I’m reading “Total volcanic stratospheric aerosol optical depths and implications for global climate change
D. A Ridley1, S. Solomon2, J. E. Barnes3, V.D. Burlakov4, T. Deshler5, S.I. Dolgii4, A.B. Herber6, T. Nagai7, R. R. Neely III8, A.V. Nevzorov4, C. Ritter9, T. Sakai7, B. D. Santer10, M. Sato11, A. Schmidt12, O.Uchino7, J. P. Vernier13,14″
It’s an interesting paper. I have a big question and I’m hoping to that some readers might be able to point to resources. Briefly:
Is there a brief resource that lists the volcanic forcings used by groups who contributed projections to the AR5.
Specifically, I want to know which groups ‘froze’ volcanic forcings after 2000 and which did not. For groups that did not freeze volcanic forcings in 2000, I’d be interested in knowing when the year they did freeze them, and at what level those forcings were frozen.
The reason I wish to know: Ridley seems to suggest “many” froze forcings. I don’t know what fraction ‘many climate model studies to date’ constitutes nor which models. Are the “many climate model[s]” the AOGCM’s used to create projections in the AR5? Or are they EMICs? Etc. Of the AOGCM runs, is ‘many’ 20% ‘froze’ or was it more like 80%?
My impression (which could be incorrect) is that Model E did not freeze volcanic aerosols in 2000. (NASA’s Model E page says,
“The simulations (using TCADI) denoted by p3001 are continuations from 1991 of the p3 simulations including further updates to the volcanic and solar forcings through to 2012. The volcanic forcings are from a more recent version of the Sato et al. data than used in the historicalExt runs described below.”
But perhaps I’m jumping to the conclusion that these were the runs used for “projections” in the AR5 and perhaps they did ‘freeze’ volcanic aerosols in 2000 and then use that to create projections. (Note: if they ‘froze’ in 2012, one might expect the ‘mean’ for their trends from 2012-2014 should be lower than the earths, because the volcanic aerosol cleared somewhat. Any discrepancy would be undetectable as it would be swamped by ‘weather noise’.)
I would like to know the year other modeling groups who contributed to the AR5 (or AR4) ‘froze’ volcanic aerosols.
BTW: I’m pretty sure it’s true that of those that included volcanic aerosols in the AR4, ‘many’ did freeze in 2000, though once again, I believe Model E did not. I think they froze later– around 2003 or so. That said: many models in the AR4 did not include volcanic aerosols at all; that makes it very difficult to speculate how the variation in aerosols in 2000 mattered– as one ought to two off-setting factors: (a) that those models were not including the tail end of the ‘recovery’ to Pinatubo — which might be small but still not zero– and (b)also did not include the ‘cooling’ effect of newer, but much smaller, eruptions. Nevertheless, it would be interesting to have a listing.
I know someone is going to be telling me I can hunt these down at PCMDI: I prefer not to slog away at PCMDI. What I want is for someone to tell me if someone else has already gone through and at least has information on a ‘yes/no’ froze in 2000 level and/or ‘which year froze’. Or if someone else wants to slog through PCMDI and find out the year any particular group ‘froze’ volcanic aerosols, that would be lovely. This is not a task that requires high technical skills: just time. So if you are curious, and have time, you could look. 🙂 )
The effort is interesting because it is important because the degree to which one ‘ought’ to believe the discrepancy between either AR4 or AR5 models and observations can be ‘explained’ by projections being based on ‘frozen in 2000’ aerosols depends on the fraction of modeling groups that froze volcanic aerosol forcings in their input files when creating runs to actually contributed to the AR4 or AR5. I have no idea what this fraction is.
If “many” froze them means roughly 20% did, then the discrepancy between model mean and runs is difficult to explain by the difference in ‘real’ and ‘modeled’ volcanic aerosols. In contrast, if 80% froze them, we can test that too. We can also dig through and see whether there is any systematic difference between 2000th century trends between models that did ‘freeze’ volcanic aerosols and those that did not. (Assuming some did and some did not, of course.)
I have a few other comments that I could make on this paper. The main one that first comes to me is this:
When finding likely effect of forcings on trends in the 2000’s it strikes me as a bit ambitious to simply do everything relative to the volcanic forcing in 2000. The reason is that the atmosphere does have a response time. So, if one wants to find out the effect incorporating forcings in the lower stratosphere into the recent trends, one ought to know what those were in past years before deciding the effect of any increase in Stratospheric Aerosol Optical Depth (SAOD) during the 2000’s. It appears no AERONET data exists prior to 1995; I’ll take the researchers word that the data are tenuous prior to 2000. But this is a factor we should consider– and possibly one ought to widen the range of possible effect on temperature in that paper. (Perhaps doubling it.)
