* Astronomy

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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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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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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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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