Volcanoes Erupt Again

Guest Post by Willis Eschenbach

I see that Susan Solomon and her climate police have rounded up the usual suspects, which in this case are volcanic eruptions, in their desperation to explain the so-called “pause” in global warming that’s stretching towards two decades now. Their problem is that for a long while the climate alarmists have been shouting about about TWO DEGREES! PREPARE FOR TWO DEGREES OF DOOM BY 2100!! But to warm two degrees by 2100, you have to warm at 0.2°C per decade, or around 0.4°C during “the pause” … so they are now left trying to explain a missing warming that’s two-thirds of the 20th century warming of 0.6°C. One hates to confess to schadenfreude, but I’m sworn to honesty in these pages … 

In any case, I got to thinking about their explanation that it wuz the volcanoes what done it, guv’nor, honest it wuz, and I did something I’d never thought to do. I calculated how much actual loss of solar energy occurs when there is a volcanic eruption. I did this by using the Mauna Loa atmospheric transmission data. These observations record what percentage of the solar energy is being absorbed by the atmosphere above the observatory. I multiplied this absorption percentage by the 24/7 average amount of solar energy (after albedo) which strikes Mauna Loa, which turns out to be 287 W/m2. (As you’d expect from their tropical location, this is larger than the global average of 240 W/m2 of sunlight after albedo). Figure 1 shows that result, which was a surprise to me:

Figure 1. Amount of solar energy absorbed by the atmosphere above Mauna Loa, Hawaii. Data Source

Now, before I discuss the surprising aspects of this graph, let me note that the Mauna Loa data very sensitively measures the effect of volcanic eruptions. Even small volcanoes show up in the record, and the big volcanoes are clearly visible. Given that … is there anyone out there foolish enough to buy the Susan Solomon explanation that the cause of the pause can be found in the volcanoes? I guess there must be people like that, the claim has been uncritically accepted in far too many circles, but really … who ya gonna trust? Susan Solomon, or your own lying eyes?

I’ll return to the question of the pause, but first let me talk of surprises. The thing that was surprising to me in this was the size of the loss of solar energy. The El Chichón and Pinatubo eruptions reduced the downwelling solar energy by maxima of forty and thirty watts per square metre at Mauna Loa. This is a huge reduction, much more than I would have guessed.

One measure of how much energy is lost is the total loss until such time as the absorption returns to its pre-eruption value. It turns out that in the case of both El Chichon and Pinatubo, the net loss of solar energy was about 450 watt-months per square metre. The loss was spread more widely (5 years) in the case of El Chichon than in the case of Pinatubo (3 years) before it returned to normal.

This means that for the period 1982-1987, Mauna Loa was running at 450 W-months/m2 divided by 60 months equals an average deficit of no less than 7.5 W/m2 of incoming energy over the five-year period … and it’s worse for Pinatubo, since that involved the same total energy but only lasted for three years. So for the three years from 1991-1994, Mauna Loa was running at a whacking great average solar energy deficit of 14 W/m2 …

Now, how much difference did this surprisingly large lack of incoming energy make? According to the IPCC, climate sensitivity is 3° per doubling of CO2, and a doubling of CO2 is a forcing increase of 3.7 W/m2 … and Mauna Loa was running at 14W/m2 shy of normal, that’s almost four doublings of CO2. So according to the IPCC, that kind of a decrease in forcing should have lead to a temperature drop of 11°C … so what actually happened?

Well, we’re in fantastic luck, because the temperature records at Mauna Loa are very good. Here’s what they say (study here):

Figure 2. Mauna Loa temperatures. Vertical red lines show the dates of the El Chichon (March 1982) and Pinatubo (June 1991) Graph from B. D. Malamud et al.: Temperature trends at the Mauna Loa observatory, Hawaii.

As you can see, despite the large decrease in incoming sunshine, there is absolutely no visible change in either the noon or the midnight temperatures … go figure. What happened from the volcano is nothing at all. No effect.

