LC10C. Stay Current—The Ice Ages

2024-02-22. Dramatic shift in ice age rhythm pinned to carbon dioxide. [https://www.science.org/content/article/dramatic-shift-ice-age-rhythm-pinned-carbon-dioxide] By PAUL VOOSEN, Science. Excerpt: Roughly 1.5 million years ago, Earth went through a radical climatic shift. The planet had already been slipping in and out of ice ages every 40,000 years, provoked by wobbles in its orbit. But then, something flipped. The ice ages began to grow stronger and longer, with durations of 100,000 years, and overall, the planet grew cooler. And nothing about Earth’s orbit could explain it. The cause of this Mid-Pleistocene Transition (MPT), as it’s known, has been a major mystery for decades. A new compilation of global temperatures covering the past 4.5 million years, published this week in Science, points a finger at a familiar molecule: carbon dioxide. It suggests that a strengthening of an ocean pump in the waters around Antarctica sucked carbon dioxide out of the air and sent it plunging to the abyss, cooling the planet and intensifying the ice ages. The study even suggests the climate, then and now, could be more sensitive to carbon dioxide than modelers expect. “The power of the [carbon dioxide] control knob on the climate system really comes out of this work,” says Ruth Mottram, a climate scientist at the Danish Meteorological Institute….

2024-01-17. Dogged by climate change and human hunters, a mammoth’s life is written in her tusks. [https://www.science.org/content/article/dogged-climate-change-and-human-hunters-mammoth-s-life-written-her-tusks] By MICHAEL PRICE, Science. Excerpt: …the 14,000-year-old woolly mammoth whose tusks were found in 2009 near Fairbanks, Alaska, …, Elma (for short) needed a life story, which a detailed analysis of the tusks has now provided. Her travels are giving Combs and colleagues a rare glimpse into the ways of her species at the end of the last ice age—and insight into how pressure from a changing climate as well as hunting by early humans may have helped spur mammoths’ extinction….

2023-12-21. Lost history of Antarctica revealed in octopus DNA. [https://www.science.org/content/article/lost-history-antarctica-revealed-octopus-dna] By ERIK STOKSTAD. Excerpt: Some 100,000 years ago, scientists believe Antarctica’s massive western ice sheet collapsed, temporarily opening waterways between a trio of seas surrounding the continent. New evidence for that scenario comes from a surprising source: octopus DNA. …About 129,000 to 116,000 years ago, a warm spell called the last interglacial gave our planet a brief break in between several million years of ice ages. The average temperature of the planet was about 0.5°C warmer than it is today—and climate projections predict it will be again within decades. The global sea level was also 5 meters to 10 meters higher than current levels. Many scientists believe the collapse of the West Antarctic Ice Sheet and consequent melting could have been a primary reason. …The findings are consistent with growing geological evidence supporting the ice sheet collapse….

2023-10-05. Independent age estimates resolve the controversy of ancient human footprints at White Sands. [https://www.science.org/doi/10.1126/science.adh5007] By JEFFREY S. PIGATI et al, Science. Excerpt: Traditionally, researchers believed that humans arrived in North America around 16,000 to 13,000 years ago. Recently, however, evidence has accumulated supporting a much earlier date. In 2021, fossilized footprints from White Sands National Park in New Mexico were dated to between 20,000 and 23,000 years ago, providing key evidence for earlier occupation, although this finding was controversial. Pigati et al. returned to the White Sands footprints and obtained new dates from multiple, highly reliable sources (see the Perspective by Philippsen). They, too, resolved dates of 20,000 to 23,000 years ago, reconfirming that humans were present far south of the ice sheets during the Last Glacial Maximum. —Sacha Vignieri….

