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Polar and Paleoclimate Modeling Research Group

The Polar and Paleoclimate group in April 2022. From left, front row: Rajan Patel, Patrick Ugrinow, Alex Jahn, Daphne Quint. Back row, from left: Jed Lenetsky, Chris Wyburn Powell, Nate Farmer.


Current projects

Reducing projection uncertainty in CMIP6 models

In this NSF-funded project, we aim to identify drivers of the model spread in the CMIP6 sea ice simulations, in order to ultimatly reduce Arctic sea ice projection uncertainty. This includes an assessment of thermodynamic and dynamic drivers of sea ice loss and improving the understanding of the contribution of internal variability to sea ice loss as well as its dynamic drivers. Group members contributing to this project are Alexandra Jahn, Chris Wyburn-Powell, Patricia DeRepentigny and Abigail Smith. First papers from this project are a Sea Ice Modeling Intercomparison Project community paper assessing the CMIP6 sea ice simulations (SIMIP 2020), a paper using sea ice melt season charcteristics to assess model differences (Smith et al. 2020), and a paper assessing the sea ice simulation in the new CESM2 (DeRepentigny et al. 2020).

C-iTRACE: Isotope-enabled paleo ocean modeling for the deglacial

In this NSF-funded project, we are using recenty developed carbon, water, neodynium, and Pa/Th isotopes within the CESM ocean model to assess the simulated deglacial climate evolution against proxy records and isotope observations. Collaborators include Zhengyu Liu (The Ohio State University), Sifan Gu (Shanghai Jiao Tong University), Bette Otto-Blienser (NCAR), Hannah Zanowski (CU), and Sara Reinelt. Project website: CiTRACE output is available at

Paleoceanographic impacts of the onset of Arctic-Baffin Bay throughflow

In this NSF-funded project, we are using modeling and multi-proxy analyses of sediment cores from northern Baffin Bay to discover the timing and climatic consequences of the opening of the western gateway for Arctic freshwater to the Labrador Sea. For this project, we will perform mid-Holocene model simulations with the CESM to assess the impacts of the opening of the western freshwater route of the Arctic-Atlantic throughflow on the freshwater outflow to the North Atlantic, the watermass structure in Baffin Bay, and the formation of the North Water Polynia. Collaborators include A. Jennings, T. Marchitto, L. Woelder, J. T. Andrews, and H. Zanowski (all INSTAAR).

The Arctic Observing Network - Capturing and understanding Arctic change with renewed observations at the Davis Strait gateway

In this NSF-funded project, we will perform model simulations to help assess the dynamical drivers of Davis Strait flux changes and their downstream impacts on the NOrth Atlantic. Collaborators include Craig Lee (UW) and Paul Myers (Univ. of Alberta)

Integrating Eocene shark paleoecology and climate modeling to reveal Southern Ocean circulation and Antarctic glaciation

In this NSF-funded project, we will perform CESM simulations with Neodynium isotopes to simulate the Eocene Southern Ocean circulation and compare the model results with neodynium isotope records from shark teeth. Collaborators include Sora Kim, Matthew Huber, and Howie Scher.

Completed projects

Assessing the simulated Arctic freshwater system in CMIP5 Models, the CESM Large Ensemble, and forced simulations

In this NSF-funded project, we worked to assess various aspects of the the Arctic freshwater budget, including simulated by CMIP6 climate models (Zanowski et al., 2021), changes in freshwater pathways on various timescales (Otto-Bliesner et al. 2017, DeRepentigny et al. 2020), and the influence of internal variability on the simulated Arctic freshwater budget (Jahn and Laiho, 2019) and Arctic sea ice (England et al., 2019), as well as on the predictability of an ice-free Arctic (Jahn et al. 2016, Jahn 2018). Collaborators on this project include Marika Holland (NCAR), Bruno Tremblay (Columbia University & McGill University), Rory Laiho (CU), Patricia DeRepentigny (CU), and Hannah Zanowski (CU). Timeseries of the Arctic freshwater terms from the CESM Large Ensemble and the CESM Low warming ensemble are archived at the NSF Arctic Dater Center (Jahn 2020) and CMIP6 model Arctic freshwater terms are also archived there (Zanowski and Jahn, 2021).

Understanding Arctic melt season changes through modeling

In this project funded through a NSF-GRF and NASA FINESST grant to Abigail Smith, we contributed to a better understanding the melt season changes in the Arctic Ocean. The first part of this project was focused on assessing the impact of definition choices and internal variability on melt season charcteristics. This work is published as Smith and Jahn (2019). A paper on useing melt season characteristics to provide an improved assessment of sea ice simulations from CMIP6 models in collaboration with M. Wang (UW) was published as Smith et al. (2020). As final step, Abigail Smith adapted a passive microwave sea ice emulator for the use in earth system models for melt onset in the CESM2, to better compare sea ice simulatons of melt onset from earth system models with satellite retrievals. This work was done in collaboration with Dirk Notz and Clara Burgard from the Max Plank Institute of Meoerology in Hamburg and is currently in prepartion for publication.

Climate of the past 2000 years: past2k CESM simulation

In this project, we performed a transient CESM model simulation for the last 2000 years, called past2k. In the analysis, we have focussed on the assessment of the drivers of the asymetric cooling rates of the Atlantic and Pacific Arctic. Collaborators on this project are Y. Zhong (University of Wisconsin Madison), G. Miller (INSTAAR) and A. Geirsdottir (Univ. of Iceland). Results are published in Zhong et al. 2018.  Forcing data for the past2k simulation is published as Zhong et al. (2018). Outout from the past2k simulation is freely available at: