My post showing shifting trends in world surface temperature and in carbon emissions brought a suggestion from Martin Shafer that allowing for the PDO could straighten the trend. I think that perhaps it could, but I have tried the IPO (Inter-decadal Pacific Oscillation) rather than the PDO (Pacific inter-Decadal Oscillation). (See below.)
Along the top of the graph I have marked in the climate shifts that prevent the trace of world temperature from being anything like a straight line. The blue line is the IPO, as updated to 2008.
The IPO is positive in the space between the last two climate shifts, negative in the next earlier space, and positive in part of the space before that. By plotting the CUSUM values of the IPO (red), it is clear that the pattern of the IPO relates very closely to the climate shift dates. Four of the seven extreme points of the IPO CUSUM trace match climate shifts. In addition, since 1925, the CUSUM trace between the sharply-defined extreme points has been a series of nearly straight lines. These represent near-constant values of the IPO, a rising line representing a positive IPO and a falling line a negative one.
As shown by the map in the Figure copied below, a positive extreme of the IPO has higher than normal sea surface temperatures in the equatorial parts of the Pacific. Could the transfer of heat from the ocean to the atmosphere be enhanced at such times?
This conjecture is developed in the post “Hammering Global Warming Into Line”.
The PDO and the IPO
The PDO is the Pacific Decadal Oscillation (or Pacific inter-Decadal Oscillation). It is one of a number of climate indicators that rise and fall over periods of a decade or more. These indicators have been introduced by different research groups at different times.
A current list of such indicators is in the contribution of Working Group I to the Fifth Assessment Report (5AR) of the Intergovernmental Panel on Climate Change (IPCC). The list is in Chapter 2 (38MB). It is at the end, in a special section: “Box 2.5: Patterns and Indices of Climate Variability”.
The PDO (Pacific Decadal Oscillation) is based on data from the north Pacific only, being introduced in studies of the salmon fishery.
I prefer to use the more general Inter-decadal Pacific Oscillation (IPO). It is described in a paper by Power, Casey, Folland, Colman and Mehta, 1999: “Inter-decadal modulation of the impact of ENSO on Australia”.
Note added 11 May 2017. That link no longer works. Currently this one does.
The caption of their Fig. 2 is explicit. (SST = Sea Surface Temperature; EOF = Empirical Orthogonal Function)
I thank Chris Folland for helpful correspondence.