effects of volcanic eruptions, and climate-carbon cycle feedbacks.
Discrepancies between observed temperature trends in the 20th century and climate simulations that consider only a limited number of factors have hindered the ability of some models to predict future climate change. The ALL model was, however, able to recreate observed temperature records for the 20th century, illustrating the importance of including multiple factors in climate change projections. Also, the rise in carbon dioxide simulated by ALL more closely matches the observed carbon dioxide rise than did previous models. The researchers say that this indicates that mechanisms other than direct carbon dioxide emissions caused by human activity also contribute to the observed trend. Jones and his colleagues were also able to replicate estimates of the amount of carbon currently stored in the oceans and on land worldwide.
With regard to future climate predictions, ALL shows that predicted reductions in human sulphate emissions will cause a reduction in the cooling effect associated with sulphates in the atmosphere, or a net warming. The model predicts that the resultant warming will enhance soil respiration, meaning that the increased amounts of carbon stored in the soil during the 20th century will be released into the atmosphere, causing a faster rise in atmospheric carbon dioxide. By the end of the 21st century, the authors state, the increase in carbon dioxide and decrease of sulphates will cause a substantially higher global warming of 5.5 degrees Celsius [9.9 degrees Fahrenheit] compared with 4 degrees Celsius [7 degrees Fahrenheit] when these interactions are neglected.
### The research was supported by the UK Department for the Environment, Food and Regional Affairs.
This story has been adapted from a news release issued by American Geophysical Union.
Climate Sensitivity May Be Higher Than Many Think, Researchers Say
Source: University Of Illinois At Urbana-Champaign
Date: 2001-06-05
CHAMPAIGN, Ill. — In the wake of mounting evidence of global warming, decision-makers are wrestling with related policy issues. Now, researchers at the University of Illinois have shown that the probability of severe climate change is much greater than many scientists or policy-makers had thought. "The size and impacts of anthropogenically induced climate change strongly depend on the climate sensitivity – the change in equilibrium surface warming due to a doubling of the concentration of carbon dioxide in the atmosphere," said Michael Schlesinger, a UI atmospheric scientist. "According to the Intergovernmental Panel on Climate Change, the climate sensitivity lies between 1.5 and 4.5 degrees Centigrade."
If the climate sensitivity is less than 1.5 degrees Centigrade, then climate change may not be a serious problem, Schlesinger said. "If, however, the climate sensitivity is greater than the IPCC’s upper bound, then climate change may be one of humanity’s most severe problems of the 21st century. By judging the likelihood of the climate sensitivity having any particular value – that is, by its probability density function – the crafting of robust adaptive climate-change policy could be greatly facilitated."
Schlesinger and UI atmospheric scientist Natalia Andronova used a simple climate/ocean model and the near-surface temperature record to estimate the probability density function for climate sensitivity. They considered 16 radiative-forcing models, which included such factors as greenhouse gases, anthropogenic sulfate aerosol, solar irradiance and volcanoes. For each model, the changes in global-mean near-surface temperature were calculated for the years 1765 through 1997.
The researchers found that, as a result of natural variability and uncertainty in the radiative forcing, the climate sensitivity could lie between 1 and 10 degrees Centigrade. "Consequently, there is a 54 percent likelihood that the climate sensitivity lies outside the IPCC range," Schlesinger said. "Our results show that the probability density function very strongly depends on which radiative forcing factors have actually been at work during the period of the temperature measurements," he said. "At present, the most likely scenario is one that includes anthropogenic sulfate aerosol forcing but not solar variation. Although the value of the climate sensitivity in that case is most uncertain, there is a 70 percent chance that it exceeds the maximum IPCC value. This is not good news."
One way to reduce the uncertainty of which probability distribution is the appropriate one to use in impact and policy studies is "to determine whether the sun’s irradiance has actually changed during the past 150 years," Andronova said. "Another way would be to consider the net radiative forcing of all the anthropogenic aerosols, not just the sulfate aerosol."
A paper discussing the researchers’ findings has been accepted for publication in the Journal of Geophysical Research. The National Science Foundation and the U.S. Department of Energy supported the work.
This story has been adapted from a news release issued by University Of Illinois At Urbana-Champaign.
