Guest Post by Willis Eschenbach
Richard Muller and the good folks over at the Berkeley Earth Surface Temperature (BEST) project have released their temperature analysis back to 1750, and are making their usual unsupportable claims. I don’t mean his risible statements that the temperature changes are due to CO2 because the curves look alike—that joke has been widely discussed and discounted, even by anthropogenic global warming (AGW) supporters. Heck, even Michael Mann jumped on him for that one, saying
It seems, in the end–quite sadly–that this is all really about Richard Muller’s self-aggrandizement 🙁
And if anyone should know about “self-aggrandizement”, it’s Michael Mann … but I’m not talking about Muller’s claim that humans caused the warming. No, I mean the following statement:
The historic temperature pattern we observe has abrupt dips that match the emissions of known explosive volcanic eruptions; the particulates from such events reflect sunlight and cool the Earth’s surface for a few years.
In support of this statement, Richard Muller offers up the following chart:
Figure 1. BEST claims about temperature and volcanoes. SOURCE
So what’s not to like?
Well, first it appears he has included and excluded volcanoes depending on whether they show up in his temperature record. If we look at big eruptions, eruptions with a “volcanic explosively index” (VEI) of 6 or above, since 1750 we have the following volcanoes:
Mount Pinatubo, 1991
Santa María, 1902
Mount Tambora, 1815
Grímsvötn and Laki, 1783
So Muller has left off Santa Maria and Novarupta, and included El Chichon and Cosiguina. But that’s not the real problem. The real problem is that many of these occurred after or during the temperature drop that they are supposed to have caused … here’s the BEST data including all relevant volcanoes, without the style of overlay that they have used that obscures the actual timing:
So let’s look at the volcanoes, one by one:
LAKI, 1783: Occurred near the end of the fall in temperature that it is supposed to have caused.
TAMBORA, 1815: Occurred at the end of the fall in temperature that it is supposed to have caused.
COSIGUINA, 1835: Occurred near the middle of the fall in temperature that it is supposed to have caused.
KRAKATOA, 1883: Occurred at the end of the fall in temperature that it is supposed to have caused.
SANTA MARIA, 1902: Occurred in the middle of the fall in temperature that it is supposed to have caused.
NOVARUPTA, 1912: I can see why Muller omitted this eruption, which occurred just before a rise in temperature …
EL CHICHON, 1982: Occurred during the fall in temperature that it is supposed to have caused.
PINATUBO, 1991: This is arguably the only one of the eight volcanoes that could legitimately be claimed to cause a detectable fall in temperature … a whopping fall of 0.15°C or so.
So while volcanoes certainly may cause a minor drop in global temperature, the claim of Richard Muller and the BEST folks that there are “abrupt dips that match the emissions of known explosive volcanic eruptions” is simply not true. There are abrupt dips, but they don’t match up with the volcanic eruptions.
[Update] Further reading:
Prediction is hard, especially of the future discusses the GISS analysis of Pinatubo.
Missing the Missing Summer is about the eruption of Tambora.
Dronning Maud Meets the Little Ice Age investigates a claim that the Little Ice Age was triggered by vulcanism.
Volcanic Disruptions plays the game “Spot the Volcano”
[Update] Another way to investigate the question is to look at the average temperature anomaly during the two years before and the two years after the eruption. Figure 3 shows that result.
After some eruptions it cooled a bit, after some it warmed a bit, and after some there was no change … go figure.