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TOPIC: Ancient climate


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Drumlin Formation
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A new study threatens to overturn our understanding of how glaciers deposit whale-shaped hills known as drumlins. The findings could have implications for the computer models used to predict glacier flow and subsequent changes in sea-level.
Andy Smith of the British Antarctic Survey and his colleagues are the first to see a drumlin during formation. They have visited the same spot of the Rutford Ice Stream in Antarctica three times since 1991. Each time, they have mapped the shape of the glacier bed, which lies 2000 metres under the surface of the ice.
The maps are created by sinking explosives in the ice and recording the echo of the detonation after it is reflected off the riverbed. The time it takes for the echo to return to the surface reveals how deep the riverbed is, while the researchers can judge how hard it is from the echo's quality and loudness.
The most recent data, from 2004, revealed a big surprise: a large lump of sediment, 10 metres high and 100 m wide that "plainly wasn't there last time we looked" in 1997.

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RE: Ancient climate
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New research concerning the transition of the Earth's climate 300 million years ago from an ice age to an ice-free planet has yielded new insights into the processes of climate change. The new findings will also tell us about how Earth's changing climate throughout history has affected the development of life on Earth.
The transition from an ice age to an ice-free planet 300 million years ago was highly unstable, marked by dips and rises in carbon dioxide, extreme swings in climate and drastic effects on tropical vegetation, according to a study published in the journal Science Jan. 5.

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Global warming
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How severe will global warming get?

Jason P. Briner is looking for an answer buried deep in mud dozens of feet below the surface of lakes in the frigid Canadian Arctic.
His group is gathering the first quantitative temperature data over the last millennium from areas in extreme northeastern sections of the Canadian Arctic, such as Baffin Island.
Every spring, Briner, Ph.D., assistant professor of geology in the College of Arts and Sciences at the University at Buffalo, travels to the region to sample Arctic lake sediments and glaciers and analyses them to reconstruct past climates.
During the 'Holocene thermal maximum,' the warmest period of the past 10,000 years, the Arctic average temperature was two to three degrees warmer than it is today, while the global average was only a degree or so warmer.

"But based on lake sediments from Baffin Island, our data show that this area of the Arctic experienced temperatures five degrees warmer than today" - Jason P. Briner.

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RE: Ancient climate
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Global warming is one of the greatest threats to present day civilisation but work by a team of Scots scientists suggests the ancient Egyptians may have been earlier victims of climate change.
The pharaohs ruled their empire for hundreds of years, spreading culture, architecture and the arts before it collapsed into economic ruin. Why that happened is one of the great mysteries of history.
Click to learn more...
Now a team of scientists from Scotland and Wales believe the answer lies beneath the waters of Lake Tana, high in the Ethiopian Highlands, and the source of the all-important Blue Nile.
Samples taken over the past two years from sediments beneath Tana, which supplies the water which makes the lower Nile valley so fertile, reveal the lake may have almost dried up during the critical period around 4,200 years ago due to climate change.

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The downfall of the one of the greatest Chinese dynasties may have been catalysed by severe changes in climate. The same climate changes may have simultaneously led to the end of the Maya civilisation depicted in Mel Gibson's new film Apocalypto.
So says Gerald Haug of the GeoForschungsZentrum in Germany and colleagues, who studied geological records of monsoons over the past 16,000 years. They have found a startling correlation between climate extremes and the fall of two great civilisations: the Tang dynasty in China and the Maya of South America.

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Weak winter monsoon rains may have contributed to the decline of both China's Tang Dynasty and the Mayan civilisation in Mexico, suggests an article published in Nature (4 January).
The authors speculate that global climate change, causing a tropical rain belt to migrate, may have been a factor — with the same system affecting monsoon rains in Southeast Asia today.
They link shifts in an area of low pressure that follows the equator, known as an intertropical convergence zone, with weakened monsoon rains in winters during the eighth and ninth centuries. They write that dynastic changes often involved popular uprisings during phases of crop failure and famine, and these are consistent with periods of reduced rainfall.

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New research suggests that climate change led to the collapse of the most splendid imperial dynasty in China’s history and to the extinction of the Maya civilisation in Central America more than 1,000 years ago.
There has never been a satisfactory explanation for the decline and fall of the Tang emperors, whose era is viewed as a highpoint of Chinese civilisation, while the disappearance of the Maya world perplexes scholars.
Now a team of scientists has found evidence that a shift in monsoons led to drought and famine in the final century of Tang power. The weather pattern may also have spelt doom for the Maya in faraway Mexico at about the same time, they say.

