The El Niño/Southern Oscillation is Earth’s most prominent
source of interannual climate variability, alternating irregularly
between El Niño and La Niña, and resulting in global
disruption of weather patterns, ecosystems, fisheries and
agriculture1–5. The 1998–1999 extreme La Niña event that
followed the 1997–1998 extreme El Niño event6 switched
extreme El Niño-induced severe droughts to devastating
floods in western Pacific countries, and vice versa in the
southwestern United States4,7. During extreme La Niña events,
cold sea surface conditions develop in the central Pacific8,9,
creating an enhanced temperature gradient from the Maritime
continent to the central Pacific. Recent studies have revealed
robust changes in El Niño characteristics in response to
simulated future greenhousewarming10–12, but howLa Niña will
change remains unclear. Here we present climate modelling
evidence, from simulations conducted for the Coupled Model
Intercomparison Project phase 5 (ref. 13), for a near doubling
in the frequency of future extreme La Niña events, from one in
every 23 years to one in every 13 years. This occurs because
projected faster mean warming of the Maritime continent than
the central Pacific, enhanced upper ocean vertical temperature
gradients, and increased frequency of extreme El Niño events
are conducive to development of the extreme La Niña events.
Approximately 75% of the increase occurs in years following
extreme El Niño events, thus projecting more frequent swings
between opposite extremes from one year to the next.