2023-08-31. Greenland Was Much Greener 416,000 Years Ago. [https://eos.org/articles/greenland-was-much-greener-416000-years-ago] By Bill Morris, Eos/AGU. Excerpt: In 2019, a team of scientists glimpsed an ancient, shrubby landscape at the base of a long-forgotten ice core—rare evidence that Greenland wasn’t always completely covered in ice. Now, they have pinpointed the age of that ecosystem, and the implications are disturbing—Greenland’s ice sheet, the finds show, could melt at any time, contributing to catastrophic sea level rise. …The team reported the find in 2021 but at the time were unable to accurately date the deposits. Doing so, said coauthor Tammy Rittenour, a paleoclimatologist with Utah State University, is crucial for “understanding the conditions at which you can melt the Greenland ice sheet.” …Climate variability driven by the El Niño–Southern Oscillation, North Atlantic Oscillation, and other patterns, Cronin said, could have driven Earth’s climate, ocean circulation, and ice dynamics to tipping points not predicted by current CO₂ modeling. “I think this variability represents aspects of Earth’s climate system that we don’t fully understand or appreciate,” Cronin said. …Although it is not yet possible to say whether Greenland was completely ice free during this period, the scale of the loss was immense. At Camp Century, “nearly a mile of ice disappeared,” Bierman said. “It means that nature on its own, without fossil fuel emissions in the atmosphere, removed a significant portion of the ice sheet.” …At the very minimum, the melting detected at Camp Century would have added around 1.4 meters (5 feet) to sea level. If the entire Greenland ice sheet melted, it would have added 7 meters (23 feet). If that happened today, it would devastate most of the world’s coastal towns and cities….

2023-08-25. A Lake Paves the Way for Defining the Anthropocene. [https://eos.org/articles/a-lake-paves-the-way-for-defining-the-anthropocene] By Katherine Kornei, Eos/AGU. Excerpt: Just as chemists have their periodic table, Earth scientists can lay claim to their own brightly colored reference diagram: the International Chronostratigraphic Chart, which divides our planet’s 4.5-billion-year history into meaningful chunks of time. Last month, researchers laid the groundwork for defining the current epoch of geologic time—a new line on that chart—that would cap the Holocene. They voted that Crawford Lake, a small body of water in southern Canada, serve as the reference site of the new proposed geologic epoch: the Anthropocene. …deciding on one location that typifies humans’ influence on the planet was no small feat, said Waters. The proverbial fingerprints of our species—fallout from nuclear weapons testing, particulate matter from combustion, and nitrogen from fertilizer runoff, to name a few—are littered across the recent geologic record….

2023-08-17. Uncovering Death by Fire. [https://www.science.org/content/article/raging-wildfires-may-doomed-californias-ancient-megamammals-tar-pit-fossils-reveal] By MICHAEL PRICE, Science. Excerpt: Paleontologists have long tried to understand why once-numerous populations of these and other megafauna vanished across North America toward the end of the last ice age. A study published in this issue of Science points to a new catalyst that ties together the two leading hypotheses: human activity and climate change. Each played a role, but fire was the key mediator, the authors argue. In their scenario, when the climate suddenly became warmer and drier toward the end of the last ice age, human-caused blazes grew out of control, permanently altering the landscape—and spelling the end for the animals….

2023-06-16. Humanity’s groundwater pumping has altered Earth’s tilt. [https://www.science.org/content/article/humanity-s-groundwater-pumping-has-altered-earth-s-tilt] By Warren Cornwall, Science. Excerpt: While spinning on its axis, Earth wobbles like an off-kilter top. Sloshing molten iron in Earth’s core, melting ice, ocean currents, and even hurricanes can all cause the poles to wander. Now, scientists have found that a significant amount of the polar drift results from human activity: pumping groundwater for drinking and irrigation. …scientists built a model of the polar wander, accounting for factors such as reservoirs filling because of new dams and ice sheets melting, to see how well they explained the polar movements observed between 1993 and 2010. During that time, satellite measurements were precise enough to detect a shift in the poles as small as a few millimeters. Dams and ice changes were not enough to match the observed polar motion. But when the researchers also put in 2150 gigatons of groundwater that hydrologic models estimate were pumped between 1993 and 2010, the predicted polar motion aligned much more closely with observations. Wilson and his colleagues conclude that the redistribution of that water weight to the world’s oceans has caused Earth’s poles to shift nearly 80 centimeters during that time. In fact, groundwater removal appears to have played a bigger role in that period than the release of meltwater from ice in either Greenland or Antarctica, the scientists reported Thursday in Geophysical Research Letters….