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A team of American and French scientists has developed a method to determine the influence of past volcanic eruptions on climate and the chemistry of the upper atmosphere, and significantly reduce uncertainty in models of future climate change.
In the January 5 issue of the journal Science, the researchers from the University of California, San Diego, the National Centre for Scientific Research (CNRS) and the University of Grenoble in France report that the chemical fingerprint of fallout from past eruptions reveals how high the volcanic material reached, and what chemical reactions occurred while it was in the atmosphere. The work is particularly relevant because the effect of atmospheric particles, or aerosols, is a large uncertainty in models of climate, according to Mark Thiemens, Dean of UCSD’s Division of Physical Sciences and professor of chemistry and biochemistry.

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The mid-Permian transition from ice age to an ice-free planet was marked by dips and rises in carbon dioxide and extreme swings in climate, according to University of California, Davis (UC) researchers writing in Science. During the mid-Permian, 300 million years ago, much of the southern hemisphere was covered in thick ice sheets and floating pack ice likely covered the northern polar ocean. But forty million years later, all the ice was gone and the climate hot and dry with sparse vegetation.

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Ancient climate record preserved in prehistoric plants
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Ancestor of modern trees preserves record of ancient climate change
About 350 million years ago, at the boundary of the Devonian and Carboniferous ages, the climate changed. There was no one around to record it, but there are records nonetheless in the rocks deposited by glaciers and in tissues preserved in fossils of ancient life.

"Events at the transition had terrific biological impact, marked by extinctions and the beginnings of new life forms" - Stephen Scheckler of Blacksburg, professor of biological sciences and geosciences at Virginia Tech.

He reported on evidence of climate change that he found in the fossils of the ancestors of modern trees at the Geological Society of America national meeting in Philadelphia Oct. 22-25.
Scheckler studied the ancient plants that had the same genetics for controlling wood growth and produced the same signatures for dormancy. He has documented that the fossil “trees” from most of the Devonian period show tropical growth rings, but those from the latest Devonian and earliest Carboniferous show growth rings that resemble those of temperate trees.

"That plants of this time responded as modern plants would to cold supports the idea that there was a sudden chilling at the end of the Devonian. Later in the Carboniferous period, you no longer see the temperate signature rings because the glacial event went away."

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Cosmic connection to climate
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Getting closer to the cosmic connection to climate

A team at the Danish National Space Centre has discovered how cosmic rays from exploding stars can help to make clouds in the atmosphere. The results support the theory that cosmic rays influence Earth’s climate.
An essential role for remote stars in everyday weather on Earth has been revealed by an experiment at the Danish National Space Centre in Copenhagen. It is already well-established that when cosmic rays, which are high-speed atomic particles originating in exploded stars far away in the Milky Way, penetrate Earth’s atmosphere they produce substantial amounts of ions and release free electrons. Now, results from the Danish experiment show that the released electrons significantly promote the formation of building blocks for cloud condensation nuclei on which water vapour condenses to make clouds. Hence, a causal mechanism by which cosmic rays can facilitate the production of clouds in Earth’s atmosphere has been experimentally identified for the first time.
The Danish team officially announce their discovery on Wednesday in Proceedings of the Royal Society A, published by the Royal Society, the British national academy of science.

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Climate change
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New research suggests the existence of periods of dramatic climate change during the Mesozoic Era, a time when dinosaurs ruled the Earth.

The research, published in the September issue of Geology, presents evidence that ocean surface temperatures varied as much as 6 degrees Celsius during the Aptian Epoch of the Cretaceous Period 120 million years ago according to scientists from Indiana University Bloomington and the Royal Netherlands Institute for Sea Research who examined ancient rocks from the bottom of the Pacific Ocean. The results challenge the idea that the period was characterised by a stable, hot and humid climate.
The researchers say the research is significant because it presents a case where "temperatures shifted erratically due to changes in carbon cycling and did so without human input" according to a news release from Indiana University.

"Combined with data from the Atlantic, it appears clear that climate changes were taking place on a global scale during this time period. The data we collected suggest significant global fluctuations in temperature" - Indiana University geologist Simon Brassell, who led the study.

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