The Volcano Blows! Dealing with Effect of Forcing for Global Climate Change
Yesterday, I announced my prediction of the global mean surface temperature (GMST) based on GISS Land/Ocean data. My prediction based on a very simple phenomenological model of climate with two parameters: time constant τ and inverse heat capacity α. I haven’t knocked all the kinks out of data analysis, but I made the prediction anyway. (This is, after all, a blog, and one does need to predict in January before half the year’s weather has occurred.)
Meanwhile, I made a checklist of things I think I need to do to knock the kinks out of the model. One was to incorporate more temporally refined volcano forcing, and afterwards re-run the computation using monthly temperature data. This should give improved estimates of the two parameters.
I had no idea where to get the volcano data, so I emailed Gavin Schmidt of Real Climate who pointed me to the proper data. Processed the data to created a file with average forcing each month, and plotted. Here it is:
Details
- The ‘Stratospheric Aerosol Optical Thickness’ values were obtained from this ascii file. To estimate the effective forcing, I multiplied by the optical thickness τoptical by -23, as advised by Forcings in GISS Climate Model: Stratospheric Aerosol Optical Thickness
- I used the effective forcings file provided by Gavin Schmidt at Real Climate. All forcings except those due to volcanic eruptions vary fairly smoothly with time. To created a monthly series, I assumed each contribution for the forcing achieved the annual average value at midyear and varied linearly in between.
- I plotted to compare the monthly stratospheric aerosol forcing with the annual averaged values. As expected, the spikes are deeper when I use monthly averages rather than annual averages; this is particularly true for the more recent eruptions, which NASA monitored contemporaneously.
Next: Start processing this along with the monthly GMST temperature data. (I think I many also need to include the possibility of a shift in the zero temperature anomaly in the next round of data processing. After all, the zero point for the temperature anomalies differ in various data sets and are, strictly speaking, arbitrary.)
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5 Responses to “The Volcano Blows! Dealing with Effect of Forcing for Global Climate Change”
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terry(tpguydk) January 18th, 2008 at 6:28 am
What big volcano is that in the 1960s? And, for that matter, between 1900 and 1920? It’s just to satisfy my curiosity—I can guess the others (Krakatoa, El Chichon, Pinatubo)
lucia January 18th, 2008 at 7:24 am
Terry– I did some googling about the ‘63 volcano, because I lived through an eruption in El Salvador in the early 60s. But, evidently, “my” volcano experience isn’t the cause of the ‘63 spike: Agung in Bali blew its top big time in ‘63.
Here’s one page: volcanos USGS
Here’s a page of just large eruptions
I think to matter, the eruption must be both large and spew forth aerosols of some type. So some large eruptions don’t do much because they only result in tons of oozing lava. I have vague recollections about my husband saying all things being equal, equatorial volcanos matter more. (Possibly because we get more sun at the equator, and so they block more sun. If there were a big volcano on the south pole, maybe aerosols would drop out before they blocked much sun? )
Anyway, I didn’t check the namea of all of these, but I’m sure the NASA people know which volcanos they think spewed for the the aerosols. (I’ll eventually be looking them all up. I’m trying to process some data right now.)
FWIW, I looked quickly for the minima and the years are:
1884, 1891, 1896, 1903, 1912, 1963, 1968, 1975, 1982, 1991.
So, if you want to google big volcanos eruptions, those are the years to look for.
terry(tpguydk) January 18th, 2008 at 9:58 am
cool! thanks for this data, lucia!
your husband is right. Equatorial volcanos do “matter more” because air rises at the equator and sinks at the poles, which is an oversimplification of the process I think but it is true to a large extent. That being said, 1912 is Katmai/Novarupta in Alaska, I remember reading about it in a geology course I took. I’ll look up the other ones.
Are Five Year Long Downtrends Consistent With +2C/century? | The Blackboard March 17th, 2008 at 1:07 pm
[...] In case you think it’s a coincidence, or I’m exaggerating the effect of volcanic eruptions, here is a graph showing how much anomalous forcing is caused by volcanic eruptions. I created it when comparing the annual average value to monthly values. [...]
What Period Should We Use to Compare Uncertainty Bands. | The Blackboard May 21st, 2008 at 1:58 pm
[...] It happens, that I have posted graphs showing estimates of stratospheric volcanic eruptoins veiling of the earth and causing cooling. In one post, I included a graph from Robok showing veiling as estimated by Mitchel, in another I showed a graph showing the forcings as used by NASA GISS. [...]