10. The Ice Ages

2021-06-02. [https://eos.org/articles/an-ancient-meltwater-pulse-raised-sea-levels-by-18-meters] - An Ancient Meltwater Pulse Raised Sea Levels by 18 Meters. Source: By Tim Hornyak, Eos/AGU. Excerpt: The period of time when sea levels shot up at the end of the last glacial period, roughly 14,600 years ago, is known as meltwater pulse 1A (MWP-1A). Ever since this pulse was identified from coral records in 1989, the origins of the meltwater have been the subject of debate. Some researchers have hypothesized that Antarctica was the major source of the meltwater, whereas other scientists have suggested that it came from the Northern Hemisphere. A new study in Nature Communications has concluded that melting ice sheets in North America, followed by Scandinavia, were the dominant drivers of MWP-1A and that the world’s mean sea level rise was 17.9 meters over 500 years.... 

A forgotten Cold War experiment has revealed its icy secret. It’s bad news for the planet. By Sarah Kaplan, The Washington Post. Excerpt: At first, Andrew Christ was ecstatic. In soil taken from the bottom of the Greenland ice sheet, he’d discovered the remains of ancient plants. Only one other team of researchers had ever found greenery beneath the mile-high ice mass. But then Christ determined how long it had been since that soil had seen sunlight: Less than a million years. Just the blink of an eye in geologic terms. And it dawned on him. If plants once grew at multiple spots on the surface of Greenland, that meant the ice that now covers the island had entirely melted. And if the whole Greenland ice sheet had melted once in the not-so-distant past, that meant it could go again. ...The findings, published Monday in the Proceedings of the National Academy of Sciences, indicate that the biggest reservoir of ice in the Northern Hemisphere can collapse due to relatively small increases in temperature over a long period of time. That makes it even more vulnerable to human-caused warming, which is causing the Earth to warm faster now than at any other period in its history. ...If the island’s entire ice sheet were to melt..., global sea levels would rise by more than 20 feet. ...The story of this soil sample is almost as dramatic as the data it contains. It comes from the bottom of an ice core taken during “Project Iceworm,” a failed Cold War effort to hide nuclear missiles beneath Greenland’s ice. Camp Century, in the far northwest of Greenland, was to be a base for the U.S. military project. Housing, dining and medical facilities, all powered by a nuclear reactor, were dug into the ice.... [https://www.washingtonpost.com/climate-environment/2021/03/15/greenland-ice-sheet-more-vulnerable/

The Terrifying Warning Lurking in the Earth’s Ancient Rock Record. By Peter Brannen, The Atlantic. Excerpt: Our climate models could be missing something big. ...Taking in the whole sweep of Earth’s history, now we see how unnatural, nightmarish, and profound our current experiment on the planet really is. A small population of our particular species of primate has, in only a few decades, unlocked a massive reservoir of old carbon slumbering in the Earth, gathering since the dawn of life, and set off on a global immolation of Earth’s history to power the modern world. As a result, up to half of the tropical coral reefs on Earth have died, 10 trillion tons of ice have melted, the ocean has grown 30 percent more acidic, and global temperatures have spiked. ...The next few fleeting moments are ours, but they will echo for hundreds of thousands, even millions, of years. This is one of the most important times to be alive in the history of life.... [https://www.theatlantic.com/magazine/archive/2021/03/extreme-climate-change-history/617793/]

A Hitchhiker’s Guide to an Ancient Geomagnetic Disruption. By Alanna Mitchell, The New York Times. Excerpt: About 42,000 years ago, Earth was beset with oddness. Its magnetic field collapsed. Ice sheets surged across North America, Australasia and the Andes. Wind belts shifted across the Pacific and Southern Oceans. Prolonged drought hit Australia; that continent’s biggest mammals went extinct. Humans took to caves to make ochre-color art. Neanderthals died off for good. Through it all, one giant kauri tree stood tall — until, after nearly two millenniums, it died and fell in a swamp, where the chemical records embedded in its flesh were immaculately preserved. That tree, unearthed a few years ago near Ngawha Springs in northern New Zealand, finally allowed researchers to fit a tight timeline to what before had seemed like an intriguing but only vaguely correlated series of events. What if, the researchers posited, the crash of the magnetic field spawned the climatic changes of that era? ...By comparing tree-ring age data and radioactive carbon concentrations from that kauri tree and three others of similar vintage to recent dating information derived from two stalagmites in the Hulu caves in China, Dr. Turney and his 32 co-authors were able to pinpoint when the tree lived and died. That gave them what they call a “calibration curve,” allowing them to convert radiocarbon dating from that period into calendar years.... [https://www.nytimes.com/2021/02/18/science/laschamp-earth-magnetic-climate.html]

