Volcanoes: Active, Inactive, and Retroactive

Guest Post by Willis Eschenbach

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 other alia to be precise. I agree that it’s an interesting and important paper, mostly because of who the authors are. However, I have to say there were some parts that I couldn’t fit together. Here’s their figure S2, showing the radiative forcing since 1850:

otto figure S2Figure 1. Forcings used in Otto 2013. Grey lines represent possible variations based on a monte carlo analysis of the errors in the parts that make up the total radiative forcing. They divide the total forcings into greenhouse gases (GHGs), volcanoes and solar, and a “residual” forcing which is assumed to be mostly aerosols. The estimated errors in these are used to generate a host of possible realizations, shown in gray above.

Now, when I saw that, I just rolled my eyes. Here we go again with the volcanoes, I thought.

See those big dips in the black line above? Those are reckoned to be the change in forcing due to volcanic eruptions. What happens is that the volcanoes spew light-colored aerosols into the stratosphere. This reflects more sunlight, and thus reduces the forcing in a measurable manner. As you can see, the larger volcanoes make a very significant change in the forcing. So I set out once again to see if the claimed temperature change due to the volcanic forcing held up in the real world.

But as often happens, before getting to the volcanoes I got sidetractored, this time by discovering that Otto et al. to the sixteenth power are not discussing eruptions from ordinary active volcanoes . Oh, no indeed.

Otto and his hexadecagonic cohort are discussing retroactive volcanoes.

Here’s why I say that. I digitized the Otto data. Figure 2 shows the results, including the dates of the larger eruptions which are responsible for the large dips in the amount of sunlight reaching the earth:

retroactive volcanoes per otto 2013Figure 2. Forcings from the Otto 2013 paper, along with the volcanoes associated with each of the large dips in forcing. The earliest eruption is assumed to be Cotopaxi because of the very large dust veil index associated with that eruption.

Here’s the oddity I noticed. As you can see, not only are the volcanoes associated with the large drops in forcing. They also apparently are able to cause the temperatures to drop during the year before they occur … in other words, they cool retroactively. In each case, there’s a drop in forcing, not only in the year of the eruption, but in the previous year as well …

Here’s the likely reason why the retroactive drop in forcing occurs. It’s not a timing error in the data. Figure 3 shows the Otto forcing data compared to the GISS forcing data.

volcanoes and forcing giss and ottoFigure 3. Forcings from the Otto paper compared with the GISS forcings.

Note that in both the GISS and the Otto forcings, the lowest points after the eruptions coincide perfectly, so it’s not from timing … but the years immediately before the eruptions are quite different. Rather than the forcing falling in the year prior to the eruption as the Otto data does, the GISS forcing remains high until the actual year of the eruption. Additionally, the size of the GISS volcanic forcings is about twice the size of the Otto volcanic forcings.

Now, the paper says that they are using the average model forcings from the Forster paper that I discussed recently. However, the Forster forcings look much like the GISS forcing shown above, with large volcanic excursions. In addition, the Forster results are not retroactive—as with the GISS data, the Forster forcing drops in the year of the volcano, and not the previous year as in the Otto forcings.

I suspect (and let me emphasize suspect) that what has happened is that either rashly or quite possibly inadvertently, someone has slightly smoothed the Forster forcing data. The difference is subtle, I didn’t notice myself until I looked at Figure 2 and went whaa?

I say it’s smoothed because if I use a simple 3-year centered moving average on the Forster data, I get something very near to the Otto forcing data. Such a smoothing makes the volcanic drops “retroactive”, since the centered moving average includes the following year’s data. Figure 4 shows those results.

volcanoes and forcing forster dataFigure 4. The Forster (blue) and Otto (red) forcing data, along with a smoothed version of the Forster data. The smoothing is done using a simple centered 3-year moving average. The years prior to the eruptions of Krakatoa (orange diamond) and Pinatubo (red squares) are highlighted in both datasets to show the “retroactive” effect of the smoothing on the previous year’s data. The Forster data has a 0.3 W/m2 trend added to match the Otto data, as described in the Otto paper SOI.

Note how similar the simple smooth of the Forster data is to the Otto data. This is the only explanation I can think of for the retroactive nature of the Otto volcanoes.

If the Otto data is indeed incorrect, that could make a large difference in their results. It’s difficult to say, but since the size of the volcanic excursions in forcing have been cut in half in the Otto data, it seems like it might be important. In addition, when you are using a forcing time series dataset for predicting (hind casting or forecasting) results, it’s a lot easier to forecast next years temperature data when your forcing data for this year contains some information about next year … using a smoothed dataset as input to another calculation is almost always a huge mistake.

