Volcanic Northern Winters

I see there’s a new study, unfortunately paywalled, which starts out by saying:

Observations show that all recent large tropical volcanic eruptions (1850-present) were followed by surface winter warming in the first Northern Hemisphere (NH) winter after the eruption. Recent studies show that climate models produce a surface winter warming response in the first winter after the largest eruptions, but require a large ensemble of simulations to see significant changes.

OK, so far that’s interesting … but they continue:

It is also generally required that the eruption be very large, and only two such eruptions occurred in the historical period: Krakatau in 1883 and Pinatubo in 1991.

So, when they say “all recent large tropical volcanic eruptions”, they actually mean “only two of all recent large tropical volcanic eruptions”.

It’s enough to make a man wish that there was the equivalent in science of the “Truth In Advertising” laws. These guys actually think that they can make large-scale generalizations from two, count’em two, measly examples.

In any case, I thought I’d take a look at the winters (December-January-February, DJF) following the two large volcano years. Here’s that result.

Figure 1. Northern Hemisphere land-only temperature anomalies for individual years (including January and February of the following year), plus the overall average (mean) and the two volcano years. Fourteen months are shown to include the winter following the year of the eruptions.

As you can see, neither of the large eruption years (1991 and 1883) is unusual.

Now, they claim that the winter following large eruptions shows “warming” … but warming compared to what? To me, the logical measure would be to compare it to the preceding fall (September-October November, SON)—if the fall is warmer than average I’d think that the winter would be warmer than average. Figure 2 shows the comparison of winter and fall temperatures:

Figure 2. Histogram of winter (DJF) minus fall (SON) Northern Hemisphere land-only temperatures. Dotted lines show one standard deviation from the mean.

As you can see, while in both volcano years the winter is slightly warmer than the fall, in neither case is the difference statistically significant. In particular, Krakatau, largest eruption in recent history, shows almost no effect on the winter. It’s just about average.

In short, their claim that “Observations show that all recent large tropical volcanic eruptions (1850-present) were followed by surface winter warming in the first Northern Hemisphere (NH) winter after the eruption” is not supported by the evidence. And evidently, according to them, the other volcanoes are not large enough to lead to warmer winters …

Now if they actually were serious scientists, they would have noted that large volcanic eruptions are NOT followed by statistically significantly warmer winters, and they would have looked at something else. But these are not serious scientists, they are climate model believers. So instead they reached for a climate model, one of the models which are known to exaggerate the effects of volcanoes.

However, results from individual models are mixed, so they grabbed a whole bunch of models, averaged them, and PRESTO! Their unsupported allegation about the large eruptions causing warmer winters is now claimed as fact.

Man … this use of untested, unverified, and un-validated climate models gets old.

Finally, we’ve been told for years that volcanic eruptions cause COOLING … although what cooling is visible in the historical record is generally local, small, and short-lasting. But now, they say eruptions cause Northern Hemisphere winter warming? What’s up with that?

w.

PS—When you comment, please QUOTE THE EXACT WORDS YOU ARE DISCUSSING, so we can all be clear about your subject.