AMO & PDO Cycles

By Paul Homewood

 

We discussed the role of the PDO and ENSO changes in the earth’s climate yesterday.

I though it worthwhile republishing one of my posts from October 2013 (frightening – it only seemed a few months ago!). This related the PDO and AMO cycles to global temperatures.

( The ESRL graph is updated, but only to the end of 2013).

 

It is well established that both the Atlantic Multidecadal & the Pacific Decadal Oscillations affect global temperatures. According to NOAA, the AMO alternatively obscures and exaggerates global warming.

 

 

The solid blue curve shows the observed northern Hemisphere temperatures and the dashed blue curve is a smoothed version. The red curve is the temperature history for a model that responds to the external forcing of greenhouse gases and solar variability but not to natural climate variations. The blue alternations about the red curve represent the natural AMO oscillations. When the AMO decreases, as from 1950 to 1975, global warming may appear to be reversed. When the AMO increases, as from 1975 to the present, the global warming (red) is exaggerated.

 

And Roy Spencer tells us :

The Pacific Decadal Oscillation (PDO) is an internal switch between two slightly different circulation patterns that occurs every 30 years or so in the North Pacific Ocean. It was originally described in 1997 in the context of salmon production. It has a positive (warm) phase that tends to warm the land masses of the Northern Hemisphere, as well as a negative (cool) phase.

 

http://www.drroyspencer.com/global-warming-background-articles/the-pacific-decadal-oscillation/

 

Things get particularly interesting though, when you put the two cycles together, as below.

 

 

http://www.esrl.noaa.gov/psd/cgi-bin/gcos_wgsp/tsanalysis.pl?tstype1=91&tstype2=20&year1=1900&year2=&itypea=0&axistype=1&anom=0&plotstyle=0&climo1=&climo2=&y1=&y2=&y21=&y22=&length=&lag=&iall=0&iseas=1&mon1=0&mon2=11&Submit=Calculate+Results

 

 

• In the 1930’s, both PDO and AMO warm phases come together.
• Both cold phases come together in the 1960’s and 70’s, the time of the “ice age scares”.
• And, the warm phases come together again for about 10 years from the mid 1990’s, when we saw the last spike in temperatures.

The PDO has now turned cold, and, with the AMO still in its warm phase, temperatures are flatlining.

It is likely that the AMO will remain in warm mode for another 10 years or so, but by the mid 2020’s we are likely to see both great ocean patterns stuck together in their cold phases well into the 2030’s.

When they do, will we see a similar drop in global temperatures such as we did in the 1970’s? I would not bet against it.