Guest Post by Willis Eschenbach
Once again, Anthony has highlighted a paper claiming that volcanoes have great power over the global temperature. Indeed, they go so far as to say:
From the reconstruction it can be seen that large eruptions, such as Mount Tambora in 1815, or clusters of eruptions, may result in a hiatus of over 20 years, a finding supported by model results.
SOURCE: Determining the likelihood of pauses and surges in global warming, Andrew P. Schurer et al, hereinafter Schurer2015, paywalled here.
Here we go again, sez I, another excuse for the current temperature plateau … and right out of the box, I note that we are dealing with a “reconstruction”, with findings that are “verified by model results”. Be still, my beating heart …
So I thought I’d give their claim a looksee by comparing their recent (post-1800) eruption dates with the Berkeley Earth land temperature record. You know, first see what the observations have to say.
I’m using a variant of the method that they use in the paper, which is to “stack” the temperature records, aligning them at the year of the eruption. I have used the years since 1800 that they have identified in the ice cores as being the years of the big injections of sulfates into the stratosphere from volcanic eruptions. These include inter alia the eruptions of Pinatubo (1991), El Chichon (1982), Mt. Agung (1963), the big eruption of Krakatoa (1883), and the largest eruption during the period, Tambora (1815). Tambora was the volcano responsible for a few areas having a “Year Without A Summer” in 1816. Here are all of the years of big stratospheric eruptions:
Figure 1. Table S3 from Schurer2015.
Now, “Crowley and Untermann” is reconstruction of historical stratospheric eruptions based on sulfate levels in ice cores in Greenland and Antarctica. After a bit of searching I found the data here. Figure 2 shows their best estimate from the data of the tropical AOD, based on the ice core sulfates.
Figure 2. Aerosol Optical Depth (AOD), a measure of the amount of stratospheric aerosols, based on ice core records of the sulfate levels. The dotted horizontal line was the accept/reject line for consideration in Schurer2015. One hemisphere had to be above an AOD of 0.1 to be considered for the paper.
Now, in this graph we can see how much more sulfate aerosols were ejected into the stratosphere by Tambora in 1815 than by any other volcano in the last two centuries.
So I’ve taken those years shown by the dotted lines, and I’ve “stacked’ them in Figure 3, showing the span from five years before to five years after each eruption. In the background of Figure 3 are all of the 11-year spans in the dataset, shown in gray. This indicates the expected variation of the data. Over that, I’ve shown the nine eruptions used for this period in Schurer2015.
Figure 3. Stacked eruptions, aligned on the eruption date at Year 0. In gray in the background are all possible 11-year spans from 1800 to 2014.
There are several things of interest. First, as I’ve discussed before, even the mighty eruption of Tambora doesn’t change the global temperature much if at all. Globally the “Year Without A Summer” is the “Year Without A Difference”. Yes, I understand that in some locations the summer was cooler. But it seems the anecdotes have far outpaced the reality. In Missing The Missing Summer I showed eight datasets which cover the time period. None of them shows an unusual summer in 1816. And in Figure 3 you can see that according to the Berkeley Earth data, globally the “missing summer” of Tambora is scarcely a blip.
More to the point, the average of the stack shows that in general there’s no significant effect from the volcanoes. Nor is there any “dose-related” effect. Tambora, with the largest AOD, doesn’t have a significant temperature drop after the eruption. On the other hand, the largest post-eruption drop is from the eruption with the smallest AOD, that of 1903.
I know that this is difficult to accept after years of hearing how volcanoes strongly affect the climate, but here’s what I say is happening. When the stratospheric aerosols cut down the sun slightly, the tropical surface cools slightly. Because the tropical surface is cooler, the cumulus clouds form later in the day, allowing in more sun. So the weaker sun is compensated for by the longer time that it is striking the surface, and as a result there is very little change in the global average temperature.
In this manner, despite even the size of the 1815 Tambora eruption, and despite the fact that local areas showed cooling after Tambora, the stratospheric aerosols from this huge eruption had little effect on the global average temperature. More stratospheric aerosols are simply balanced out by less tropospheric clouds, and the beat goes on.
Conclusions? Well, my main conclusion is that Schurer2015 way overstates the effect of volcanoes on the global surface air temperature. For them to have a 20-year effect is very doubtful, particularly given the short lifespan of the stratospheric aerosols, as shown in Figure 2. In no case do they remain airborne for more than six years or so. How could their effect last another fourteen years?
