Guest Post by Willis Eschenbach
Inspired by Richard Keen’s interesting WUWT post on using eclipses to determine the clarity of the atmosphere, I went to the website of the Hawaiian Mauna Loa Observatory. They have some very fascinating datasets. One of them is a measurement of direct solar radiation, minute by minute, since about 1980.
I thought that I could use that dataset to determine the clarity of the atmosphere by looking at the maximum downwelling solar energy on a month by month basis. I’ve described my method of extracting the maximum solar energy from the minute by minute data in the appendix for those interested.
Now, according to Dr. Keen, the air is cleaner now than it’s been in a while:
“Based on the color and brightness of recent eclipses, we can say that Earth’s stratosphere is as clear as it has been in decades. There are very few volcanic aerosols up there,” he explains.
Now, the Mauna Loa Observatory (“MLO”) is a great place for taking measurements of a variety of things. Located at an elevation of 11,135 feet (3,394 m), it is above the low-lying clouds (although not all clouds, it gets snow …).
So what it is measuring is basically what Dr. Keen is measuring, the clarity of the upper part of the troposphere and the stratosphere above that. Any aerosols in the stratosphere will cut down on the maximum amount of sunshine that makes it through. With that as prologue, here is the record of maximum sunlight at MLO.
Figure 1. Maximum sunshine, month by month, at MLO. Vertical colored bars show a 2-year period starting at the eruption dates of the two volcanos, El Chichon and Pinatubo. Values are in watts/metre squared (W/m2).
To start with, we can see that whether Dr. Keen is right on a global basis about the atmosphere being as clear as it has been in decades, it is certainly not true at MLO. Other than after the volcanic eruptions, the clarity of the atmosphere is unchanged since 1980.
However, I had a deeper purpose. My theory, as I have discussed many times, is that the clouds respond to changes in total forcing in such a manner as to oppose them. Given that, I wondered what I could determine about what happens at MLO after big volcanic eruptions of the type shown in Figure 1.
To investigate this question, I looked at the minute by minute maximum solar energy and compared it to the average solar energy. I divided the dataset shown above into two parts—the two 2-year volcanic sections shown as vertical colored bars in Figure 1, and the rest of the data. Figure 2 shows just the part of the dataset that does not contain the eruptions. It lays out both the maximum solar energy and the average solar energy after losses due mostly to clouds.
Figure 2. Average minute-by-minute evolution of the daily maximum and average solar radiation at MLO.
Fresh powder snow in the Hawaiian Islands, what’s not to like? But I digress …
In Figure 2, you can see how the clouds start building up in the morning. By one in the afternoon, they are knocking the instantaneous solar radiation down to about 700 W/m2 from the morning peak about 1,100 W/m2
Now, that’s interesting in itself … but what is more interesting is what happens after a volcanic eruption. Figure three shows the same data as in Figure 2, with the addition of the maximum and average solar energy during the two-year period after each of the volcanic eruptions.
Figure 3. As in Figure 2, with the addition of the maximum and average solar energy values for the two-year period following the eruptions of El Chichon (orange) and Pinatubo (yellow).
For me, the best part of doing scientific research is when I get surprised by my first view of the data. In this case what was surprising was how very similar the results of the two volcanoes were. Despite the difference of the size and location of the two eruptions, both the maximums and the averages of solar radiation after the two eruptions are very nearly identical … go figure. It makes me think that over a certain point, the stratosphere somehow maxes out and doesn’t cut out any more light.
As expected, the maximum energy making it through the upper atmosphere is significantly lower during the volcanic periods. And the averages were smaller as well. The average downwelling total solar radiation (direct and diffuse) was about 24.5 w/m2 less during the volcanic periods than when there were no volcanos.
So … how did my theory fare? My theory predicts that during the volcanic periods, the clouds would rearrange in order to cut out less sunshine, opposing the effects of the volcanic aerosols.
And in fact, this is exactly what they did.
During the time when there were eruptions, the clouds prevented the period from about 11AM to about 4 PM from decreasing at all … in fact, around 1PM the solar input during the volcanic periods was actually larger than during the non-volcano periods.
