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  • 1
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    The Impact of Different Atmospheric CO2 Concentrations on Large Scale Miocene Temperature Signatures (2023)
    Hossain, Akil ; Knorr, Gregor ; Jokat, Wilfried ; [et al.]
    Details
    Publication Date: 2023-11-23
    Description: Based on inferences from proxy records the Miocene (23.03–5.33 Ma) was a time of amplified polar warmth compared to today. However, it remains a challenge to simulate a warm Miocene climate and pronounced polar warmth at reconstructed Miocene CO〈sub〉2〈/sub〉 concentrations. Using a state‐of‐the‐art Earth‐System‐Model, we implement a high‐resolution paleobathymetry and simulate Miocene climate at different atmospheric CO〈sub〉2〈/sub〉 concentrations. We estimate global mean surface warming of +3.1°C relative to the preindustrial at a CO〈sub〉2〈/sub〉 level of 450 ppm. An increase of atmospheric CO〈sub〉2〈/sub〉 from 280 to 450 ppm provides an individual warming of ∼1.4°C, which is as strong as all other Miocene forcing contributions combined. Substantial changes in surface albedo are vital to explain Miocene surface warming. Simulated surface temperatures fit well with proxy reconstructions at low‐ to mid‐latitudes. The high latitude cooling bias becomes less pronounced for higher atmospheric CO〈sub〉2〈/sub〉 concentrations. At such CO〈sub〉2〈/sub〉 levels simulated Miocene climate shows a reduced polar amplification, linked to a breakdown of seasonality in the Arctic Ocean. A pronounced warming in boreal fall is detected for a CO〈sub〉2〈/sub〉 increase from 280 to 450 ppm, in comparison to weaker warming for CO〈sub〉2〈/sub〉 changes from 450 to 720 ppm. Moreover, a pronounced warming in winter is detected for a CO〈sub〉2〈/sub〉 increase from 450 to 720 ppm, in contrast to a moderate summer temperature increase, which is accompanied by a strong sea‐ice concentration decline that promotes cloud formation in summer via enhanced moisture availability. As a consequence planetary albedo increases and dampens the temperature response to CO〈sub〉2〈/sub〉 forcing at a warmer Miocene background climate.
    Description: Key Points: At a CO〈sub〉2〈/sub〉 level of 450 ppm, a Miocene simulation shows a global mean surface warming of +3.1°C relative to the preindustrial state. Atmospheric CO〈sub〉2〈/sub〉 increase from 280 to 450 ppm causes a warming of ∼1.4°C, which is as strong as all other forcing factors combined. At higher atmospheric CO〈sub〉2〈/sub〉 levels, the Miocene climate shows a reduced polar amplification linked to a breakdown of seasonality in the Arctic.
    Description: Alfred Wegener Institute
    Description: Helmholtz Centre for Polar and Marine Research
    Description: https://doi.org/10.1594/PANGAEA.943430
    Description: https://github.com/FESOM/fesom2/
    Description: https://mpimet.mpg.de/en/science/modeling-with-icon/code-avilability
    Keywords: atmospheric CO2 ; Miocene ; Miocene temperature change ; polar amplification ; climate modeling ; Miocene bathymetry
    Language: English
    Type: doc-type:article
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  • 2
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    East Asian summer precipitation in AWI‐CM3: Comparison with observations and CMIP6 models (2023)
    John Wiley & Sons, Ltd. | Chichester, UK
    Details
    Publication Date: 2023-11-13
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Owing to the complicated spatial–temporal characteristics of East Asian precipitation (EAP), climate models have limited skills in simulating the modern Asian climate. This consequently leads to large uncertainties in simulations of the past EAP variation and future projections. Here, we explore the performance of the newly developed Alfred Wegener Institute Climate Model, version 3 (AWI‐CM3) in simulating the climatological summer EAP. To test whether the model's skill depends on its atmosphere resolution, we design two AWI‐CM3 simulations with different horizontal resolutions. The result shows that both simulations have acceptable performance in simulating the summer mean EAP, generally better than the majority of individual models participating in the Coupled Model Intercomparison Project (CMIP6). However, for the monthly EAP from June to August, AWI‐CM3 exhibits a decayed skill, which is due to the subseasonal movement of the western Pacific subtropical high bias. The higher‐resolution AWI‐CM3 simulation shows an overall improvement relative to the one performed at a relatively lower resolution in all aspects taken into account regarding the EAP. We conclude that AWI‐CM3 is a suitable tool for exploring the EAP for the observational period. Having verified the model's skill for modern climate, we suggest employing the AWI‐CM3, especially with high atmosphere resolution, both for applications in paleoclimate studies and future projections.