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.
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Willis: Where did you get your figure for 287 watts/m3 at the equator? Doveryai, no proveryai.
For what its worth, I get similar numbers when I calculate it out.
As another commenter had posted, have you seen this? Very similar work to yours, and one chart in particular is identical to your Fig 4 and 5.
http://notrickszone.com/2013/12/22/disappearing-excuses-aerosols-likely-not-behind-the-warming-pause/
I also agree with your comments about Mosher. He comes across as bit too smug. He needs, IMHO, to expand his rather cryptic comments. Perhaps he is smarter than the rest of us, but unless he explains it better, he does not actually prove he is the brightest crayon in the pack.
Good work. I always enjoy your postings.
How about a link to current volcano eruptions on WUWT?
http://volcano.si.edu/reports_weekly.cfm
http://volcano.oregonstate.edu/aggregator/sources/1
Thanks very much for your answer, Willis. Much appreciated.
First, all volcanoes erupt differently and eject different things because the molten rock inside them is made of different minerals and differing amounts of gases also exist in every volcano. To study only a certain type of eruption-and the amount of particulates and gases they eject and assume that all other volcanic activity is the same is an unscientific and false assumption.
Some kinds of volcanoes erupt violently and suddenly and eject clouds of heat and gas and ash into the air for miles. Some volcanoes erupt sluggishly with a less explosive start and more magma crawl than particulate matter. And every range in between. Some volcanoes simply vent gas constantly into the air so their magma chambers either never erupt (no pressure build up) or take a very long time or experience sudden changes that cause a rapid buildup beyond their ability to vent and they erupt.
I’m currently (as in right now) watching a science show featuring the volcanic activity in Iceland. The vulcanologist just said that the volcanic eruption in 2010 that grounded all of the airplanes for days created a special kind of ASH that was powdery thin and remained airborne for a long time-thus threatening the airplane engines. That ash is caused when an older magma chamber has built up an “enriched gas content” over the years and ICE or WATER is suddenly introduced into the chamber. That ice/steam expansion causes the magma to explode into very tiny, dust like particles as it explodes, and drives those particles HIGH into the atmosphere along with it’s gases.
But other volcanic explosions on the same continent have produced larger, round pebble like matter that doesn’t stay in the air at all.
SO-as I’m watching, they start talking about a volcanic eruption in 1783 of an Icelandic volcano called Laki. Laki literally rained FIRE and ash and magma on it’s location for 8 months. It caused famines and droughts and lowered the temperature of the entire planet. It’s effects are estimated to have killed over 6 MILLION people globally, making it the deadliest eruption in historical times. It is suspected to be the cause of one of the coldest periods during the Little Ice Age.
From wiki-
“On June 8 1783, a fissure with 130 craters opened with phreatomagmatic explosions because of the groundwater interacting with the rising basalt magma. Over a few days the eruptions became less explosive, Strombolian, and later Hawaiian in character, with high rates of lava effusion. This event is rated as 6 on the Volcanic Explosivity Index, but the eight-month emission of sulfuric aerosols resulted in one of the most important climatic and socially repercussive events of the last millennium.”
So having said the above, here’s my point for Willis-it wasn’t so much the fine ash/rock particulates in the air, or the magma, or the cooler earth that affected the climate so much-it was 8 months of outgassing of toxic sulfuric aerosols-which became sulfuric acid rain, and caused sulfuric acid rivers and water, and covered entire countries in sulfuric dust.
So what of ALL the volcanoes, both known and unknown, that don’t “erupt” particulates into the air, or cause ash clouds that block the sun…but literally spew GASES-CO2, Sulfur, methane etc into our atmosphere 24/7. They won’t show up on the atmospheric records as “eruptions”, they don’t get any attention, they aren’t recorded or talked about. What about the submarine volcanoes, they suspect thousands of them, that are either venting OR actually erupting on the ocean floor 24/7 (thermal vents spew HOT water into cold oceans 24 hours a day, for decades that is more than 300 degrees) that no one has profiled or accounted for or measured? Where does all of THAT gas go? The heat? If a handful of land eruptions occurring on 30% of our planet (the surface) can affect our atmosphere, what can both large and small eruptions occurring in greater number, for longer periods of time, on 70% of our planet (the ocean floor) do to it?
When we talk about the energy budget, why does not one study take into account the ENORMOUS amount of energy it takes to move JUST the Icelandic and American tectonic plates away from each other at just the surface a measurable rate of an inch per year, not to mention all the other movement going on, on the ocean floor? Where is that energy coming from? Why isn’t the geothermal energy coming FROM this planet accounted for, and if it is, how do we know the measurement of it is even accurate? How accurately are we “estimating” the energy that is generated on this planet as compared to the energy that “leaves” it?
[ Ferdinand Engelbeen says:
February 24, 2014 at 11:48 pm ]
I can accept as a theory that less light results in less photosynthesis (although light is very, very rarely the most limiting factor), but I’m having serious issues with your alledged light scattering in the stratosphere reducing incident radiation on understory leaves. Was that /sarc/ or a joke?