For me, the best thing about the Otto paper was that via the Forster paper, it provided the data and the impetus to write my last post on climate sensitivity. It also provided an insight into how to analyze the effects of the volcanoes on the historical data versus the claims of the models regarding the volcanic effects … stay tuned, my new findings in that regard are the subject of my next post, interesting stuff.

Best wishes to all,

w.

DATA

Dust veil index

GISS Forcings

Otto and Forster Forcings

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Dave

Oops, they’ll take care of that. Just a shift here and a shift there and voila!

Too many cooks…
This is why looking really hard at the data, all the data, is so important.
Thanks Willis.

kadaka (KD Knoebel)

Greg Goodman will come by to explain how Willis got the volcano forcings all screwed up in 4… 3… 2….

I haven’t read the paper. Did they estimate the magnitude of each eruption and use those values in their model or did they adjust the values to fit the Hadcrut data? Is the Hadcrut data a running average?

Reich.Eschhaus

Why don’t you ask Nic?

eo

A drop in temperature and forcing is an indication a large volcanic eruption is underway. Is the current temperature drop in the northern hemisphere a warning of a impending large volcanic eruption? Yellowstone national park ?

Nice find, Willis. The forcings are anticipating the volcano–a pre-active forcing.

Toto

Here is a study of how the weather was affected in the area right after Mount Saint Helens blew up in 1980. “Interestingly, this eruption had virtually no climatic effects.”
http://cliffmass.blogspot.com/2013/05/weather-impacts-of-mount-saint-helens.html
Weather Impacts of the Mount Saint Helens Eruption
They show that the eruption caused cooling during the day and warming during the night for a brief time period.
The full paper is here:
http://journals.ametsoc.org/doi/pdf/10.1175/1520-0493%281982%29110%3C0614%3ATSTIOT%3E2.0.CO%3B2

Pamela Gray

Hey…animals can detect an earthquake before humans can. So it could happen. In this “Gaia smokes pot” age, Maria is sentient!

Pamela Gray

The Willamette Valley can rain the feathers off a duck. So I would hazard a guess that whatever Mt. St. Helens coughed up ended up in the water treatment facilities PDQ.

BarryW

I’ve often thought there must be a case where a trailing smoothing is better than one that’s symmetric about the point being smoothed. I seems like this a case where that might be valid. At least you wouldn’t get the event starting before it happened (you would delay it I guess which might be just as bad), but then is smoothing even appropriate for something like this?

There is no reason why….seven volcanoes would lie….
maybe….they just wanted to put some warts on Mann’s hockey stick.

Arizona CJ

Oh come on, Willis… you’re completely ignoring the possibility of time-traveling volcanic ash!
Seriously though, great sleuthing!
If I might interject a note of further caution; it seems that they have cherry-picked their eruption list. For example, no sign of Askja, a VE5 in 1875, and most glaringly, the VE5+ of Cerro Azul of April 1932, followed a few months later in January of ’33 by Kharimkotan’s VE5. There is no indication of any effects from this on the graph… well, assuming, that is, that we exclude the downward blip in 1920 through 1921. (Retrovolcanos in action?)

climatereason

willis
there was a big fuss about the real effects of a massive eruption in 1258AD
“Reconstructions of past climate on the basis of tree rings may miss the short-lived cooling events caused by volcanic eruptions, reports a paper published online this week in Nature Geoscience. The work suggests that, in particular, the tree-ring-based reconstructions may be missing cooling linked to the ad 1258-1259 eruption of an unidentified volcano. Tree-ring chronologies are often collected from regions that are at or near the minimum temperature for tree growth. Michael Mann and colleagues used numerical simulations of climate and tree growth to show that when temperatures fall abruptly for one or two growing seasons, trees in these regions undergo little or no growth. The resultant lack of a tree ring corresponding to the period of cooling thus masks the climate event in subsequent reconstructions. These results show that a 2 °C cooling associated with the ad 1258-1259 eruption (as indicated by climate models) cannot be excluded by existing tree-ring data.
http://www.natureasia.com/en/research/highlight/1558
It would be very interesting if you could digitise the Mann hockey stick to see if there is a retroactive effect in the 1258 incident. It was so large it probably had an effect two years before it blew
tonyb

