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S S Drijfhout - One of the best experts on this subject based on the ideXlab platform.
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spontaneous Abrupt Climate Change due to an atmospheric blocking sea ice ocean feedback in an unforced Climate model simulation
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: S S Drijfhout, Emily Gleeson, Henk A Dijkstra, V N LivinaAbstract:Abrupt Climate Change is abundant in geological records, but Climate models rarely have been able to simulate such events in response to realistic forcing. Here we report on a spontaneous Abrupt cooling event, lasting for more than a century, with a temperature anomaly similar to that of the Little Ice Age. The event was simulated in the preindustrial control run of a high-resolution Climate model, without imposing external perturbations. Initial cooling started with a period of enhanced atmospheric blocking over the eastern subpolar gyre. In response, a southward progression of the sea-ice margin occurred, and the sea-level pressure anomaly was locked to the sea-ice margin through thermal forcing. The cold-core high steered more cold air to the area, reinforcing the sea-ice concentration anomaly east of Greenland. The sea-ice surplus was carried southward by ocean currents around the tip of Greenland. South of 70°N, sea ice already started melting and the associated freshwater anomaly was carried to the Labrador Sea, shutting off deep convection. There, surface waters were exposed longer to atmospheric cooling and sea surface temperature dropped, causing an even larger thermally forced high above the Labrador Sea. In consequence, east of Greenland, anomalous winds Changed from north to south, terminating the event with similar Abruptness to its onset. Our results imply that only Climate models that possess sufficient resolution to correctly represent atmospheric blocking, in combination with a sensitive sea-ice model, are able to simulate this kind of Abrupt Climate Change.
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spontaneous Abrupt Climate Change due to an atmospheric blocking sea ice ocean feedback in an unforced Climate model simulation
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: S S Drijfhout, Emily Gleeson, Henk A Dijkstra, V N LivinaAbstract:There is a long-standing debate about whether Climate models are able to simulate large, Abrupt events that characterized past Climates. Here, we document a large, spontaneously occurring cold event in a preindustrial control run of a new Climate model. The event is comparable to the Little Ice Age both in amplitude and duration; it is Abrupt in its onset and termination, and it is characterized by a long period in which the atmospheric circulation over the North Atlantic is locked into a state with enhanced blocking. To simulate this type of Abrupt Climate Change, Climate models should possess sufficient resolution to correctly represent atmospheric blocking and a sufficiently sensitive sea-ice model.
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Spontaneous Abrupt Climate Change due to an atmospheric blocking–sea-ice–ocean feedback in an unforced Climate model simulation
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: S S Drijfhout, Emily Gleeson, Henk A Dijkstra, V N LivinaAbstract:Abrupt Climate Change is abundant in geological records, but Climate models rarely have been able to simulate such events in response to realistic forcing. Here we report on a spontaneous Abrupt cooling event, lasting for more than a century, with a temperature anomaly similar to that of the Little Ice Age. The event was simulated in the preindustrial control run of a high-resolution Climate model, without imposing external perturbations. Initial cooling started with a period of enhanced atmospheric blocking over the eastern subpolar gyre. In response, a southward progression of the sea-ice margin occurred, and the sea-level pressure anomaly was locked to the sea-ice margin through thermal forcing. The cold-core high steered more cold air to the area, reinforcing the sea-ice concentration anomaly east of Greenland. The sea-ice surplus was carried southward by ocean currents around the tip of Greenland. South of 70°N, sea ice already started melting and the associated freshwater anomaly was carried to the Labrador Sea, shutting off deep convection. There, surface waters were exposed longer to atmospheric cooling and sea surface temperature dropped, causing an even larger thermally forced high above the Labrador Sea. In consequence, east of Greenland, anomalous winds Changed from north to south, terminating the event with similar Abruptness to its onset. Our results imply that only Climate models that possess sufficient resolution to correctly represent atmospheric blocking, in combination with a sensitive sea-ice model, are able to simulate this kind of Abrupt Climate Change.
Marisa Montoya - One of the best experts on this subject based on the ideXlab platform.
