Large-scale features and evaluation of the PMIP4-CMIP6 midHolocene simulations

Brierley, Chris; Zhao, Anni; Harrison, Sandy P.; Braconnot, Pascale

doi:10.5194/egusphere-egu2020-8911

Cited by 35 publications

(69 citation statements)

References 22 publications

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“…This moisture is relatively 18 O‐poor by the time it reaches India, resulting in lower δ 18 O p (Tabor et al, 2018). The North African monsoon (NAM) also intensifies under MH orbital forcing, as found in many other works (e.g., Braconnot et al, 2007; Brierley et al, 2020). This combination of greater precipitation in Northern Africa and a stronger Indian monsoon (IM), makes the Sahara a primary source of relatively 18 O‐poor moisture to the AM during the MH (Tabor et al, 2018).…”

Section: Resultssupporting

confidence: 60%

“…Earth system models often struggle to replicate the proxy reconstructed climate changes of the MH (e.g., Braconnot et al, 2007; Brierley et al, 2020; Liu, Wen, et al, 2014). Generally, simulations of the MH are too cold and the monsoon responses are too weak.…”

Section: Discussionmentioning

confidence: 99%

“…All analyses come from climatology of the final 50 years of model simulation. Despite changes in eccentricity during the MH, we do not convert model outputs to an angular calendar because conversion techniques do not work well in areas with abrupt seasonal shifts such as monsoon regions (Brierley et al, 2020). Further, we limit our analyses to seasonal averages of 5 months or more, which should dampen calendar effects.…”

Section: Methodsmentioning

confidence: 99%

“…Climate models, when forced with MH orbit and greenhouse gases (GHGs), simulate greater and extended monsoon moisture over Northern Africa (Brierley et al, 2020; Harrison et al, 2014). In most models, however, the amplification of precipitation in Northern Africa is only a fraction of the amount estimated by proxy records (Bartlein et al, 2011; Collins et al, 2013; Perez‐Sanz et al, 2014; Tierney et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

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Speleothems of South American and Asian Monsoons Influenced by a Green Sahara

Tabor

Otto‐Bliesner

Liu

2020

Geophysical Research Letters

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The mid-Holocene is frequently used for climate model-proxy comparison studies, yet models often struggle to replicate the proxy signals from this period. Here, we use an Earth system model that tracks water isotopologies to determine the importance of a vegetated Sahara in the simulation of mid-Holocene climate, with a focus on δ 18 O values recorded in speleothems from the South American and Asian monsoon regions. We find that inclusion of a vegetated Sahara during the mid-Holocene leads to global warming and generally amplifies the changes in the δ 18 O values of the precipitation in the South American and Asian monsoon regions relative to preindustrial; both feedbacks improve model-proxy agreement. Our results highlight the importance of regional vegetation alteration for accurate simulation of past climate, even when the region of study is far from the source of vegetation change. Plain Language Summary The mid-Holocene (6,000 years ago) had slightly lower greenhouse gas concentrations and significantly higher Northern Hemisphere summer sunlight than preindustrial (1850 CE). There is also evidence for vegetation changes during the mid-Holocene, most notably increased vegetation over the now arid Sahara. Most climate model simulations of the mid-Holocene account for the greenhouse gas and orbital changes but frequently neglect the vegetation changes. Here, we use a climate model to separate the effects of a vegetated Sahara from those due to greenhouse gases and orbit during the mid-Holocene. Our mid-Holocene simulation with the addition of a vegetated Sahara better represents measurement-based climate reconstructions of the period than our mid-Holocene simulation that only includes greenhouse gas and orbital changes. These simulated improvements are particularly pronounced in the South American and Asian monsoon regions, despite their distance from the Sahara. Our results emphasize the importance of vegetation feedbacks when simulating past and future climate change.

