Tuesday, July 28, 2009

NIH LAUNCHES THE HUMAN CONNECTOME PROJECT TO UNRAVEL THE BRAINS CONNECTIONS

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The National Institutes of Health Blueprint for Neuroscience Research is launching a $30 million project that will use cutting-edge brain imaging technologies to map the circuitry of the healthy adult human brain. By systematically collecting brain imaging data from hundreds of subjects, the Human Connectome Project (HCP) will yield insight into how brain connections underlie brain function, and will open up new lines of inquiry for human neuroscience.

Investigators have been invited to submit detailed proposals to carry out the HCP, which will be funded at up to $6 million per year for five years. The HCP is the first of three Blueprint Grand Challenges, projects that address major questions and issues in neuroscience research.

The Blueprint Grand Challenges are intended to promote major leaps in the understanding of brain function, and in approaches for treating brain disorders. The three Blueprint Grand Challenges to be launched in 2009 and 2010 address:

-The connectivity of the adult, human brain
-Targeted drug development for neurological diseases
-The neural basis of chronic pain disorders

"The HCP is truly a grand and critical challenge: to map the wiring diagram of the entire, living human brain. Mapping the circuits and linking these circuits to the full spectrum of brain function in health and disease is an old challenge but one that can finally be addressed rigorously by combining powerful, emerging technologies," says Thomas Insel, M.D., director of the National Institute of Mental Health (NIMH), which is part of the NIH Blueprint.

Scientists have studied the relationship between the structure and function of the human brain since the 1800s. Some parts of the brain serve basic functions such as movement, sensation, emotion, learning and memory. Others are more important for uniquely human functions such as abstract thinking. The connections between brain regions are important for shaping and coordinating these functions, but scientists know little about how different parts of the human brain connect.

"Neuroscientists have only a piecemeal understanding of brain connectivity. If we knew more about the connections within the brain — and especially their susceptibility to change — we would know more about brain dysfunction in aging, mental health disorders, addiction and neurological disease," says Story Landis, Ph.D., director of the National Institute of Neurological Disorders and Stroke (NINDS), also part of the NIH Blueprint.

For example, there is evidence that the growth of abnormal brain connections during early life contributes to autism and schizophrenia. Changes in connectivity also appear to occur when neurons degenerate, either as a consequence of normal aging or of diseases such as Alzheimer’s.

In addition to brain imaging, the HCP will involve collection of DNA samples, demographic information and behavioral data from the subjects. Together, these data could hint at how brain connectivity is influenced by genetics and the environment, and in turn, how individual differences in brain connectivity relate to individual differences in behavior. Primarily, however, the data will serve as a baseline for future studies. These data will be freely available to the research community.

The complexity of the brain and a lack of adequate imaging technology have hampered past research on human brain connectivity. The brain is estimated to contain more than 100 billion neurons that form trillions of connections with each other. Neurons can connect across distant regions of the brain by extending long, slender projections called axons — but the trajectories that axons take within the human brain are almost entirely uncharted.

In the HCP, researchers will optimize and combine state-of-the-art brain imaging technologies to probe axonal pathways and other brain connections. In recent years, sophisticated versions of magnetic resonance imaging (MRI) have emerged that are capable of looking beyond the brain’s gross anatomy to find functional connections. Functional MRI (fMRI), for example, uses changes in blood flow and oxygen consumption within the brain as markers for neuronal activity, and can highlight the brain circuits that become active during different behaviors. Three imaging techniques are suggested, but are not required, for carrying out the HCP:

-High angular resolution diffusion imaging with magnetic resonance (HARDI), which detects the diffusion of water along fibrous tissue, and can be used to visualize axon bundles.
-Resting state fMRI (R-fMRI), which detects fluctuations in brain activity while a person is at rest, and can be used to look for coordinated networks within the brain.
-Electrophysiology and magnetoencephalography (MEG) combined with fMRI (E/M fMRI), which adds information about the brain’s electrical activity to the fMRI signal. In this procedure, the person performs a task so that the brain regions associated with that task become active.

Since this is the first time that researchers will combine these brain imaging technologies to systematically map the brain’s connections, the HCP will support development of new data models, informatics and analytic tools to help researchers make the most of the data. Funds will be provided for building an on-line platform to disseminate HCP data and tools, and for engaging and educating the research community about how to use these data and tools.

"Human connectomics has been gaining momentum in the research community for a few years," says Michael Huerta, Ph.D., associate director of NIMH and the lead NIH contact for the HCP. "The data, the imaging tools and the analytical tools produced through the HCP will play a major role in launching connectomics as a field."