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an interhemispheric mechanism for glacial Abrupt Climate Change
Climate Dynamics, 2015Co-Authors: Rubén Banderas, Marisa Montoya, Jorge Alvarezsolas, Alexander RobinsonAbstract:The last glacial period was punctuated by Abrupt Climate Changes that are widely considered to result from millennial-scale variability of the Atlantic meridional overturning circulation (AMOC). However, the origin of these AMOC reorganizations remains poorly understood. The climatic connection between both hemispheres indicated by proxies suggests that the Southern Ocean (SO) could regulate this variability through Changes in winds and atmospheric CO\(_{2}\) concentration. Here, we investigate this hypothesis using a coupled Climate model forced by prescribed CO\(_{2}\) and SO wind-stress variations. We find that the AMOC exhibits an oscillatory behavior between weak and strong circulation regimes which is ultimately caused by Changes in the meridional density gradient of the Atlantic Ocean. The evolution of the simulated climatic patterns matches the amplitude and timing of the largest events that occurred during the last glacial period and their widespread climatic impacts. Our results suggest the existence of an internal interhemispheric oscillation mediated by the bipolar seesaw that could promote glacial Abrupt Climate Changes through variations in atmospheric CO\(_{2}\) levels, the strength of the SO winds and AMOC reorganizations, and provide an explanation for the pervasive Antarctic-like Climate signal found in proxy records worldwide.
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Role of CO2 and Southern Ocean winds in glacial Abrupt Climate Change
Climate of The Past, 2011Co-Authors: Rubén Banderas, Jorge Alvarez-solas, Marisa MontoyaAbstract:The study of Greenland ice cores revealed two decades ago the Abrupt character of glacial millennial-scale Climate variability. Several triggering mechanisms have been proposed and confronted against growing proxy-data evidence. Although the implication of North Atlantic deep water (NADW) formation reorganisations in glacial Abrupt Climate Change seems robust nowadays, the final cause of these reorganisations remains unclear. Here, the role of CO2 and Southern Ocean winds is investigated using a coupled model of intermediate complexity in an experimental setup designed such that the Climate system resides close to a threshold found in previous studies. An initial Abrupt surface air temperature (SAT) increase over the North Atlantic by 4 K in less than a decade, followed by a more gradual warming greater than 10 K on centennial timescales, is simulated in response to increasing atmospheric CO2 levels and/or enhancing southern westerlies. The simulated peak warming shows a similar pattern and amplitude over Greenland as registered in ice core records of Dansgaard-Oeschger (D/O) events. This is accompanied by a strong Atlantic meridional overturning circulation (AMOC) intensification. The AMOC strengthening is found to be caused by a northward shift of NADW formation sites into the Nordic Seas as a result of a northward retreat of the sea-ice front in response to higher temperatures. This leads to enhanced heat loss to the atmosphere as well as reduced freshwater fluxes via reduced sea-ice import into the region. In this way, a new mechanism that is consistent with proxy data is identified by which Abrupt Climate Change can be promoted.
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role of co 2 and southern ocean winds in glacial Abrupt Climate Change
Climate of The Past, 2011Co-Authors: Rubén Banderas, Marisa Montoya, Jorge AlvarezsolasAbstract:The study of Greenland ice cores revealed two decades ago the Abrupt character of glacial millennial-scale Climate variability. Several triggering mechanisms have been proposed and confronted against growing proxy-data evidence. Although the implication of North Atlantic deep water (NADW) formation reorganisations in glacial Abrupt Climate Change seems robust nowadays, the final cause of these reorganisations remains unclear. Here, the role of CO2 and Southern Ocean winds is investigated using a coupled model of intermediate complexity in an experimental setup designed such that the Climate system resides close to a threshold found in previous studies. An initial Abrupt surface air temperature (SAT) increase over the North Atlantic by 4 K in less than a decade, followed by a more gradual warming greater than 10 K on centennial timescales, is simulated in response to increasing atmospheric CO2 levels and/or enhancing southern westerlies. The simulated peak warming shows a similar pattern and amplitude over Greenland as registered in ice core records of Dansgaard-Oeschger (D/O) events. This is accompanied by a strong Atlantic meridional overturning circulation (AMOC) intensification. The AMOC strengthening is found to be caused by a northward shift of NADW formation sites into the Nordic Seas as a result of a northward retreat of the sea-ice front in response to higher temperatures. This leads to enhanced heat loss to the atmosphere as well as reduced freshwater fluxes via reduced sea-ice import into the region. In this way, a new mechanism that is consistent with proxy data is identified by which Abrupt Climate Change can be promoted.
