Monday, June 29, 2009
Transition to El Nino becomes official
According to the latest, today's weekly report,
At the end of 2007 and beginning of 2008, we had a La Nina episode (see page 26) which is partly responsible for the last year's status of the coldest year of the century so far.
At the end of 2008 and beginning of 2009, La Nina conditions were in place once again. However, they didn't make it to another La Nina episode because the average index failed to drop below -0.5 °C for five consecutive overlapping three-month periods - a defining criterion for an episode.
However, now we're back to El Nino conditions that have a big chance to make it into another episode. That would probably mean that the global mean temperatures would get a positive boost, too. The ENSO "ONI" index for the end of June 2009 is probably at the highest end-of-June level since 1997 when it was even higher, getting ready for the El Nino of the century that has made 1998 the warmest year on record.
I expect that the monthly temperatures for June 2009 - to be released in a few days - will already show a substantial warming relatively to May 2009, and if they won't (as some commenters revealed!), we will see a warming one month later, and it will continue for several months. A majority of ENSO models suggest that the El Nino could continue through early 2010.
People say that the lag between ENSO and its effects on the global mean temperature is 4-6 months. I don't disagree with that! But the ENSO index has been largely increasing since early January (see page 5/30 of the PDF file above), so even with the 6-month lag, we should be seeing signs of ENSO warming soon.
The PDO cool phase has apparently weakened, too. On the other hand, the Sun remains pretty quiet (5-day spotless streak) and it may contribute some cooling.