Simulation of an abrupt change in Saharan vegetation in the Mid‐Holocene

Claußen, Martin; Kubatzki, Claudia; Brovkin, Victor; Ganopolski, Andrey; Hoelzmann, Philipp; Pachur, Hans-Joachim

doi:10.1029/1999gl900494

Cited by 550 publications

(393 citation statements)

References 22 publications

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“…In good agreement with the Holocene climate evolution modelling experiments have demonstrated an intensification of summer monsoon activity in response to precession-forced changes (Claussen et al, 1999;Schefuß et al, 2003, Marzin andBraconnot, 2009). Proxy data indicate that the Holocene Wet African Period (12 to 5.5 ka) coincided with the regional climate optimum and major insolation change (deMenocal et al, 2000a, b;Adkins et al, 2006;Tjallingii et al, 2008).…”

Section: Dynamics Of Sea-surface Properties In the Lower Latitudessupporting

confidence: 59%

The meridional temperature gradient in the eastern North Atlantic during MIS 11 and its link to the ocean–atmosphere system

Kandiano

Bauch

Fahl

et al. 2012

Palaeogeography, Palaeoclimatology, Palaeoecology

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Temporal and spatial patterns in eastern North Atlantic sea-surface temperatures (SST) were reconstructed for marine isotope stage (MIS) 11c using a submeridional transect of five sediment cores. The SST reconstructions are based on planktic foraminiferal abundances and alkenone indices, and are supported by benthic and planktic stable isotope measurements, as well as by ice-rafted debris content in polar and middle latitudes. Additionally, the larger-scale dynamics of the precipitation regime over northern Africa and the western Mediterranean region was evaluated from iron concentrations in marine sediments off NW Africa and planktic δ 13 C in combination with analysis of planktic foraminiferal abundances down to the species level in the Mediterranean Sea. Compared to the modern situation, it is revealed that during entire MIS 11c sensu stricto (ss), i.e., between 420 and 398 ka according to our age models, a cold SST anomaly in the Nordic seas co-existed with a warm SST anomaly in the middle latitudes and the subtropics, resulting in steeper meridional SST gradients than during the Holocene. Such a SST pattern correlates well with a prevalence of a negative mode of the modern North Atlantic Oscillation. We suggest that our scenario might partly explain the longer duration of wet conditions in the northern Africa during MIS 11c compared to the Holocene.

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Section: Dynamics Of Sea-surface Properties In the Lower Latitudessupporting

confidence: 59%

The meridional temperature gradient in the eastern North Atlantic during MIS 11 and its link to the ocean–atmosphere system

Kandiano

Bauch

Fahl

et al. 2012

Palaeogeography, Palaeoclimatology, Palaeoecology

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“…He argued that a reduction in the coverage of the former in favor of the latter would increase atmospheric subsidence and weaken the monsoon precipitation, which in turn could lead to further land degradation. Other modeling studies indicate that such mechanism might even be responsible for the relatively rapid transition of the Sahara from a savanna to desert during the mid-Holocene period (Claussen et al 1999;Patricola and Cook 2008). Given the rapid expansion of agriculture over the last 60 years, a similar interaction of human induced land degradation with monsoon precipitation is not inconceivable.…”

Section: Introductionmentioning

confidence: 98%

Assessment of uncertainties in the response of the African monsoon precipitation to land use change simulated by a regional model

et al. 2014

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Land use and land cover (LULC) over Africa have changed substantially over the last 60 years and this change has been proposed to affect monsoon circulation and precipitation. This study examines the uncertainties of model simulated response in the African monsoon system and Sahel precipitation due to LULC change using a set of regional model simulations with different combinations of land surface and cumulus parameterization schemes. Although the magnitude of the response covers a broad range of values, most of the simulations show a decline in Sahel precipitation due to the expansion of pasture and croplands at the expense of trees and shrubs and an increase in surface air temperature. The relationship between the model responses to LULC change and the climatologists of the control simulations is also examined. Simulations that are climatologically too dry or too wet compared to observations and reanalyses have weak response to land use change because they are in moisture or energy limited regimes respectively. The ones that lie in between have stronger response to the LULC changes, showing a more significant role in land-atmosphere interactions. Much of the change in precipitation is related to changes in circulation, particularly to the response of the intensity and latitudinal position of the African Easterly Jet, which varies with the changes in meridional surface temperature gradients. The study highlights the need for measurements of the surface fluxes across the meridional cross-section of the Sahel to evaluate models and thereby allowing human impacts such as land use change on the monsoon to be projected more realistically.

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“…Past greening of the Sahara occurred in the mid-Holocene (71)(72)(73) and may have happened rapidly in the earlier Bölling-Allerod warming. Collapse of vegetation in the Sahara Ϸ5,000 years ago occurred more rapidly than orbital forcing (71,72).…”

Section: Sahara/sahel and West African Monsoon (Wam)mentioning

confidence: 99%

Tipping elements in the Earth's climate system

Lenton

Held

Kriegler

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

2,950

2,253

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The term ''tipping point'' commonly refers to a critical threshold at which a tiny perturbation can qualitatively alter the state or development of a system. Here we introduce the term ''tipping element'' to describe large-scale components of the Earth system that may pass a tipping point. We critically evaluate potential policy-relevant tipping elements in the climate system under anthropogenic forcing, drawing on the pertinent literature and a recent international workshop to compile a short list, and we assess where their tipping points lie. An expert elicitation is used to help rank their sensitivity to global warming and the uncertainty about the underlying physical mechanisms. Then we explain how, in principle, early warning systems could be established to detect the proximity of some tipping points.Earth system ͉ tipping points ͉ climate change ͉ large-scale impacts ͉ climate policy

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Simulation of an abrupt change in Saharan vegetation in the Mid‐Holocene

Cited by 550 publications

References 22 publications

The meridional temperature gradient in the eastern North Atlantic during MIS 11 and its link to the ocean–atmosphere system

The meridional temperature gradient in the eastern North Atlantic during MIS 11 and its link to the ocean–atmosphere system

Assessment of uncertainties in the response of the African monsoon precipitation to land use change simulated by a regional model

Tipping elements in the Earth's climate system

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