Wallace S Broecker - One of the best experts on this subject based on the ideXlab platform.
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The Fate of Greenland: Lessons from Abrupt Climate Change
2011Co-Authors: Philip W. Conkling, Richard B Alley, Wallace S Broecker, George H. DentonAbstract:Viewed from above, Greenland offers an endless vista of whiteness interrupted only by scattered ponds of azure-colored melt water. Ninety percent of Greenland is covered by ice; its ice sheet, the largest outside Antarctica, stretches almost 1,000 miles from north to south and 600 miles from east to west. But this stark view of ice and snow is changing -- and changing rapidly. Greenland's ice sheet is melting; the dazzling, photogenic display of icebergs breaking off Greenland's rapidly melting glaciers has become a tourist attraction. The Fate of Greenland documents Greenland's warming with dramatic color photographs and investigates episodes in Greenland's Climate history for clues about what happens when Climate Change is Abrupt rather than gradual. Greenland's Climate past and present could presage our Climate future. Abrupt Climate Change would be cataclysmic: the melting of Greenland's ice shelf would cause sea levels to rise twenty-four feet worldwide; lower Manhattan would be underwater and Florida's coastline would recede to Orlando. The planet appears to be in a period of acute Climate instability, exacerbated by carbon dioxide we pour into the atmosphere. As this book makes clear, it is in all of our interests to pay attention to Greenland.
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the great ocean conveyor discovering the trigger for Abrupt Climate Change
2010Co-Authors: Wallace S BroeckerAbstract:Preface vii Chapter 1 . The Setting 1 Chapter 2 . A Surprise 19 Chapter 3 . The Villain 35 Chapter 4 . Puzzles 51 Chapter 5 . Hot Clues 66 Chapter 6 . The Solution 77 Chapter 7 . A Confirmation 88 Chapter 8 . The Last Hurrah 102 Chapter 9 . Holocene Wobbles 113 Chapter 10 . The Anthropocene 126 Glossary 139 Figure Credits 145 Supplementary Readings 147 Index 149
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Abrupt Climate Change revisited
Global and Planetary Change, 2006Co-Authors: Wallace S BroeckerAbstract:Taken together, evidence from east Greenland's mountain moraines and results from atmospheric models appear to provide the answer to a question which has long dogged Abrupt Climate Change research: namely, how were impacts of the Younger Dryas (YD), Dansgaard–Oeschger (D–O) and Heinrich (H) events transmitted so quickly and efficiently throughout the northern hemisphere and tropics? The answer appears to lie in extensive winter sea ice formation which created Siberian-like conditions in the regions surrounding the northern Atlantic. Not only would this account for the ultra cold conditions in the north, but, as suggested by models, it would have pushed the tropical rain belt southward and weakened the monsoons. The requisite Abrupt Changes in the extent of sea ice cover are of course best explained by the turning on and turning off of the Atlantic's conveyor circulation.
