Dr Jones drew my attention to a paper by Vecchi (2006) that he feels rebuts the view that increased frequency and intensity of El Nino events are responsible for global warming and not increasing greenhouse gases — so I give a quick analysis of it here.

Dr Jones mentions a confusion cause and effect, so let’s try to clarify the different positions first. The two views are something like this for global temperature (GT) and Walker circulation (WC):

H1: Increasing ENSO causes increasing GT
H2: Increasing GHG causes decreasing WC AND increasing ENSO causing increasing GT

The primary evidence for H2 is the weakening of the delta sea level pressure between the east and west tropical Pacific (ΔSLP), representing weakening of the Walker circulation as a response to increasing GHGs. The Figure 3 from Vecchi that is supposed to supply this evidence is below.

The declining slope of the linear fit to the ΔSLP is supposed to prove that the Walker circulation has been decreasing over the last century.

The first thing I notice is that the negative slope is almost certainly due to the period I have marked with red lines between 1976 and 1998 — the period between the Great Pacific Climate Shift in 1976 and the potential shift we identified in 1998 in our ‘breaks’ paper. For comparison, below is an image of PDO over the period, showing that 1976-1998 corresponds to a warm phase of the PDO.

Here also is our ‘break’ figure with the statistically significant breaks at 1976 and 1998 indicated.

Note the coincidence between the period of greatest increase in temperature, period of warm PDO, and low ΔSLP. Outside that period: nada, zilch. ΔSLP seems to have returned to normal after 1998, further contradicting the projections in Vecchi that the decline in the strength of the Walker circulation will continue to 2100.

If so, this paper will be easy to discredit. Simply update the ΔSLP to 2009, and show that the downtrend is simply due to a single anomalous period of high El Nino activity. That the GCM predicts a decline in the Walker circulation — which does not occur in reality — is further evidence of unreliability of GCM’s in this area.

So many comments — so little time.

h/t Dr Jones for bringing this to my attention.