Climate Models Predict Wetter Winters, Warmer Summers In The West
Source: USDA Forest Service, Pacific Northwest Research Station
Date: 2003-11-14
Portland, Ore. November 13, 2003 -- When you turn on the television news for the latest weather report, usually a week-long forecast is given. But what if you could learn what to expect in the coming decades?
Scientists have now developed computer models that are producing the first simulations of how ecosystems and fire regimes could change in the 21st century. Some of these simulations are showing that the Western United States may get wetter during the winter and experience warmer summers throughout the 21st century. These results have been used in national and global assessments of global climate change.
The research, conducted by scientists from the USDA Forest Service Pacific Northwest Research (PNW) Station, Oregon State University, and others from around the world, provides key evidence that fire and fuel loads in Western forests are linked to global carbon balance.
The research team, led by PNW Research Station bioclimatologist Ron Neilson, developed the mapped-atmosphere-plant-soil system model (MAPSS) that can simulate vegetation type in any area of the world and can determine the impact of global climate change.
"Climate change shows up in forests first as changes in growth," says Neilson. "The second way is through changes in disturbance regimes--the long-term patterns of fire, drought, insects, and diseases that are basic to forest development."
Because fire plays a big role in changing ecosystems, Neilson and his team combined the MAPPS model with CENTURY (MC1), a biogeochemical model produced by a team at Colorado State University, as well as a new fire model.
"MC1 accurately simulated the fire pulses of the last 100 years, with the big fires in the same areas where they actually occurred," says Neilson. "It simulated the 1910 fires in Idaho, and it nailed Yellowstone in 1988. It was in the ballpark on the Tillamook Burn of the 1930s and a year early on the Biscuit Fire in southwest Oregon, which actually burned in 2002."
Uncertainty Of Rapid Climate Change More Crucial Than Ice Ages
Source: Penn State
Date: 2001-02-21
San Francisco, Calif. – Climate always changes and what we are used to today is about as stable as climate gets, according to a Penn State glaciologist who has investigated climate records from both poles.
"Today, because of the circulation of the Atlantic Ocean, we can grow roses in Norway and we have been able to do that for a long time," says Dr. Richard Alley, Evan Pugh Professor of Geosciences. "But there is no such thing as a stable climate; if the warm current were not there, we would see more polar bears and fewer roses."
While ice ages that come on over tens of thousands of years have periodically covered large areas of the globe with glaciers, Alley is more concerned with rapid climate changes -- within a decade -- that effect the northern and southern hemispheres differently. "The secret of why the whole world rides a roller coaster in the ice age and freezes and thaws is probably greenhouse gases, especially carbon dioxide," Alley told attendees today (Feb. 17) at the annual meeting of the American Association for the Advancement of Science. "The seesaw effect of rapid climate change is probably caused by ocean circulation and the keys to this change are locked in the polar ice."
While during an ice age the whole Earth becomes cold together and warms up together, episodes of rapid climate change have chilled only the northern Atlantic and warmed the area around Antarctica or warmed the Atlantic and cooled Antarctica. Normally, warm surface water off the coast of Brazil moves northward toward Scandinavia. When the current reaches the areas of cold air, the water cools, becoming more dense, and sinks. This sinking current then travels down to the tip of South America.
If something interrupts this current, the north becomes cold and can rapidly freeze while the heat south of the equator remains there. The north becomes cold and the south becomes warm.
Despite the frozen north, the trade winds continue to blow westward over the Atlantic and the Isthmus of Panama. The moisture picked up by the wind rains out in the Pacific, leaving the Atlantic saltier. Pacific rain never makes it to the Atlantic because of the large continents in between, and the salty water that used to leave the Atlantic around the tip of South America cannot because the current no longer flows. Eventually, the Atlantic becomes salty enough that the sinking resumes and turns on the ocean circulation. "We don't know how this cycle begins, nor do we know geographically where the salty water begins to sinks to return circulation. However, this pattern of cold north with warm far south has occurred repeatedly," says Alley.
With global warming, more precipitation in the far north and melting of glaciers there may freshen the north Atlantic and slow or stop the ocean circulation.
