Bob Tisdale has a major post up at WUWT. I broadly agree with his analysis, but think he has missed something important. The graph below shows NINO 3.4 SST anomalies scaled to compare with ‘Rest of World’ SST anomalies. The divergences where ‘Rest of World’ drops below NINO 3.4 SST are attributed by Bob to the effects of the El Chichon and Pinatubo volcano eruptions in 1983 and 1991. I think there’s more going on than that though, so I’ve added the TSI record (in red) to the graph and shaded in green the 2003-2006 series of mini El Nino’s too.
As you can see, the big El Ninos in 87, 97 and 2010 all started around solar minimum, and the SST’s rose worldwide as the solar cycles grew. These were the events where the ‘rest of world’ SST’s stayed higher while the East Pacific dropped into La Nina conditions. I suggest this is largely due to reduced cloud.
Contrast this with the El Nino events in 83, 93-96 and 2003-2006. These all occur on the trailing side of the solar cycles, and afterwards, the ‘rest of world’ SST’s drop below the East Pacific SST’s. Notice though, that in 83 and 2003-2006 the ‘rest of world’ SST’s do rise, but not as much as the scaled NINO index. It’s only really the Pinatubo eruption that seems to send the ‘rest of world’ SST’s strongly downwards. It seems likely that increased cloud as the solar cycle weakened, along with the volcanic aerosol from Pinatubo muted the ‘rest of world’ SST response at the time of these solar max lagging events.
So in conclusion, I’m saying that the volcanic forcing is over-rated, because a goodly proportion of the negative forcing attributed to them in the satellite age is actually due to to solar forcing of cloud variation. This viewpoint is further backed up by the general reduction in cloud from ~1960-1998 while the Sun was strong revealed by the new Spanish and Chinese studies published in the literature this year.
Of course, the co2 theorists need a strong negative volcanic forcing to get their models to work, given the overblown positive forcing they attribute to co2. So I expect continued studied ignorance of the solar effect on cloud to continue.