El Niño diversity in CMIP5 and CMIP6 models: projected changes compared to past and present — Australian Meteorological and Oceanographic Society
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  2. 27(ii). Tropical climate variability: dynamics, teleconnections and impacts
  3. El Niño diversity in CMIP5 and CMIP6 models: projected changes compared to past and present

El Niño diversity in CMIP5 and CMIP6 models: projected changes compared to past and present (#150)

Mandy B Freund 1 , Josephine R Brown 2 , Benjamin J Henley 2 , Jaclyn N Brown 3 , Helen V McGregor 4
  1. CSIRO, Melbourne, VIC, Australia
  2. University of Melbourne, Melbourne, VIC, Australia
  3. CSIRO, Hobart, TAS, Australia
  4. University of Wollongong, Wollongong, NSW, Australia

El Niño events differ substantially in their spatial pattern and intensity. Each event has unique physical characteristics and events often show substantial spatio-temporal differences in ocean and atmosphere conditions. This complexity can be simplified into two distinct warming patterns differentiated by the location of strongest sea surface temperature warming in either the central (CP) or eastern tropical Pacific (EP). The recognition of the diverse characteristics of El Niño events presents a challenge in light of recent changes and possible future El Niño behaviour. Reconstructed El Nino variability derived from coral records has revealed a higher frequency of Central Pacific El Niño events since the late twentieth century, and, fewer but more intense Eastern Pacific El Niño events (Freund et. al 2019). This recent change towards more El Niño’s occurring in the central Pacific rather than the eastern Pacific motivates us to investigate the processes leading to those changes and attribute possible future changes. Here we assess the representation of El Niño diversity in models taking part in the Coupled Model Intercomparison Project (CMIP5 & CMIP6). We compare simulated El Niño characteristics to observed and reconstructed El Niño activity. Future changes of El Niño remain model dependent but we show that frequency changes are not related to the overall climate sensitivity of the models but rather depend on the model mean-state sea surface temperature response to anthropogenic forcing. Models with a La Niña-like mean state warming show a tendency towards more EP and fewer CP events, compared to models with El Niño-like warming. Among the El Niño-like warming models, differences can be partially explained by the differentiated response of El Niño to decadal-scale variability related to active and inactive ENSO phases. Similarly, changes of event intensity depend on the projected changes in those ENSO phases, rather than mean state changes.

 

 

 

  1. Freund, M. B., Henley, B. J., Karoly, D. J., McGregor, H. V., Abram, N. J. and Dommenget, D.: Higher frequency of Central Pacific El Niño events in recent decades relative to past centuries, Nature Geosci, 6, 450–455, doi:10.1038/s41561-019-0353-3, 2019.
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