The field of neuroscience emerged in the late 19th century, when scientists observed individual brain cells for the first time. Since then, researchers have made breathtaking progress in understanding the anatomy, cell biology, physiology and chemistry of the brain in both health and disease. Yet many fundamental questions remain unanswered, including how brain function translates into mental function and why brain function declines with age. Advances in neuroimaging, genomics, computational neuroscience and engineering have put us on the brink of another great era in neuroscience, when we can expect to make unprecedented discoveries regarding normal brain activity, disorders of the brain and our very sense of self.

National Institutes of Health

NOAA SCIENTISTS FIND TSUNAMI SHADOW VISIBLE FROM SPACE

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For the first time, NOAA scientists have demonstrated that tsunamis in the open ocean can change sea surface texture in a way that can be measured by satellite-borne radars. The finding could one day help save lives through improved detection and forecasting of tsunami intensity and direction at the ocean surface.

“We’ve found that roughness of the surface water provides a good measure of the true strength of the tsunami along its entire leading edge. This is the first time that we can see tsunami propagation in this way across the open ocean,” said lead author Oleg Godin of NOAA’s Earth System Research Laboratory and the Cooperative Institute for Research in Environmental Sciences, in Boulder, Colo.

Large tsunamis crossing the open ocean stir up and darken the surface waters along the leading edge of the wave, according to the study. The rougher water forms a long, shadow-like strip parallel to the wave and proportional to the strength of the tsunami. That shadow can be measured by orbiting radars and may one day help scientists improve early warning systems. The research is published online this week in the journal, Natural Hazards and Earth System Sciences.

The new research challenges the traditional belief that tsunamis are too subtle in the open ocean to be seen at the surface. The findings confirm a theory, developed by Godin and published in 2002-05, that tsunamis in the deep ocean can be detected remotely through changes in surface roughness.

In 1994, a tsunami shadow was captured by video from shore moments before the wave struck Hawaii. That observation and earlier written documentation of a shadow that accompanied a deadly tsunami on April 1, 1946, inspired Godin to develop his theory. He tested the theory during the deadly December 26, 2004, Indian Ocean tsunami, the result of the Sumatra-Andaman earthquake.

Godin and colleagues analyzed altimeter measurements of the 2004 tsunami from NASA’s Jason-1 satellite. The data revealed clear evidence of an increased surface roughness along the leading edge of the tsunami as it passed across the Indian Ocean between two and six degrees south latitude.

Tsunamis can be detected in several ways. One detection method uses a buoy system that warns coastal communities in the United States of an approaching tsunami. NOAA’s Deep-ocean Assessment and Reporting of Tsunamis (DART) early warning system uses sensors on the ocean floor to measure changes in pressure at each location. The DART network of 39 stations extends around the perimeter of the Pacific Ocean and along the western edge of the North Atlantic Ocean and Gulf of Mexico. The technology provides accurate, real-time information on the amplitude, over time, of an approaching tsunami. NOAA's tsunami warning centers then use this information to forecast the tsunami's impact on coastlines.

A second method uses space-borne altimeters to detect tsunamis by measuring small changes in sea surface height. Only a handful of these instruments are in orbit and the observations are limited to points along a line.

The new study presents a third way to detect tsunamis — by changes in the texture of the surface water across a wide span of the open ocean.

Godin’s research confirmed his theory that a tsunami wave roughens the surface water through air-sea interaction. First the leading edge of the tsunami wave stirs up the surface winds. Those same winds, which become more chaotic than the wave itself, then churn the surface waters along the slope of the wave.

Because rough water is darker than smooth water, a contrast forms between the dark, rough water of the wave and the bright, smooth water on either side of it. Common scientific instruments, called microwave radars and radiometers, are able to detect this contrast, known as a tsunami shadow.

When orbiting the Earth, microwave radars and radiometers can observe a band of ocean surface hundreds of kilometers wide and thousands of kilometers long. If programmed correctly to observe sea surface roughness, they could potentially map an entire tsunami, said Godin.

(Photo: NOAA)

National Oceanic and Atmospheric Administration

STEALTHY GENE NETWORK MAKES BRAIN TUMORS FLOURISH

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The brain tumor afflicting Sen. Edward Kennedy – a glioblastoma – is the most aggressive and wily form of brain cancer. It has foiled researchers’ decades-long efforts to thwart its explosive growth in the brain. The lethal tumor – the most common brain tumor in humans -- nimbly alters its genes like a quick-change artist to elude treatments to destroy it.

