Contribution of the coupled atmosphere–ocean–sea ice–vegetation model COSMOS to the PlioMIP2

Stepanek, Christian; Samakinwa, Eric; Lohmann, Gerrit

doi:10.5194/cp-2020-10

Cited by 11 publications

(17 citation statements)

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“…Similar changes in ice sheets and vegetation may occur in future equilibrium warm climates, but the changes in orography are definitively non-analogous to future warming. Several groups isolated the effects of the changed orography on global warming in PlioMIP2 simulations and found that it contributes, respectively, around 23 % (IPSL6-CM6A-LR; Tan et al, 2020), 27 % (COS-MOS; Stepanek et al, 2020), and 41 % (CCSM4-UoT; Chandan and Peltier, 2018) to the annual mean global warming in the mPWP simulations. Furthermore, this warming was strongest in the high latitudes (Chandan and Peltier, 2018; indicating that the additional Arctic warming in PlioMIP2 simulations, as compared to future climate simulations, are likely partially caused by changes in orography that are non-analogous with the modern-day orography.…”

Section: Arctic Amplificationmentioning

confidence: 99%

“…The dominant mechanism for global warming in mid-Pliocene simulations is through changes in radiative forcing following increases in greenhouse gas concentrations (Chandan and Peltier, 2017;Hill et al, 2014;Hunter et al, 2019;Kamae et al, 2016;Lunt et al, 2012b;Stepanek et al, 2020;. Polar warming is also dominated by changes in greenhouse gas emissivity (Hill et al, 2014;Tindall and Haywood, 2020).…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of Arctic warming in mid-Pliocene climate simulations

Nooijer

Zhang

et al. 2020

Clim. Past

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Abstract. Palaeoclimate simulations improve our understanding of the climate, inform us about the performance of climate models in a different climate scenario, and help to identify robust features of the climate system. Here, we analyse Arctic warming in an ensemble of 16 simulations of the mid-Pliocene Warm Period (mPWP), derived from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The PlioMIP2 ensemble simulates Arctic (60–90∘ N) annual mean surface air temperature (SAT) increases of 3.7 to 11.6 ∘C compared to the pre-industrial period, with a multi-model mean (MMM) increase of 7.2 ∘C. The Arctic warming amplification ratio relative to global SAT anomalies in the ensemble ranges from 1.8 to 3.1 (MMM is 2.3). Sea ice extent anomalies range from −3.0 to -10.4×106 km2, with a MMM anomaly of -5.6×106 km2, which constitutes a decrease of 53 % compared to the pre-industrial period. The majority (11 out of 16) of models simulate summer sea-ice-free conditions (≤1×106 km2) in their mPWP simulation. The ensemble tends to underestimate SAT in the Arctic when compared to available reconstructions, although the degree of underestimation varies strongly between the simulations. The simulations with the highest Arctic SAT anomalies tend to match the proxy dataset in its current form better. The ensemble shows some agreement with reconstructions of sea ice, particularly with regard to seasonal sea ice. Large uncertainties limit the confidence that can be placed in the findings and the compatibility of the different proxy datasets. We show that while reducing uncertainties in the reconstructions could decrease the SAT data–model discord substantially, further improvements are likely to be found in enhanced boundary conditions or model physics. Lastly, we compare the Arctic warming in the mPWP to projections of future Arctic warming and find that the PlioMIP2 ensemble simulates greater Arctic amplification than CMIP5 future climate simulations and an increase instead of a decrease in Atlantic Meridional Overturning Circulation (AMOC) strength compared to pre-industrial period. The results highlight the importance of slow feedbacks in equilibrium climate simulations, and that caution must be taken when using simulations of the mPWP as an analogue for future climate change.

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Section: Arctic Amplificationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evaluation of Arctic warming in mid-Pliocene climate simulations

Nooijer

Zhang

et al. 2020

Clim. Past

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“…COSMOS has already proven to be a valuable tool for the study of paleoclimate, also beyond the Pliocene epoch. The various time slices studied by means of COSMOS include, but are not limited to, the last millennium (Jungclaus et al, 2010), warm climates of the Miocene (e.g., Knorr et al, 2011), the mid-Pliocene (Stepanek and Lohmann, 2012), and glacial (e.g., Gong et al, 2013;Kageyema et al, 2013; and interglacial climates (e.g., Pfeiffer and Lohmann, 2016;Varma et al, 2012;Wei and Lohmann, 2012). A detailed description of the COSMOS model components is given by Stepanek and Lohmann (2012).…”

Section: Model Description Cosmosmentioning

confidence: 99%

Sensitivity of mid-Pliocene climate to changes in orbital forcing and PlioMIP's boundary conditions

