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Blobrana


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Northern Ice Sheets Younger Than Believed
Climatologist Robert DeConto of the University of Massachusetts Amherst and colleagues at four institutions are reporting in the Oct. 2 issue of the journal Nature that their latest climate model of the Northern Hemisphere suggests conditions would have allowed ice sheets to form there for the last 25 million years, or about 22 million years earlier than generally assumed. Their research has implications for the evaluation of global climate change.

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90,000 Yr Old Data Suggests Interlink Between Warming, CO2 and Ocean Currents
Scientists have presented new data from their analysis of ice core samples and ocean deposits dating as far back as 90,000 years ago and have suggested that warming, carbon dioxide levels and ocean currents are tightly inter-related.

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Atmospheric pressure is a key characteristic of the climate on Earth and on other planets. Mars, for example, is dry and cold partly because of its very thin atmosphere the low air pressure means the planet is unable to trap heat or retain water vapour. Air pressure also can affect the chemical reactions that life depends upon.

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An analysis of the global carbon cycle and climate for a 70,000-year period in the most recent Ice Age shows a remarkable correlation between carbon dioxide levels and surprisingly abrupt changes in climate.
The findings, to be published this week in the online edition of the journal Science, shed further light on the fluctuations in greenhouse gases and climate in Earths past, and appear to confirm the validity of the types of computer models that are used to project a warmer climate in the future, researchers said.

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Blobrana


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Ancient Canadian ice survived previous warm periods.
A 740,000-year-old wedge of ice discovered in central Yukon Territory, Canada, is the oldest known ice in North America. It suggests that permafrost has survived climates warmer than today's, according to a new study.

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Blobrana


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Ancient hurricanes
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Reaching down into the muck below a lagoon off Puerto Rico, two geologists at Woods Hole Oceanographic Institution reached back 5,000 years to compile the longest record of strong hurricanes in the Atlantic region.
The record showed that the dominant forces spawning heightened hurricane activity appeared to be atmospheric conditions generated by weak El Niņos in the tropical Pacific and strong West African monsoons, Jeff Donnelly and Jon Woodruff reported May 24, 2007, in the journal Nature.
Somewhat to their surprise, they also found extensive periods of intense hurricanes in the past, when ocean temperatures were cooler than they are now. Today, concerns about global warming have focused public attention on warmer ocean waters as a prime suspect for increased hurricane activity.

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Blobrana


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Dips in the sun's activity have triggered centuries-long droughts in eastern North America, according to a new study that examined the geologic record stored within a stalagmite from a West Virginia cave.
The link between periodic droughts and changes in solar activity initially was proposed by geologist Gerald Bond. He suggested that every 1,500 years, weak solar activity caused by fluctuations in the sun's magnetic fields cooled the North Atlantic Ocean and created more icebergs and ice rafting, or the movement of sediment to the ocean floor. This caused less precipitation to fall, creating drought conditions.
The climate record preserved by trace elements such as strontium, carbon and oxygen in stalagmites is clearer and more detailed than records previously taken from lake sediments. During dry periods, strontium is concentrated in stalagmites. Carbon isotopes also record drought because drier soils slow biological activity.

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A study of New Zealand's climate 42 million years ago shows greenhouse conditions with warmer seas and little or no ice.
The study - based on analysis of fossilised micro-organisms at Hampden Beach, near the Moeraki Boulders in North Otago - suggests Antarctica at that time was yet to develop extensive ice sheets.
Back then, New Zealand was about 1100km further south, closer to Antarctica, at the same latitude as the southern tip of South America.
But the researchers found the water temperature was 23C to 25C at the sea surface and 11C to 13C at the bottom.

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New research by a team of scientists in the School of Earth and Ocean Sciences is presenting a snapshot of New Zealands climate 40 million years ago which reveals a greenhouse Earth, with warmer seas and little or no ice in Antarctica.
Led by PhD researcher Catherine Burgess, with Professor Paul Pearson and Dr Caroline Lear, the study suggests that Antarctica at that time was yet to develop extensive ice sheets.

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Title: Surface wind-stress threshold for glacial Atlantic overturning
Authors: Marisa Montoya, Anders Levermann.

Using a coupled model of intermediate complexity the sensitivity of the last glacial maximum (LGM) Atlantic meridional overturning circulation (AMOC) to the strength of surface wind-stress is investigated. A threshold is found below which North Atlantic deep water formation (DWF) takes place south of Greenland and the AMOC is relatively weak. Above this threshold, DWF occurs north of the Greenland-Scotland ridge, leading to a vigorous AMOC. This non-linear behaviour is explained through enhanced salt transport by the wind-driven gyre circulation and the overturning itself. Both pattern and magnitude of the Nordic Sea's temperature difference between strong and weak AMOC states are consistent with those reconstructed for abrupt climate changes of the last glacial period.

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