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the role of seasonality in Abrupt Climate Change
Quaternary Science Reviews, 2005Co-Authors: George H. Denton, Richard B Alley, Gary Comer, Wallace S BroeckerAbstract:Abstract A case is made that seasonality switches dominated by wintertime were instrumental in Abrupt Climate Changes in the North Atlantic region during the last glaciation and into the Holocene. The primary evidence comes from mismatches between mean annual temperatures from Greenland ice cores in comparison with snowline Changes in East Greenland, northern Europe, and North America. The most likely explanation is a shutdown (or reduction in strength) of the conveyor. This allows the spread of winter sea ice across the North Atlantic, thus causing the northern region to experience much colder winters. Because they mimic the Greenland temperature rather than the snowline signal, Changes in the Atlantic Intertropical Convergence Zone and the Asian monsoon may also share a winter linkage with Greenland. Thus the paleoClimate record is consistent with the notion that a huge continental sector of the Northern Hemisphere, stretching from Greenland to Asia, was close to an extreme winter threshold during much of the last glaciation. Winter Climate crossed this threshold repeatedly, with marked Changes in seasonality that may well have amplified and propagated a signal of Abrupt Change throughout the hemisphere and into the tropics.
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Abrupt Climate Change causal constraints provided by the paleoClimate record
Earth-Science Reviews, 2000Co-Authors: Wallace S BroeckerAbstract:Abstract Important aspects of the physics involved in the Climate Changes of late Quaternary time elude us. The paleoclimatic record documents in detail that these Changes were vast and in many cases happened Abruptly. Every element of the global Climate system was involved. While a case can be made that these reorganizations of the ocean's thermohaline circulation acted as the trigger for these jumps, no one has as yet been able to articulate exactly how it is that these reorganizations are capable of inducing such large Changes in the way in which the atmosphere operates. In this review, I point out what to me are the key constraints placed by the records kept in ice and in sediments. The timing of these Changes suggests that they have been paced by seasonality Changes related to periodicities in the Earth's orbital elements and by a curious 1500-year cycle imprinted on sediments in the northern Atlantic. But as these pacemakers are inherently weak, in order for them to generate what we see in the record, there must exist powerful and likely nonlinear feedbacks in the system. It is my hope that by bringing together this information, I will provide an impetus for creative thinking with regard to physical scenarios capable of illuminating these feedbacks. Not only is this the crucial step in understanding our past, but it is also a necessary step if we are to properly evaluate the possible consequences of the ongoing greenhouse gas buildup.
V N Livina - One of the best experts on this subject based on the ideXlab platform.
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spontaneous Abrupt Climate Change due to an atmospheric blocking sea ice ocean feedback in an unforced Climate model simulation
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: S S Drijfhout, Emily Gleeson, Henk A Dijkstra, V N LivinaAbstract:Abrupt Climate Change is abundant in geological records, but Climate models rarely have been able to simulate such events in response to realistic forcing. Here we report on a spontaneous Abrupt cooling event, lasting for more than a century, with a temperature anomaly similar to that of the Little Ice Age. The event was simulated in the preindustrial control run of a high-resolution Climate model, without imposing external perturbations. Initial cooling started with a period of enhanced atmospheric blocking over the eastern subpolar gyre. In response, a southward progression of the sea-ice margin occurred, and the sea-level pressure anomaly was locked to the sea-ice margin through thermal forcing. The cold-core high steered more cold air to the area, reinforcing the sea-ice concentration anomaly east of Greenland. The sea-ice surplus was carried southward by ocean currents around the tip of Greenland. South of 70°N, sea ice already started melting and the associated freshwater anomaly was carried to the Labrador Sea, shutting off deep convection. There, surface waters were exposed longer to atmospheric cooling and sea surface temperature dropped, causing an even larger thermally forced high above the Labrador Sea. In consequence, east of Greenland, anomalous winds Changed from north to south, terminating the event with similar Abruptness to its onset. Our results imply that only Climate models that possess sufficient resolution to correctly represent atmospheric blocking, in combination with a sensitive sea-ice model, are able to simulate this kind of Abrupt Climate Change.
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spontaneous Abrupt Climate Change due to an atmospheric blocking sea ice ocean feedback in an unforced Climate model simulation
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: S S Drijfhout, Emily Gleeson, Henk A Dijkstra, V N LivinaAbstract:There is a long-standing debate about whether Climate models are able to simulate large, Abrupt events that characterized past Climates. Here, we document a large, spontaneously occurring cold event in a preindustrial control run of a new Climate model. The event is comparable to the Little Ice Age both in amplitude and duration; it is Abrupt in its onset and termination, and it is characterized by a long period in which the atmospheric circulation over the North Atlantic is locked into a state with enhanced blocking. To simulate this type of Abrupt Climate Change, Climate models should possess sufficient resolution to correctly represent atmospheric blocking and a sufficiently sensitive sea-ice model.