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉This figure shows the skill scores of AWI‐CM3 and CMIP6 models in simulating the climatological summer East Asian precipitation (EAP), which indicates that AWI‐CM3 simulations perform better than most CMIP6 individual models for the summer mean EAP, while AWI‐CM3's skills decay from June to August.〈boxed-text position="anchor" content-type="graphic" id="joc8075-blkfxd-0001" xml:lang="en"〉 〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:08998418:media:joc8075:joc8075-toc-0001"〉 〈alt-text〉image〈/alt-text〉 〈/graphic〉 〈/boxed-text〉〈/p〉
    Description: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Helmholtz Climate Initiative REKLIM
    Description: Helmholtz Program
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Description: https://opendata.dwd.de/climate_environment/GPCC/html/fulldata-monthly_v2022_doi_download.html
    Description: https://crudata.uea.ac.uk/cru/data/hrg/cru_ts_4.05
    Description: http://aphrodite.st.hirosaki-u.ac.jp/products.html
    Description: https://jra.kishou.go.jp/JRA-55/index_en.html
    Description: https://esgf-node.llnl.gov/search/cmip6
    Keywords: ddc:551.6 ; AWI‐CM3 ; CMIP6 ; East Asia ; summer precipitation
    Language: English
    Type: doc-type:article
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  • 3
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    Middle Miocene Climate and Stable Oxygen Isotopes in Europe Based on Numerical Modeling (2022)
    Details
    Publication Date: 2023-11-24
    Description: The Middle Miocene (15.99–11.65 Ma) of Europe witnessed major climatic, environmental, and vegetational change, yet we are lacking detailed reconstructions of Middle Miocene temperature and precipitation patterns over Europe. Here, we use a high‐resolution (∼0.75°) isotope‐enabled general circulation model (ECHAM5‐wiso) with time‐specific boundary conditions to investigate changes in temperature, precipitation, and δ〈sup〉18〈/sup〉O in precipitation (δ〈sup〉18〈/sup〉O〈sub〉p〈/sub〉). Experiments were designed with variable elevation configurations of the European Alps and different atmospheric CO〈sub〉2〈/sub〉 levels to examine the influence of Alpine elevation and global climate forcing on regional climate and δ〈sup〉18〈/sup〉Op patterns. Modeling results are in agreement with available paleobotanical temperature data and with low‐resolution Middle Miocene experiments of the Miocene Model Intercomparison Project (MioMIP1). However, simulated precipitation rates are 300–500 mm/yr lower in the Middle Miocene than for pre‐industrial times for central Europe. This result is consistent with precipitation estimates from herpetological fossil assemblages, but contradicts precipitation estimates from paleobotanical data. We attribute the Middle Miocene precipitation change in Europe to shifts in large‐scale pressure patterns in the North Atlantic and over Europe and associated changes in wind direction and humidity. We suggest that global climate forcing contributed to a maximum δ〈sup〉18〈/sup〉O〈sub〉p〈/sub〉 change of ∼2‰ over high elevation (Alps) and ∼1‰ over low elevation regions. In contrast, we observe a maximum modeled δ〈sup〉18〈/sup〉O〈sub〉p〈/sub〉 decrease of 8‰ across the Alpine orogen due to Alpine topography. However, the elevation‐δ〈sup〉18〈/sup〉O〈sub〉p〈/sub〉 lapse rate shallows in the Middle Miocene, leading to a possible underestimation of paleotopography when using present‐day δ〈sup〉18〈/sup〉O〈sub〉p〈/sub〉—elevation relationships data for stable isotope paleoaltimetry studies.
    Description: Key Points: A high‐resolution isotope‐enabled general circulation model is used to explore Middle Miocene climate and precipitation δ〈sup〉18〈/sup〉O across Europe. Middle Miocene bi‐directional precipitation change consistent with herpetological fossils and account for precipitation δ〈sup〉18〈/sup〉O variations. Global Miocene climate forcing contributed a max δ〈sup〉18〈/sup〉O change of ∼2‰ over the high Alpine elevation and to ∼1‰ over low elevation.