The El Chichón and Pinatubo eruptions reduced the downwelling solar energy by maxima of forty and thirty watts per square metre at Mauna Loa. Yes, however your chart clearly shows a significant drop in Mauna Loa Temp Anomaly during the following time periods which is similar what happened to the GLOBAL Temp Anomaly. I drop in temp, is a drop in temp no matter how you parse it.
Your conclusion is faulty in that you too broadly applied a regional temperature record of Mauna Loa (a single climate system) to the GAT which is composed of a wide variety of land and sea climate systems, so what you really proved is the homogenizing and buffering effect of the surrounding Pacific Ocean around the Island of Hawaii that smooths out temperature changes. Whereas, if you look at the SH you see no increase in average temp but in the NH you do see an increase from 1980 to 1998. Global Warming isn’t global if it isn’t happening elsewhere on the planet, but by the same token, both SH and NH average temps recorded a DROP after volcanic events.
There is little doubt that Solomon et al is a bad paper. And there is little doubt that the effect of volcanoes is widely exaggerated.
That said, as “proof” that volcanoes have no effect at all this article utterly fails.
And to be clear, that is what it purports to be:
“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.”
Well, no. For several reasons.
To begin with, one cannot demonstrate anything about global temperature by using a dataset of local temperature. On needs something more like a closed system so that one can actually deal with the temperature characteristic of it and the heat flow in and out. So the temperature data for Mauna Loa itself are utterly irrelevant.
Of course, you also purport to demonstrate this finding scales up to the global scale using satellite data and the “eyeball method.” You claim you don’t see the effect. But an inability to see the effect, is not a demonstration that an effect does not exist.
What you could have done, instead, is something that I actually did do: try to isolate an effect if it exists.
If you would like me to explain to you what I did, I can. I walk through the steps in the post itself but it may be difficult to follow. I note that I find there is an effect from volcanoes, contrary to Willis arguing one does not exist at all.
I also note that I find the effect of volcanoes is small, unlike other analysts more inclined toward the other end of the spectrum. Even the largest volcanic eruptions since 1850 have not resulted in peak cooling of global surface temps of even a quarter of a degree.
Claude Grandpey says:
February 25, 2014 at 4:59 am
Thanks, Claude. However, I fear your information is a bit out of date. In fact, since the switch in the PDO, Alaska has been cooling, not warming. See e.g. The First Decade of the New Century: A Cooling Trend for Most of Alaska, where the abstract says:
Regards,
w.
LT says:
February 25, 2014 at 5:23 am
Dear heavens, protect me from the blind … the earth WARMED after El Chichon. Look at Figures 4 & 5 … the clue is, when the blue line goes up it means warming.
w.
Tom G(ologist) says:
February 25, 2014 at 6:18 am
Thanks, Tom. And despite that, at Mauna Loa the reduction in sunshine from El Chichon was greater than from Pinatubo … which proves, if anything, that reduction in sunshine is NOT solely a function of the volume ejected.
w.
Baa Humbug says:
February 25, 2014 at 2:53 am
This is an excellent post as usual.
I wonder if there are any data sets showing the atmospheric pressure around Mauna Loa for the same time period?
I’d suspect we would see high [er than normal] pressure at about the time of the eruptions and back to normal after 3 years (Pinatubo) and 5 years (El Chichon).
Good point – this would be very interesting too compare, do you agree Willis?
kb says:
February 25, 2014 at 7:39 am
Good question. I covered a variety of possibilities in my initial post some years ago entitled “The Thermostat Hypothesis“. See the section called “Gradual Equilibrium Variation and Drift”.
In passing, I’d say that paper, from five years ago, has held up well.
w.
oops meant to say “Good point – this would be very interesting to compare, do you agree Willis?”
rgbatduke says:
February 25, 2014 at 7:52 am
Robert, as always, thank you for your detailed and insightful posting. I was with you until I got to this part:
Actually, we do have a very good idea of how likely this sort of catastrophe is for the real climate—as near as we can tell, it never happened in the last few hundred million years. We haven’t spiraled into a snowball earth, nor have we gone into Venusian heat death, despite large changes in the “forcings”.
You say we shouldn’t kick the climate in the balls because it might go haywire … you mean like say slamming a million-tonne comet into the Gulf of Mexico? Yeah, it blew things right out of the water … then the dust settled and guess what? Right back to the same old same old.
How did we get back there? Well, since the physics governing the time of the daily formation of the cumulus and cumulonimbus hadn’t changed, that meant the equilibrium temperature hadn’t changed, and so we ended up where we started.
