Why did the researchers base their volcanic study on a model?

In an article at WUWT today, Eric Worrall asks what he claims is an obvious question (archived here), but wasn't - at least not to me (see below). He was writing about an article published in the Journal of Geophysical Research: Atmosphere. The paper was by a team led by Thomas J Aubry from the University of British Columbia. The scientists were exploring the impact of global warming on future volcanic eruptions.

Eruption at Eyjafjallajökull April 17, 2010. Credit: Árni Friðriksson

What the authors found was that under two of three Representative Concentration Pathways (RCP4.5 and RCP8.5, but not so much under RCP2.6), global warming will likely have the effect of reducing the cooling effect of volcanoes.

The reason for this is, as the authors write: "the critical mass eruption rate required to reach the tropopause will increase as a consequence of:

• a decrease in the heights of tropospheric plumes driven by a decrease of the tropospheric temperature lapse rate; and 
• an increase of the tropopause height."

My understanding of this is that with global warming, the height of the tropopause increases, more so as you move more toward the equator than at the poles. That means that a volcanic eruption will need to be more powerful if the plume is to reach the (higher) stratosphere.

Also, as the temperature lapse rate decreases, this is what the authors wrote (supported by references and equations):

Volcanic plume heights vary with projected temperature and geopotential height changes (Figure 5, panels c and d). In particular, where the lapse rate decreases, plume height decreases and vice-versa.

I probably should go back one step further. Volcanic eruptions spit out sulphur aerosols, which have a cooling effect. In the troposphere, these aerosols get washed out fairly quickly (days to weeks). In the stratosphere they last for longer - months or even years. (Over recent years, scientists have reported that there have been more mid-sized volcanoes than assumed in CMIP5 models, which have counteracted greenhouse warming to some extent.)

So if volcanic eruptions continue about the same, then they'll have less of a cooling effect in the future than they would have in recent years. The impact of this isn't huge, according to the scientists. However it's big enough that the assumption of status quo may need a rethink when making projections.

In the paper, the authors explain the assumptions, caveats and possible variations on their basic findings. I found it a good read.

Eric Worrall thinks he knows better than the experts

Eric Worrall posted some of the press release about the paper, and added his own comments at the bottom (archived here). He started with this:

I don’t have access to the full study, but the obvious question – why did the researchers base their study on a model?

First off, he does have access to the full study - he just has to pay for it. (Anthony says he's a member of AGU, so he should have been able to provide Eric with a copy, assuming he's taken out a subscription to the journals.) 

Secondly - what sort of dumb question is that? The scientists were looking at the future. How does Eric expect anyone to explore potential future scenarios as complex as climate/volcanic interactions without using a model?

Eric had his own naive suggestion for the scientists:

Why not send a few weather balloons through volcanic plumes at different latitudes and different times of year, to actually measure the impact of different atmospheric conditions on the formation of volcanic stratospheric aerosols?

Well, scientists have undoubtedly taken lots of observations of volcanic plumes over the years (though I'm not sure how long a weather balloon would last at more than 1000 degrees Celsius). Analysis of observations is how researchers know about volcanoes and what affects them. Looking at what happens now under current climatic conditions is only the first step in figuring out what will happen in the future under different climatic conditions. For that you need sophisticated general circulation models.

Eric has learnt something about the troposphere, which is nice but doesn't seem to have helped him much. I don't know why he used miles rather than kilometres:

The atmosphere is much thicker at the equator than at the poles – the troposphere is only around 4 miles thick at the poles during winter, but reaches 12 miles thick in equatorial regions. 

From the WUWT comments

The "post-truth" people at WUWT weren't very interested in the paper or the findings. As usual, they used Eric Worrall's WUWT article to express their dislike of knowledge and contempt for the people who discover new things. Dunning and Kruger would have a field day at WUWT, as would scientists who study how and why people embrace wacky conspiracy theories.

ClimateOtter uses the fallacy of personal incredulity. Personally, I'm incredulous that ClimateOtter thinks that scientists don't know that volcanic plumes can reach the stratosphere. 