Brent Walker

We should be worried by this paper. It looks to me as if the data has been cherry picked.There were at least fifty significant eruptions during this period, many with a volcanic explosive index greater than the volcanoes included in the analysis. Their effect on climate is determined by a number of factors: how much SO2 is emitted, how high it is emitted, how long the eruption lasted, the latitude of the volcano (because the higher the latitude the closer the stratosphere is to ground level), the height of the volcano (where it erupts if the new eruption is lower than the peak), etc.
For example: Cotopaxi erupted at least once each year for the whole of the 1850’s decade. So why was only the 1855 eruption shown?.
Probably the most important volcanic eruption for the Northern Hemisphere in the 1750-1850 period was the Laki fissure of Grimsvotn in 1783/84. It was only a VE4 eruption but it lasted 8 months and put much more SO2 into the stratosphere than Tambora in 1815, which was a VE7 but only lasted about 10 days. However Tambora is in the tropics and so affected the climate in both hemispheres.
Finally don’t forget volcanoes generally emit huge quantities of CO2. Surely volcanic emissions of CO2 must have the same effect as CO2 emissions from burning coal.

RoHa

Retroactive volcanoes?
We’re doomed!

ruvfsy

Smoothing.

thingodonta

The volcano takes heat out of the atmosphere in order to build up a bigger burst. /sarc.
For those interested, there is a book called Melting the Earth which looks at historical explanations for volcanism going back thousands of years. It’s an interesting look at human psychology and the development of scientific ideas-it was a VERY long time before humans got anywhere near right about what causes volcanos in the first place. The same goes for mountain ranges, earthquakes, and most other things in the earth sciences. Humans just don’t seem very good at picking the right ideas about how the earth operates, and it doesn’t help that the earth is very complex in the first place. ‘Trust us’ climate scientists should take notice, the earth sciences have a very long history of premature, ill-conceived, model-based, politically compromised and plain wrong ideas, which are very often overturned by empirical data, which only becomes available later. History seems to be repeating itself with the modern AGW movement.

Willis, if you go back and look at the simulations that start in 850, you’ll find other interesting things WRT volcanoes.

Master_Of_Puppets

“Note that in both the GISS and the Otto forcings, the lowest points after the eruptions coincide perfectly, so it’s not from timing”
Oh yes. They (the models, HADCUT GISS el al. ) are ‘adjusted’ at least monthly to agree. Yes the ‘Hand Of Mann’ is quite apparent.
A ‘Sea Change’ to the ‘IPCC’ ? No ! The real sea change will occur on the death of Hansen, Jones, Schmidt and Trendberth and a few other misanthropes like the Emperor of the IPCC.
I left out Mann ! Yes ! I want Mann to stay alive well into 104 at least and by electrical-mechanical methods (I’ll buy those for him).
No holding breath till blue from me, this is a battle of attrition and time is not on the side of Hansen, Jones, Schmidt (multiple physiological afflictions and addictions) and Trendberth.
Lovely graves all.

John Parsons

Willis, You say,”…since the size of the volcanic excursions in forcing have been cut in half in the Otto data…”
That being the case, what would you estimate the effect to be on Otto, et al’s climate sensitivity estimates? JP

Neo

So we can now credit Otto with discovering a volcano predictor ?

Mark Bofill

Never underestimate the power of the great god Vulcan; for lo! His retroactive volcanoes spew aerosols across the very fabric of Time!

I have to echo Arizona CJ sentiment about the missing eruptions. Another item that is sort of a burr in my saddle is Carbonyl Sulfide (OCS). It’s long lived in the atmosphere (I’ve read up to 9 year life span) until it gets up into 200nm – 270nm light where it dissociates. Once it does that, it can become a sulfate and participate in the aerosol layer screening games. I don’t have anything to back it up, but I think that this could be a mechanism where the more sedate flood basalt events (Eldga, Laki, Tolbachik, etc.) could provide an influence on the aerosol index. With it’s long stay time, it can be wafted up the edge of the troposphere between the large scale circulation cells. If it crosses the tropopause, there is plenty of hard UV there to dissociate the molecule. And, as you probably know, the latitudes of the general upward circulation are 0°, and 60°. Within a few hundred miles of 60°N are the Kamchatka volcanoes and Icelandic volcanoes. I have no idea of what percentage of the sulfur budget for a volcano is in the form of OCS. Usually you only find data on H2S and SO2.
Just a thought. Your mileage may vary.

