Monday, December 28, 2009

BLACK CARBON DEPOSITS ON HIMALAYAN ICE THREATEN EARTH'S 'THIRD POLE'

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Black soot deposited on Tibetan glaciers has contributed significantly to the retreat of the world's largest non-polar ice masses, according to new research by scientists from NASA and the Chinese Academy of Sciences. Soot absorbs incoming solar radiation and can speed glacial melting when deposited on snow in sufficient quantities.

Temperatures on the Tibetan Plateau -- sometimes called Earth's "third pole" -- have warmed by 0.3°C (0.5°F) per decade over the past 30 years, about twice the rate of observed global temperature increases. New field research and ongoing quantitative modeling suggests that soot's warming influence on Tibetan glaciers could rival that of greenhouse gases.

"Tibet's glaciers are retreating at an alarming rate," said James Hansen, coauthor of the study and director of NASA's Goddard Institute for Space Studies (GISS) in New York City. "Black soot is probably responsible for as much as half of the glacial melt, and greenhouse gases are responsible for the rest."

"During the last 20 years, the black soot concentration has increased two- to three-fold relative to its concentration in 1975," said Junji Cao, a researcher from the Chinese Academy of Sciences in Beijing and a coauthor of the paper.

The study was published December 7th in the Proceedings of the National Academy of Sciences.

"Fifty percent of the glaciers were retreating from 1950 to 1980 in the Tibetan region; that rose to 95 percent in the early 21st century," said Tandong Yao, director of the Chinese Academy's Institute of Tibetan Plateau Research. Some glaciers are retreating so quickly that they could disappear by mid-century if current trends continue, the researchers suggest.

Since melt water from Tibetan glaciers replenishes many of Asia's major rivers—including the Indus, Ganges, Yellow, and Brahmaputra—such losses could have a profound impact on the billion people who rely on the rivers for fresh water. While rain and snow would still help replenish Asian rivers in the absence of glaciers, the change could hamper efforts to manage seasonal water resources by altering when fresh water supplies are available in areas already prone to water shortages.

Researchers led by Baiqing Xu of the Chinese Academy drilled and analyzed five ice cores from various locations across the Tibetan Plateau, looking for black carbon (a key component of soot) as well as organic carbon. The cores support the hypothesis that black soot amounts in the Himalayan glaciers correlate with black carbon emissions in Europe and South Asia.

At Zuoqiupu glacier -- a bellwether site on the southern edge of the plateau and downwind from the Indian subcontinent -- black soot deposition increased by 30 percent between 1990 and 2003. The rise in soot levels at Zuoqiupu follows a dip that followed the enacting of clean air regulations in Europe in the 1970s.

Most soot in the region comes from diesel engines, coal-fired power plants, and outdoor cooking stoves. Many industrial processes produce both black carbon and organic carbon, but often in different proportions. Burning diesel fuel produces mainly black carbon, for example, while burning wood produces mainly organic carbon. Since black carbon is darker and absorbs more radiation, it's thought to have a stronger warming effect than organic carbon.

To refine this emerging understanding of soot's impact on glaciers, scientists are striving to gather even more robust measurements. "We can't expect this study to clarify the effect of black soot on the melting of Tibetan snow and glaciers entirely," said Cao. "Additional work that looks at albedo measurements, melting rate, and other types of reconnaissance is also needed."

For example, scientists are using satellite instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the NASA satellites Terra and Aqua to enhance understanding of the region's albedo. And a new NASA climate satellite called Glory, which will launch late in 2010, will carry a new type of aerosol sensor that should be able to distinguish between aerosol types more accurately than previous instruments.

"Reduced black soot emissions, in addition to reduced greenhouse gases, may be required to avoid demise of Himalayan glaciers and retain the benefits of glaciers for seasonal fresh water supplies," Hansen said.

(Photo: NASA/Sally Bensusen)

THEORISTS PROPOSE A NEW WAY TO SHINE -- AND A NEW KIND OF STAR

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Dying, for stars, has just gotten more complicated. For some stellar objects, the final phase before or instead of collapsing into a black hole may be what a group of physicists is calling an electroweak star.

Glenn Starkman, a professor of physics at Case Western Reserve University, together with former graduate students and post-docs De-Chang Dai and Dejan Stojkovic, now at the State University of New York in Buffalo, and Arthur Lue, at MIT's Lincoln Lab, offer a description of the structure of an electroweak star in a paper submitted to Physical Review Letters and posted online at http://arxiv.org/abs/0912.0520.

Ordinary stars are powered by the fusion of light nuclei into heavier ones – such as hydrogen into helium in the center of our sun. Electroweak stars, they theorize, would be powered by the total conversion of quarks – the particles that make up the proton and neutron building blocks of those nuclei – into much lighter particles called leptons. These leptons include electrons, but especially elusive – and nearly massless – neutrinos.

"This is a process predicted by the well-tested Standard Model of particle physics," Starkman said. At ordinary temperatures it is so incredibly rare that it probably hasn't happened within the visible universe anytime in the last 10 billion years, except perhaps in the core of these electroweak stars and in the laboratories of some advanced alien civilizations, he said.

In their dying days, stars smaller than 2.1 times our sun's mass die and collapse into neutron stars – objects dense enough that the neutrons and protons push against each other. More massive stars are thought to head toward collapse into a black hole. But at the extreme temperatures and densities that might be reached when a star begins to collapse into a black hole, electroweak conversion of quarks into leptons should proceed at a rapid rate, the scientists say.

The energy generated could halt the collapse, much as the energy generated by nuclear fusion prevents ordinary stars like the Sun from collapsing. In other words, an electroweak star is the possible next step before total collapse into a black hole. If the electroweak burning is efficient, it could consume enough mass to prevent what's left from ever becoming a black hole.

Most of the energy eventually emitted from electroweak stars is in the form of neutrinos, which are hard to detect. A small fraction comes out as light and this is where the electroweak star's signature will likely be found, Starkman, said. But, "To understand that small fraction, we have to understand the star better than we do."

And until they do, it's hard to know how we can tell electroweak stars from other stars.

There's time, however, to learn. The theorists have calculated that this phase of a star's life can last more than 10 million years – a long time for us, though just an instant in the life of a star.

Case Western Reserve University

THE MAMMOTHS' SWAN SONG REVISED

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Woolly mammoths and prehistoric horses grazed on the North American plains for several thousand years longer than hitherto assumed.

This is shown by samples of ancient DNA, analysed by an international team of research scientists under the leadership of Professor Eske Willerslev from Copenhagen University. Analyses of ancient DNA thereby once again revoke results of more common methods of dating, such as carbon 14 analysis of bone and tooth remains from extinct animals. These methods which had previously dated the extinction of mammoths and prehistoric horses in Central Asia to within 13-15,000 years ago. But with the DNA-test methods of Eske Willerslev and his colleagues, this boundary has now moved between 2,600 and 5,600 years closer to our time and has thus revised our previous opinion of when the last mammoths and prehistoric horses grazed on the North American Plains.

The ancient DNA that formed the basis for this sensational result, was discovered by scientists in samples of soil from the permafrost tundra surrounding the windswept town of Stevens Village on the bank of the Yukon River in Central Alaska.

Professor Eske Willerslev says about his discovery:

"In principle, one can take a pinch of soil and uncover which living creatures, animals and plants lived in the area half a million years back in time. With ancient DNA analysis, we are completely independent of skeletons, bones, teeth and other macro-fossil evidence from extinct animals. This greatly increases the possibility of finding evidence of the existence of a species through time. Whilst an animal leaves only a single corpse when it dies, it leaves quantities of DNA traces through urine and faeces whilst it is still alive. It is these DNA traces which we find in the soil."

When the remains of the last member of an extinct species were hard to find, Willerslev and a team of international research scientists decided to carry out an expedition to Central Alaska to solve the riddle of "The last surviving mammoths" using ancient-DNA tests from permafrost soil.

Surprisingly, the scientists found that the later samples with mammoth DNA could be dated back to between 10,500 and 7,500 years ago, and are therefore between 2,600 and 5,600 years after the supposed extinction of the mammoths from mainland Alaska. Thus, the scientists found proof that mammoths had walked the earth several thousand years longer than previously believed; presumably by lesser herds of these animals threatened with extinction, surviving in small, isolated enclaves, where living conditions were intact.

The findings breathe new life into the debate about why prehistoric animals, such as sabre-toothed tigers, giant sloths, woolly rhinos, and mammoths apparently suddenly disappeared from the face of the earth.

"Our findings show that the mammoth and the horse existed side by side with the first human immigrants in America for certainly 3,500 years and were therefore not wiped out by human beings or natural disasters within a few hundred years, as common theories otherwise argue. The technique behind ancient-DNA analysis has the potential to greatly contribute to the debate about the extermination of prehistoric species, but can also be used to gather knowledge of contemporary animal species which are so shy that they are hard to detect. Not to mention the forensic possibilities opened up by the technique," Eske Willerslev points out.

(Photo: U. Copenhagen)

University of Copenhagen

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