2023-04-06. Wisconsin Stalagmite Records North American Warming. [https://eos.org/articles/wisconsin-stalagmite-records-north-american-warming] By Stacy Kish, Eos/AGU. Excerpt: A new record, obtained from a tiny stalagmite in North America, has revealed eight abrupt periods of warming, likely greater than 10°C, that punctuated the last glacial episode. The new research was published last month in Nature Geoscience. The last glacial period began 115,000 years ago and ended at the start of the Holocene, 11,700 years ago. Ice core data from Greenland previously revealed 25 rapid episodes of warming, called Dansgaard-Oeschger (DO) events, largely attributed to changes in deepwater circulation in the North Atlantic. …Paleoclimate studies from central North America rely heavily on lake records, which range from 15,000 to 20,000 years old. The stalagmite extends that time back another 40,000 years, making it one of the longest and oldest records in this part of the world. The new record also illustrates how quickly DO warming telescoped across the Northern Hemisphere and the implications of this warming for the environment and ice sheet dynamics that could take place during a human lifetime….

2023-03-17. Ice Cores Record Long-Ago Seasons in Antarctica. [https://eos.org/articles/ice-cores-record-long-ago-seasons-in-antarctica] By Caroline Hasler, Eos/AGU. Excerpt: Researchers used ice core data to reconstruct seasonal temperatures throughout the Holocene. The results link especially hot summers with patterns in Earth’s orbit. …In January, a team of scientists presented a seasonal temperature record dating back 11,000 years. The ice revealed a connection between intense solar radiation and hot summers in Antarctica. …“[This] is the first record of its kind,” said Tyler Jones, a polar climatologist at the University of Colorado Boulder’s Institute of Arctic and Alpine Research (INSTAAR) and lead author of the study. Seasonal temperature data help researchers understand Antarctica’s natural rhythm, which is critical for anticipating the polar regions’ responses to warming. …The data showed that summer temperatures in West Antarctica were higher when the region received a more intense dose of sunlight. This deceptively simple observation is connected to Milankovitch cycles, a major tenet of climate science. According to Milankovitch theory, the amount of sunlight reaching Earth’s surface—which depends on Earth’s rotation and orbit around the Sun—drives long-term climate change. The study validated the link between sunlight and climate on a seasonal scale: Intensely sunny summers lead to warm temperatures that can potentially trigger large-scale melting of ice….

2022-07-11. Precession Helped Drive Glacial Cycles in the Pleistocene. [https://eos.org/articles/precession-helped-drive-glacial-cycles-in-the-pleistocene] By Katherine Kornei, Eos/AGU. Excerpt: …scientists have analyzed tiny bits of rock transported by glaciers and gained a better understanding of recent glacial cycles. The team found that precession—gradual changes in the direction of Earth’s axis of rotation—has played an important role in the breakup of Northern Hemisphere ice sheets over the past 1.7 million years. And during the late Pleistocene, that precession-driven collapse coincided with deglaciation, the researchers reported in May in Science. …energy received from the Sun at any one point on Earth varies according to two long-term cycles: precession and obliquity. Precession refers to changes in the direction of Earth’s axis of rotation, and obliquity is the tilt of Earth’s rotational axis as the planet orbits the Sun. These two so-called Milankovitch cycles modulate the amount of solar energy received by Earth’s surface over periods of roughly 23,000 and 41,000 years, respectively. …Barker and his colleagues found that glacial cycles before and after the Mid-Pleistocene Transition were correlated with both precession and changes in obliquity. The team showed that minima in precession—meaning that summer in the Northern Hemisphere occurs when the planet is closest to the Sun—were tied to ice sheet breakup. And times of decreasing obliquity were associated with ice sheet growth. It was particularly surprising to uncover the role of precession prior to the Mid-Pleistocene Transition, said Barker. That’s because the shorter glacial cycles long have been assumed to have been driven solely by changes in obliquity occurring at the same cadence, without any influence from precession, he said. “I nearly fell off my chair when I saw that.”.…