Bill Illis

Obviously, one should not be using any kind of multi-year smoothing functions for the volcano forcing.
It is just a matter of a few weeks before the stratosphere responds to the volcanoes, maybe another few weeks before the surface temperatures start falling (less than would be expected I might add).
With all these lags and delayed forcing/temperature responses, climate science needs to quit smoothing the factors beyond the timelines which they actually operate on.
GHGs operate on the order of hours, water vapor feedback has to be on the order of days, cloud optical depth feedback is also on the order of days, volcanoes are weeks (extending out to 3 years before the aerosols dissapate), albedo changes from ice melt might be decades to 1000s of years but all these impacts must have the time resolution that they operate on.

MattA

How is the total radiative forceing found.
1. Is this solar plus gh radiation (in which case this graph clearly shows an anthopogenic signal).
2. Solar only (in which case it shows a solar signal).
3. Something else???
help appreciated

richard verney

Willis
I am pleased to see that you have posted this article, it is an interesting read.
You open up stating: “Here’s their figure S2, showing the radiative forcing since 1850: Now, when I saw that, I just rolled my eyes. Here we go again with the volcanoes, I thought.” This was my reaction, and it appeared to me that something was not quite right. Unfortunately, I was rather lazy and I respect your analytical skills so I commented on your Model Climate Sensitivity Calculated Directly From Model Results article (richard verney says: May 22, 2013 at 2:39 am):–
“Willis
It would be useful to list the major volcanic eruptions since 1850 and the claimed negative feedback with respect to each.
Does anyone really think that Pinatubo (1991) had the same impact as Krakatoa (1883). Without digitalizing, to my unaided eye, the negative forcings appear similar.
Does anyone really have any confidence in the temperatures? Surely few people hold the view that today is about 0.6degC warmer than it was in the 1930s, or for that matter some 0.8degC warmer than the 1880s. I would have tjought that within the margins error, it is difficult to conclude that temperatures today today truly are warmer than those either in the 1930s or 1880s such that the present temperature record does not show the full extent of variability in past temperatures…..”
Thanks for dealing with my enquiry. Strange goings on indeed. I do consider that it is time for a detailed analysis of the effects of volcanoes on the temperature record/model outputs is required since I consider this an area where there is the potential for much fudging to try and assist back tuning.

Effect of land volcanoes on the atmosphere is temporary and minor except for the strongest eruptions.
Effect of submarine volcanic ‘slow eruptions’ in three critical areas (Arctic, Aleutian archipelago and Solomon Islands) in form of an ocean currents disturbance, may be far longer lasting and far more critical to the climate change.

Robin Michaels

I find it astonishing that anyone would use a time-symmetric filter for smoothing data to be used like this, precisely because of this effect.
If you HAVE to smooth data then using a backwards-only Savitsky-Golay filter would do the trick without introducing any forward-looking information content (see, for example, Numerical Recipes in C++, 3rd Ed. for details on constructing SG filters).
There is little excuse for such laziness of analysis, other, perhaps, than ignorance, which isn’t much of as excuse.

Greg Goodman

This seems pretty obviously to be a filter as Willis suggests. There is absolutely no reason to smooth volcanic forcing data so I don’t know why anyone would.
The question then is does it “matter”.
The area under the graph (the integral) should be the same in both cases, so it’s not going to change the energy in.
Does it make that resulting temperatures “look” more realistic. Possibly.
http://climategrog.wordpress.com/?attachment_id=258
If we look at the rate of change of CO2 at Mauna Loa as here (or other data such as SST , AO index ) we see that other climate variables drop BEFORE eruptions. This is purely coincidental but leads to a false attribution.
Now if modellers start spreading volcanic forcings back in time by smoothing them the results will correlate better with climate data that show variations prior to eruption that are nothing to do with volcanism.
This will lead to a spurious impression that the mode is somehow “capturing” real climate variation and correctly modelling the effect of volcanoes.
Since volcanoes are the pillar on which rests the exaggeration of CO2 forcing, making it look like the models fit the data better than they would if they did not probably IS significant.
Now we should always assume good faith so we should probably conclude that someone chose to smooth the volcanic data for no good reason , thus degrading the accuracy of the model but fortuitously this made the model output correlate better with the real climate data which was dropping before the eruption for other reasons.
The result of this unfortunate error is to make it look like the volcanic forcing is more accurate than it is which in turn supports pumping up CO2 with parametrised feedbacks.
Since that was the “expected” result anyway , this will not be a visible problem to the authors.