In fact, as Figure 3 shows, on average there is no global effect at all visible in the first five years.
So I’ll say, as I’ve said before, that while volcanoes can certainly affect local areas, rumors of the power of volcanoes to affect global average temperatures have been greatly exaggerated.
Best to all,
A Strong Request: If you disagree with something that has been said, please quote the exact words you disagree with. That lets us all be clear about a) the person you are addressing, and b) just what they said that you object to.
Further Reading: As I mentioned above, I’ve written extensively on how little the eruptions affect the temperature. Here is a list of my previous posts on the subject:
Overshoot and Undershoot
Today I thought I’d discuss my research into what is put forward as one of the key pieces of evidence that GCMs (global climate models) are able to accurately reproduce the climate. This is the claim that the GCMs are able to reproduce the effects of volcanoes on the climate.…
Prediction is hard, especially of the future.
[UPDATE]: I have added a discussion of the size of the model error at the end of this post. Over at Judith Curry’s climate blog, the NASA climate scientist Dr. Andrew Lacis has been providing some comments. He was asked: Please provide 5- 10 recent ‘proof points’ which you would…
The claim is often made that volcanoes support the theory that forcing rules temperature. The aerosols from the eruptions are injected into the stratosphere. This reflects additional sunlight, and cuts the amount of sunshine that strikes the surface. As a result of this reduction in forcing, the biggest volcanic eruptions…
Dronning Maud Meets the Little Ice Age
I have to learn to keep my blood pressure down … this new paper, “Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks“, hereinafter M2012, has me shaking my head. It has gotten favorable reports in the scientific blogs … I don’t see it at…
Missing the Missing Summer
Since I was a kid I’ve been reading stories about “The Year Without A Summer”. This was the summer of 1816, one year after the great eruption of the Tambora volcano in Indonesia. The Tambora eruption, in April of 1815, was so huge it could be heard from 2,600 km…
New Data, Old Claims About Volcanoes
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…
BEST, Volcanoes and Climate Sensitivity
I’ve argued in a variety of posts that the usual canonical estimate of climate sensitivity, which is 3°C of warming for a doubling of CO2, is an order of magnitude too large. Today, at the urging of Steven Mosher in a thread on Lucia Liljegren’s excellent blog “The Blackboard”, I’ve…
Back in 2010, I wrote a post called “Prediction is hard, especially of the future“. It turned out to be the first of a series of posts that I ended up writing on the inability of climate models to successfully replicate the effects of volcanoes. It was an investigation occasioned…
Volcanoes: Active, Inactive, and Retroactive
Anthony put up a post titled “Why the new Otto et al climate sensitivity paper is important – it’s a sea change for some IPCC authors” The paper in question is “Energy budget constraints on climate response” (free registration required), supplementary online information (SOI) here, by Otto et alia, sixteen…
Stacked Volcanoes Falsify Models
Well, this has been a circuitous journey. I started out to research volcanoes. First I got distracted by the question of model sensitivity, as I described in Model Climate Sensitivity Calculated Directly From Model Results. Then I was diverted by the question of smoothing of the Otto data, as I reported…
The Eruption Over the IPCC AR5
In the leaked version of the upcoming United Nations Intergovernmental Panel on Climate Change (UN IPCC) Fifth Assessment Report (AR5) Chapter 1, we find the following claims regarding volcanoes. The forcing from stratospheric volcanic aerosols can have a large impact on the climate for some years after volcanic eruptions. Several…
Volcanoes Erupt Again
I see that Susan Solomon and her climate police have rounded up the usual suspects, which in this case are volcanic eruptions, in their desperation to explain the so-called “pause” in global warming that’s stretching towards two decades now. Their problem is that for a long while the climate alarmists…
Eruptions and Ocean Heat Content
I was out trolling for science the other day at the AGW Observer site. It’s a great place, they list lots and lots of science including the good, the bad, and the ugly, like for example all the references from the UN IPCC AR5. The beauty part is that the…
Get Laki, Get Unlaki
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…
Volcanoes Once Again, Again
[also, see update at the end of the post] Anthony recently highlighted a couple of new papers claiming to explain the current plateau in global warming. This time, it’s volcanoes, but the claim this time is that it’s not the big volcanoes. It’s the small volcanoes. The studies both seem to…
UPDATE: I don’t think Willis will mind if I include this excellent graph prepared by Joe D’Aleo of Weatherbell:
As you can see in the bottom panel, the aerosol loading during “the pause” is close to zero. So much for Schurer2015 and their claims – Anthony