As I mentioned in my post here about one of the satellite data sets (RSS) that showed a marked cooling globally in 2008, La Niña and PDO seem to be drivers of this change. Here is Joe D’Aleo’s take on it below. – Anthony
By Joseph D’Aleo, CCM ICECAP
Evidence is growing this La Niña will be a longer term event. Most similar important La Niñas are often multi year events (1949-1951,1954-1956, 1961-63, 1970-1972, 1973-1976, 1998-2001). Though the easternmost Pacific near South America has warmed at the surface as the seasonal weakening of the tropical easterlies led to weakened upwelling, it is still cold beneath. Below you can see the latest depth-section of ocean temperatures (top) and anomalies (bottom). Temperature are in degree Celsius. Note the large reservoir of subsurface anomalously cold water (up to 4 degrees C) in the eastern tropical Pacific at 50 to 100 meters.
Also see the latest CPC depicted ocean heat content in the tropical Pacific. This shows the heat content remains at near maximum deficit levels.
These suggest as the easterlies increase again, cooling will return to the east Pacific and La Niña will persist at least well into 2008. The Pacific Decadal Oscillation (PDO) has dropped strongly negative (latest value from NCEP is -1.54 STD). This decline may represent another Great Pacific Climate Shift as the PDO warm and cold phases tend last 25 to 30 years and the last change , to a warm Pacific, occurred in 1976. See more in this pdf here. If indeed the PDO shift is the real deal, we might expect more La Niñas and fewer weaker El Niños over the next few decades with a net tendency for cooling. Add to that a quieter sun and eventually a cooling Atlantic, and you have a recipe for global cooling.
However, this has its own drawbacks, La Ninas bring more drought and summer heat waves, landfalling hurricanes, large tornado outbreaks, spring floods, winter snows and cold outbreaks than their more famous counterpart, El Niño, which has dominated during the warm PDO era. A while back, Stan Changnon did an interesting analysis which I reported on recently here that suggests the era we have gone through since the late 1970s with dominant El Niños was unusually benign with more benefits than damages and will be looked on as the golden era, a modern climate optimum. Even if all this is correct, you might expect the media and enviro-alarmists ‘evidence’ we are affecting our climate to morph from warming and ice melt to the climate extremes characteristic of La Niñas.
See full pdf here.