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Publication Date
15 January 2023

Evolution of the Internal Climate Modes under Future Warming

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Science

Output from 58 realizations from a wide range of CMIP6 generation ESMs is used to derive projections of spatiotemporal characteristics of key internal climate modes. NAM, SAM, and ENSO tend to evolve towards the increased prevalence of the positive phase. The degree to which modes change scale with skill in the contemporary period (generally smaller for higher skill) and radiative forcing (larger changes for higher forcing).

Impact

Climate modes forced by internal processes play an important role in weather and climate variability over multiple spatial and temporal scales. Future climate changes will not only be affected by the variability arising from these modes, but the modes will themselves change in response to the externally-forced changing climate. This work quantifies how these modes may evolve.

Summary

Climate modes forced by internal processes play an important role in weather and climate variability over multiple spatial and temporal scales. Future climate changes will not only be affected by the variability arising from these modes, but the modes will themselves change in response to the externally-forced changing climate. This research uses the output from 58 realizations from 11 CMIP6 generation Earth System Models (ESM) to derive projections of the spatiotemporal characteristics of three key internal atmospheric (the Northern Annular Mode (NAM), the Southern Annular Mode (SAM), and the Pacific-North American (PNA) pattern), and three oceanic modes (El Niño-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO)) under high (SSP585) and low (SSP126) radiative forcing scenarios. The resulting projections indicate NAM, SAM, and ENSO tend to evolve towards the increased prevalence of the positive phase up to 2100 across the multi-model ensemble while the PNA and PDO exhibit little trend but increasing phase intensity. AMO characteristics are shown to depend on the method used to remove the external signal. ESM that show higher historical fidelity tend to show more modest changes in those modes under global non-stationarity. Changes in mode interactions are found to be highly ESM dependent but exhibit broadly similar behavior to historical relationships. These findings have implications for our understanding of internal variability and make clear that the choice of ESM, and even the ESM realization, matters for applications of climate projections.

Point of Contact
Sara C Pryor
Institution(s)
Cornell University
Funding Program Area(s)
Publication