Ancient “Pickled” Leaves Give a Glimpse of Global Greening. By Kate Evans, Eos/AGU. Excerpt: From the surface, the fossil deposit of Foulden Maar looks like a typical New Zealand sheep paddock. But the ground beneath it contains both a world-class collection of leaf fossils and a 120,000-year record of Earth’s climate during the Miocene, 23 million years ago. Those features have allowed international researchers to show, for the first time, that carbon dioxide levels in the atmosphere during that period were relatively high and that some plants could harvest that atmospheric carbon more efficiently for photosynthesis, leading to increased growth and more drought tolerance. This insight has important implications for what we can expect later this century as the climate warms. Those features have allowed international researchers to show, for the first time, that carbon dioxide levels in the atmosphere during that period were relatively high and that some plants could harvest that atmospheric carbon more efficiently for photosynthesis, leading to increased growth and more drought tolerance. This insight has important implications for what we can expect later this century as the climate warms. ...Using a variety of different proxies, scientists estimate that average global temperatures during the Miocene were 5°C or 6°C warmer than today. The Antarctic ice sheet was larger, though, and then rapidly melted over a period of 100,000 years to about half of its current size. ... results indicated that in the early Miocene, atmospheric CO2 shifted from 450 to 550 parts per million and then back to 450 parts per million over the 100,000 years represented in the Foulden Maar deposit. “That seems like a smoking gun to us: an increase in carbon dioxide that was responsible for a temperature increase that then led to the Antarctic deglaciation,” Reichgelt said.... [https://eos.org/articles/ancient-pickled-leaves-give-a-glimpse-of-global-greening]  

2020-08-20. Surprising pulses of ancient warming found in Antarctic ice samples. By Sid Perkins, Science  Magazine. Excerpt: Earth’s ice ages are typically thought of as seemingly unending periods of bitter cold. But a new study suggests bursts of carbon dioxide (CO2) often entered the atmosphere during these times, providing decades or even centuries of relative warmth amid 10,000-year stretches of chill. Such pulses may have caused glaciers and ice sheets to retreat somewhat, thus opening up new areas for plants and animals. ... Nehrbass-Ahles’s team then analyzed portions of a 3.5-kilometer-long ice core drilled at one of the highest points in eastern Antarctica. Their samples capture times between 330,000 and 450,000 years ago—an interval that includes one complete ice age as well as the warm spells on either side. On average, each data point was separated from its neighbors by about 300 years, a four- to sixfold improvement in time resolution over previous studies. ...The team’s new analysis shows Earth’s climate “can change a lot faster than we’ve previously thought,” says Shaun Marcott, a paleoclimatologist at the University of Wisconsin, Madison, who wasn’t involved in the new study. The resulting shifts in ecosystems, although short-lived, could have been profound. Nehrbass-Ahles and his colleagues suggest the jumps in atmospheric CO2 result from changes in a conveyor belt of ocean currents in the Atlantic Ocean. When the Gulf Stream weakens, that warm current brings less heat to North Atlantic waters. Those changes in sea-surface temperature, in turn, cause weather patterns in the tropics to shift, triggering a shrinkage of wetlands, Nehrbass-Ahles says. The carbon-rich material stored in those formerly swampy zones then decomposes, sending a pulse of CO2 into the air to warm the climate. In modern times, these ancient pulses wouldn’t be impressive: A 10-part-per-million jump in CO2, which may have unfolded over 100 years or more in preindustrial times, could these days take only 4 or 5 years to transpire.... [https://www.sciencemag.org/news/2020/08/surprising-pulses-ancient-warming-found-antarctic-ice-samples]  

2020-02-11. Southern California Climate Change over 100,000 Years. 
By Kate Wheeling, Eos/AGU. Excerpt: Southern California is one of only a few places outside the Mediterranean Basin to enjoy a Mediterranean-like climate. Mild summers and wet winters have long supported some of the state’s (and the country’s) most biodiverse locations. But Southern California is warming faster than nearly anywhere else in the contiguous United States, and climate projections for the state forecast higher temperatures and increasingly erratic precipitation—conditions that could drive the Mediterranean region farther north and leave in its place a subtropical desert. Indeed, new research suggests this has happened before. Glover et al. looked at natural variation in vegetation and wildfire to better understand how Southern California will respond to climate change in the future.... [https://eos.org/research-spotlights/southern-california-climate-change-over-100000-years] For GSS Life and Climate chapter 10. 

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.