Meike D. W. Scherrenberg, Constantijn J. Berends, Roderik S. W. van de Wal
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Changes in climate forcing are caused by variations in CO<sub>2</sub>, insolation, as well as implicit climate–ice sheet feedbacks. Using this method, we were able to capture glacial-interglacial variability during the past 1.5 million years and reproduce the shift from 41 kyr to 100 kyr cycles without any additional drivers. Instead, the modelled frequency change results from the prescribed CO<sub>2</sub> combined with orbital forcing, and ice sheet feedbacks. Early Pleistocene terminations are initiated by insolation maxima. After the MPT, low CO<sub>2</sub> levels can compensate insolation maxima which favour deglaciation, leading to an increasing glacial cycle periodicity. These deglaciations are also prevented by a relatively small North American ice sheet, which, through its location and feedback processes, can generate a relatively stable climate. Larger North American ice sheets become more sensitive to small temperature increases. Therefore, Late Pleistocene terminations are facilitated by the large ice-sheet volume, were small changes in temperature lead to self-sustained melt instead. This concept is confirmed by experiments using constant insolation or CO<sub>2</sub>. The constant CO<sub>2</sub> experiments generally capture only the Early Pleistocene cycles, while those with constant insolation only capture Late Pleistocene cycles. Additionally, we find that a lowering of CO<sub>2</sub>concentrations leads to an increasing number of insolation maxima that fail to initiate terminations. These results therefore suggest a regime shift, where during the Early Pleistocene, glacial cycles are dominated by orbital oscillations, while Late Pleistocene cycles tend to be more dominated by CO<sub>2</sub>. This implies that the MPT can be explained by a decrease in glacial CO<sub>2</sub> concentration superimposed on orbital forcing.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"10 1","pages":""},"PeriodicalIF":3.8000,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"CO2 and summer insolation as drivers for the Mid-Pleistocene transition\",\"authors\":\"Meike D. W. Scherrenberg, Constantijn J. Berends, Roderik S. W. van de Wal\",\"doi\":\"10.5194/cp-2024-57\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<strong>Abstract.</strong> During the Mid-Pleistocene transition (MPT) the dominant periodicity of glacial cycles increased from 41 thousand years (kyr) to an average of 100 kyr, without any appreciable change in the orbital pacing. As the MPT is not a linear response to orbital forcing, it must have resulted from feedback processes in the Earth system. However, the precise mechanisms underlying the transition are still under debate. In this study, we investigate the MPT by simulating the Northern Hemisphere ice sheet evolution over the past 1.5 million years. The transient climate forcing of the ice-sheet model was obtained using a matrix method, by interpolating between two snapshots of global climate model simulations. Changes in climate forcing are caused by variations in CO<sub>2</sub>, insolation, as well as implicit climate–ice sheet feedbacks. Using this method, we were able to capture glacial-interglacial variability during the past 1.5 million years and reproduce the shift from 41 kyr to 100 kyr cycles without any additional drivers. Instead, the modelled frequency change results from the prescribed CO<sub>2</sub> combined with orbital forcing, and ice sheet feedbacks. Early Pleistocene terminations are initiated by insolation maxima. After the MPT, low CO<sub>2</sub> levels can compensate insolation maxima which favour deglaciation, leading to an increasing glacial cycle periodicity. These deglaciations are also prevented by a relatively small North American ice sheet, which, through its location and feedback processes, can generate a relatively stable climate. Larger North American ice sheets become more sensitive to small temperature increases. Therefore, Late Pleistocene terminations are facilitated by the large ice-sheet volume, were small changes in temperature lead to self-sustained melt instead. This concept is confirmed by experiments using constant insolation or CO<sub>2</sub>. The constant CO<sub>2</sub> experiments generally capture only the Early Pleistocene cycles, while those with constant insolation only capture Late Pleistocene cycles. Additionally, we find that a lowering of CO<sub>2</sub>concentrations leads to an increasing number of insolation maxima that fail to initiate terminations. These results therefore suggest a regime shift, where during the Early Pleistocene, glacial cycles are dominated by orbital oscillations, while Late Pleistocene cycles tend to be more dominated by CO<sub>2</sub>. 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CO2 and summer insolation as drivers for the Mid-Pleistocene transition
Abstract. During the Mid-Pleistocene transition (MPT) the dominant periodicity of glacial cycles increased from 41 thousand years (kyr) to an average of 100 kyr, without any appreciable change in the orbital pacing. As the MPT is not a linear response to orbital forcing, it must have resulted from feedback processes in the Earth system. However, the precise mechanisms underlying the transition are still under debate. In this study, we investigate the MPT by simulating the Northern Hemisphere ice sheet evolution over the past 1.5 million years. The transient climate forcing of the ice-sheet model was obtained using a matrix method, by interpolating between two snapshots of global climate model simulations. Changes in climate forcing are caused by variations in CO2, insolation, as well as implicit climate–ice sheet feedbacks. Using this method, we were able to capture glacial-interglacial variability during the past 1.5 million years and reproduce the shift from 41 kyr to 100 kyr cycles without any additional drivers. Instead, the modelled frequency change results from the prescribed CO2 combined with orbital forcing, and ice sheet feedbacks. Early Pleistocene terminations are initiated by insolation maxima. After the MPT, low CO2 levels can compensate insolation maxima which favour deglaciation, leading to an increasing glacial cycle periodicity. These deglaciations are also prevented by a relatively small North American ice sheet, which, through its location and feedback processes, can generate a relatively stable climate. Larger North American ice sheets become more sensitive to small temperature increases. Therefore, Late Pleistocene terminations are facilitated by the large ice-sheet volume, were small changes in temperature lead to self-sustained melt instead. This concept is confirmed by experiments using constant insolation or CO2. The constant CO2 experiments generally capture only the Early Pleistocene cycles, while those with constant insolation only capture Late Pleistocene cycles. Additionally, we find that a lowering of CO2concentrations leads to an increasing number of insolation maxima that fail to initiate terminations. These results therefore suggest a regime shift, where during the Early Pleistocene, glacial cycles are dominated by orbital oscillations, while Late Pleistocene cycles tend to be more dominated by CO2. This implies that the MPT can be explained by a decrease in glacial CO2 concentration superimposed on orbital forcing.
期刊介绍:
Climate of the Past (CP) is a not-for-profit international scientific journal dedicated to the publication and discussion of research articles, short communications, and review papers on the climate history of the Earth. CP covers all temporal scales of climate change and variability, from geological time through to multidecadal studies of the last century. Studies focusing mainly on present and future climate are not within scope.
The main subject areas are the following:
reconstructions of past climate based on instrumental and historical data as well as proxy data from marine and terrestrial (including ice) archives;
development and validation of new proxies, improvements of the precision and accuracy of proxy data;
theoretical and empirical studies of processes in and feedback mechanisms between all climate system components in relation to past climate change on all space scales and timescales;
simulation of past climate and model-based interpretation of palaeoclimate data for a better understanding of present and future climate variability and climate change.