2022-06-23. Hidden carbon layer may have sparked ancient bout of global warming. [https://www.science.org/content/article/hidden-carbon-layer-may-have-sparked-ancient-bout-global-warming] By Paul Voosen, Science Magazine. Excerpt: There is no perfect parallel in Earth’s past for present-day climate change—human-driven warming is simply happening too fast and furiously. The closest analog came 56 million years ago, when over the course of 3000 to 5000 years, greenhouse gases soared in the atmosphere, causing at least 5°C of warming and pushing tropical species to the poles. The cause of the Paleocene-Eocene Thermal Maximum (PETM) has long been debated, with researchers invoking exotic mechanisms such as catastrophic releases of methane from the sea floor or even asteroid strikes. But over the past few years, evidence has mounted for a more prosaic culprit: carbon-spewing volcanoes that emerged underneath Greenland as it tore away from Europe. Now, researchers have found signs of an effect that would have supercharged the warming effect of the volcanoes, making them a stronger suspect. The underside of Greenland is thought to be encrusted with carbon-rich rocks, like barnacles on the keel of a ship. During the rifting, they might have liberated a gusher of carbon dioxide (CO₂), says Thomas Gernon, a geologist at the University of Southampton and leader of the new study. “It’s a perfect storm of conditions.” Mudrocks on the sea floor also contain carbon that originated in living things, and magma from submarine eruptions could have heated the rocks and liberated the carbon. But in 2017, researchers analyzed plankton fossils from an ocean core and found the carbon released during the PETM was heavier than previously thought. For some, that indicated the carbon wasn’t from living sources. “Given the current state of knowledge, it seems likely to be volcanism,” says Marcus Gutjahr, a geochemist at GEOMAR Helmholtz Centre for Ocean Research Kiel, who led the 2017 study. …CO₂ and other gases can bubble out of tectonic plates as they dive into the mantle, percolating up into the underside of thick crusts like Greenland’s, and forming carbonate formations that can be stable for millions or even billions of years.…

2022-03-14. Holes the size of city blocks are forming in the Arctic seafloor. By Katie Hunt, CNN. Excerpt: Marine scientists have discovered deep sinkholes — one larger than a city block of six-story buildings — and ice-filled hills that have formed “extraordinarily” rapidly on a remote part of the Arctic seafloor. Mapping of Canada’s Beaufort Sea, using a remotely operated underwater vehicle and ship-mounted sonar, revealed the dramatic changes, which the researchers said are taking place as a result of thawing permafrost submerged underneath the seabed. …On land, thawing permafrost has led to radical shifts in the Arctic landscape, including ground collapses, the formation and disappearance of lakes, the emergence of moundscalled pingos, and craters formed by blowouts of methane gas contained in the permafrost. These extreme featureshave affected infrastructure such as roads and pipelines. …Many of the landscape changes seen on terrestrial permafrost have been attributed to warmer temperatures as a result of the climate crisis — the Arctic is warming two times faster than the global average. However, the authors said the changes they’d identified could not be explained by human-caused climate change. …Instead, the holes were likely caused by much older, slower climatic shifts that are related, he said, to our emergence from the last ice age and appear to have been happening for thousands of years.… [https://www.cnn.com/2022/03/14/world/arctic-seafloor-holes-permafrost-scn/index.html]

2021-11-19. Mammoths Lost Their Steppe Habitat to Climate Change. By Elise Cutts, Eos/AGU. Excerpt: Ancient plant and animal DNA buried in Arctic sediments preserve a 50,000-year history of Arctic ecosystems, suggesting that climate change contributed to mammoth extinction.… [https://eos.org/articles/mammoths-lost-their-steppe-habitat-to-climate-change]

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…. 

2021-03-15. 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/] 

2021-03. 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/]

2021-02-18. 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]

2020-09-03. 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. [https://eos.org/articles/antarctic-ice-cores-offer-a-whiff-of-earths-ancient-atmosphere] Excerpt: To determine how Earth’s climate has varied over time, scientists are constantly on the lookout for the oldest whiffs of our planet’s atmosphere. The current record holders, recently extracted from Antarctic ice cores and dated to over 2 million years old, reveal concentrations of gases like carbon dioxide (CO₂) and methane in ancient Earth’s atmosphere. Researchers have now shown that levels of these greenhouse gases fluctuated less millions of years ago than they did in more recent times. That discovery has implications for how Earth transitioned between two climatic periods roughly a million years ago, the team reported. …The climatic history of Earth has been far from constant: For the past 800,000 years, continental-scale ice sheets have repeatedly grown and retreated in glacial-interglacial cycles occurring roughly every 100,000 years (the “100K world”). (The current interglacial period, which has persisted for about the past 11,000 years, is known as the Holocene.) But records stretching back further in time—to between 2.8 million and 1.2 million years ago—suggest that glacial-interglacial cycles were shorter and lasted only about 40,000 years (the “40K world”). However, there have been no direct observations of atmospheric greenhouse gases from that long ago. Until now. Yuzhen Yan, a geoscientist at Princeton University when this research was conducted, and his collaborators spent 7 weeks in Antarctica during the 2015–2016 austral summer collecting ice cores. …Yan and his colleagues drilled into “blue ice,” a rare type of ice that’s been compressed over time. Scientists value it because it’s often very old, even when relatively near the surface. In the Allan Hills, blue ice is being pushed toward a mountain and is slowly uplifting, Yan said. “What used to be buried very deep…is progressively getting closer to the surface.” At the same time, strong winds ablate the ice from the top, progressively removing younger material….

