The effect of reduced ocean overturning on the climate of the last glacial maximum

Oerlemans, J.

doi:10.1007/bf00207936

Cited by 14 publications

(9 citation statements)

References 43 publications

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“…S2, red line). On the other hand, it is uncertain how accurately our climate model simulates very warm climates; the climate model is designed and tested for PD and LGM climates (Bintanja and Oerlemans, 1996). This argument favours the shorter 5 Myr run as the more trustworthy result, implying that CO 2 levels over the last 5 Myr may have been up to 470 ppm.…”

Section: Retuning: New Reference Simulationmentioning

confidence: 99%

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

et al. 2017

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Abstract. Since the inception of the Antarctic ice sheet at the Eocene-Oligocene transition ( ∼ 34 Myr ago), land ice has played a crucial role in Earth's climate. Through feedbacks in the climate system, land ice variability modifies atmospheric temperature changes induced by orbital, topographical, and greenhouse gas variations. Quantification of these feedbacks on long timescales has hitherto scarcely been undertaken. In this study, we use a zonally averaged energy balance climate model bidirectionally coupled to a one-dimensional ice sheet model, capturing the ice-albedo and surface-height-temperature feedbacks. Potentially important transient changes in topographic boundary conditions by tectonics and erosion are not taken into account but are briefly discussed. The relative simplicity of the coupled model allows us to perform integrations over the past 38 Myr in a fully transient fashion using a benthic oxygen isotope record as forcing to inversely simulate CO 2 . Firstly, we find that the results of the simulations over the past 5 Myr are dependent on whether the model run is started at 5 or 38 Myr ago. This is because the relation between CO 2 and temperature is subject to hysteresis. When the climate cools from very high CO 2 levels, as in the longer transient 38 Myr run, temperatures in the lower CO 2 range of the past 5 Myr are higher than when the climate is initialised at low temperatures. Consequently, the modelled CO 2 concentrations depend on the initial state. Taking the realistic warm initialisation into account, we come to a best estimate of CO 2 , temperature, ice-volume-equivalent sea level, and benthic δ 18 O over the past 38 Myr. Secondly, we study the influence of ice sheets on the evolution of global temperature and polar amplification by comparing runs with ice sheet-climate interaction switched on and off. By passing only albedo or surface height changes to the climate model, we can distinguish the separate effects of the ice-albedo and surfaceheight-temperature feedbacks. We find that ice volume variability has a strong enhancing effect on atmospheric temperature changes, particularly in the regions where the ice sheets are located. As a result, polar amplification in the Northern Hemisphere decreases towards warmer climates as there is little land ice left to melt. Conversely, decay of the Antarctic ice sheet increases polar amplification in the Southern Hemisphere in the high-CO 2 regime. Our results also show that in cooler climates than the pre-industrial, the ice-albedo feedback predominates the surface-heighttemperature feedback, while in warmer climates they are more equal in strength.

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Section: Retuning: New Reference Simulationmentioning

confidence: 99%

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

et al. 2017

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“…Both processes are related to surface air temperature. Models describe these relationships: an ice-sheet model (Bintanja et al, 2002) that links air temperature to ice volume and δ 18 O stored in ice, and an ocean-temperature model (Bintanja and Oerlemans, 1996) that couples surface air temperature to deep ocean temperature. An inverse method deconvolves the two components of δ 18 O for the LR04 δ 18 O record leading to mutually consistent records of atmospheric temperature, ice volume, ice area, ice-free area, albedo on both ice and icefree land (all continents in the latitudinal band of 40 − 80…”

Section: Land Cryospherementioning

confidence: 99%

What caused Earth's temperature variations during the last 800,000 years? Data-based evidence on radiative forcing and constraints on climate sensitivity

