Smaller volcanic eruptions helped slow warming, but deniers at WUWT don't believe it

There was a paper that came out last week that you might have heard about. It was by David Ridley from MIT and a team of others, including some very high profile scientists. What they did was investigate the impact of volcanoes over the past few years. They found that the cooling effect of volcanoes since 2000 could be from 0.05°C up to as much as 0.12 °C, which would be quite a bit more than previously thought.

The Sarychev Peak Volcano, on Matua Island, erupted on June 12, 2009.
Credit: NASA via AGU

There have been other recent studies looking at the impact of volcanoes, including by some of the co-authors of this paper. I've written previously about the article by Gavin Schmidt, Drew Shindell and Kostas Tsigaridis,  in a special edition of Nature Geoscience, "Focus on recent slowdown in global warming". That issue also had an article on volcanoes, two of whose co-authors were also co-authors on the Ridley paper.

This new work was different.

What this team did was look particularly at the impact of volcanic aerosols in the stratosphere below 15 km. From satellite observations, scientists know that above 15 km, volcanic eruptions that are smallish in size can perturb incoming solar radiation. David Ridley found that below 15 km in the stratosphere, there has also been a measurable impact by volcanoes.

Here is Figure 1 from Ridley14, showing different data going back to 1995. Click to enlarge it:

Fig. 1 (a) The SAOD time series for the period 1995 – 2013 for satellite data from Vernier et al. (blue), Sato et al. (orange), AERONET mean, averaged from 30-45°N, (white) with 25th to 75th percentile uncertainty (grey shading), Tsukuba lidar retrievals (36.1°N, 140.1°E) above the tropopause (thick black line) and 15 km (thin black line), and aerosol sonde measurements at Laramie (41°N) above the tropopause (red dots) and 15 km (red crosses). Potentially important equatorial (solid lines) and mid-to-high latitude (dashed lines) volcanic eruptions are shown for Ulawun (Ul), Shiveluch (Sh), Ruang (Ru), Reventador (Re), Manam (Ma), Soufrière Hills (So), Tavurvur (Ta), Kasatochi (Ka), Sarychev (Sa), Eyjafjallajökull (Ey), and Nabro (Na). (b) Ratio of integrated optical depth above the tropopause to that above 15 km from three different lidars and from the in situ observations. The inset contains the same data on a log scale to indicate the ratios greater than 5 that are cropped for clarity on Fig. 1 (a). Source: Ridley14

In the mid to high latitudes the tropopause that divides the troposphere from the stratosphere is not as high as it is in the tropics. Once you get to the poles, the troposphere is only around 8 km in height, and the height increases getting to around 16 km or higher near the equator. So in the mid latitudes, depending on the season, the troposphere can be as low as 8 or 10 km up. This team looked at the lowest regions of the stratosphere and found that there was a "significant contribution" to SAOD from these regions. (Stratospheric aerosol optical depth, or SAOD, is used as a measure of how transparent the stratosphere is.)

Based on observations from lidar retrievals, balloon-borne aerosol sondes, ground-based AERONET sun photometers, and satellite data, we estimate increases in global total SAOD since 2000, together with associated uncertainties. The resulting total estimated volcanic aerosol forcing averaged over the period 2000-2013 is found to be -0.19 ± 0.09 Wm-2, up to 80% larger than the estimate of Solomon et al. [2011].

Here's a paper I came across discussing how lidar is used to estimate aerosols. The rest are probably self-explanatory except perhaps for the AERONET sun photometers. AERONET is AErosol RObotic NETwork, and is an international collaboration described on this NASA website. This was probably the most novel part of the research. The paper describes how that information was used:

To provide an independent estimate of the total column SAOD, we make use of observations from AERONET sun photometers deployed at ground sites worldwide to measure total aerosol optical depth. The widespread coverage of these stations, which span a wide range of elevations, is key to a global analysis. These measurements are often used as calibration for satellite retrievals and are considered to have an aerosol optical depth retrieval error of <0.01 at wavelengths 440 nm and greater [Holben et al., 1998]. While the majority of the aerosol detected is often tropospheric, we will show that the quality of the retrieval, availability of daily data, and the large number of stations providing information make estimation of SAOD feasible. Because the measured SAOD at certain locations and times may be close to the retrieval accuracy of the instrument, we employ a range of methods to ensure data quality and robust results (see Supplement)....

...To ensure that AERONET measurements can provide a reliable estimate of volcanic SAOD, we demonstrate that the timing of the increase in SAOD is significantly correlated with volcanic eruptions, and that the ability to detect volcanic signatures is not significantly affected by station location and sampling periods. We also compare AERONET data to lidar observations.

What the team calculated is that global aerosol forcing from volcanoes since 2000, was -0.19 ± 0.09 Wm-2, which is between 0.05 to 0.12 °C of cooling.