2019-11-01. Oceans Vented Carbon Dioxide During the Last Deglaciation. By Kate Wheeling, Eos/AGU. [https://eos.org/research-spotlights/oceans-vented-carbon-dioxide-during-the-last-deglaciation] Excerpt: A new boron isotope record from South Pacific marine sediments offers a more complete picture of ocean-atmosphere carbon dioxide exchange during the late Pleistocene. During the late Pleistocene epoch, ice sheets advanced and retreated in tandem with changing atmospheric carbon dioxide levels. Researchers have long sought to understand the complex processes that modulate rising and falling carbon dioxide concentrations—a line of research with important implications today as levels reach highs not seen since roughly 3 million years ago in the Pliocene, when the Arctic was forested. … The authors …found widespread outgassing of carbon dioxide, particularly during the last deglaciation, which could be explained by an increase in upwelling of the gas from the deep ocean, according to the authors. …The study fills an important gap in boron isotope–based reconstructions of the ocean-atmosphere carbon dioxide exchange throughout the last deglaciation. A better understanding of this exchange in the past could provide insights about impacts that rising atmospheric carbon dioxide levels will have on the climate today….

2018-08-08. Massive drought or myth? Scientists spar over an ancient climate event behind our new geological age.By Paul Voosen, Science Magazine.  Last month, the International Commission on Stratigraphy (ICS), the bureaucracy that governs geological time, declared we are living in a new geological age. No, it’s not the Anthropocene, the much-debated proposal for a geological division defined by human impact on Earth. The new age anointed by ICS is called the Meghalayan, based on signs in the rock record of a global drought that began about 4200 years ago. It is one of three newly named subdivisions of the Holocene, the geological epoch that began 11,700 years ago with the retreat of ice age glaciers. And the name will now filter its way into textbooks….http://www.sciencemag.org/news/2018/08/massive-drought-or-myth-scientists-spar-over-ancient-climate-event-behind-our-new

2018-06-05. How the Ice Age Shaped New York. By William J. Broad, The New York Times. Excerpt: At the start of the last ice age, 2.6 million years ago, a sheet of frozen water formed atop North America that kept expanding and thickening until it reached a maximum depth of roughly two miles. At its southern edge, the vast body deposited tons of rocky debris — from sand and pebbles to boulders the size of school buses. Then, some 18,000 years ago, the planet began to warm and the gargantuan sheet of ice began to melt and retreat. Today, the southernmost edge of that frozen expanse is marked by a line of rubble that extends across the northern United States for thousands of miles. The largest deposits form what geologists call a terminal moraine. The intermittent ridge runs from Puget Sound to the Missouri River to Montauk Point on Long Island, forming the prominence that supports its old lighthouse. The ancient sheet of ice also left its mark on a very modern phenomenon: New York City. The ice over Manhattan would have buried even the tallest skyscraper and was so heavy that it depressed the underlying bedrock. As it melted, giant boulders embedded deep within its flanks landed throughout what became the city. Many are still visible in Central Park, unlikely obelisks scored by time. But the island was the last hurrah, and the mammoth sheet of ice ended immediately to the south, in Brooklyn, Queens and Staten Island…. https://www.nytimes.com/2018/06/05/science/how-the-ice-age-shaped-new-york.html

