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TOPIC: Ancient climate
Blobrana


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RE: Ancient climate
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For at least 3,000 years, a series of potent droughts, far longer and more severe than any experienced recently, have seared a belt of sub-Saharan Africa that is now home to tens of millions of the worlds poorest people, climate researchers report in a new study.
The last such drought, persisting more than three centuries, ended around 1750, the research team writes in a recent issue of the journal Science.

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Blobrana


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Maunder Minimum
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Astronomers have reported that the Sun is at its dimmest for almost a century.
Some scientists believe a similar "quiet spell" is connected to a cooling of temperatures in a period of time called the Maunder Minimum.
Also known as the Little Ice Age, it lasted 70 years from 1645 to 1715 and featured The Great Frost which froze the River Thames in London for days.
Interestingly, this period coincided with some of the most dramatic events in Scotland's history.

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Blobrana


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A new research by an international team of scientists has determined that an expansion of wetlands and not a large-scale melting of frozen methane deposits is the likely cause of a spike in atmospheric methane gas that took place some 11,600 years ago.
The international research team was led by Scripps Institution of Oceanography at UC (University of California) San Diego.
The finding is expected to come as a relief to scientists and climate watchers concerned that huge accelerations of global warming might have been touched off by methane melts in the past and could happen again now as the planet warms.

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Blobrana


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Title: The Late Eocene Earth - Hothouse, Icehouse, and Impacts
Authors: Christian Koeberl, Alessandro Montanari (editors)

The Late Eocene and the Eocene-Oligocene (E-O) transition mark the most profound oceanographic and climatic changes of the past 50 million years of Earth history, with cooling beginning in the middle Eocene and culminating in the major earliest Oligocene Oi-1 isotopic event. The Late Eocene is characterised by an accelerated global cooling, with a sharp temperature drop near the E-O boundary, and significant stepwise floral and faunal turnovers. These global climate changes are commonly attributed to the expansion of the Antarctic ice cap following its gradual isolation from other continental masses. However, multiple extraterrestrial bolide impacts, possibly related to a comet shower that lasted more than 2 million years, may have played an important role in deteriorating the global climate at that time. This book provides an up-to-date review of what happened on Earth at the end of the Eocene Epoch.

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Blobrana


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Ancient stalagmites from a submerged Italian cave have revealed sea level rises caused by global warming more than 200,000 years ago, according to a joint European-Australian study.
The finding, which appears in the journal Nature Geoscience, suggests the current melting of ice sheets may happen faster than expected.

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Blobrana


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Until recently, researchers studying climate history in Brazil's dry Nordeste region expected it to have wet and dry periods similar to the rest of South America. But over the past 9,000 years, the region has shown just the opposite, drought when rain was expected, and vice versa. Geoscientists from the University of Massachusetts Amherst and the University of Sao Paolo, Brazil, with others, report this week that they've identified the cause as a surprising air circulation pattern.

"In general, the Northern Hemisphere tropics have been getting drier and the Southern Hemisphere tropics have been getting wetter as maximum summer solar heating shifts southward. But Northeast Brazil has been acting like a Northern Hemisphere site and it's been getting steadily drier from about 9,000 years ago to today" - Stephen Burns, a UMass Amherst geoscientist.

Millions of people there must cope with severely disruptive, recurring droughts, Burns and colleagues point out. A more accurate model of past conditions could help predict what to expect in the future.

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Blobrana


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Baltic Sea climate change
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Changes in the environmental conditions of the Baltic Sea have been archived in the layers of its bottom sediment. By studying the seabed, we can obtain information about environmental changes in the Baltic Sea and the factors affecting them over several thousand years. The bottom sediment of the Baltic Sea is being studied in a Finnish-led research project as part of the joint European BONUS research programme.

"The area of research extends from the marine environment of Skagerrak to the almost fresh water of the Northern Baltic Sea. By studying the bottom sediment, we're aiming to obtain information on the natural variations in the environmental conditions of the Baltic Sea and on the effect of human activity on environmental changes" - Research Professor Aarno Kotilainen of the Geological Survey of Finland, who is coordinating the project.

Climatic conditions affect the temperature, salinity and changes of current in the Baltic Sea. They regulate such things as the salt water pulses that occasionally flow from the North Sea to the Baltic Sea. The eco-system and environmental conditions of the Baltic Sea are influenced both by local climate and that of the North-East Atlantic. This project coordinated by the Geological Survey of Finland is studying Baltic surface- and deep water conditions and their temporal variation, by looking at the layers of sediment on the seabed, using multivariate analysis.
By modelling, the project also aims to forecast the effects of climate change on the Baltic Sea.

"A deeper understanding of the factors affecting the long-term changes in the Baltic Sea and of possible future changes is important. This knowledge is needed to support planning for the sustainable use of the marine regions and in preparation for the effects of climate change" - Professor Kotilainen.

In addition to the Geological Survey of Finland and the Department of Geology at the University of Helsinki, other participants in the research come from Russia, Germany, Denmark, Sweden, Poland and Norway.

Source Suomen Akatemia  (Academy of Finland)

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Blobrana


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In a new study, which involved analyses of deposits of pollen grains, it has been determined that Sweden may have been virtually free of ice for long periods during the latest ice age, which suggests that the glaciation might have started some 20,000 years later than was previously assumed.
The study is part of a new doctoral dissertation at Stockholm University in Sweden.
According to Martina Hattestrand, a doctoral candidate at the Department of Physical Geography and Quaternary Geology, Stockholm University, Its important that we get to the bottom of when the great ice sheets covered Sweden and how warm it might have been when there was no ice.
In order to understand the climate system of the earth, researchers today are studying the climatic variations of ice ages.
Since the most land forms and geological traces have been preserved from the latest ice age, much of the research focuses on that particular period.
An important aspect of the research is to study when the huge continental ice sheets grew and when they melted away, and to study the environment and climate of the areas that were free of ice.
The size and movement patterns of the ice sheets can be calculated by studying land forms and moraine deposits.
The ice-free periods can be studied by pollen analysis, among other methods.

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Blobrana


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The decline of the Roman and Byzantine empires in the Eastern Mediterranean more than 1,400 years ago may have been driven by unfavourable climate changes.
Based on chemical signatures in a piece of calcite from a cave near Jerusalem, a team of American and Israeli geologists pieced together a detailed record of the area's climate from roughly 200 B.C. to 1100 A.D. Their analysis, to be reported in an upcoming issue of the journal Quaternary Research, reveals increasingly dry weather from 100 A.D. to 700 A.D. that coincided with the fall of both Roman and Byzantine rule in the region.
The researchers, led by University of Wisconsin-Madison geology graduate student Ian Orland and professor John Valley, reconstructed the high-resolution climate record based on geochemical analysis of a stalagmite from Soreq Cave, located in the Stalactite Cave Nature Reserve near Jerusalem.

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Blobrana


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Monsoon link to fall of dynasties
The demise of some of China's ruling dynasties may have been linked to changes in the strength of monsoon rains, a new study suggests.
The findings come from 1,800-year record of the Asian monsoon preserved in a stalagmite from a Chinese cave.
Weak - and therefore dry - monsoon periods coincided with the demise of the Tang, Yuan and Ming imperial dynasties, the scientists said.
A US-Chinese team report their work in the journal Science.

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