Further reading

There are some very good articles on the work. There's one by Sid Perkins, writing for Science magazine, with another very good article by Leon Clifford on Reporting Climate Science and a press release from AGU. The paper also made news at CBS and Australia's ABC (h/t Billy t Mt).

You might also be interested in this paper by Ryan Neely and co from last year, which suggested something similar. There's an article about it here.

BTW - many thanks to all who gave me a copy of the Ridley paper - David Ridley, Kate Wheeling and Martin L and RP/TB.

From the WUWT comments

WUWT copied and pasted the press release, with no comment from Anthony Watts other than his usual dog-whistle of a "claim" headline (archived here). Here is some of the reaction:

This first comment typifies the reaction from the WUWT illiterati. AP couldn't even get his list correct and wrote:

November 19, 2014 at 2:29 am
What excuse number are we up to now? Anyone keeping track?
Trade winds
No trade winds
Deep ocean heat
Volcanoes
El Niño
Upper atmosphere
Clouds

Greg Goodman indulges in some unconventional thinking and says, no, because he said so,  when Wondering Willis' went nuts about volcanoes - volcanoes cause warming, don'cha know!

November 19, 2014 at 6:00 am (extract)
No, this counter-intuitive volcano argument has already been tried. Excuse no. 8 IIRC ;)
I already commented on this today in Willis’ thread.
[link redacted by Sou]
The haitus is caused by the LACK of volcanoes because it was the volcanoes that caused the late 20th warming in the first place....

Richard G thinks "robust" is a dirty word and says:

November 19, 2014 at 5:44 pm
As soon as I saw the word “robust” I stopped reading. 

This is the sentence he saw that foul word in: To build the best climate models, he said, a more robust monitoring system for stratospheric aerosols will need to be developed. To get to it, he had to read the entire press release. All he missed out on was the abstract.


Karl Compton goes for the "it can't be us" option. Well, Karl, it isn't "us" this time. We didn't cause the volcanoes to erupt, believe it or not.

November 19, 2014 at 11:19 am
Kinda reminds me of the Ozone Hole. It was there when we first had the tools to see it, so it must be our fault, or some kind of flawed logic like that. Blame America first. Then the West. Then technology. Then humanity in general.

mpainter decides that the scientists shouldn't have used actual observations in their calculation.

November 19, 2014 at 2:05 pm
From the abstract:
” Incorporating these estimates into a simple climate model..”
“Estimates” into a climate model= GIGO

johnmarshall writes something about able gulls. Not sure that birds have much to do with global cooling.

November 21, 2014 at 5:39 am
Another government paper written to sway the gullable. Government papers are good at cherry picking but little else.
See my reply to a comment above. 

Catherine Ronconi is a newcomer I think. She wants to work out global average surface temperature in a test tube, figuring there would not be any "enhanced greenhouse effect" in a laboratory.

November 19, 2014 at 2:54 pm
It’s more insidious than a fantasy. It’s adjusted, interpolated, folded, bent, spindled & mutilated.
Granted that if anything GISS is even smellier garbage, but just. Is it better than BEST? Possibly.
If they’re all the best that “climate science” has to offer, then IMO better not to use any global reconstruction at all. Compare to best stations for regions, such as (admittedly adjusted, too) CET or the US or well maintained oceanic island stations, without trying to create a global average sure to be execrable at best and more likely worse than worthless, except, as I say and others have said, to demonstrate how miserably the CO2-based models fail.
IMO a truly valid GASTA, if such a creature be possible, should and would show at most the ECS found in the lab, although feedbacks are probably net negative, so no enhanced GHG effect would be at least as likely.

There are lots more comments that I haven't bothered reading. If you want to, you can read the rest of the protests here.

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Ridley, D. A., S. Solomon, J. E. Barnes, V. D. Burlakov, T. Deshler, S. I. Dolgii, A. B. Herber et al. "Total volcanic stratospheric aerosol optical depths and implications for global climate change." Geophysical Research Letters (2014). DOI: 10.1002/2014GL061541

Gavin A. Schmidt, Drew T. Shindell & Kostas Tsigaridis, "Reconciling warming trends", Nature Geoscience 7, 158–160 (2014) doi:10.1038/ngeo2105

Santer, Benjamin D., Céline Bonfils, Jeffrey F. Painter, Mark D. Zelinka, Carl Mears, Susan Solomon, Gavin A. Schmidt et al. "Volcanic contribution to decadal changes in tropospheric temperature." Nature Geoscience 7, no. 3 (2014): 185-189. doi:10.1038/ngeo2098

Neely, R. R., O. B. Toon, Susan Solomon, J‐P. Vernier, C. Alvarez, J. M. English, K. H. Rosenlof et al. "Recent anthropogenic increases in SO2 from Asia have minimal impact on stratospheric aerosol." Geophysical Research Letters 40, no. 5 (2013): 999-1004. DOI: 10.1002/grl.50263