By Kevin Krajick
(Note: This feature first appeared in 2012. It has been periodically updated.)
Much of the modern understanding of climate has been shaped by pioneering studies done at Columbia University’s Lamont-Doherty Earth Observatory. Starting in the 1950s and extending through today, researchers in oceanography, atmospheric physics, geochemistry and other disciplines have shown how natural climate cycles work; how carbon dioxide influences the earth’s temperature; the hidden roles that oceans play in regulating climate; and, most recently, how ongoing rapid climate change is affecting nature and human societies. Here is a timeline of some of the studies that have changed the way the world looks at climate.
1956: A theory of ice ages Maurice Ewing and William Donn, Science Maurice “Doc” Ewing, one of the world’s most influential oceanographers and Lamont’s first director, teamed with geologist Donn to propose that ice ages are driven by self-perpetuating natural cycles of freezing and thawing of the Arctic Ocean. This paper and two followups were seized upon in popular literature of the time to suggest that a new ice age would arrive soon. Although the views of Ewing and others shifted radically as more evidence came in, this study initiated Lamont’s tradition of studying large-scale climate swings.
1960: Natural radiocarbon in the Atlantic Ocean Wallace Broecker et al., Journal of Geophysical Research Wallace Broecker, one of the founders of modern climate science, showed how isotopes of carbon produced by both natural and human processes could be used to map long-distance ocean currents that we now know form a series of global-scale loops. This led to Broecker’s overarching model of the “Great Ocean Conveyor Belt” and the idea that changes in the conveyor may bring sudden, powerful shifts in the global climate.
1966: Paleomagnetic study of Antarctic deep-sea cores Neil Opdyke et al., Science By systematically examining Antarctic seabed sediments, Opdyke and colleagues showed that periodic shifts in earth’s magnetic polarity could be used to accurately date sediment layers back beyond 2 million years—and thus climate shifts from those ancient times. Previously, the limit was only 25,000 years. This set the stage to test theories of climate change in deep time.
1973: Are we on the brink of a pronounced global warming? Wallace Broecker, Science This is the paper generally credited with introducing the phrase “global warming” into scientific literature. The planet at that time was emerging from a decades-long natural cooling cycle, which Broecker postulated had been masking an ongoing warming effect caused by rising industrial carbon-dioxide emissions. He predicted that as the cooling cycle bottomed out, global temperatures would rise swiftly. He was right.
1976: The surface of the ice-age Earth CLIMAP, Science CLIMAP, a large international project in the 1970s-80s, reconstructed the world’s sea-surface temperatures, and thus overall climate, during the last glaciation. The main evidence came from deep-sea cores—many taken by Lamont scientists and held in the Lamont Deep-Sea Core Repository. It was the first comprehensive look at earth’s temperature for a time markedly different from our own.
1976: Variations in earth’s orbit—pacemaker of ice ages James Hays, John Imbrie, Nicholas Shackleton, Science In the 1920s, Serb mathematician Milutin Milankovic proposed that the earth’s ice ages coincide with cyclic changes in the eccentricity, axis orientation and wobble of the earth as it orbits the sun. The idea was long debated. This paper finally proved to most scientists’ satisfaction that Milankovic cycles are real. Lamont’s James Hays worked with two other giants of modern science: Brown University’s John Imbrie and Cambridge’s Nicholas Shackleton.
1978: The Marine oxygen isotope record in Pleistocene coral, Barbados, West Indies Richard G. Fairbanks et al., Quaternary Research This paper documented the magnitude and rapidity of sea-level rises when ice sheets and glaciers melted at the ends of several previous ice ages. Up to the present, many other Lamont researchers have followed with studies seeking to quantify past changes in sea level. These studies are key to understanding how current melting of the planet’s ice may affect us in the near future.
1986: Experimental forecasts of El Niño Mark Cane, Stephen Zebiak et al., Nature El Niño is earth’s most powerful natural medium-term climate cycle, shifting precipitation and temperature patterns, and affecting crops, disease outbreaks and natural hazards globally. Its physics and variable timing were long cloaked in mystery. Cane and Zebiak were the first to construct a model that explained how it worked, and to show that the cycles could be predicted. This and related work led to forecasts that are now used worldwide to plan for crop planting, public-health initiatives and planning of emergency relief efforts.
