Guest Post by Willis Eschenbach
Well, we haven’t had a game of “Spot The Volcano” in a while, so I thought I’d take a look at what is likely the earliest volcanic eruption for which we have actual temperature records. This was the eruption of the Icelandic volcano Laki in June of 1783. It is claimed to have caused a very cold winter in 1783-1784. A study of the effects (see end notes) says:
… the 1783-1784 winter was extremely cold and snowy around the circum-North Atlantic. European temperatures were ~2°C below average for the late 1700s, and it was among the coldest winters in Central England …
Well dang … that sounds pretty scary. However, being a naturally suspicious fellow, I thought I’d take a look and see just what the temperatures actually said. I found eight records in the Berkeley Earth Surface Temperature dataset that went back that far, there may be others, but these cover a wide area of Europe. Here’s your puzzle:
So … is the year of the “extremely cold and snowy winter” location number 1, 2, 3, or 4?
While you consider that question, let me point out that despite frequent claims of “unusual” or “extremely” or “unprecedented” and the like, I’ve shown in the past even very large volcanic eruptions cause little in the way of temperature changes (see end notes). The Laki volcano is in Iceland, so you’d think that the signal from it would be strong in Europe. And indeed, as the quote above shows, this is the common wisdom.
But as the temperature graphs show, the actual eruption makes little difference to the temperatures. The winter following the eruption of Laki is actually at location number 3, so there is some effect from it visible in all of the records. Looks like it is the one winter that was unusually cold in every one of the eight records.
But even then, it’s not that large and … and … oops … hang on a minute, sorry ’bout that. I got the numbers wrong. Here’s the actual situation regarding the winter of 1783-1784:
As you can see, the winter following the Laki eruption is not the one marked with the red “3”. Actually it’s the one marked by the red “2” … and it is pretty unremarkable. In general it is NOT “~2°C below average for the late 1700s” as the quoted study says, that’s simply untrue. And in several of the datasets, it’s no colder than normal.
We do have one other dataset going back that far, the Central England temperature dataset. Here’s that data:
Remembering that the study claimed that this was “among the coldest winters in Central England”, which winter looks like the big winner here?
In fact, far from being among the coldest all-time winters, the winter of 1783-1784 was not even in the top three for the quarter century 1775-1800 …
My point is simple. We have been told a story all of our lives about how volcanic eruptions have large, widespread, and long-lasting effects on the global weather. It turns out that this was a scientific urban legend. In fact, the effects are small, localized, and short-lived.
UPDATE: For those who like averages, here are the averages of the eight station records.
Regards to everyone,
AS ALWAYS: If you disagree with someone, please QUOTE THE EXACT WORDS YOU DISAGREE WITH, so we can all understand the substance and nature of your objections.
FURTHER READING: I’ve analyzed the effects of a number of large volcanic eruptions. In all cases, their effects have been small. See:
DATA: Monthly mean HadCET data
Berkeley Earth Surface Temperature data
Laki Winter study quoted above