Abstract
In this study, we address the question of whether the mid-Pliocene climate can act as an analogue for a future warm climate with elevated CO2 concentrations, specifically regarding Northern Hemisphere winter variability. We use a set of sensitivity simulations with the global coupled climate model CESM1.0.5 (CCSM4-Utr), which is part of the PlioMIP2 model ensemble, to separate the response to a CO2 doubling and to mid-Pliocene boundary conditions other than CO2. In the CO2 doubling simulation, the Aleutian low deepens, and the Pacific-North American pattern (PNA) strengthens. In response to the mid-Pliocene boundary conditions, sea-level pressure variance decreases over the North Pacific, the PNA becomes weaker and the North Pacific Oscillation (NPO) becomes the dominant mode of variability. The mid-Pliocene simulation shows a weak North Pacific jet stream that is less variable in intensity but has a high level of variation in jet latitude, consistent with a dominant NPO and indicating that North Pacific atmospheric dynamics become more North Atlantic-like. We demonstrate that the weakening of the Aleutian low, and subsequent relative dominance of the NPO over the PNA, is related to shifts in tropical Pacific convection. Variability in the North Atlantic shows little variation between all simulations. The opposite response in North Pacific winter variability to elevated CO2 or mid-Pliocene boundary conditions demonstrates that the mid-Pliocene climate cannot serve as a future analogue in this regard.
| Original language | English |
|---|---|
| Pages (from-to) | 395-417 |
| Number of pages | 23 |
| Journal | Weather and Climate Dynamics |
| Volume | 5 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 18 Mar 2024 |
Bibliographical note
Publisher Copyright:© 2024 Arthur Merlijn Oldeman et al.
Funding
Output from CCSM4-Utr simulations is available upon request. Please contact Michiel Baatsen ([email protected]) for access. NOAA/CIRES/DOE 20th Century Reanalysis (V3) data are provided by the NOAA PSL, Boulder, Colorado, USA, from their website at https://psl.noaa.gov/data/gridded/data.20thC_ReanV3.html (last access: 28 February 2023, Slivinski et al., 2021). An evaluation of the performance of the CR20v3 can be found in . Support for the Twentieth Century Reanalysis Project version 3 dataset is provided by the U.S. Department of Energy, Office of Science Biological and Environmental Research (BER); by the National Oceanic and Atmospheric Administration Climate Program Office; and by the NOAA Earth System Research Laboratory Physical Sciences Laboratory. This research has been supported by the Netherlands Earth System Science Centre (grant no. OCW 024.002.001). Simulations were performed at the SURFsara Dutch national computing facilities and were sponsored by NWO-EW (Netherlands Organisation for Scientific Research, Exact Sciences) (project nos. 17189 and 2020.022). The authors would like to thank Michael Kliphuis for setting up and managing the CCSM4-Utr model simulations and Ezekiel Djeribi Stevens for their performed analysis and interpretation on the CCSM4-Utr NAO. The authors express their gratitude to two anonymous reviewers and the co-editor for providing useful feedback on an earlier version of the manuscript.
| Funders | Funder number |
|---|---|
| NOAA Earth System Research Laboratory Physical Sciences Laboratory | |
| Biological and Environmental Research | |
| National Oceanic and Atmospheric Administration | |
| U.S. Department of Energy | |
| Netherlands Earth System Science Centre | OCW 024.002.001 |
| NWO-EW | 17189, 2020.022 |
Keywords
- Atmospheric circulation
- Atlantic oscillation
- Arctic oscillation
- Sea-ice
- Teleconnections
- Pacific
- Uncertainty
- Mechanisms