But scientists from Northwestern University Feinberg School of Medicine have discovered the formidable tumor’s soft underbelly. They have identified a network of 31 mutated genes that stealthily work together to create the perfect molecular landscape to allow the tumor to flourish and mushroom to the size of an apple in just a few months.

Northwestern researchers have also identified a new gene, Annexin A7, a vital guard whose job is to halt tumor growth and whose level in the tumor predicts how long a glioblastoma patient will survive. The genetic landscape of glioblastomas eliminates Annexin A7 by wiping out its home base, chromosome 10.

The discoveries help researchers understand the tumor's vulnerabilities and offer new targets for therapies to treat the disease.

"These 31 genes are the kingpins in what you could call an organized crime network of genes that enable the tumor to grow with breathtaking speed," said Markus Bredel, M.D., director of the Northwestern Brain Tumor Institute research program, assistant professor of neurological surgery at the Feinberg School and the principal investigator of the two studies reporting these new findings. "These 31 genes are highly connected to and affect hundreds of other genes involved in this process." Bredel also is a member of the Robert H. Lurie Comprehensive Cancer Center of Northwestern University.

The studies are published in the July 15 issue of Journal of the American Medical Association.

It was no small task for Bredel to identify the kingpins of the network. Glioblastomas are among the most biologically complex cancers, involving changes in thousands of genes. Leukemia, by contrast, involves changes in just a few genes.

Bredel said the way to identify the key players was to determine which genes had the most connections to other genes in the network. "We don't care about the gangster on the street. We wanted to find the big bosses," Bredel said. "If you knock them out, then you have a big effect on all the other genes in the network."

To accomplish that, Bredel and colleagues looked at the molecular levels and genetic profiles of more than 500 brain tumors of patients from around the country as well as the clinical profiles of the patients. Bredel's first study reports on the 31 key mutated genes he discovered that comprise the tumor’s primary network. These genes represent a recurrent pattern of the most important mutations in the tumor.

"If many of those genes were mutated, the more aggressive the tumor and the less time the patient would survive," Bredel said. These are called hub genes because they are at the hub of all the mutated gene interaction.

In the second study, Bredel reports on the interaction of two of the 31 genes that are most frequently and concurrently affected by genetic alterations. One of those genes is EGFR (epidermal growth factor receptor), a well-known player in many cancers and known as an oncogene. EGFR has physiological importance in normal development. In nearly half of the glioblastoma patients, EGFR is mutated and abnormally activated, as if its dial is cranked permanently to "high."

Bredel discovered that the other gene, Annexin A7, is a vital guard whose job is to halt tumor growth by regulating the EGFR gene. Bredel found Annexin A7 was lost or diminished in many of the patients' malignant brain tumors. The reason was its home base -- chromosome 10 -- had been wiped out in about 75% of the tumors.

The study showed the presence and quantity of Annexin A7 in the malignant brain tumor accurately predicts how long a glioblastoma patient will survive. The more Annexin A7, the more restrictions on the tumor growth and the longer the survival. Bredel said the identification of Annexin A7 as a major regulator of EGFR provides a biological reason for the frequent parallel loss of chromosome 10 and gain of the EGFR gene in glioblastomas.

In the laboratory, Bredel tested the relationship between EGFR and Annexin A7 to try to understand exactly how they affected the tumor. Working with brain tumor cells, Bredel increased the level of EGFR and, in parallel, knocked out Annexin A7. The tumor cells grew much faster compared to tumor cells in which only one gene was modified.

"It's like a 'buy two, get one free' sale," Bredel said. "The tumor says, 'I'm making a good deal. I'm going to buy those two mutations because it's going to be very rewarding for me'."

With one mutation that increased EFGR and the other that eliminated chromosome 10 and Annexin A7, the tumor was free to proliferate unchecked.

“Understanding the key role of Annexin A7 in malignant brain tumors offers the opportunity for a new therapeutic target,” Bredel said. "The challenge is now that we've established that this gene is important, how can we modulate it through molecular cancer therapy?"

"We want to extend the survival of the patients, transform this hyper-acute disease into a more chronic tumor disease," Bredel said. "Maybe someday, a glioblastoma patient will be able to live for 10 or 20 years after a diagnosis."