If the same percentage of sunlight had been cut out by the clouds during the volcanic periods as when there were no volcanos, instead of an observed loss of 24.5 W/m2, we would have expected a loss of 31.3 W/m2. This means that the rearrangement of the clouds increased downwelling solar radiation by about seven W/m2 …
However, despite the countervailing action of the clouds, there was still a significant loss of radiation, about twenty-five watts per square metre (W/m2). How much is 25 W/m2? The IPCC says that a doubling of CO2 will cause an increase of 3.7 W/m2. So to get the 25 W/m2 change seen during the eruptions, the CO2 would have to go from the current 400 ppmv to 43,250 ppmv …
So what difference did the loss of 25 W/m2 of sunshine make to the local temperatures? Now that’s an interesting question, and one which we can answer. The MLO also has taken temperature readings over that period, so we can compare apples to apples. Here is the result:
Curious, huh? On average the MLO site received a full 25 W/m2 less solar radiation for an entire two years, and the temperature was unchanged …
I thought, well, maybe I’m reading things wrong. So I went and got some other temperature records from the Hawaiian Islands, because since MLO received less solar energy, all of Hawaii would have received less solar energy … here are the records that cover the times in question. Some don’t cover all of the volcanic periods, but there’s enough data to see if the eruptions actually affected the temperature.
I looked at other Hawaiian Island stations from the nearest to MLO to the furthest. Here’s the nearest station, Hilo, on the same island as MLO. It doesn’t contain the entire El Chichon record, but there’s enough there to see it didn’t cool down during the first year after the eruption. And there was obviously no effect from Pinatubo.
Next, here’s the record from Molokai, a couple of islands over from MLO … no effect from either eruption on Molokai Temperatures.
Next, Barber’s point on Oahu … same story. No effect.
And finally, at the far end of the Hawaiian Island chain from MLO, here’s Lihue, on Kauaii. Like the other stations, Lihue apparently didn’t get the memo about the 25 W/m2 reduction in solar radiation …
So … why was there no reduction in the temperatures anywhere in the islands from that large a change in forcing? That one is easy to answer …
I don’t know, and I doubt if anyone knows.
After all, in mainstream climate science it is accepted as an article of faith that the reduction in solar energy will and must cause a fall in temperatures … I’m the only person I know of who is heretical enough to seriously question this dogma. See, e.g. my posts called “Volcanic Disruptions” and “Missing The Missing Summer“.
My theory is that the climate system is not like a pool table, where you can calculate from the force applied to the cueball precisely how the other balls will move. Instead of being fixed, the climate system responds to any change in conditions in a number of ways, both seen and unseen. And following both the Constructal Law and Le Chatelier’s Principle, the changes all tend to restore the status quo ante.
But hey, that’s just my explanation why neither Pinatubo nor El Chichon affected Hawaiian temperatures. If someone else has a better idea why a drop in the amount of solar radiation reaching the ground of some 25 W/m2 for two years hasn’t affected the local temperatures, I’m all ears.
[UPDATE] Commenters asked about something I’d considered, whether it was a change in the wind speed that had affected the temperature. It appears that the answer is no.
The difference between eruptions and no eruptions is well within the uncertainty of the data.
A foggy morning here. We’re six miles from the coast, and despite how far it is, the sea breeze brings me the distant sound of the surf and the foghorn on the breakwater … this is assuredly the most audacious and finest planet I’ve ever lived on.
Best wishes to everyone, my thanks to Richard Keen for setting off this train of thought,
AS ALWAYS: I ask that when you comment, you quote the exact words you are referring to. This lets all of us be crystal clear about just who and what you are talking about. Can’t tell you how tired I am of comments that start with “You are …” when I have no clue who the “You” in the sentence refers to. Makes me want to tell the kids to get off my lawn …
DATA: The Hawaii temperatures are from GISS.
The MLO data is available by FTP from here. Big files, because the data is taken every minute.
The MLO meteorological data (temperature, wind, pressure, etc.) is available by FTP from here. There is both minute and hourly data, I used the hourly data for the graph above.
There is also downwelling longwave data there … but unfortunately, it doesn’t start until 1994 … rats …
METHODS: The MLO solar radiation data is in two versions in different years—every three minutes in the early version and every ten minutes more recently. I first converted them all to ten-minute intervals, in part to reduce dataset size.
There are a couple of datasets of interest, the direct solar and the diffuse solar values.
For each month, I calculated the maximum and the average direct solar values for each ten-minute interval. Then, I took the time of the maximum direct solar, and I extracted the diffuse solar for that instant. That gave me the maximum total direct solar, plus the corresponding diffuse solar values.
Once I had the direct and diffuse maximum and average values I divided the datasets into volcano and no volcano sections by removing the data from the date of each eruption and for two years afterward. This let me compare average values for when there were and were not eruptions and their aftermath.