    Description: German research fondation
    Description: Alexander‐von‐Humboldt foundation, Feodor‐Lynen‐Fellowship
    Description: Alexander‐von‐Humboldt foundation, Humboldt Research Fellowship
    Description: Scientific Steering Committee
    Description: https://mpimet.mpg.de/fileadmin/projekte/ICON-ESM/mpi-m_sla_201202.pdf
    Description: https://gitlab.awi.de/mwerner/mpi-esm-wiso
    Description: https://zenodo.org/record/6308475#.Y0gmDSFS-2w
    Keywords: ddc:550.724 ; Europe ; Middle Miocene ; climate modeling ; stable water isotopes ; temperature ; precipitation ; paleoclimate ; paleoelevation ; Alps
    Language: English
    Type: doc-type:article
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  • 4
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    Effects of CO2 and Ocean Mixing on Miocene and Pliocene Temperature Gradients (2022)
    Details
    Publication Date: 2022-03-28
    Description: Cenozoic climate changes have been linked to tectonic activity and variations in atmospheric CO2 concentrations. Here, we present Miocene and Pliocene sensitivity experiments performed with the climate model COSMOS. The experiments contain changes with respect to paleogeography, ocean gateway configuration, and atmospheric CO2 concentrations, as well as a range of vertical mixing coefficients in the ocean. For the mid‐Miocene, we show that the impact of ocean mixing on surface temperature is comparable to the effect of the possible range in reconstructed CO2 concentrations. In combination with stronger vertical mixing, relatively moderate CO2 concentrations of 450 ppmv enable global‐mean surface, deep‐water, and meridional temperature characteristics representative of mid‐Miocene Climatic Optimum (MMCO) reconstructions. The Miocene climate shows a reduced meridional temperature gradient and reduced seasonality. In the case of enhanced mixing, surface and deep ocean temperatures show significant warming of up to 5–10°C and an Arctic temperature anomaly of 〉12°C. In the Pliocene simulations, the impact of vertical mixing and CO2 is less important for the deep ocean, which we interpret as a different sensitivity dependence on the background state and mixed layer dynamics. We find a significant reduction in surface albedo and effective emissivity for either a high level of atmospheric CO2 or increased vertical mixing. Our mixing sensitivity experiments provide a warm deep ocean via ocean heat uptake. We propose that the mixing hypothesis can be tested by reconstructions of the thermocline and seasonal paleoclimate data indicating a lower seasonality relative to today.
    Description: Plain Language Summary: Cenozoic climate changes have been associated with tectonic changes and altered atmospheric CO2 concentrations. Here, we present Miocene and Pliocene computer simulations where we changed paleogeography, ocean gateways, and atmospheric CO2 concentrations as well as vertical mixing in the ocean. We show that the effect of ocean mixing on temperature is comparable to the respective effect of a possible range of CO2 concentrations. In combination with stronger vertical mixing, relatively moderate CO2 concentrations of 450 ppmv allow surface and deep‐water temperatures representative for reconstructions of the climate optimum of the mid‐Miocene. In the Pliocene simulations, the influence of vertical mixing and CO2 is less important than in the Miocene. We provide a possible mechanism of ocean heat absorption, albedo, and emissivity changes including a deeper oceanic mixing layer and a lower seasonality in the Miocene compared to today.
    Description: Key Points: Miocene experiment with standard mixing and atmospheric CO2 of 600 ppm captures large‐scale temperature characteristics of the mid‐Miocene. With enhanced ocean mixing the temperature characteristics and meridional temperature gradient can be reproduced with a CO2 level of 450 ppm. Miocene shows a strong warming at polar latitudes and reduced seasonality, vertical mixing, and CO2 are less important for the Pliocene.
    Description: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) http://dx.doi.org/10.13039/501100003207
    Description: Helmholtz Association (亥姆霍兹联合会致力) http://dx.doi.org/10.13039/501100009318
    Description: Helmholtz Climate Initiative RE‐KLIM
    Keywords: ddc:550.78
    Language: English
    Type: doc-type:article
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