November 21, 2016 at 3:36 am
I don’t even know where to begin on this one….. if convection in a thunderstorm can break through to the Stratosphere I can’t see why a much more powerful event like an eruption would have much trouble.

Greg seems quite annoyed that scientists did this piece of research. (Deniers don't approve of scientific research in general.) Instead of reading the paper or press release to get answers to his question, he jumped to silly conclusions. (No, the researchers did not conclude that no volcanic plume would ever reach the stratosphere in the future, just in case you wondered.)

November 21, 2016 at 6:28 am
This is the kind of inane drivel that Journal of Geophysical Research has made its hallmark over the years. Recall Mickey Mann in the climategate emails saying they must not lose over JGR.
How much higher do they expect the tropopause to get ? Out of reach to a VEI 5 ? Come on!
Junk science yet again. And this is the kind of stupid crap that Trump is supposed to accept without question and not “deny climate science” according to DeGrasse Tyson.

Ian Magness' training "in earch sciences" may have consisted of him building a model volcano in primary school. Clearly that wasn't sufficient for him to understand global warming. He didn't even understand the article Eric wrote about. CO2 doesn't damp down volcanoes. What happens is that in a warmer world the undamped volcanoes won't have quite the cooling effect they had in the past.

November 21, 2016 at 3:44 am
I’m sorry, but as someone who once trained in earth sciences, this just has to go down as so much horse-sh** on a volcanic scale. The very idea that the incredibly powerful effusions of a significant volcano will be damped down by a few extra CO2 and similar molecules (on a parts per million scale!) in the troposphere is beyond stupid. Back to class, pack to primary school science even.

JB wrote a very odd comment. I've no idea what was going through his or her mind and from the lack of reaction at WUWT, no-one else did either:

November 21, 2016 at 4:23 am
Just some layman’s questions but ….
if ‘global warming’ is so nefariously good (as their theories/models claim) at preventing cooling mechanisms, then:
a) why is recent geological history so full of ice ages ?
b) why is this still a pretty green planet instead of a heat-blasted desert world ?
Just curious – unless of course, there’s more hot air than actual evidence in effect (pun very much intended)

Alan the Brit didn't understand the research either. Again, the scientists weren't suggesting that global warming "controlled" powerful volcanic eruptions, or not-so-powerful ones either. All they were showing was the fewer eruptions would have plumes that reached the stratosphere.

November 21, 2016 at 4:23 am
ensemble of global climate models (GCM)! Says it all really! The very idea that a ppm of CO2, o.o4% ofthe atmosphere, can control a powerful volcanic eruption is ridiculous! These bozos & their colleagues trying to scare us about the volcanic desruction impending to wipe out America need to do some joined up thinking!

Informed Consumer is not too informed about atmospheric CO2, which is now above 400 parts per million (ppm), and in a reply to the above comment wrote:

November 21, 2016 at 5:02 am
Isn’t 4ppm 0.0004%?

The "thoughts" were full of silly comments like this one from ozspeaksup. Some people are driven to see their name on the computer screen. They have a deep desire to be accepted and recognised as part of the denier community, though it's obvious they don't have a clue about the general subject, let alone the specific paper:

November 21, 2016 at 4:38 am
wow isnt the desperation showing?
whatta load

Is this the first time arthur4563 has learnt that global warming is here to stay for a very long time?  (Under RCP8.5, radiative forcing peaks in the 2200's with temperature anomalies of 7.8 C ± 2.9 C in 2281-2300).

November 21, 2016 at 4:38 am
“For the comimg THREE CENTURIES” !!!
BOY, are these guys making one stupid-ass assumption. They really think that man’s greenhouse emisssions will continue for three centuries? 

References and further reading

Thomas J. Aubry, A. Mark Jellinek, Wim Degruyter, Costanza Bonadonna, Valentina Radić, Margot Clyne, Adjoa Quainoo. Impact of global warming on the rise of volcanic plumes and implications for future volcanic aerosol forcing. Journal of Geophysical Research: Atmosphere, 2016; DOI: 10.1002/2016JD025405

Climate change may prevent volcanoes from cooling the planet - press release at ScienceDaily.com