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Section: Resultssupporting

confidence: 60%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Speleothems of South American and Asian Monsoons Influenced by a Green Sahara

Tabor

Otto‐Bliesner

Liu

2020

Geophysical Research Letters

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“…The lig127k simulation simulates the strong summer warming reconstructed for the Baffin region. Both the areal extent and cumulative rainfall is greater for the North African monsoon in the lig127k than midHolocene simulation (Brierley et al, 2020; Otto‐Bliesner et al, 2020).…”

Section: Summary and Discussionmentioning

confidence: 99%

A Comparison of the CMIP6midHoloceneandlig127kSimulations in CESM2

Otto‐Bliesner

Brady

Tomas

et al. 2020

Paleoceanog and Paleoclimatol

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Results are presented and compared for the Community Earth System Model version 2 (CESM2) simulations of the middle Holocene (MH, 6 ka) and Last Interglacial (LIG, 127 ka). These simulations are designated as Tier 1 experiments (midHolocene and lig127k) for the Coupled Model Intercomparison Project phase 6 (CMIP6) and the Paleoclimate Modeling Intercomparison Project phase 4 (PMIP4). They use the low-top, standard 1°version of CESM2 contributing to CMIP6 DECK, historical, and future projection simulations, and to other modeling intercomparison projects. The midHolocene and lig127k provide the opportunity to examine the responses in CESM2 to the orbitally induced changes in the seasonal and latitudinal distribution of insolation. The insolation anomalies result in summer warming over the Northern Hemisphere continents, reduced Arctic summer minimum sea ice, and increased areal extent of the North African monsoon. The Arctic remains warm throughout the year. These changes are greater in the lig127k than midHolocene simulation. Other notable changes are reduction of the Niño3.4 variability and Drake Passage transport and a small increase in the Atlantic Meridional Overturning Circulation from the piControl to midHolocene to lig127k simulation. Comparisons to paleo-data and to simulations from previous model versions are discussed. Possible reasons for mismatches with the paleo-observations are proposed, including missing processes in CESM2, simplifications in the CMIP6 protocols for these experiments, and dating and calibration uncertainties in the data reconstructions. Plain Language Summary The modeling of past climates, using physically based tools and comparing to paleo-observations, is increasingly seen as a strong test of the models that are used for the projection of future climate changes. We report on simulations by one of the latest large-scale climate models, the Community Earth System Model version 2 (CESM2), for the two most recent warm epochs: the current interglacial-the Holocene, which began 11,650 years agoand the previous interglacial-the Last Interglacial, which extended from 129,000 to 116,000 years ago. The simulations find summer warming over the Northern Hemisphere continents, reduced Arctic summer sea ice, and increased areal extent of the North African monsoon. Cryospheric and oceanic feedbacks drive year-round Arctic warmth. The CESM2 middle Holocene and Last Interglacial simulations are an important resource for the community participating in the Coupled Model Intercomparison Project phase 6 (CMIP6).

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Eurasian Holocene climate trends in transient coupled climate simulations and stable oxygen isotope records

Danek

Gierz

Kostrova

et al. 2021

J Quaternary Science

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Transient simulations of the global fully coupled climate model COSMOS under realistic varying orbital and greenhouse gas forcings are systematically compared to diatom oxygen isotope ( δ 18 O 0.1em diatom0.1em) records from Russian lakes with focus on Eurasian Holocene climate trends. The measured δ 18 O 0.1em diatom0.1em decrease and other temperature proxies are interpreted as large‐scale cooling throughout the Holocene while the model simulations are biased too warm, likely through missing radiative forcings. This large‐scale warm bias also dictates the modeled δ 18 O 0.1em precipitation. Hence, at locations where the signs of model and proxy temperature/precipitation trends agree, measured δ 18 O 0.1em diatom0.1em and modeled δ 18 O 0.1em precipitation0.1em trends show notable accordance. An increased temporal variability of modeled δ 18 O 0.1em precipitation0.1em is linked to persistent atmospheric circulation patterns. Applying the transient forcings in an accelerated way (every 10th year only) yields a similar, yet weaker or delayed model response, especially in the ocean.

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Large-scale features and evaluation of the PMIP4-CMIP6 midHolocene simulations

Cited by 35 publications

References 22 publications

Speleothems of South American and Asian Monsoons Influenced by a Green Sahara

Speleothems of South American and Asian Monsoons Influenced by a Green Sahara

A Comparison of the CMIP6midHoloceneandlig127kSimulations in CESM2

Eurasian Holocene climate trends in transient coupled climate simulations and stable oxygen isotope records

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