1986: Inter-Ocean Exchange of Thermocline Water Arnold Gordon, Journal of Geophysical Research In conjunction with earlier oceanographic work, this study laid out how differences in temperature and salt levels in different water layers drive the exchange of water between the world’s oceans, and, ultimately, affect climate over vast distances. Gordon and colleagues continue to work on questions of large-scale ocean circulation in Indonesia, the Southern Ocean and elsewhere.
1988: Influence of late Cenozoic mountain building on ocean geochemical cycles Maureen Raymo et al., Geology While still a grad student, Raymo published the first of a series of papers on the Uplift-Weathering Hypothesis. This proposes that earth’s climate started cooling when tectonic forces caused the Himalayas and Tibetan Plateau to start rising some 40 million years ago. The elevation increased the weathering of minerals, which drew more carbon dioxide from the air, weakening the greenhouse effect and bringing the glaciation of the poles we see today. This still controversial idea has stimulated a large, continuing body of research. Raymo is now director of Lamont-Doherty Earth Observatory.
1989: The role of ocean-atmosphere reorganizations in glacial cycles Wallace Broecker and George Denton, Geochimica Cosmochimica Acta This study explored the role of freshwater inflow into the northern North Atlantic via melting ice in governing the oceanic “conveyor belt,” and its possible association with disruptions of currents that could cause sudden, large-scale climate changes. Followed by many other papers including 1992’s Evidence for Massive Discharges of Icebergs into the North Atlantic Ocean During the Last Glacial Period (Gerard Bond et al., Nature).
1995: Temperature histories from tree rings and corals Edward Cook, Climate Dynamics Cook, now head of Lamont’s Tree Ring Lab, showed how tree rings dating back as far as 1,000 years correlated with both modern instrumental records and marine corals to show anomalous warming during the 20th century. Collecting tree-ring samples in remote places including Tasmania, Mongolia, the Himalayas and subarctic regions, the lab’s scientists have since published many more papers on how tree rings illuminate regional and global climate histories, going back 6,000 years or more. These include monumental drought atlases of North America, South America, the Mediterranean and Europe and Asia, widely used by the scientific community.
1995: Plio-Pleistocene African climate Peter de Menocal, Science This connected the evolution of humans with a shift toward more arid conditions in East Africa’s climate after 2.8 million years ago. The change resulted in the development of open savannas, where newly upright human hunters are thought to have thrived and developed new skills. It was one of the early papers in this field, and continues to be cited.
2000: Climate change and the collapse of the Akkadian Empire: evidence from the deep-sea Heidi Cullen et al. Geology The sophisticated Akkadians ruled much of the Middle East until 4,200 years ago, when their empire suddenly collapsed. Heidi Cullen (who later became a popular TV personality covering climate) linked the collapse with an abrupt 300-year drought. The evidence: layers of dust found on the surrounding ocean floor. The study helped nourish the emerging awareness of how environmental changes may decimate societies. Later related Lamont papers include a 2010 study exploring the collapse of southeast Asia’s Angkor culture, and other Asian societies.
2002: Global sea-air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects Taro Takahashi et al., Deep-Sea Research Part II Based on some 940,000 measurements taken over four decades, Taro Takahashi and colleagues mapped for the first time on a global scale the exchange of carbon dioxide between the atmosphere and oceans—a flux that we now know plays a key role in regulating climate. This was followed by papers including 2009’s Reconstruction of the history of anthropogenic CO2 concentrations in the ocean (Samar Khatiwala et al., Nature), which suggested that the world’s oceans may have begun losing their ability to absorb rising human emissions of carbon.
2004: Long-Term Aridity Changes in the Western United States Edward Cook et al., Science Tree rings showed that a then ongoing drought in the U.S. Southwest probably paled in comparison to one during an unusually warm period about 1,000 years ago. It suggested the region’s vulnerability to global warming. An influential followup 2007 paper led by Lamont climate modeler Richard Seager, Model Projections of an imminent transition to a more arid climate in southwestern North America, added evidence that the region would dry significantly in the 21st century. The studies proved prophetic.