"If this happens in the near future, then the north may become colder even though global warming is affecting the rest of the world," says the Penn State researcher. "However, ultimately, the warming will take over and not just the mountain glaciers, but the Greenland glacier could melt as well."
What will melt under various conditions is difficult to predict. The mountain glaciers, which are currently melting, will raise sea level only a little. If Greenland melts, it will raise sea levels much higher. While these sea-level increases will be noticeable and perhaps inconvenient, people will adapt to them, according to Alley.
"The question always asked is if the West Antarctic Ice sheet will fall into the ocean in the next 100 years," says Alley. "This event would have high impact on continental shores and terrestrial lowlands. It is a low probability event, but not a zero possibility."
The mountain glaciers only hold enough frozen water to raise sea level a foot or two if they all melt. Greenland could melt over many millennia, raising sea level 20 feet or more. However, changes in West Antarctica could raise sea level 20 feet in centuries or faster. To monitor the potential for the unlikely event of West Antarctica melting and to try to predict and plan for rapid climate change, researchers must continue to study the past climate record locked in the frozen poles, according to Alley.
This story has been adapted from a news release issued by Penn State.
University Of California Study Sheds New Light On Climate-change Processes
Source: University Of California - Davis
Date: 2004-03-11
A new study from the University of California shows, for the first time, that the deep-ocean circulation system of the north Atlantic, which controls ice-age cycles of cold and warm periods in the Northern Hemisphere, is integrally coupled to salinity levels in the Caribbean Sea.
This research reinforces concerns that global warming, by melting the glacial ice of Greenland, could quickly and profoundly change salinity and temperatures in the north Atlantic Ocean. One consequence might be much colder weather in northern Europe and Britain and perhaps even in eastern Canada and the U.S. northeast.
The study is published by the journal Nature in its online edition today (March 10) and its print edition tomorrow. The authors are graduate student Matthew Schmidt and geology professor Howard Spero of UC Davis, and geology professor David Lea of UC Santa Barbara.
During Earth's warm periods, like the present one, surface ocean currents transport heat from the tropics to the cool northern latitudes. The new data, a record of Caribbean salinity for the past 120,000 years, show that when the northern hemisphere warmed, Caribbean salinity levels dropped.
The authors hypothesize that elevated Caribbean salinity, which is transported via the Gulf Stream to the north Atlantic, amplifies the heat transport system by increasing the deep-ocean circulation rate. When the North Atlantic cools, Caribbean salinity builds up because the deep ocean circulation drops to a fraction of its previous rate and the Gulf Stream no longer transports salty water away.
If Caribbean salinity helps power the heat-transport system, then what might happen if melting ice from Greenland dilutes the salinity of the north Atlantic at a time when Caribbean salinity is low, like today?
"Our atmospheric and oceanic systems are integrally linked," Spero said. "Unnatural climate perturbations, such as global warming, can impact ocean circulation and nudge the system towards a threshold that could produce an abrupt climatic change."
Spero and Lea have a long collaboration in using chemical analyses of the fossil shells of tiny sea animals, called foraminifera, to reconstruct Earth's climate.
In their new study, they teamed up with Schmidt, Spero's Ph.D. student, to analyze fossil foraminifera to reconstruct the rise and fall of the temperature and salinity of the Caribbean Sea throughout the last full ice-age cycle, when huge glaciers reached far south into North America and Europe.
They then compared those salinity cycles with published reconstructions of ice-age oscillations of deep Atlantic Ocean circulation patterns. The correlations were striking.
"I don't believe the Earth can plummet into an ice age today," Spero said. "But human-caused global warming has the ability to affect climate in ways we haven't seen before and do it very quickly."
A paper that refers to similar events occurring today was recently published in the journal Nature by an international group of scientists led by Ruth Curry of Woods Hole Oceanographic Institute in Massachusetts.
Curry's study showed that in the past 50 years, salinity in the tropical Atlantic Ocean has risen and salinity in the north Atlantic has fallen. That is the pattern that Schmidt, Spero and Lea say has led to colder climates in the past. "We present a historical analog to the salinity buildup that is observed in the tropics today by Dr. Curry and others," said Spero and Lea.
### The University of California study was funded by the USSSP Schlanger Ocean Drilling Graduate Fellowship and grants from the U.S. National Science Foundation.
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