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Spontaneous Abrupt Climate Change due to an atmospheric blocking–sea-ice–ocean feedback in an unforced Climate model simulation
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: S S Drijfhout, Emily Gleeson, Henk A Dijkstra, V N LivinaAbstract:Abrupt Climate Change is abundant in geological records, but Climate models rarely have been able to simulate such events in response to realistic forcing. Here we report on a spontaneous Abrupt cooling event, lasting for more than a century, with a temperature anomaly similar to that of the Little Ice Age. The event was simulated in the preindustrial control run of a high-resolution Climate model, without imposing external perturbations. Initial cooling started with a period of enhanced atmospheric blocking over the eastern subpolar gyre. In response, a southward progression of the sea-ice margin occurred, and the sea-level pressure anomaly was locked to the sea-ice margin through thermal forcing. The cold-core high steered more cold air to the area, reinforcing the sea-ice concentration anomaly east of Greenland. The sea-ice surplus was carried southward by ocean currents around the tip of Greenland. South of 70°N, sea ice already started melting and the associated freshwater anomaly was carried to the Labrador Sea, shutting off deep convection. There, surface waters were exposed longer to atmospheric cooling and sea surface temperature dropped, causing an even larger thermally forced high above the Labrador Sea. In consequence, east of Greenland, anomalous winds Changed from north to south, terminating the event with similar Abruptness to its onset. Our results imply that only Climate models that possess sufficient resolution to correctly represent atmospheric blocking, in combination with a sensitive sea-ice model, are able to simulate this kind of Abrupt Climate Change.
Alexi M Grachev - One of the best experts on this subject based on the ideXlab platform.
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Precise timing and characterization of Abrupt Climate Change 8200 years ago from air trapped in polar ice
Quaternary Science Reviews, 2020Co-Authors: Takuro Kobashi, Jeffrey P Severinghaus, Edward J Brook, Jeanmarc Barnola, Alexi M GrachevAbstract:International audienceHow fast and how much Climate can Change has significant implications for concerns about future Climate Changes and their potential impacts on society. An Abrupt Climate Change 8200 years ago (8.2 ka event) provides a test case to understand possible future climatic variability. Here, methane concentration (taken as an indicator for terrestrial hydrology) and nitrogen isotopes (Greenland temperature) in trapped air in a Greenland ice core (GISP2) are employed to scrutinize the evolution of the 8.2 ka event. The synchronous Change in methane and nitrogen implies that the 8.2 ka event was a synchronous event (within ±4 years) at a hemispheric scale, as indicated by recent Climate model results [Legrande, A. N., Schmidt, G. A., Shindell, D. T., Field, C. V., Miller, R. L., Koch, D. M., Faluvegi, G., Hoffmann, G., 2006. Consistent simulations of multiple proxy responses to an Abrupt Climate Change event. Proceedings of the National Academy of Sciences 103, 837–842]. The event began with a large-scale general cooling and drying around 8175±30 years BP (Before Present, where Present is 1950 AD). Greenland temperature cooled by 3.3±1.1 °C (decadal average) in less than 20 years, and atmospheric methane concentration decreased by 80±25 ppb over 40 years, corresponding to a 15±5% emission reduction. Hemispheric scale cooling and drying, inferred from many paleoClimate proxies, likely contributed to this emission reduction. In central Greenland, the coldest period lasted for 60 years, interrupted by a milder interval of a few decades, and temperature subsequently warmed in several steps over 70 years. The total duration of the 8.2 ka event was roughly 150 years
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precise timing and characterization of Abrupt Climate Change 8200 years ago from air trapped in polar ice
