Response of ENSO amplitude to global warming in CESM large ensemble: uncertainty due to internal variability
El Niño–Southern Oscillation (ENSO) is the dominant mode of variability in the coupled ocean-atmospheric system. Future projections of ENSO change under global warming are highly uncertain among models. In this study, the effect of internal variability on ENSO amplitude change in future climate projections is investigated based on a 40-member ensemble from the Community Earth System Model Large Ensemble (CESM-LE) project. A large uncertainty is identified among ensemble members due to internal variability. The inter-member diversity is associated with a zonal dipole pattern of sea surface temperature (SST) change in the mean along the equator, which is similar to the second empirical orthogonal function (EOF) mode of tropical Pacific decadal variability (TPDV) in the unforced control simulation. The uncertainty in CESM-LE is comparable in magnitude to that among models of the Coupled Model Intercomparison Project phase 5 (CMIP5), suggesting the contribution of internal variability to the intermodel uncertainty in ENSO amplitude change. However, the causations between changes in ENSO amplitude and the mean state are distinct between CESM-LE and CMIP5 ensemble. The CESM-LE results indicate that a large ensemble of ~15 members is needed to separate the relative contributions to ENSO amplitude change over the twenty-first century between forced response and internal variability.
- Neale RB et al. (2012) Description of the NCAR community atmosphere model (CAM 5.0). NCAR tech note TN-486, pp 274Google Scholar
- Philander SG (1990) El Niño, La Niña and the southern oscillation. Academic Press, San Diego, CA, 293 ppGoogle Scholar
- Smith RD et al (2010) The parallel ocean program (POP) reference manual: ocean component of the community climate system model (CCSM) and community earth system model (CESM). Los Alamos National Laboratory Tech Rep LAUR-10-01853, p 141Google Scholar
- Wittenberg AT (2002) ENSO response to altered climates. Ph.D. thesis, Princeton UniversityGoogle Scholar