I wanted to post about this when I first saw it, but was unable due to personal reasons (see previous post). Tamino had a post last week that pretty much demolishes a post at Watt’s Up originally by Joe D’Aleo. The original post compared temperatures from the United States Historical Climatology Network (USHCN) to several climate indices and the CO2 record.

Comparing US temperatures with climate indices is silly, as Tamino points out. Therefore, I’ll be comparing global temperatures from HadCRUt. Before I get to the comparison, let’s look at what the PDO is, and why it might correlate well to North American temperatures. The University of Washington website defines the PDO as “the leading principal component of North Pacific monthly sea surface temperature variability (poleward of 20N for the 1900-93 period).” The Pacific Ocean is to the west of the United States, and the general atmospheric circulation blows the air from west to east in the mid-latitudes. Therefore, one would expect a large correlation between the PDO and North American temperatures, based solely upon the location of the US and the definition of the PDO.

But we would not expect a high correlation between the PDO and, for instance, temperatures in Northern Europe. Another climate indice, such as the North Atlantic Oscillation, may be a better predictor of the temperatures for Northern Europe. But just because it is correlated in Northern Europe does not mean it will be correlated with temperatures in Australia. Is there a pattern forming here? Regional temperatures may be correlated with climate indices that are in the same geographic area, but that does not imply that the climate indices will be correlated with the global temperature.

I now present the plots of standardized temperature versus several standardized climate indices and CO2. The data were standardzed, mean of zero and a variance of 1, so that they would appear on the same axis. The correlation coefficient is computed from the non-standardized data. First, CO2.

Here we have a very high correlation between the CO2 level as measured at Mauna Loa and the global average temperature. Notice that short-term variations in the temperature are not very correlated with the CO2 level, but the overall upward trend is.

El Nino (Nino3.4 index) has better correlation at the shorter timescales, but it does not show an upward or downward trend in recent years as the temperature. The same is true for the PDO below.

The worst correlation is with the NAO (North Atlantic Oscillation). This climate index has almost no long-term information in it. It picks up mostly the year-to-year and interannual variability. From a global climate perspective, this is mostly just noise.

(No Ratings Yet)

 Loading ...

Related Posts:

Trackback URI |