Northwestern University

CALTECH, JPL SCIENTISTS SAY THAT MICROBIAL MATS BUILT 3.4-BILLION-YEAR-OLD STROMATOLITES

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Stromatolites are dome- or column-like sedimentary rock structures that are formed in shallow water, layer by layer, over long periods of geologic time. Now, researchers from the California Institute of Technology (Caltech) and the Jet Propulsion Laboratory (JPL) have provided evidence that some of the most ancient stromatolites on our planet were built with the help of communities of equally ancient microorganisms, a finding that "adds unexpected depth to our understanding of the earliest record of life on Earth," notes JPL astrobiologist Abigail Allwood, a visitor in geology at Caltech.

Their research, published in a recent issue of the Proceedings of the National Academy of Sciences (PNAS), might also provide a new avenue for exploration in the search for signs of life on Mars.

"Stromatolites grow by accreting sediment in shallow water," says John Grotzinger, the Fletcher Jones Professor of Geology at Caltech. "They get molded into these wave forms and, over time, the waves turn into discrete columns that propagate upward, like little knobs sticking up."

Geologists have long known that the large majority of the relatively young stromatolites they study—those half a billion years old or so—have a biological origin; they're formed with the help of layers of microbes that grow in a thin film on the seafloor.
How? The microbes' surface is coated in a mucilaginous substance to which sediment particles rolling past get stuck. "It has a strong flypaper effect," says Grotzinger. In addition, the microbes sprout a tangle of filaments that almost seem to grab the particles as they move along.

"The end result," says Grotzinger, "is that wherever the mat is, sediment gets trapped."

Thus it has become accepted that a dark band in a young stromatolite is indicative of organic material, he adds. "It's matter left behind where there once was a mat."

But when you look back 3.45 billion years, to the early Archean period of geologic history, things aren't quite so simple.

"Because stromatolites from this period of time have been around longer, more geologic processing has happened," Grotzinger says. Pushed deeper toward the center of Earth as time went by, these stromatolites were exposed to increasing, unrelenting heat. This is a problem when it comes to examining the stromatolites' potential biological beginnings, he explains, because heat degrades organic matter. "The hydrocarbons are driven off," he says. "What's left behind is a residue of nothing but carbon."

This is why there has been an ongoing debate among geologists as to whether or not the carbon found in these ancient rocks is diagnostic of life or not.

Proving the existence of life in younger rocks is fairly simple—all you have to do is extract the organic matter, and show that it came from the microorganisms. But there's no such cut-and-dried method for analyzing the older stromatolites. "When the rocks are old and have been heated up and beaten up," says Grotzinger, "all you have to look at is their texture and morphology."

Which is exactly what Allwood and Grotzinger did with samples gathered at the Strelley Pool stromatolite formation in Western Australia. The samples, says Grotzinger, were "incredibly well preserved." Dark lines of what was potentially organic matter were "clearly associated with the lamination, just like we see in younger rocks. That sort of relationship would be hard to explain without a biological mechanism."

"We already knew from our earlier work that we had an assemblage of stromatolites that was most plausibly interpreted as a microbial reef built by Early Archean microorganisms," adds Allwood, "but direct evidence of actual microorganisms was lacking in these ancient, altered rocks. There were no microfossils, no organic material, not even any of the microtextural hallmarks typically associated with microbially mediated sedimentary rocks."

So Allwood set about trying to find other types of evidence to test the biological hypothesis. To do so, she looked at what she calls the "microscale textures and fabrics in the rocks, patterns of textural variation through the stromatolites and—importantly—organic layers that looked like actual fossilized organic remnants of microbial mats within the stromatolites."

What she saw were "discrete, matlike layers of organic material that contoured the stromatolites from edge to edge, following steep slopes and continuing along low areas without thickening." She also found pieces of microbial mat incorporated into storm deposits, which disproved the idea that the organic material had been introduced into the rock more recently, rather than being laid down with the original sediment. "In addition," Allwood notes, "Raman spectroscopy showed that the organics had been 'cooked' to the same burial temperature as the host rock, again indicating the organics are not young contaminants."

Allwood says she, Grotzinger, and their team have collected enough evidence that it's no longer any "great leap" to accept these stromatolites as biological in origin. "I think the more we dig at these stromatolites, the more evidence we'll find of Early Archean life and the nature of Earth's early ecosystems," she says.

That's no small feat, since it's been difficult to prove that life existed at all that far back in the geologic record. "Recently there has been increasing but still indirect evidence suggesting life existed back then, but direct evidence of microorganisms, at the microscale, remained elusive due to poor preservation of the rocks," Allwood notes. "I think most people probably thought that these Early Archean rocks were too poorly preserved to yield such information."

