For the last couple of months I have watched many statements about the developing La Nina in the Pacific. I keep a close eye on the ocean temperatures and while technically the Pacific is in a La Nina, it is a very mild one. Since La Nina is the cold phase of the ENSO (El Nino Southern Oscillation) there are certain weather patterns associated with it. For instance, the peak years of the Texas drought in the 1950’s took place when there was a period of strong La Nina, much like the current drought started last year during another strong La Nina. While the Pacific is technically in La Nina, there is no real comparison between the two years.
One problem is that the rating itself is not a very useful measure by itself. The index is too narrowly defined to really describe what the Pacific Ocean is doing. This past summer the index reached zero, but the overall pattern was akin to La Nina and that is how the weather responded. The 1998 El Nino was without compare in strength (over a 100 year period), but the index itself does not do a good job in describing just how powerful it really was.
It is far more useful to show the year-to-year comparison of the ocean temperatures. (click on image to see in proper color)
Not only were the equatorial waters much colder last year, but the regions away from the equator were also cooler. The entire triangular region from California to Chile to Indonesia was on average colder last year that it is this year. The actual rating of the ENSO is strictly based on the regions at the equator. It is a very limited measure of what the Pacific Ocean is doing, but especially by that measure the current La Nina is very weak.
The typical La Nina effect should be lesser this year which should be good news for places suffering droughts from last year. The northern Pacific is also interesting and needs a little bit of attention. The warm water off of Asia and the cold water off of the Canadian coast is very different than the pattern that developed last year. There is more of an East-West divide than what existed last year. I have no idea what that pattern will cause to happen, but needless to say I will be paying close attention to it.
I am also intrigued by the cooler water around Greenland at this time of the year. Last year there was a lot of warm water in that region and not surprisingly the Arctic ice was low last winter and into the summer. The cooler ocean there should lead to a nice rebound in the sea ice this winter. Warm oceans take a lot of heat loss to freeze and the closer to freezing they start the less heat loss before ice forms.
The more I look at the patterns to the ocean surface temperatures the more convinced I become that science is being foolish in how they measure the temperature of the Earth’s oceans. Broader definitions of the the different patterns and greater effort at determining the specific effect would be far more useful in predicting the weather and the climate. It was clear at this point last year that droughts would be forming in some places while extra rain would be falling in others. Having an extra six months to prepare would make prevention and mitigation much more successful.