Will There Be a Signi¿cant Change to El Nino in the Twenty-First Century?

TY - JOUR

T1 - Will There Be a Signi¿cant Change to El Nino in the Twenty-First Century?

AU - Stevenson, S.

AU - Fox-Kemper, B.

AU - Jochum, Markus

AU - Neale, R.

AU - Deser, C.

AU - Meehl, G.

PY - 2012/3/15

Y1 - 2012/3/15

N2 - The El Niño-Southern Oscillation (ENSO) response to anthropogenic climate change is assessed in the following 1° nominal resolution Community Climate System Model, version 4 (CCSM4) Coupled Model Intercomparison Project phase 5 (CMIP5) simulations: twentieth-century ensemble, preindustrial control, twenty-first-century projections, and stabilized 2100-2300 "extension runs." ENSO variability weakens slightly withCO 2; however, various significance tests reveal that changes are insignificant at all but the highest CO 2 levels. Comparison with the 1850 control simulation suggests thatENSO changes may become significant on centennial time scales; the lack of signal in the twentieth- versus twenty-first-century ensembles is due to their limited duration. Changes to the mean state are consistent with previous studies: a weakening of the subtropical wind stress curl, an eastward shift of the tropical convective cells, a reduction in the zonal SST gradient, and an increase in vertical thermal stratification take place as CO 2 increases. The extratropical thermocline deepens throughout the twenty-first century, with the tropical thermocline changing slowly in response. The adjustment time scale is set by the relevant ocean dynamics, and the delay in its effect on ENSO variability is not diminished by increasing ensemble size. The CCSM4 results imply that twenty-first-century simulations may simply be too short for identification of significant tropical variability response to climate change. An examination of atmospheric teleconnections, in contrast, shows that the remote influences of ENSO do respond rapidly to climate change in some regions, particularly during boreal winter. This suggests that changes toENSO impacts may take place well before changes to oceanic tropical variability itself become significant.

AB - The El Niño-Southern Oscillation (ENSO) response to anthropogenic climate change is assessed in the following 1° nominal resolution Community Climate System Model, version 4 (CCSM4) Coupled Model Intercomparison Project phase 5 (CMIP5) simulations: twentieth-century ensemble, preindustrial control, twenty-first-century projections, and stabilized 2100-2300 "extension runs." ENSO variability weakens slightly withCO 2; however, various significance tests reveal that changes are insignificant at all but the highest CO 2 levels. Comparison with the 1850 control simulation suggests thatENSO changes may become significant on centennial time scales; the lack of signal in the twentieth- versus twenty-first-century ensembles is due to their limited duration. Changes to the mean state are consistent with previous studies: a weakening of the subtropical wind stress curl, an eastward shift of the tropical convective cells, a reduction in the zonal SST gradient, and an increase in vertical thermal stratification take place as CO 2 increases. The extratropical thermocline deepens throughout the twenty-first century, with the tropical thermocline changing slowly in response. The adjustment time scale is set by the relevant ocean dynamics, and the delay in its effect on ENSO variability is not diminished by increasing ensemble size. The CCSM4 results imply that twenty-first-century simulations may simply be too short for identification of significant tropical variability response to climate change. An examination of atmospheric teleconnections, in contrast, shows that the remote influences of ENSO do respond rapidly to climate change in some regions, particularly during boreal winter. This suggests that changes toENSO impacts may take place well before changes to oceanic tropical variability itself become significant.

M3 - Journal article

SN - 0894-8755

VL - 25

SP - 2129

EP - 2145

JO - Journal of Climate

JF - Journal of Climate

ER -