The implications of the findings don't stop at life on Earth.

"One of my motivations for understanding stromatolites," Allwood says, "is the knowledge that if microbial communities once flourished on Mars, of all the traces they might leave in the rock record for us to discover, stromatolite and microbial reefs are arguably the most easily preserved and readily detected. Moreover, they're particularly likely to form in evaporative, mineral-precipitating settings such as those that have been identified on Mars. But to be able to interpret stromatolitic structures, we need a much more detailed understanding of how they form."

(Photo: Abigail Allwood)

California Institute of Technology

SOLAR CYCLE LINKED TO GLOBAL CLIMATE

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Establishing a key link between the solar cycle and global climate, research led by scientists at the National Science Foundation (NSF)-funded National Center for Atmospheric Research (NCAR) in Boulder, Colo., shows that maximum solar activity and its aftermath have impacts on Earth that resemble La Niña and El Niño events in the tropical Pacific Ocean.

The research may pave the way toward predictions of temperature and precipitation patterns at certain times during the approximately 11-year solar cycle.

"These results are striking in that they point to a scientifically feasible series of events that link the 11-year solar cycle with ENSO, the tropical Pacific phenomenon that so strongly influences climate variability around the world," says Jay Fein, program director in NSF's Division of Atmospheric Sciences. "The next step is to confirm or dispute these intriguing model results with observational data analyses and targeted new observations."

The total energy reaching Earth from the sun varies by only 0.1 percent across the solar cycle. Scientists have sought for decades to link these ups and downs to natural weather and climate variations and distinguish their subtle effects from the larger pattern of human-caused global warming.

Building on previous work, the NCAR researchers used computer models of global climate and more than a century of ocean temperature to answer longstanding questions about the connection between solar activity and global climate.

The research, published this month in a paper in the Journal of Climate, was funded by NSF, NCAR's sponsor, and by the U.S. Department of Energy.

"We have fleshed out the effects of a new mechanism to understand what happens in the tropical Pacific when there is a maximum of solar activity," says NCAR scientist Gerald Meehl, the paper's lead author. "When the sun's output peaks, it has far-ranging and often subtle impacts on tropical precipitation and on weather systems around much of the world."

The new paper, along with an earlier one by Meehl and colleagues, shows that as the Sun reaches maximum activity, it heats cloud-free parts of the Pacific Ocean enough to increase evaporation, intensify tropical rainfall and the trade winds, and cool the eastern tropical Pacific.

The result of this chain of events is similar to a La Niña event, although the cooling of about 1-2 degrees Fahrenheit is focused further east and is only about half as strong as for a typical La Niña.

Over the following year or two, the La Niña-like pattern triggered by the solar maximum tends to evolve into an El Niño-like pattern, as slow-moving currents replace the cool water over the eastern tropical Pacific with warmer-than-usual water.

Again, the ocean response is only about half as strong as with El Niño.

True La Niña and El Niño events are associated with changes in the temperatures of surface waters of the eastern Pacific Ocean. They can affect weather patterns worldwide.

The paper does not analyze the weather impacts of the solar-driven events. But Meehl and his co-author, Julie Arblaster of both NCAR and the Australian Bureau of Meteorology, found that the solar-driven La Niña tends to cause relatively warm and dry conditions across parts of western North America.

More research will be needed to determine the additional impacts of these events on weather across the world.

"Building on our understanding of the solar cycle, we may be able to connect its influences with weather probabilities in a way that can feed into longer-term predictions, a decade at a time," Meehl says.

Scientists have known for years that long-term solar variations affect certain weather patterns, including droughts and regional temperatures.

But establishing a physical connection between the decadal solar cycle and global climate patterns has proven elusive.

One reason is that only in recent years have computer models been able to realistically simulate the processes associated with tropical Pacific warming and cooling associated with El Niño and La Niña.

With those models now in hand, scientists can reproduce the last century's solar behavior and see how it affects the Pacific.

To tease out these sometimes subtle connections between the sun and Earth, Meehl and his colleagues analyzed sea surface temperatures from 1890 to 2006. They then used two computer models based at NCAR to simulate the response of the oceans to changes in solar output.

They found that, as the sun's output reaches a peak, the small amount of extra sunshine over several years causes a slight increase in local atmospheric heating, especially across parts of the tropical and subtropical Pacific where Sun-blocking clouds are normally scarce.