2017-11-22. How Earth’s Orbit Affected Ice Sheets Millions of Years Ago. By Emily Underwood, Eos/AGU. Excerpt: When Earth’s atmosphere warms, the vast sheets of ice over Antarctica and Greenland melt. This melting, in addition to the thermal expansion of water, leads to rising sea levels. Although it’s clear that seas are rising at an increasing rate, scientists can’t yet precisely predict how fast or how much they will rise in the future.  Now, scientists are using climate and fossil data from one of the warmest periods in Earth’s history to help improve our understanding of ice sheet and sea level behavior in a warmer-than-modern world. When scientists look for hints of how Earth’s warming climate will affect ice sheets, they often refer to the late Pliocene era, between 3.264 and 3.025 million years ago. During this period, the concentration of carbon dioxide in the atmosphere ranged between 300 and 450 parts per million (ppm)—as a reference point, the concentration of atmospheric carbon dioxide in October 2017 was 404.3 ppm. On average, the late Pliocene was warmer than today’s climate by about 2°C–3°C. Although the late Pliocene was relatively stable climatically, there were cool periods when ice sheets expanded and warm “interglacial” periods in which they retreated, according to climate models. However, marine fossil evidence indicates that sea levels did not always rise and fall in sync with global temperatures.  In a new study, de Boer et al. explore a likely culprit for the mismatch: wobbles in Earth’s orbit that affect how solar energy is distributed around the planet….  https://eos.org/research-spotlights/how-earths-orbit-affected-ice-sheets-millions-of-years-ago

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. Excerpt: Following Earth’s last ice age, which peaked 20,000 years ago, the Antarctic warmed between two and three times the average temperature increase worldwide, according to a new study by a team of American geophysicists. The disparity – Antarctica warmed about 11 degrees Celsius, nearly 20 degrees Fahrenheit, between about 20,000 and 10,000 years ago, while the average temperature worldwide rose only about 4 degrees Celsius, or 7 degrees Fahrenheit – highlights the fact that the poles, both the Arctic in the north and the Antarctic in the south, amplify the effects of a changing climate, whether it gets warmer or cooler. The calculations are in line with estimates from most climate models, proving that these models do a good job of estimating past climatic conditions and, very likely, future conditions in an era of climate change and global warming. …These models currently predict that as a result of today’s global climate change, Antarctica will warm twice as much as the rest of the planet, though it won’t reach its peak for a couple of hundred years. While the most likely climate change scenario, given business-as-usual greenhouse gas emissions, is a global average increase of 3 degrees Celsius (5 degrees Fahrenheit) by 2100, the Antarctic is predicted to warm eventually by around 6 degrees Celsius (10 degrees Fahrenheit)….  http://news.berkeley.edu/2016/12/05/during-last-period-of-global-warming-antarctica-warmed-2-to-3-times-more-than-planet-average/

2016-09-26. Study: Earth’s roughly warmest in about 100,000 years. By Seth Borenstein, Associated Press.  Excerpt: WASHINGTON — A new study paints a picture of an Earth that is warmer than it has been in about 120,000 years, and is locked into eventually hitting its hottest mark in more than 2 million years. As part of her doctoral dissertation at Stanford University, Carolyn Snyder, now a climate policy official at the U.S. Environmental Protection Agency, created a continuous 2 million year temperature record, much longer than a previous 22,000 year record. Snyder’s temperature reconstruction, published Monday in the journal Nature, doesn’t estimate temperature for a single year, but averages 5,000-year time periods going back a couple million years. Snyder based her reconstruction on 61 different sea surface temperature proxies from across the globe, such as ratios between magnesium and calcium, species makeup and acidity. But the further the study goes back in time, especially after half a million years, the fewer of those proxies are available, making the estimates less certain, she said. …two interglacial time periods, the one 120,000 years ago and another just about 2 million years ago, were the warmest Snyder tracked. They were about 3.6 degrees (2 degrees Celsius) warmer than the current 5,000-year average. …Snyder said if climate factors are the same as in the past — and that’s a big if — Earth is already committed to another 7 degrees or so (about 4 degrees Celsius) of warming over the next few thousand years. “This is based on what happened in the past,” Snyder said. “In the past it wasn’t humans messing with the atmosphere.”…  https://www.washingtonpost.com/politics/study-earths-roughly-warmest-in-about-100000-years/2016/09/26/2672bb28-8412-11e6-b57d-dd49277af02f_story.html See also Nature article.

