Impacts of Low-Frequency Internal Climate Variability and Greenhouse Warming on El Nino–Southern Oscillation

Ng, Benjamin and Cai, Wenju and Cowan, Tim and Bi, Daohua (2021) Impacts of Low-Frequency Internal Climate Variability and Greenhouse Warming on El Nino–Southern Oscillation. Journal of Climate, 34 (6). pp. 2205-2218. ISSN 0894-8755


Abstract

El Nino–Southern Oscillation (ENSO) is the dominant mode of interannual climate fluctuations with wide- ranging socioeconomic and environmental impacts. Understanding the eastern Pacific (EP) and central Pacific (CP) El Nino response to a warmer climate is paramount, yet the role of internal climate variability in modulating their response is not clear. Using large ensembles, we find that internal variability generates a spread in the standard deviation and skewness of these two El Nino types that is similar to the spread of 17 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) that realistically simulate ENSO diversity. Based on 40 Community Earth System Model Large Ensemble (CESM-LE) and 99 Max Planck Institute for Meteorology Grand Ensemble (MPI-GE) members, unforced variability can explain more than 90% of the historical EP and CP El Nino standard deviation and all of the ENSO skewness spread in the 17 CMIP5 models. Both CESM-LE and the selected CMIP5 models show increased EP and CP El Nino variability in a warmer climate, driven by a stronger mean vertical temperature gradient in the upper ocean and faster surface warming of the eastern equatorial Pacific. However, MPI-GE shows no agreement in EP or CP standard deviation change. This is due to weaker sensitivity to the warming signal, such that when the eastern equatorial Pacific surface warming is faster, the change in upper ocean vertical temperature gradient tends to be weaker. This highlights that individual models produce a different ENSO response in a warmer climate, and that considerable uncertainty within the CMIP5 ensemble may be caused by internal climate variability.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: Current - Institute for Life Sciences and the Environment - Centre for Applied Climate Sciences (1 Aug 2018 -)
Faculty/School / Institute/Centre: Current - Institute for Life Sciences and the Environment - Centre for Applied Climate Sciences (1 Aug 2018 -)
Date Deposited: 25 Feb 2021 04:31
Last Modified: 12 Jul 2021 03:47
Uncontrolled Keywords: El Nino; ENSO; Climate change; Tropical variability
Fields of Research (2008): 04 Earth Sciences > 0401 Atmospheric Sciences > 040104 Climate Change Processes
04 Earth Sciences > 0401 Atmospheric Sciences > 040105 Climatology (excl.Climate Change Processes)
Fields of Research (2020): 37 EARTH SCIENCES > 3702 Climate change science > 370202 Climatology
37 EARTH SCIENCES > 3702 Climate change science > 370201 Climate change processes
37 EARTH SCIENCES > 3708 Oceanography > 370803 Physical oceanography
Socio-Economic Objectives (2008): D Environment > 96 Environment > 9603 Climate and Climate Change > 960303 Climate Change Models
D Environment > 96 Environment > 9603 Climate and Climate Change > 960304 Climate Variability (excl. Social Impacts)
Socio-Economic Objectives (2020): 19 ENVIRONMENTAL POLICY, CLIMATE CHANGE AND NATURAL HAZARDS > 1905 Understanding climate change > 190502 Climate variability (excl. social impacts)
19 ENVIRONMENTAL POLICY, CLIMATE CHANGE AND NATURAL HAZARDS > 1905 Understanding climate change > 190501 Climate change models
Identification Number or DOI: https://doi.org/10.1175/JCLI-D-20-0232.1
URI: http://eprints.usq.edu.au/id/eprint/41485

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