Abstract. El Niño–Southern Oscillation (ENSO) is the strongest
mode of interannual climate variability in the current climate, influencing
ecosystems, agriculture, and weather systems across the globe, but future
projections of ENSO frequency and amplitude remain highly uncertain. A
comparison of changes in ENSO in a range of past and future climate
simulations can provide insights into the sensitivity of ENSO to changes in
the mean state, including changes in the seasonality of incoming solar
radiation, global average temperatures, and spatial patterns of sea surface
temperatures. As a comprehensive set of coupled model simulations is now
available for both palaeoclimate time slices (the Last Glacial Maximum,
mid-Holocene, and last interglacial) and idealised future warming scenarios
(1 % per year CO2 increase, abrupt four-time CO2
increase), this allows a detailed evaluation of ENSO changes in this wide
range of climates. Such a comparison can assist in constraining uncertainty
in future projections, providing insights into model agreement and the
sensitivity of ENSO to a range of factors. The majority of models simulate a
consistent weakening of ENSO activity in the last interglacial and
mid-Holocene experiments, and there is an ensemble mean reduction of
variability in the western equatorial Pacific in the Last Glacial Maximum
experiments. Changes in global temperature produce a weaker precipitation
response to ENSO in the cold Last Glacial Maximum experiments and an
enhanced precipitation response to ENSO in the warm increased CO2
experiments. No consistent relationship between changes in ENSO amplitude
and annual cycle was identified across experiments.
Reduced El Nino-Southern Oscillation during the Last Glacial Maximum