On the very busy and interesting El Nino in relation to solar cycles thread Erl Happ made a comment about volcanos and El Nino which reminded me about a graph I did of the similarity between late C19th and late C20th solar slowdowns and the El Nino events occurring at those epochs. I ‘ve made a new pair of graphs to improve clarity and to include the timing of the two biggest volcanic events of the last 120 years.
Comparison of SST SSN and volcanic effects around 1883 and 1991
Here’s what Erl said:
The 1997-8 event was indeed a big event. It was made so by the effects of Pinatubo erupting in June 1991. From Wikipedia:
The effects of the eruption were felt worldwide. It ejected roughly 10 billion metric tonnes (10 cubic kilometres) of magma, and 20 million tons of SO2, bringing vast quantities of minerals and metals to the surface environment. It injected large amounts of aerosol into the stratosphere – more than any eruption since that of Krakatoa in 1883. Over the following months, the aerosols formed a global layer of sulfuric acid haze. Global temperatures dropped by about 0.5 °C (0.9 °F), and ozone depletion temporarily increased substantially.”
As a result of the induced cooling, a product of the haze and the ozone loss (affecting the annular modes thereby increasing cloud cover) precipitation increased and the global atmosphere dried out. The drying persisted to 1996. Ozone levels began to recover. The increase in ozone flux into the polar stratosphere induced a loss of cloud and the result was a warming event of spectacular amplitude. The atmosphere recovered its water vapour content due to enhanced evaporation during the 1997-98 event and an equally spectacular cooling event followed.
In the mid 1990′s cooling in the southern hemisphere was stronger than in the northern hemisphere, a neat practical demonstration of the relative importance of the Antarctic circulation as it determines cloud cover in the southern hemisphere.
I think there is merit in Erl’s analysis, but I also think that the role of the Sun in the El Nino events following Krakatoa and Pinatubo needs to be considered, in order to widen the perspective on the timing of El Nino and the relative strengths of Solar and volcanic effects.
A couple of observations before I throw it open to the floor:
1) The big El Nino’s during both epochs start to build around solar minimum.
2) The El Nino following Pinatubo, seven years later, was a really big one, and so was the previous solar cycle. The El Nino following Krakatoa, five years later, wasn’t such a big one, and neither was the preceding solar cycle. (note the scaling difference on the plots for sunspot number)
3) The cooling following both volcanic events coincided with drops in solar activity too.
4) Their were smaller El Nino events on the declining side of the solar cycles following both volcanic eruptions before the big ones.
5) I detrended the modern SST data for clarity, if anyone thinks the 0.2C leveling makes a big difference to the El nino’s we can discuss that too.
My conclusion is that while I’m sure Erl has made a valid analysis of atmospheric chemistry and it’s effects on albedo, the solar effect on albedo is a lot stronger. By which mechanism remains an open question, but apart from a possible Svensmark effect, I think this correlation may have a lot to do with it:
Tallbloke's Talkshop 
Can’t see a good correlation between either of volcano and SST , although I suspect the SST data from the 19th century is crap and, like the modern temperature reconstructions, which are subject to the confirmation bias of those doing the series (see Climategate Harry.readme file to see how this works).
Conclusion – I don’t think we have enough good enough data to know either way, although I think Erl’s conjecture has merit and is plausible. Proving that volcanoes can have major long-term climate changing significance is almost impossible.
Tenuc says:
Proving that volcanoes can have major long-term climate changing significance is almost impossible.
My guess is that prolonged increases in general volcanic activity (not just big eruptions) will have an effect on global surface T. Whether such prolonged eruption patterns accompany deep/long solar minima remains to be seen.
you realize the specific humidity numbers are largely garbage and not suitable for analysis
We will see what happens in the near future with the current volcanic activity vs. temperatures, as we are living the first solar minimum with the current world information capabilities.
Mosh, you keep saying this, but you never substantiate it. I can see why Phil Jones would play down the radiosonde data in favour of ERA 40 though. I think the unexpected agreement between solar data and specific humidity data from radiosondes shows that the data isn’t as bad as you make out.
What level of error do you believe there is and why? Come on, don’t be coy.
@ Adolfo,
I agree.
We should observe current events with all sensor capabilities at our disposal.
We’re having a front row seat but only can cash in with honest scientists who haven’t sold their sole and their scientific integrity to the AGW gravy train.
The latest sea level rise scam doesn’t provide any basis for optimism.
What I mean with that is the fact that major tax payer funded sensor platforms are in the “wrong hands” and their findings could very well be manipulated.
[…] the last 120 years didn’t cause cooling at a global scale. Also, Pinatubo coincided with a drop in solar activity, and global temperature had been on an upswing prior to the eruption anyway, and was about ready […]