That small amount of extra heat leads to more evaporation, producing extra water vapor. In turn, the moisture is carried by trade winds to the normally rainy areas of the western tropical Pacific, fueling heavier rains.

As this climatic loop intensifies, the trade winds strengthen. That keeps the eastern Pacific even cooler and drier than usual, producing La Niña-like conditions.

Although this Pacific pattern is produced by the solar maximum, the authors found that its switch to an El Niño-like state is likely triggered by the same kind of processes that normally lead from La Niña to El Niño.

The transition starts when the changes of the strength of the trade winds produce slow-moving off-equatorial pulses known as Rossby waves in the upper ocean, which take about a year to travel back west across the Pacific.

The energy then reflects from the western boundary of the tropical Pacific and ricochets eastward along the equator, deepening the upper layer of water and warming the ocean surface.

As a result, the Pacific experiences an El Niño-like event about two years after solar maximum. The event settles down after about a year, and the system returns to a neutral state.

"El Niño and La Niña seem to have their own separate mechanisms," says Meehl, "but the solar maximum can come along and tilt the probabilities toward a weak La Niña. If the system was heading toward a La Niña anyway," he adds, "it would presumably be a larger one."

(Photo: NCAR)

National Science Foundation

RESEARCH INDICATES OCEAN CURRENT SHUTDOWN MAY BE GRADUAL

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The findings of a major new study are consistent with gradual changes of current systems in the North Atlantic Ocean, rather than a more sudden shutdown that could lead to rapid climate changes in Europe and elsewhere.

The research, based on the longest experiment of its type ever run on a "general circulation model" that simulated the Earth's climate for 21,000 years back to the height of the last Ice Age, shows that major changes in these important ocean current systems can occur, but they may take place more slowly and gradually than had been suggested.

The newest findings, published in the journal Science, are consistent with other recent studies that are moving away from the theory of an abrupt "tipping point" that might cause dramatic atmospheric temperature and ocean circulation changes in as little as 50 years.

"Research is now indicating that this phenomenon may happen, but probably not as a sudden threshold we're crossing," said Peter Clark, a professor of geosciences at Oregon State University. "For those who have been concerned about extremely abrupt changes in these ocean current patterns, that's good news.

"In the past it appears the ocean did change abruptly, but only because of a sudden change in the forcing," he said. "But when the ocean is forced gradually, such as we anticipate for the future, its response is gradual. That would give ecosystems more time to adjust to new conditions."

The findings do not change broader concerns about global warming. Temperatures are still projected to increase about four to 11 degrees by the end of this century, and the study actually confirms that some of the world's most sophisticated climate models are accurate.

"The findings from this study, which also match other data we have on recorded climate change, are an important validation of the global climate models," Clark said. "They seem to be accurately reflecting both the type and speed of changes that have taken place in the past, and that increases our ability to trust their predictions of the future."

The intensity of computation on this experiment, involving a quadrillion calculations each second, was so great that it took more than a year to run, Clark said. It was the longest such study of its type that ever examined past climate in such detail and complexity. The research was supported by the National Science Foundation and other agencies.

It included the height of the last Ice Age about 21,000 years ago, the emergence of the Earth from that Ice Age around 14,000 years ago, and some other fairly sudden warming and cooling events during those periods that are of considerable interest to paleoclimatologists.

The period when the Earth emerged from its last Ice Age actually had amounts of natural warming similar to those that may be expected in the next century or two, with some of the same effects - melting of ice sheets, sea level rise, increases in atmospheric carbon dioxide. Studies of those periods, researchers say, will provide valuable insights into how the Earth may respond to its current warming.

A particular concern for some time has been the operation of an ocean current pattern called the Atlantic meridional overturning circulation, or AMOC. This current system is part of what keeps Europe much warmer than it would otherwise be, given its far northern latitudes, and there is evidence that it has "shut down" with some regularity in Earth's past - apparently in response to large influxes of fresh water, and sometimes quite rapidly.

"Our data still show that current is slowing, and may decline by 30 percent by the end of this century," Clark said. "That's very significant, and it could cause substantial climate change. But it's not as abrupt as some concerns that it could shut down within a few decades."

Climate changes, Clark said, are actually continuing to occur somewhat more rapidly than had been predicted in recent years. Arctic Sea ice is both thinning and shrinking, and atmospheric carbon dioxide levels are going up faster than had been projected by the Intergovernmental Panel on Climate Change.

Oregon State University

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