Details

Autor(en) / Beteiligte

• Feng, Ran
• Otto‐Bliesner, Bette L.
• Brady, Esther C.
• Rosenbloom, Nan

Titel

Increased Climate Response and Earth System Sensitivity From CCSM4 to CESM2 in Mid‐Pliocene Simulations

Ist Teil von

• Journal of advances in modeling earth systems, 2020-08, Vol.12 (8), p.n/a

Ort / Verlag

Washington: John Wiley & Sons, Inc

Erscheinungsjahr

2020

Link zum Volltext

Quelle

Wiley Online Library Journals【キャンパス外アクセス可】

Beschreibungen/Notizen

• Three new equilibrium mid‐Pliocene (MP) simulations are implemented with the Community Climate System Model version 4 (CCSM4) and Community Earth System Model versions 1.2 (CESM1.2) and 2 (CESM2). All simulations are carried out with the same boundary and forcing conditions following the protocol of Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). These simulations reveal amplified MP climate change relative to the preindustrial going from CCSM4 to CESM2, seen in global and polar averages of surface warming, sea ice reduction in both the Arctic and the Antarctic, and weakened Hadley circulation. The enhanced global mean warming arises from enhanced Earth system sensitivity (ESS) to not only CO2 change but also changes in boundary conditions primarily from vegetation and ice sheets. ESS is amplified by up to 70% in CCSM4 and up to 100% in CESM1.2 and CESM2 relative to the equilibrium climate sensitivity of respective models. Simulations disagree on several climate metrics. Different from CCSM4, both CESM1.2 and CESM2 show reduction of cloud cover, and weakened Walker circulation accompanied by an El Niño‐like mean state of the tropical Pacific in MP simulations relative to the preindustrial. This El Niño‐like mean state is consistent with paleo‐observational sea surface temperatures, suggesting an improvement upon CCSM4. The performances of MP simulations are assessed with a new compilation of observational MP sea surface temperature. The model‐data comparison suggests that CCSM4 is not sensitivity enough to the MP forcings, but CESM2 is likely too sensitive, especially in the tropics. Plain Language Summary Our knowledge of past climate evolves with both new paleo‐observations and advancements in modeling past climates. Using the mid‐Pliocene (MP, 3.205 million years ago) as an example, we demonstrate how to implement geological reconstructions of past topography, bathymetry, and vegetation distribution in Earth system models (ESMs); how to initialize these experiments; and, finally, the new knowledge learnt from simulations with three consecutive versions of the ESMs from the same model lineage. In our simulations, the MP climate warms substantially more than the estimated amount of warming that only consider changes in CO2 radiative forcing. The simulated MP climate features strongly amplified polar warmth, massive loss of Arctic and Antarctic summer sea ice, and weakened Northern Hemispheric cell of the Hadley circulation. Interestingly, two newer versions of ESMs are more sensitive to not only CO2 changes but also changes in biome range and ice sheets than the earlier version. Paleo‐observations suggest that MP global warming is underestimated by the previous versions of models but may be overestimated by the latest version. Key Points PlioMIP2 simulations are completed with Earth System Models from the NCAR family: CCSM4, CESM1, and CESM2 Simulated mid‐Pliocene climate by CESM2 features greater changes in many climate metrics than simulations by previous versions CESM1 and CESM2 match paleo‐observations better than CCSM4, yet CESM2 likely overestimates the Earth System Sensitivity