richard verney

Greg Goodman says:
May 23, 2013 at 1:22 am
“…Now if modellers start spreading volcanic forcings back in time by smoothing them the results will correlate better with climate data that show variations prior to eruption that are nothing to do with volcanism.
This will lead to a spurious impression that the mode is somehow “capturing” real climate variation and correctly modelling the effect of volcanoes.
Since volcanoes are the pillar on which rests the exaggeration of CO2 forcing, making it look like the models fit the data better than they would if they did not probably IS significant…”
//////////////////////////////////////////////////////////////
This is exactly my concern as noted in my post of 10:20pm.
I am particularly concerned since do we really have reliable quantative data for any volcano eruption, let alone those before say the late 1970s?
How were we measuring what quantity of gases, aerosls and the like were emitted, at what height did these emissions take place, what were the jet streams at the relevant time etc.
The potential for fudging is simply enormous since the required data simply does not exist. All we can do is talk in generalties such as Krakatoa was a larger eruption thann Novarupta which in turn was larger than Pinatubo.
Further, how many volcanoes of note are simply excluded from the record (cannot be seen in the record), perhaps because if they were to be included then discrepancies would become apparent.
I really do consider that a summary of every major volcano eruption since 1850 should be listed with the ‘guestimates’ of the contents of the eruptions etc. I consider that a further review of the applied forcings in the light of that summary should be conducted.

Greg Goodman

“The potential for fudging is simply enormous since the required data simply does not exist.”
Indeed, all guestimates of how much of what got thrown how far is real back of envelop stuff.
However, what really needs closer examination is where there is any real evidence of a permanent negative shift in temperature after one of these eruptions. Every time I look at this, all I find is a not so certainly attributable negative glitch and NO permanent offset.
There has to be some radiation forcing during the time the ejections are in the atmosphere but I don’t see any evidence of a lasting effect. This implies that climate feedbacks correct for the perturbation.
Willis has already suggested a mechanism exists in tropical storms.

johnmarshall

Would not the eruption latitude also make a difference as would hemisphere. There is little mixing between hemispheres and the more polar the eruption the less insolation would be reduced by the SO2.

Greg Goodman

Willis has already suggested a mechanism exists in tropical storms. …
Tropical storms as emergent phenomena are a negative feedback with it’s own internal positive feedback (making it a more and more powerful negative f/b). These are fast responding (hourly) phenomena that reduce local hotspots.
These storms are too small-scale to be reproduced by climate models. So instead of the basic physics built into the model producing the feedback, parameters are guessed and plugged into the models as an inputs.
Now although TS are local and fast they can also provide a correction for a perturbation like a tropical eruption.
If waters are cooler there will be less local hotspots that set the local conditions that trigger a storm (and vice versa). This will be a reaction to generally cooler surface conditions and thus will react to annual or inter-annual changes in SST, not just hourly local conditions.
Now such a mechanism will not simply act as a simple negative feedback that will compensate for the lack of insolation , restoring equilibrium energy balance, and leaving a new lower equilibrium temperature. That is what the model behaviours suggest happens.
What TS feedback will do is ensure a return to the _previous_ equilibrium SST. This is a stronger response than a simple linear negative feedback. They can do this because of the internal positive feedback that makes them into NON-linear negative feedbacks.
I think this is what Willis has been trying to get over with his “governor” concept.
I have had trouble getting his point because of his insistence that they are “not feedbacks” and the imprecision of the term “governor”.
I think this description of TS feedback , which could be modelled regionally on a smaller scale than current GCMs, would better fit the real climate data than the permanent temperature offset produced by current modelling efforts.
It is not so much the volcanic forcing that is wrong but the _assumed_ climate response.

Chris Wright

Most likely this strange phenomenon is caused by bad statistical practices, something not unknown in climate science.
But let’s suppose for a moment that climate responses can indeed occur in the year preceding a major eruption.
One possible explanation did occur to me. Is it possible that there is a global increase in volcanic activity during the year running up to a major eruption? If so, then the climate responses could be caused by a general, but small, increase in global volcanic activity. It would be the equivalent of playing the overture before the main opera.
Chris

Did the eruption of the volcanoes in Iceland in 2010 not have any impact at all? There doesn’t seem to be anything showing on any of the graphs.

Greg Goodman

No, I think it is clear enough from that plot that this is the same data filtered with a 5y running mean. (Running mean because of the way it fails to follow in 1905 and 1960; 5y because of the width of the feature where it fails.)

