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10. The Ice Ages

2019-11-27. Antarctic Ice Cores Offer a Whiff of Earth’s Ancient Atmosphere. By Katherine Kornei. Eos/AGU.

2019-11-01. Oceans Vented Carbon Dioxide During the Last Deglaciation. By Kate Wheeling, Eos/AGU. 

2018-08-08. Massive drought or myth? Scientists spar over an ancient climate event behind our new geological age. By Paul Voosen, Science Magazine.

2018-06-05. How the Ice Age Shaped New York. By William J. Broad, The New York Times. 

2017-11-22. How Earth’s Orbit Affected Ice Sheets Millions of Years Ago. By Emily Underwood, Eos/AGU. 

2016-12-05. During last period of global warming, Antarctica warmed 2 to 3 times more than planet average. By Robert Sanders, UC Berkeley News, Media relations.

2016-09-26. Study: Earth’s roughly warmest in about 100,000 years. By Seth Borenstein, Associated Press. 

2016-06-30. Crippled Atlantic currents triggered ice age climate change. By Eric Hand, Science.

2016-03-02. Characterizing Interglacial Periods over the Past 800,000 Years. By Cody Sullivan, Earth & Space Science News (EoS, AGU).

2015-12-16. Plankton Reveal New Secrets About Ancient CO2 Levels. By Natalie Jacewicz, EoS Earth and Space Science News, AGU.

2015-07-23. Hot spells doomed the mammoths. By Elizabeth Pennisi, Science.

2015-05-05. Ice cores show 200-year climate lag. By Stephanie McClellan, BBC News.

2013-03-01.  Study of Ice Age Bolsters Carbon and Warming Link | Justin Gillis, The New York Times. Excerpt: ...Previous research suggested that as the world began to emerge from the depths of the ice age about 20,000 years ago, warming in Antarctica preceded changes in the global carbon dioxide level by something like 800 years. That ...led some climate-change contrarians to assert that rising carbon dioxide levels were essentially irrelevant to the earth’s temperature.... ...A wave of new research in the last few years has raised the likelihood that there was actually a small gap, if any. ...Scientists have long known that ice ages are caused by variations in the earth’s orbit around the sun. When an intensification of sunlight initiates the end of an ice age, they believe, carbon dioxide is somehow flushed out of the ocean, causing a big amplification of the initial warming. Since the 1980s, scientists have been collecting a climate record by extracting long cylinders of ice from the ice sheets in Greenland and Antarctica, and from glaciers.... Air bubbles trapped in the ice give direct evidence of the past composition of the atmosphere. And subtle chemical variations in the ice itself give an indication of the local temperature at the time it was formed. The trouble is that air does not get sealed in the ice until hundreds or even thousands of years after the snow has fallen, as it slowly gets buried and compressed. ...Instead of the 800-year lag between temperature and carbon dioxide increases found in some previous research, [Dr. Parrenin’s] work suggests that the lag as the ice age started to end was less than 200 years, and possibly there was no lag at all. ...“What this does, again and more clearly than ever, is to show that the large temperature changes are tightly coupled to the large CO2 changes,” ...said Richard B. Alley, a climate scientist at Pennsylvania State University. ...The tight relationship in past climate between temperature and carbon dioxide is a major reason scientists have warned that modern society is running a big risk by burning CO2-producing fossil fuels. The level of carbon dioxide in the atmosphere has jumped 41 percent since the Industrial Revolution began in the 18th century, and scientists fear it could double or triple.... Even at the current concentration of the gas, ...increases in sea level of 25 feet or more may have already become inevitable…. Read the full article: http://www.nytimes.com/2013/03/01/science/earth/at-ice-age-end-a-smaller-gap-in-warming-and-carbon-dioxide.html

2012 Mar 5. Sharing the Blame for the Mammoth's Extinction. by Richard A. Kerr, ScienceNOW.  Excerpt: The past few tens of millennia were hard times for the "megafauna" of the world. Hundreds of big-bodied species—from the mammoths of North America to the 3-meter-tall kangaroos of Australia to the 200-kilogram-plus flightless birds of New Zealand—just disappeared from the fossil record. A new, broad analysis continues the century-long debate over the loss of the big animals, coming down on the middle ground between blaming migrating humans for wiping them all out and climate change alone for doing them in. …Barnosky and environmental scientist Barry Brook of the University of Adelaide in Australia have found such a human-climate synergy operating in megafaunal extinctions when severe climate change coincided with human arrivals. A similar synergy is happening today, they say, as global warming intensifies and the human population continues to grow….

