Spot The Volcano

By Willis Eschenbach – Re-Blogged From WUWT

It’s been a while since I played “Spot The Volcano”. The premise of the game is that the decrease in temperatures from volcanic eruptions is nowhere near as large as people claim. So I ask people to see if they can identify when a volcano erupted based on the temperature records of the time.

Now, I say that the main reason the temperature drop from volcanic eruptions is so small is that when we get a reduction in downwelling radiation from any cause, the equatorial oceans start to cool. When that happens the clouds form later in the day, allowing in more sunshine. And the net result is that any cooling from the volcanic eruption is mostly offset by the increase in incoming solar energy.

With that in mind, I thought I’d take a look to see what records we have for the largest volcanic eruption in modern times. This was the eruption of the Indonesian island of Tambora in April of 1815. To my surprise, I found that we have no less than forty-two temperature records from that time. As you might imagine, most of these are from Europe. The list of the forty-two stations is appended in the end-notes.

So I took the records for the period during which the Tambora eruption occurred, and I “standardized” them so that they all had an average value of zero and a standard deviation of one. Then I plotted them all on one graph. Here is that result.

Figure 1. Temperature records of forty-two temperature stations for a period during which the Tambora eruption occurred. Seasonal variations have been removed from the data, leaving only anomalies. DATA SOURCE

As you can see, there is good agreement between the various records, with the cold and warm years affecting most if not all of the records. And if that’s too fuzzy for you, here is the same data with the average of all forty-two of the stations overlaid in red on the individual station records.

Figure 2. As in Figure 1, but with the average overlaid in red.

You can see the problem. The largest eruption in modern times, and it is absolutely not obvious when it happened …

So when was the eruption? Well, it’s not where you’d expect, which would be just before one of the two biggest drops in temperature, shown on the left-hand side of the graph. Nor is it where the big temperature drop is on the far right of the graph. Nope. It’s in a very generic area where you’d never expect it to be found …

Figure 3. As in Figure 1, but with the years added.

Now, there are a couple things of note here. First, there are a number of temperature drops even in only this short record which are much larger than the temperature drop after the Tambora eruption.

Second, there are a number of cold temperature excursions even in this short record, some of which are much colder than during the period after the eruption.

My conclusion from this? Yes, there were likely areas in Europe and the US which were somewhat colder than usual after the Tambora eruption. But temperatures somewhat colder than usual occur every few years …

And overall, despite the size of the eruption, despite the megatonnes of sulfur dioxide that the eruption sent up into the stratosphere, despite the reduction in sunlight from that stratospheric dimming …  despite all of that, the effect on temperature was indistinguishable from natural fluctuations in other parts of the record.


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