Köhler

Bintanja

Fischer

et al. 2010

Quaternary Science Reviews

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The temperature on Earth varied largely in the Pleistocene from cold glacials to interglacials of different warmths. To contribute to an understanding of the underlying causes of these changes we compile various environmental records (and model-based interpretations of some of them) in order to calculate the direct effect of various processes on Earth's radiative budget and, thus, on global annual mean surface temperature over the last 800,000 years. The importance of orbital variations, of the greenhouse gases CO 2 , CH 4 and N 2 O, of the albedo of land ice sheets, annual mean snow cover, sea ice area and vegetation, and of the radiative perturbation of mineral dust in the atmosphere are investigated. Altogether we can explain with these processes a global cooling of 3.9 ± 0.8 K in the equilibrium temperature for the Last Glacial Maximum (LGM) directly from the radiative budget using only the Planck feedback that parametrises the direct effect on the radiative balance, but neglecting other feedbacks such as water vapour, cloud cover, and lapse rate. The unaccounted feedbacks and related uncertainties would, if taken at present day feedback strengths, decrease the global temperature at the LGM by −8.0 ± 1.6 K. Increased Antarctic temperatures during the Marine Isotope Stages 5.5, 7.5, 9.3 and 11.3 are in our conceptual approach difficult to explain. If compared with other studies, such as PMIP2, this gives supporting evidence that the feedbacks themselves are not constant, but depend in their strength on the mean climate state. The best estimate and uncertainty for our reconstructed radiative forcing and LGM cooling support a present day equilibrium climate sensitivity (excluding the ice sheet and vegetation components) between 1.4 and 5.2 K, with a most likely value near 2.4 K, somewhat smaller than other methods but consistent with the consensus range of 2 − 4.5 K derived from other lines of evidence. Climate sensitivities above 6 K are difficult to reconcile with Last Glacial Maximum reconstructions.

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“…Varying ocean strength increases the SH LGM-PI difference only a little, while the midpoint shift more than doubles it. The difference between NH and SH (polar) temperatures in sensitivity to oceanic heat transfer in the ZEBCM was earlier noted by Bintanja and Oerlemans (1996). They used manually set reduced SH overturning strength to obtain a lower Antarctic LGM temperature.…”

Section: Sensitivity Analysismentioning

confidence: 84%

“…Similar to the vegetation, the sea ice is subject to snow cover. In an earlier study, the model was used to study presentday (PD) and Last Glacial Maximum (LGM) climate (Bintanja and Oerlemans, 1996). In order to perform transient simulations, we now use insolation and CO 2 as timedependent input variables.…”

Section: Zonally Averaged Energy Balance Climate Modelmentioning

confidence: 99%

Interaction of ice sheets and climate during the past 800 000 years

et al. 2014

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Abstract. During the Cenozoic, land ice and climate interacted on many different timescales. On long timescales, the effect of land ice on global climate and sea level is mainly set by large ice sheets in North America, Eurasia, Greenland and Antarctica. The climatic forcing of these ice sheets is largely determined by the meridional temperature profile resulting from radiation and greenhouse gas (GHG) forcing. As a response, the ice sheets cause an increase in albedo and surface elevation, which operates as a feedback in the climate system. To quantify the importance of these climate-land ice processes, a zonally averaged energy balance climate model is coupled to five one-dimensional ice sheet models, representing the major ice sheets.In this study, we focus on the transient simulation of the past 800 000 years, where a high-confidence CO 2 record from ice core samples is used as input in combination with Milankovitch radiation changes. We obtain simulations of atmospheric temperature, ice volume and sea level that are in good agreement with recent proxy-data reconstructions. We examine long-term climate-ice-sheet interactions by a comparison of simulations with uncoupled and coupled ice sheets. We show that these interactions amplify global temperature anomalies by up to a factor of 2.6, and that they increase polar amplification by 94 %. We demonstrate that, on these long timescales, the ice-albedo feedback has a larger and more global influence on the meridional atmospheric temperature profile than the surface-height-temperature feedback. Furthermore, we assess the influence of CO 2 and insolation by performing runs with one or both of these variables held constant. We find that atmospheric temperature is controlled by a complex interaction of CO 2 and insolation, and both variables serve as thresholds for northern hemispheric glaciation.

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The effect of reduced ocean overturning on the climate of the last glacial maximum

Cited by 14 publications

References 43 publications

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

What caused Earth's temperature variations during the last 800,000 years? Data-based evidence on radiative forcing and constraints on climate sensitivity

Interaction of ice sheets and climate during the past 800 000 years

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