2016-06-30. Crippled Atlantic currents triggered ice age climate change. By Eric Hand, Science. Excerpt: The last ice age wasn’t one long big chill. Dozens of times temperatures abruptly rose or fell, causing all manner of ecological change. Mysteriously, ice cores from Greenland and Antarctica show that these sudden shifts—which occurred every 1500 years or so—were out of sync in the two hemispheres: When it got cold in the north, it grew warm in the south, and vice versa. Now, scientists have implicated the culprit behind those seesaws—changes to a conveyor belt of ocean currents known as the Atlantic Meridional Overturning Circulation (AMOC). …Still unclear is what triggered the AMOC’s sudden slowdowns. Many of the drops correspond to so-called Heinrich events: rapid releases of icebergs from Canada’s ice sheet. These iceberg armadas often chugged through the Hudson Strait of Canada and may have discharged more ice into the Atlantic Ocean than contained in the entire ice cap of Greenland, raising ancient sea levels by 10 meters. The meltwater brought incredible amounts of freshwater to the North Atlantic, precisely where ocean currents cool off and sink. Because freshwater is less dense than saltwater, it can plug up the AMOC, preventing the overturning and deep water formation the fuels the circulation’s engine. …Another question is whether the AMOC—currently known to be in decline—could drop off suddenly today, as depicted in the 2004 movie The Day After Tomorrow, causing temperatures to plummet across northwestern Europe….  http://www.sciencemag.org/news/2016/06/crippled-atlantic-conveyor-triggered-ice-age-climate-change

2016-03-02. Characterizing Interglacial Periods over the Past 800,000 Years. By Cody Sullivan, Earth & Space Science News (EoS, AGU). Excerpt: Researchers identified 11 different interglacial periods over the past 800,000 years, but the interglacial period we are experiencing now may last an exceptionally long time. …glacial cycles, consisting of cold ice ages and milder interludes, typically lasted about 40,000 years—but those weaker cycles gave way to longer-lasting icy eras with cycles lasting roughly 100,000 years. In between the cold ice ages are periods of thawing and warming known as interglacial periods, during which sea levels rise and ice retreats. …Although most interglacials typically last about 10,000 to 30,000 years, the researchers suggest that the current epoch—the Holocene—may last much longer because of the increased levels of atmospheric greenhouse gases resulting from human activity. The authors predict that this current interglacial period won’t give way to a glacial period for another 50,000 years or so. The only way the current interglacial could end earlier is if CO2 levels were reduced to well below preindustrial levels….  https://eos.org/research-spotlights/characterizing-interglacial-periods-over-the-past-800000-years

2015-12-16. Plankton Reveal New Secrets About Ancient CO2 Levels. By Natalie Jacewicz, EoS Earth and Space Science News, AGU. Excerpt: An analysis of phytoplankton shells doubles previous estimates of the amount of carbon dioxide in the atmosphere 11 million years ago. …Scientists studying past global temperatures and carbon dioxide (CO2) levels have struggled to explain a global cooling that occurred between 11 and 6 million years ago. Generally, such drops correspond with plummeting CO2, but previous measurements have found only a modest decrease in the greenhouse gas during the period. New research, however, has revealed a CO2 plunge that scientists have never before detected, and the clue lies in tiny ocean plankton….  https://eos.org/articles/plankton-reveal-new-secrets-about-ancient-co2-levels

2015-07-23. Hot spells doomed the mammoths. By Elizabeth Pennisi, Science. Excerpt: About 30,000 years ago, mammoths, giant sloths, and other massive mammals roamed the earth. Twenty thousand years later they were all gone. Some researchers blame human hunting, but a new study claims that abrupt shifts in climate set in motion a downward spiral for many of these species, one that humans aggravated. The results, the authors say, are a warning to modern humans that, if not slowed, current warming could doom many more species…. http://news.sciencemag.org/evolution/2015/07/hot-spells-doomed-mammoths

2015-05-05. Ice cores show 200-year climate lag. By Stephanie McClellan, BBC News. Excerpt: Scientists have found a 200-year lag time between past climate events at the poles. The most detailed Antarctic ice core provides the first clear comparison with Greenland records, revealing a link between northern and southern hemisphere climate change. …abrupt and large temperature changes first occurred in Greenland, with the effect delayed about 200 years in the Antarctic. The study appears in Nature journal. …In the 1990s, scientists took ice cores from Greenland that revealed very abrupt and large swings in temperature approximately 20,000 to 60,000 years ago. But it wasn’t clear how this influenced global climate change. The 3,405 metre-long ice core, taken from the centre of West Antarctica, is the longest high resolution ice core. Researchers documented 18 abrupt climate events. “This record has annual resolution, meaning we can see information about every year going back 30,000 years, and close to that resolution all the way back to 68,000 years ago,” explains Eric Steig, professor of Earth and Space Sciences at the University of Washington, who co-wrote the paper…. http://www.bbc.com/news/science-environment-32599228 0

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.