The impact of Sahara desertification on Arctic cooling during the Holocene

Davies, F. J.; Renssen, H.; Blaschek, Michael; Muschitiello, Francesco

doi:10.5194/cp-11-571-2015

Cited by 13 publications

(7 citation statements)

References 52 publications

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“…Alternatively, potential biases in the models may result from imprecise estimation of the climate sensitivity to forcing factors and the incomplete representation of feedback processes 5 , 39 . Previous studies have suggested that feedbacks in response to insolation forcing, such as vegetation 18 , 40 – 43 , sea ice 44 – 47 , clouds 18 , and dust 48 , 49 , may have large impacts on temperatures, especially winter temperatures 18 , 41 – 43 , 46 . Although most of these feedbacks were incorporated into the TraCE-21ka simulation 5 , there are large uncertainties on feedbacks in the models 18 , 44 .…”

Section: Resultsmentioning

confidence: 99%

Holocene seasonal temperature evolution and spatial variability over the Northern Hemisphere landmass

Zhang

Cheng

et al. 2022

Nat Commun

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The origin of the temperature divergence between Holocene proxy reconstructions and model simulations remains controversial, but it possibly results from potential biases in the seasonality of reconstructions or in the climate sensitivity of models. Here we present an extensive dataset of Holocene seasonal temperatures reconstructed using 1310 pollen records covering the Northern Hemisphere landmass. Our results indicate that both summer and winter temperatures warmed from the early to mid-Holocene (~11–7 ka BP) and then cooled thereafter, but with significant spatial variability. Strong early Holocene warming trend occurred mainly in Europe, eastern North America and northern Asia, which can be generally captured by model simulations and is likely associated with the retreat of continental ice sheets. The subsequent cooling trend is pervasively recorded except for northern Asia and southeastern North America, which may reflect the cross-seasonal impact of the decreasing summer insolation through climatic feedbacks, but the cooling in winter season is not well reproduced by climate models. Our results challenge the proposal that seasonal biases in proxies are the main origin of model–data discrepancies and highlight the critical impact of insolation and associated feedbacks on temperature changes, which warrant closer attention in future climate modelling.

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Section: Resultsmentioning

confidence: 99%

Holocene seasonal temperature evolution and spatial variability over the Northern Hemisphere landmass

Zhang

Cheng

et al. 2022

Nat Commun

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“…Our control simulations, PI Control and MH Control, have orbital parameters, greenhouse gas concentrations, SSTs, and land surface parameters, including soil albedo and vegetation cover, set to PI and MH values, respectively (Table S1). Our prescription of MH vegetation included changes to plant functional type percentage and values of LAI ( Figure S1 and Table S2; Davies et al, 2015;Hoelzmann et al, 1998;Levis et al, 2004;Pausata et al, 2016). MH values for dry and saturated soil albedo are prescribed separately from vegetation (Table S2), and soil texture is not changed from PI values in any simulation.…”

Section: Model Experiments and Methodsmentioning

confidence: 99%

Modulation of Mid‐Holocene African Rainfall by Dust Aerosol Direct and Indirect Effects

Thompson

Skinner

Poulsen

et al. 2019

Geophysical Research Letters

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Climate model simulations of the mid‐Holocene (MH) consistently underestimate northern African rainfall for reasons not fully understood. While most models incorporate orbital forcing and vegetation feedbacks, they neglect dust reductions associated with greater vegetation cover. Here we simulate the MH climate response to reduced Saharan dust using CESM CAM5‐chem, which resolves direct and indirect dust aerosol effects. Direct aerosol effects increase Saharan and Sahel convective rainfall by ~16% and 8%. In contrast, indirect aerosol effects decrease stratiform rainfall, damping the dust‐induced total rainfall increase by ~13% in the Sahara and ~59% in the Sahel. Sensitivity experiments indicate the dust‐induced precipitation anomaly in the Sahara and Sahel (0.27 and 0.18 mm/day) is smaller than the anomaly from MH vegetation cover (1.19 and 1.08 mm/day). Although sensitive to dust radiative properties, sea surface temperatures, and indirect aerosol effect parameterization, our results suggest that dust reductions had competing effects on MH African rainfall.

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“…Some studies suggested that the shift of Green Sahara not only locally influenced the North African monsoon but also affected the large-scale atmospheric circulation and remotely influenced the Arctic climate (Davies et al 2015;Muschitiello et al 2015) and tropical climate (Pausata et al 2017a,b;Sun et al 2019) during the MH. Proxy data from the NW Iran suggested a wetter period during the early Holocene (9-6 ka BP), which was followed by a drier and dustier condition (Sharifi et al 2015).…”

Section: Using the Climate Simulations Based On The Projection Of Mh mentioning

confidence: 99%

Middle East Climate Response to the Saharan Vegetation Collapse during the Mid-Holocene

et al. 2021

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Understanding climate change in the Middle East (ME) is crucial because people’s living environment depends on rain-fed crop systems. It remains unclear if the ME climate would be affected by the Saharan vegetation collapse at the end of the mid-Holocene (MH). Proxy data suggest a transition from humid to more arid ME conditions during the period of 6.5-5 kyr BP. Using a set of idealized sensitivity experiments with an Earth System model (EC-Earth), we infer that the shift of Saharan vegetation plays a role in this wet-to-dry transition over the ME. The experimental results show that the Saharan greening can significantly increase the late winter and early spring precipitation over the ME. The reason is that the vegetation decreases the surface albedo, which induces a warming in North Africa and generation of an anomalous low level cyclonic flow, which transports moisture from tropical North Africa and the Red Sea to the ME. The moisture also flows from the Mediterranean region to the ME through the enhanced mid-upper level westerlies. The enhanced moisture carried by westerly and southwesterly flows is lifted upon reaching the Mesopotamia and Zagros Mountains, substantially increasing the precipitation there. When the Sahara greening is removed, a drier condition happens in the ME. The crop model simulation further shows a substantial decrease in wheat yield in Mesopotamia with the reduction of Saharan vegetation, which is consistent with paleoclimatic reconstructions. These results imply that future changes in Saharan land cover may have climatic and agricultural impacts in the Middle East.

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The impact of Sahara desertification on Arctic cooling during the Holocene

Cited by 13 publications

References 52 publications

Holocene seasonal temperature evolution and spatial variability over the Northern Hemisphere landmass

Holocene seasonal temperature evolution and spatial variability over the Northern Hemisphere landmass

Modulation of Mid‐Holocene African Rainfall by Dust Aerosol Direct and Indirect Effects

Middle East Climate Response to the Saharan Vegetation Collapse during the Mid-Holocene

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