Greg Goodman

Philip Aggrey says:
Did the eruption of the volcanoes in Iceland in 2010 not have any impact at all? There doesn’t seem to be anything showing on any of the graphs.
No. too small and too high latitude.

Paul Vaughan

@ Greg Goodman
The degree of coherence between volcanic & climate indices suggests coupling. A mathematical analogy is the balance of wheel rotation acceleration across a differential with turning, but here there are multiple wheels running off each axle and the turning is in more than 2 dimensions. The universal constraints are what matter globally and they can be derived. Combining points made by Bill Illis (May 22, 2013 at 9:03 pm) with points you’ve made about false mainstream assumptions, it looks to me like we potentially have roots of convergent thinking …but there’s a big However: at some timescales the coupling most certainly does not have the appearance of unidirectionality — that’s where I see much of the commentary at WUWT about volcano-climate relations being at odds with multivariate observational records. The data clearly suggest an external governor of both volcanism & climate indices. This isn’t a point I would debate. Rather it’s a point I assert.

Greg Goodman

Willis, I’ve just seen the caption on your figure 4
The smoothing is done using a simple centered 3-year moving average
Try 5 year and I’ll bet your bang on.

Greg Goodman

“your” illiterate Goodman !

I tried to find good volcano data on line, and didn’t, as someone already posted, lots of big volcano’s (on eruption scale) don’t seem to show up in the temp data, where smaller scale ones do. Though I do think some of it is where the volcano is. I think part of it is Global effect vs a more regional effect.

Greg Goodman

Paul Vaughan says: The degree of coherence between volcanic & climate indices suggests coupling….The data clearly suggest an external governor of both volcanism & climate indices. This isn’t a point I would debate. Rather it’s a point I assert.
Could you be more specific about where this ‘coherence’ can be found?
My comments above are based on looking at annual to inter-annual scale. That is not necessarily at odds with what you are suggesting which would presumably be on inter-decadal scales.
If you are aware of any short term coherence I would also be very interested as to where this can be seen.

beng

Warmist strategy:
1. Play the arctic-ice-card
2. Play the volcano-card
3. Play the aerosol-card
4. Play the what-about-the-grandchildren-card
5. Play the mother-earth-card

Gary Pearse

Pamela Gray says:
May 22, 2013 at 6:04 pm
“Hey…animals can detect an earthquake before humans can. ”
This, and the often reported high pitched sound ahead of an earth quake. The shock wave (sound wave in rock) travels some 5000ft/second and would be felt and heard. The only thing I can think of that could get to one’s ears quicker would be electromagnetic. I’ve wondered if piezoelectric discharges from quartz in the rocks being strained, resulted in radio waves and surrounding structures acting as a receiver. I’ll probably be up for abuse again at raising this!

Greg Goodman

Paul Vaughan: The data clearly suggest an external governor of both volcanism & climate indices. This isn’t a point I would debate. Rather it’s a point I assert.
I’m quite interested in that line of investigation but I’d be a lot more interested in evidence than assertion. You seem pretty confident about it so I’m sure you’ve got something interesting.
[BTW , I would like to ask you about a comment you made on persistence of 9y cycles and your wavelet analysis, that you made recently if you would contact me http://climategrog.wordpress.com ]

Ulric Lyons

“Here’s the oddity I noticed. As you can see, not only are the volcanoes associated with the large drops in forcing. They also apparently are able to cause the temperatures to drop during the year before they occur … in other words, they cool retroactively.”
It is quite usual that land temperatures are lower in the run up to the events than afterwards:
http://wattsupwiththat.com/2012/07/30/new-data-old-claims-about-volcanoes/#comment-1050905
Also, what is the evidence for a large eruption at Cotopaxi in 1855?:
http://www.volcanolive.com/cotopaxi.html

cd

Well that is that sewn up. What are the reviewers doing? Shows you how flawed the peer reviewed process is. Obvious but takes a sharp eye to see it.

Greg Goodman

I suspect this is rather at the level of a knit pick than a grave error that should have been spotted by review process.
Perhaps Willis could plot the difference between the unfiltered data and the 5y smoothed version so we can see directly how big this is. The spread before Mt Agung in 1963 was because of other activity apparently not the filtering.

Deconvolving components of times series data is model dependent, so one should try different models to get an estimate of the model systematic errors [biases] and included this in the overall uncertainty.