2012 February 13. A Tiny Horse That Got Even Tinier As the Planet Heated Up.  By James Gorman, The NY Times.  Excerpt:  …Sifrhippus, the first horse... shrank from about 12 pounds average weight to about eight and a half pounds as the climate warmed over thousands of years, a team of researchers reported in the journal Science on Thursday….
…Its preserved fossils, abundant in the Bighorn Basin, provide an excellent record of its size change over a 175,000-year warm period in the Earth’s history known as the Paleocene-Eocene thermal maximum, when temperatures are estimated to have risen by 9 to 18 degrees Fahrenheit at the start, and dropped again at the end.
Scientists have known that many mammals appear to have shrunk during the warming period, and the phenomenon fits well with what is known as Bergmann’s rule, which says, roughly, that mammals of a given genus or species are smaller in hotter climates….

2009 May 7. Rise Of Oxygen Caused Earth's Earliest Ice Age. ScienceDaily. Excerpt: Geologists may have uncovered the answer to an age-old question - an ice-age-old question, that is. It appears that Earth's earliest ice ages may have been due to the rise of oxygen in Earth's atmosphere, which consumed atmospheric greenhouse gases and chilled the earth.
Alan J. Kaufman, professor of geology at the University of Maryland, Maryland geology colleague James Farquhar, and a team of scientists from Germany, South Africa, Canada, and the U.S.A., uncovered evidence that the oxygenation of Earth's atmosphere - generally known as the Great Oxygenation Event - coincided with the first widespread ice age on the planet.
"We can now put our hands on the rock library that preserves evidence of irreversible atmospheric change," said Kaufman. "This singular event had a profound effect on the climate, and also on life."
Using sulfur isotopes to determine the oxygen content of ~2.3 billion year-old rocks in the Transvaal Supergroup in South Africa, they found evidence of a sudden increase in atmospheric oxygen that broadly coincided with physical evidence of glacial debris, and geochemical evidence of a new world-order for the carbon cycle.
...The result of the Great Oxidation Event, according to Kaufman and his colleagues, was a complete transformation of Earth's atmosphere, of its climate, and of the life that populated its surface....

2007 March 23. MICROFOSSILS UNRAVEL CLIMATE HISTORY OF TROPICAL AFRICA. Earth Observatory News. Scientists from the Royal Netherlands Institute for Sea Research obtained for the first time a detailed temperature record for tropical central Africa over the past 25,000 years. ... a marine sediment core taken in the outflow of the Congo River... contained eroded land material and microfossils from marine algae. The results show that the land environment of tropical Africa was cooled more than the adjacent Atlantic Ocean during the last ice-age. This large temperature difference between land and ocean surface resulted in drier conditions compared to the current situation, which favors the growth of a lush rainforest. These findings provide further insight in natural variations in climate and the possible consequences of a warming earth on precipitation in central Africa. The results will be published in this week's issue of Science. ...ocean surface and land temperatures behaved differently during the past 25,000 years. During the last ice age, temperatures over tropical Africa were 21¡C, or about 4¡C lower than today, whereas the tropical Atlantic Ocean was only about 2.5¡C colder. By comparing this temperature difference with existing records of continental rainfall variability, lead author Johan Weijers and his colleagues concluded that the land-sea temperature difference has by far the largest influence on continental rainfall. This can be explained by the strong relationship of air pressure to temperature. When the temperature of the sea surface is higher than that of the continent, stronger offshore winds reduce the flow of moist sea air onto the African continent. This occurred during the last ice age and, as a consequence, the land climate in tropical Africa was drier than it is in today's world, where it favours the growth of a lush rainforest.

2006 June 8. NEW STUDY SHOWS MUCH OF THE WORLD EMERGED FROM LAST ICE AGE TOGETHER - Earth Observatory. Excerpt: The end of the recurring, 100,000-year glacial cycles is one of the most prominent and readily identifiable features in records of the Earth's recent climate history. Yet one of the most puzzling questions in climate science has been why different parts of the world, most notably Greenland, appear to have warmed at different times and at different rates after the end of the last Ice Age. However, a new study appearing in the upcoming issue of the journal Science suggests that, except for regions of the North Atlantic, most of the Earth did, in fact, begin warming at the same time roughly 17,500 years ago. In addition, scientists suggest that ice core records from Greenland, which show that average temperatures there did not warm appreciably until about 15,000 years ago, may have remained in a hyper-cold state largely as a result of events triggered by warming elsewhere....

22 December 2005. Paleoclimatology: Climate Close Up. While cave rocks and ice cores provide a long-term, annual record of past, some other climate proxies can offer a detailed record of seasonal temperature or rainfall changes.

22 December 2005. Paleoclimatology: The Ice Core Record. Ice sheets contain a record of hundreds of thousands of years of past climate, trapped in the ancient snow.


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