2020

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Abstract. We compare results obtained from modeling the mid-Pliocene warm period using the Community Earth System Models (COSMOS, version: COSMOS-landveg r2413, 2009) with the two different modeling methodologies and sets of boundary conditions prescribed for the two phases of the Pliocene Model Intercomparison Project (PlioMIP), tagged PlioMIP1 and PlioMIP2. Here, we bridge the gap between our contributions to PlioMIP1 (Stepanek and Lohmann, 2012) and PlioMIP2 (Stepanek et al., 2020). We highlight some of the effects that differences in the chosen mid-Pliocene model setup (PlioMIP2 vs. PlioMIP1) have on the climate state as derived with COSMOS, as this information will be valuable in the framework of the model–model and model–data comparison within PlioMIP2. We evaluate the model sensitivity to improved mid-Pliocene boundary conditions using PlioMIP's core mid-Pliocene experiments for PlioMIP1 and PlioMIP2 and present further simulations in which we test model sensitivity to variations in paleogeography, orbit, and the concentration of CO2. Firstly, we highlight major changes in boundary conditions from PlioMIP1 to PlioMIP2 and also the challenges recorded from the initial effort. The results derived from our simulations show that COSMOS simulates a mid-Pliocene climate state that is 0.29 ∘C colder in PlioMIP2 if compared to PlioMIP1 (17.82 ∘C in PlioMIP1, 17.53 ∘C in PlioMIP2; values based on simulated surface skin temperature). On the one hand, high-latitude warming, which is supported by proxy evidence of the mid-Pliocene, is underestimated in simulations of both PlioMIP1 and PlioMIP2. On the other hand, spatial variations in surface air temperature (SAT), sea surface temperature (SST), and the distribution of sea ice suggest improvement of simulated SAT and SST in PlioMIP2 if employing the updated paleogeography. Our PlioMIP2 mid-Pliocene simulation produces warmer SSTs in the Arctic and North Atlantic Ocean than those derived from the respective PlioMIP1 climate state. The difference in prescribed CO2 accounts for 0.5 ∘C of temperature difference in the Arctic, leading to an ice-free summer in the PlioMIP1 simulation, and a quasi ice-free summer in PlioMIP2. Beyond the official set of PlioMIP2 simulations, we present further simulations and analyses that sample the phase space of potential alternative orbital forcings that have acted during the Pliocene and may have impacted geological records. Employing orbital forcing, which differs from that proposed for PlioMIP2 (i.e., corresponding to pre-industrial conditions) but falls into the mid-Pliocene time period targeted in PlioMIP, leads to pronounced annual and seasonal temperature variations. Our result identifies the changes in mid-Pliocene paleogeography from PRISM3 to PRISM4 as the major driver of the mid-Pliocene warmth within PlioMIP and not the minor differences in forcings.

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“…the topography, bathymetry and land ice cover. COSMOS uses dynamic vegetation (Stepanek et al, 2020), while the remaining 16 models use https://doi.org/10.5194/cp-2021-16 Preprint. Discussion started: 26 February 2021 c Author(s) 2021.…”

Section: Participating Pliomip2 Modelsmentioning

confidence: 99%

Mid-Pliocene West African Monsoon Rainfall as simulated in the PlioMIP2 ensemble

Berntell¹,

Zhang²,

Li³

et al. 2021

Preprint

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Abstract. The mid-Pliocene Warm Period (mPWP; ~3.2 million years ago) is seen as the most recent time period characterized by a warm climate state, with similar modern geography and ~400 ppmv atmospheric CO2 concentration, and is therefore often considered an interesting analogue for near-future climate projections. Paleoenvironmental reconstructions indicate higher surface temperatures, decreasing tropical deserts, and a more humid climate in West Africa characterized by a strengthened West African Monsoon (WAM). Using model results from the second phase of the Pliocene Modelling Intercomparison Project (PlioMIP2) ensemble we analyze changes of the WAM rainfall during the mPWP, by comparing with the control simulations for the pre-industrial period. The ensemble shows a robust increase of the summer rainfall over West Africa and the Sahara region with an average increase of 2.7 mm/day, contrasted by a rainfall decrease over the equatorial Atlantic. An anomalous warming of the Sahara Desert and deepening of the Saharan Heat Low, seen in > 90 % of the models, leads to a strengthening of the WAM and an increased monsoonal flow into the continent. A similar warming of the Sahara Desert is seen in future projections using both phase 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5), and though previous studies of future projections indicate a west/east drying/wetting contrast over Sahel, PlioMIP2 simulations indicate a uniform rainfall increase over Sahel in warm climates characterized by increasing greenhouse gas forcing.

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Contribution of the coupled atmosphere–ocean–sea ice–vegetation model COSMOS to the PlioMIP2

Cited by 11 publications

References 64 publications

Evaluation of Arctic warming in mid-Pliocene climate simulations

Evaluation of Arctic warming in mid-Pliocene climate simulations

Sensitivity of mid-Pliocene climate to changes in orbital forcing and PlioMIP's boundary conditions

Mid-Pliocene West African Monsoon Rainfall as simulated in the PlioMIP2 ensemble

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