It’s clear that the intense El Nino, one of the three strongest on record, is now over and forecasters are expecting a transition to La Nina conditions within a few months. What does this mean for the much-discussed “pause” or “hiatus?”
Australia and NOAA have issued L Nina alerts for 2016/7. In mid-May the sea surface temperature in the diagnostic El Nino 3.4 region dropped below the 0.5°C threshold for El Nino conditions. Global surface temperatures, which reached record levels, are now declining. Lower tropospheric temperatures are also declining with May’s UAH reading of 0.55°C being 0.16°C down on the previous month.
Of course, no one knows what will happen next. Will La Nina be swift or be a multi-year event like 1998-2001? In general La Ninas are slow to leave and that there is an indication that multi-year La Nina’s tend to occur after the strongest El Ninos. Perhaps we might experience back-to-back La Ninas like 2010/11 and 2011/12.
The 2015 El Nino caused record temperatures. Many had expected this. There are indications that the El Nino tried to start in 2014 but stalled. It left behind a pool of warm water that “kick-started” the 2015 event. In October NASA Giss passed a temperature anomaly of 100 for the first time starting seven months above 100. May’s temperature anomaly is 93, still high though not unprecedented. At the moment it is likely that the very high temperatures of the first five months of 2016 will result in another record year for Giss unless the temperature decline is very rapid. HadCRUT4 shows a decline with April having a temperature anomaly of 0.926 down from 1.065 the previous month. NOAA‘s May surface data shows a global record for the 13th consecutive month although technically May 2016 tied with June and August 2015, again showing the start of a global temperature decline.
What does this mean for the much-discussed “pause” or “hiatus?” Clearly the 2015 El Nino interrupted it. According to HadCRUT4 the temperature 2001/14 gradient is 0.002 +/- 0.144°C per decade. It will be interesting to see if the La Nina decline counterbalances the El Nino rise and we return to a similar gradient sometime in the future. There are many who expect it won’t because they maintain the background rise in global temperature is continuing as will be apparent when the expected La Nina has run its course. This expectation is strong among those who played down the effect of the 2015/6 El Nino. There was much confusion and contradiction about how much the El Nino had contributed to 2016 being a record year. Some said that 2016 would have been a record year without the El Nino, other that it caused the record but did not add much to global temperature and others (not quoted very much by many media outlets) maintained that without the El Nino the “pause” would have continued. If the 2015 El Nino’s influence was small then perhaps one can expect the forthcoming La Nino to lack the strength to reestablish the pause. We will have to wait and see.