Séminaire
The extreme El Nino of 2015 was part of surprisingly persistent warm conditions in the equatorial Pacific that began in March 2014 and lasted for almost two and a half years. Here I discuss the mechanisms and global impacts of these prolonged El Nino conditions using a combination of observations, GCM experiments and simple modeling. The onset of the equatorial warming occurred after a series of strong westerly wind bursts over the western tropical Pacific in the early 2014 that generated the initial warming. However, the development of an El Nino event stalled, largely due to an exceptionally strong easterly wind burst in June. Subsequently, another series of strong westerly wind bursts in the spring of 2015 generated a further warming in the central and eastern equatorial Pacific that eventually led to an extreme El Nino event reminiscent of the 1997 El Nino. These warm conditions in the tropical Pacific Ocean induced global surface air temperature anomalies, resulting in the last three years being the warmest years on record so far and ending the much-discussed global warming "hiatus". A simple model of global mean surface temperature that incorporates CO2 emissions, and ENSO and volcanic forcings, confirm this conclusion.
muller@lmd.ens.fr