Quaternary Science Reviews, 2007Co-Authors: Takuro Kobashi, Jeffrey P Severinghaus, Edward J Brook, Jeanmarc Barnola, Alexi M GrachevAbstract:How fast and how much Climate can Change has significant implications for concerns about future Climate Changes and their potential impacts on society. An Abrupt Climate Change 8200 years ago (8.2 ka event) provides a test case to understand possible future climatic variability. Here, methane concentration (taken as an indicator for terrestrial hydrology) and nitrogen isotopes (Greenland temperature) in trapped air in a Greenland ice core (GISP2) are employed to scrutinize the evolution of the 8.2 ka event. The synchronous Change in methane and nitrogen implies that the 8.2 ka event was a synchronous event (within 74 years) at a hemispheric scale, as indicated by recent Climate model results [Legrande, A. N., Schmidt, G. A., Shindell, D. T., Field, C. V., Miller, R. L., Koch, D. M., Faluvegi, G., Hoffmann, G., 2006. Consistent simulations of multiple proxy responses to an Abrupt Climate Change event. Proceedings of the National Academy of Sciences 103, 837–842]. The event began with a large-scale general cooling and drying around � 8175730 years BP (Before Present, where Present is 1950 AD). Greenland temperature cooled by 3.371.11C (decadal average) in less than � 20 years, and atmospheric methane concentration decreased by � 80725 ppb over � 40 years, corresponding to a 1575% emission reduction. Hemispheric scale cooling and drying, inferred from many paleoClimate proxies, likely contributed to this emission reduction. In central Greenland, the coldest period lasted for � 60 years, interrupted by a milder interval of a few decades, and temperature subsequently warmed in several steps over � 70 years. The total duration of the 8.2 ka event was roughly 150 years. r 2007 Elsevier Ltd. All rights reserved.
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determining the thermal diffusion factor for 40ar 36ar in air to aid paleoreconstruction of Abrupt Climate Change
Journal of Physical Chemistry A, 2003Co-Authors: Alexi M Grachev, Jeffrey P SeveringhausAbstract:The thermal diffusion factor (αT) of 40Ar/36Ar in air has been measured in the laboratory for the first time. The mean values of αT × 103 that we find at −30.0 °C are 9.85 ± 0.04 for air and 11.25 ± 0.03 for pure argon. The latter value is more precise than the data found in the literature. The temperature dependence of the thermal diffusion factor in air in the range −60 to −10 °C can be described by an empirical equation αT × 103 = 26.08 − 3952/〈T 〉 (±1%), where 〈T 〉 is the effective average temperature. Results of this study are valuable for reconstruction of magnitudes of Abrupt Climate Change events recorded in Greenland ice cores. For one Abrupt warming event ∼15,000 years ago, near the end of the last glacial period, these results yield a warming of 11 ± 3 °C over several decades or less. Theoretical calculations are not yet able to provide the needed accuracy, and the experimental results for the thermal diffusion factor in air should be used for paleoenvironmental studies.
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Determining the Thermal Diffusion Factor for 40Ar/36Ar in Air To Aid Paleoreconstruction of Abrupt Climate Change
Journal of Physical Chemistry A, 2003Co-Authors: Alexi M Grachev, Jeffrey P SeveringhausAbstract:The thermal diffusion factor (αT) of 40Ar/36Ar in air has been measured in the laboratory for the first time. The mean values of αT × 103 that we find at −30.0 °C are 9.85 ± 0.04 for air and 11.25 ± 0.03 for pure argon. The latter value is more precise than the data found in the literature. The temperature dependence of the thermal diffusion factor in air in the range −60 to −10 °C can be described by an empirical equation αT × 103 = 26.08 − 3952/〈T 〉 (±1%), where 〈T 〉 is the effective average temperature. Results of this study are valuable for reconstruction of magnitudes of Abrupt Climate Change events recorded in Greenland ice cores. For one Abrupt warming event ∼15,000 years ago, near the end of the last glacial period, these results yield a warming of 11 ± 3 °C over several decades or less. Theoretical calculations are not yet able to provide the needed accuracy, and the experimental results for the thermal diffusion factor in air should be used for paleoenvironmental studies.