2008: In situ carbonation of peridotite for CO2 storage Peter Kelemen et al., Proceedings of the National Academy of Sciences Lamont scientists in various disciplines have been among the first to investigate possible ways to capture and store emissions of carbon dioxide underground. This paper documents efforts to speed up natural chemical reactions a million times over within deep-earth rocks in Oman so as to “freeze” emissions into solid minerals. Kelemen and colleagues continue to work on this process, with experimental injections in progress. Projects by other researchers are looking into piping emissions into the seabed off the U.S. Northeast, or using rocks common on the U.S. mainland.
2011: Civil conflicts are associated with the global climate Solomon Hsiang et al., Nature In the first study of its kind, Hsiang and his colleagues linked periodic increases in civil conflicts to the arrival of El Niño. The study found that the characteristic hotter, often dryer weather in certain areas doubled the risk of warfare across some 90 tropical countries, and accounted for a fifth of worldwide conflicts in the past 50 years. There is now speculation from studies done at Lamont and elsewhere that El Niño cycles themselves could be intensified by rising global temperatures in the future, and thus increase conflict.
2012: The geological record of ocean acidification Bärbel Hönisch et al., Science Lead author Bärbel Hönisch and her colleagues showed that the world’s oceans are turning acidic at a rate unprecedented over at least the last 300 million years, due to reactions with human emissions of CO2. This could affect marine ecosystems, and may already be having effects in widespread regions, including the U.S. Pacific Northwest.
2015: Climate Change in the Fertile Crescent and implications of the recent Syrian drought Colin P. Kelley et al., Proceedings of the National Academy of Sciences This study asserts that a record 2006-2010 drought in Syria was stoked by climate change — and that the drought in turn helped propel the vast, long-running Syrian civil war, one of the worst disasters of modern times. The study made worldwide headlines, and has become one of the most highly cited pieces of research linking ongoing climate trends with drastic consequences for humanity.
2015: Contribution of anthropogenic warming to California drought during 2012-2014 A. Park Williams et al., Geophysical Research Letters With record-breaking drought devastating California starting in 2012, many scientists began looking at whether global warming was playing a role. Bioclimatologist Williams and his colleagues showed that while natural factors were partly at play, global warming played a measurable role. The study was instantly seized by politicians and others as hard evidence that climate change is already affecting agriculture, economy and environment in the United States.
2016: Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions Juerg M. Matter et al., Science In a first-of-its kind project, a team showed that carbon dioxide emissions from a power plant in Iceland could be pumped into subsurface formations of basalt—a very common rock—and rapidly converted through natural chemical processes into a chalk-like solid. Such a process had been held up as a sort of holy grail for permanently sequestering human-produced carbon. The project has since grown greatly in scale, and the technology appears set to be deployed elsewhere.
2016: Greenland was nearly ice free for extended periods during the Pleistocene Joerg M. Schaefer et al., Nature One of the long-running questions about climate has been the extent to which the polar ice sheets melted during past warm periods. Schaefer and colleagues used newly advanced methods to show that rocks drilled in the 1990s from under the deepest part of the Greenland ice signaled that the land had been laid bare by melting once or more in the last million years. This suggests that most of the ice sheet disappeared—a drastic scenario previously considered by many to be unlikely. A related 2021 study, also involving Lamont researchers, turned up the first known samples of ancient plants from deep under the ice—further evidence that the ice has wasted away in the recent geologic past.
2020: Large contribution from anthropogenic warming to an emerging North American megadrought A. Park Williams, Edward R. Cook et al., Science Capping decades of investigations into past droughts in the western United States, and growing evidence that human-induced climate change was creating unprecedented conditions, this paper more or less announced that the feared modern megadrought is officially in progress.
2020: The emergence of heat and humidity too severe for human tolerance Colin Raymond, Radley Horton et al. Science In a 2017 paper, coauthor Horton and colleagues predicted that later in this century, literal killer combinations of heat and humidity exceeding the limits of human endurance would begin popping up in various regions. This paper, published just three years later, found that such conditions are already emerging, far ahead of schedule. They are being seen in widespread regions across Asia, Africa, Australia, South America and North America.
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