That said: it’s an interesting exercise, and worth being aware of. It could potentially explain the discrepancy between the model mean and the observed trend. (Which will mean that the discrepancy between a projected model mean trend of “about 0.2 C/decade” existed and still does as opposed to ‘did not exist’.)
For Model E
from ‘CMIP5 historical simulations (1850–2012) with GISS ModelE2 ‘
The treatment is a bit of this- a bit of that (from the POV of interprsting what Ridley might mean.)
So 2000-2005 held at 2000 values. 2006-2010 use Sato obseratins. After 2011-2012 used some small background value.
Lucia,
Paywalled…. ugg. But I suspect there may be some straw clutching going on.
There is a lot of evidence that recent volcanic forcing is historically low, and so temperatures are, if anything, running higher than they would be under ‘average’ volcanic influence. http://i57.tinypic.com/11ca4qf.png (data through 2013) The forcing is assumed to be -23 times AOD@550nm wavelength. The red line is the average volcanic forcing (0.29 watt/M^2) since 1850.
SteveF,
The paper has “definitely good” bits and “maybe … if… ” bits:
1) It’s definitely good that someone went through data and tried to get a better handels on SAOD including stuff in the lower stratosphere rather than just the upper.
2) Once that’s done everyone is going to want an order or magnitude estimate on how much effect the new measurements make on projections. So that’s interesting.
3) I’m not entirely sure about quantified numbers. Their saying “many climate studies”… welll which? Etc. It pretty obvious that one should ask: How might it affect the AR5 projections? Are they in the “many”?
I’m finding stuff like footnote in the AR5 that suggest a variety of volc. aerosol strategies:
Lucia, the essay Blowing Smoke in my new ebook of same name goes into volcanic aerosols in depth, although aimed at a different paper than this new one. VEI is a predictor (partial, since the nature of the eruption as well as its force matters) of whether any aerosol will reach the stratosphere at all. Everything else in the troposphere washes out fairly rapidly (3 months or less).The new Solomon /Santer paper pretends to find onservational evidence that others have measured (e.g. Via LIDAR) and found generally not to exist. Another IN MY OPINION very weak attempt to explain the pause. In reality, their problem is that volcanic activity has not increased from when temperatures were rising from about 1970 to about 1998. Nor has atmospheric opacity changed except for 3 VEI 5/6 eruptions (and a minor amount from a single VEI 4), and that only several months to a couple of years. The actual situation with volcanism and the atmosphere is all laid out in the illustrated essay. There are footnotes to the information sources and several other papers on this, including two previous ones from Solomon and Santer that tried but failed to explain the pause this way.
Don’t know if this is relevant, but Schmidt et al
http://www.nature.com/ngeo/journal/v7/n3/full/ngeo2105.html
apparently tried to explain the model divergence, and one of the pieces they used was external drivers like volcanos. I didn’t read it or look at it in detail, but doesn’t that mean he must have determined which models _already_ include those forcings?
MikeR: He may have. But that doesn’t mean the paper presents the information in sufficient detail for a reader to tell which include the forcings and how much.
To be clear: I can tell which ‘include’ them to some extent. But digging would be required to figure out which did something like specifically ‘freezing’ forcing in 2012. The footnotes in table 12.1 in the AR5 suggest many did not. Or at least that’s how I read things like
This sounds like forcings were not frozen in 2000. Do I know for sure? No.
Also:
This does sound like it might have been ‘frozen’ at a near zero value in ‘future’. Whether thats 2000 or 2005… dunno.
This sounds like set to average not zero value in ‘future’ which suggests not frozen to 2000 value (which was near zero.) Do I know? dunno.
Sounds like NOT frozen in 2000 and never go to 0.
So there is a list of ‘generic’ statements. Some might be ‘frozen’ in 2000. Some not. Digging is required to find out more. I think I’m going to have to dig.
Ask him?
There is a source of stratospheric particles of various kinds that might be worth considering here: rocket exhaust. It is composed
of submicron-micron soot, alumina, and “dust” falling from mesosphere from space debris that “burns up”.