Now, y’all may recall that I have argued over and over against the concept of climate sensitivity. This is the widely-accepted hypothesis that the changes in temperature are determined by the changes in forcing. I’m a climate heretic—I don’t think climate works that way at all.

In particular, despite widespread skepticism, I have persisted in saying that volcanoes basically don’t do jack in the way of affecting the global temperature. I can finally demonstrate that unequivocally because I’ve stumbled across a very well-documented and precisely measured natural experiment.

At Mauna Loa we have a clear example of a measured decrease of 7 W/m2 in the average incoming solar energy for five years (1982-1987), and a decrease of 14 W/m2 for 3 years (1991-1994) … and there is absolutely no sign of either forcing decrease in the temperature record of the very place where the solar decrease was measured.

As I’ve said over and over, the emergent phenomena of the climate system respond instantly (hours or days, not months or years) to any change in the temperature. If it cools, we rapidly get a drop in albedo, which allows in more sun, and the balance is restored. If it warms, very soon thereafter albedo increases, we get less sun, and again the balance is restored. So while I was surprised by the size of the drop in downwelling solar energy, I was not surprised that we can’t find the signal of the solar drop in the temperature records.

Setting that question aside, let me return to the “pause”. Solomon et al. used the Vernier aerosol optical depth (AOD) dataset, which is available here. It is a calculated global dataset based on various observations. The explanation of the calculations is here. If anything, there is less recent variation in that dataset than in the Mauna Loa dataset. Figure 3 compares the two over the period of the satellite temperature observations.

Figure 3. Compares the negative of the aerosol optical depth with the Mauna Loa transmissivity data. Mauna Loa data rescaled to match AOD data for comparison purposes only. 

So it doesn’t much matter which one we use to compare to the temperature data. Let me use the Mauna Loa transmissivity data, since the native units are in the same range as the temperature anomaly. Figure 4 shows the comparison of the Mauna Loa transmission data with the UAH MSU satellite-based lower troposphere temperature data:

Figure 4. Satellite lower tropospheric temperatures (blue) and Mauna Loa solar transmission (black line). Note that while Pinatubo happened at the start of a temperature drop, El Chichon happened at the start of a temperature rise. In addition, in neither case are the rise or the drop notable—the drop 1988-1989 or 2007-2009 is indistinguishable from the post-Pinatubo drop.

Finally, lest some folks claim that because Mauna Loa is in the northern hemisphere we can’t compare it to the global temperature changes, Figure 5 shows the comparison of the Mauna Loa with the northern hemisphere temperatures:

Like I said … I know there must be folks out there that can be convinced that the changes in the black line, the known effects of the volcanoes, are the reason that there is a “pause” in the global temperatures … I’m not one of them.

CONCLUSIONS:

• I may never find better evidence of the lack of connection between changes in forcing and changes in temperature than the measured large drop in solar forcing and the total lack of corresponding temperature change at Mauna Loa. It is a superb natural experiment, and has been very precisely measured for over half a century. It provides strong evidence in favor of my hypothesis that the temperature is controlled by emergent phenomena, and has very little to do with forcing.

• The change in forcing from the 21st century volcanoes is trivially small in both the Vernier AOD dataset and the Mauna Loa dataset. It is far too small to have the effect that they are claiming. I don’t care what the climate models told Solomon et al., the post-2000 changes in volcanic forcing are meaningless.

• My oft-repeated claims about the lack of effect of volcanoes on the global temperature are completely borne out by these results.

My regards to all,

w.

AS ALWAYS: If you disagree with me or anyone, please quote the words you disagree with. That way we can all know exactly what it is you have a problem with. Vague handwaving claims go nowhere.

MAUNA LOA TRANSMISSION DATA: From their website

The “apparent” transmission, or transmission ratio (Ellis & Pueschel, Science, 1971), is derived from broadband (0.3 to 2.8um) direct solar irradiance observations at the Mauna Loa Observatory (19.533 ° N, 155.578 ° W, elev. 3.4 km) in Hawaii. Data are for clear-sky mornings between solar elevations of 11.3 and 30 degrees.