As a result, while I agree with you about the complexity of the system, I disagree strongly about its fragility or instability. The only possible way that the planetary temperature could stay so stable (or recently, stay so bi-stable) for hundreds of millions of years is if there is a strong, robust, quick-recovering, disaster-resistant thermoregulatory system with a temperature based threshold … and by good fortune, that’s exactly what we have. The global temperature is a function of the physics of wind and wave and cloud and positions of the continents, it has little to do with changes in forcing … as the Mauna Loa record clearly shows. Clear-sky solar forcing dropped greatly all across the Pacific … but the temperature didn’t drop at all. Why didn’t it drop? I say in response to weakened heating, clouds formed later in the day. Bear in mind that we’re discussing a deficit of say 10 W/m2 or so, or 240W/hrs over the day. At noon in the tropics, you’re getting up to a kilowatt of power from the sun. So the deficit would be made up in its entirety by something like a half-hour delay in the average time of cloud onset …
One of the amazing parts of that system of control is that it’s virtually invisible … I mean, who would notice if the clouds on average formed a bit earlier or later? But it is that day by day response that keeps the temperature within such tight bounds.
So for the climate, the Lotka-Volterra equations are a terrible analogy. We see absolutely nothing in the climate like the huge predator prey swings. The global average surface temperature in the 20th Century didn’t vary more than ± 0.1%, a tenth of a percent … where will you find anything like that in a Lotka-Volterra evolution? L/V is all about wild highs and lows in response to changes in forcings, and the climate is all about hardly any swings in response to changes in forcings.
As always, it is a joy to read your clear and insightful comments. As your steel chips away at the dark flint, sparks of thought fly … a pleasure.
w.
MikeN says:
February 25, 2014 at 9:19 am
Yep, that’s what they say. From their Abstract …
Kristian says:
February 25, 2014 at 9:25 am
Yes, and as I’ve pointed out to Bob Tisdale on many occasions, I think that the El Nino pump functions to move warm water to the poles when too much heat builds up in the Pacific. As a result, I see the El Nino pump as a result of increasing global temperatures rather than a cause …
So your claim is that you can disentangle the climatic effect of three different things, 1) volcanoes, 2) temperature-based El Nino indices, and 3) other global temperature fluctuations from unknown causes, and you can tell us that there is a “stunted” temperature response to El Chichon? I fear I haven’t seen the math on that one.
You are correct that the Pacific leads the planet, and that the tropics leads the Pacific. The tropical Pacific warms and cools first, followed by the rest of the globe. In part this is because the generally clear tropical ocean waters are able to absorb large amounts of solar energy without changing temperature very much.
Over the following six months or so, this energy is released back into the system, with the natural result that the rest of the planet warms.
But that doesn’t mean that the El Nino pump somehow explains the variations of the planetary temperature. The El Nino pump RESPONDS to high temperatures, it doesn’t cause them. The pump just kicks in whenever too much heat builds up in the tropical Pacific, and it moves the warm water to the north and south poles.
It’s actually an ingenious design for a lovely thermoregulatory system. You use the heat in the ocean to warm the planet, so you always have a reservoir of heat to draw on. To ensure that the heat reservoir is always full, it fills up to the brim. And at that point the El Nino pump kicks in, skims off the excess heat to the poles, exposes the cooler subsurface waters to cool the atmosphere, and then the amazing Pacific-wide pumping system vanishes until it is needed again.
It is exactly what I’d expect. After El Chichon, global temperatures rose. After El Chichon, the El Nino index rose. After Pinatubo, temperatures fell. After Pinatubo the El Nino index fell. I’m not sure why you think that is significant.
Here’s the El Nino 3.4 Index, blue lines show dates of eruptions:
Or if you’d prefer, here’s the Multivariate ENSO Index, MEI:
As you can see in both cases, rising index after El Chichon, falling index after Pinatubo …
All the best,
w.
Right on, what a good read, both Willis and the comments. I think that I am now less ignorant than when I started reading… Thanks
http://www.mbari.org/volcanism/ShortStory.htm with link to: http://volcano.oregonstate.edu/submarine
Conjecture here based upon projection of known undersea volcanic activity is that 75% of all such activity occurs under water. Makes some sense since 70% of the Earth’s surface is under water. If anywhere near accurate, that is a great deal of heat and gases going into the oceans at mostly unknown times and places. So, what is going on on land is only the tip of the iceberg, or volcano in this case.
Willis.
I can really see why Tisdale, after having explained and shown you so many times how one can clearly see the impact globally of the two large volcanic eruptions of the last 35 years, why he bothers no more. Because on this you simply refuse to see the obvious even when it stares you right in the face. There simply is no talking to you. You’ve just made up your mind. And that’s it.
Try looking at this graph, global SST vs. NINO3.4 (lagged by 2 months), 1988-98:
http://i1172.photobucket.com/albums/r565/Keyell/Pinatubo-NINO34vsglSSTa_zps0a424b1d.png
Are you telling me that you do not see the impact of the Pinatubo eruption on global SSTs between ’92 and ’95? What, then, caused that ridiculously obvious global dip in temperatures just after the eruption if not the eruption itself? It sure wasn’t ENSO. What other mechanism has the ability to completely and utterly counter ENSO globally for a three year period?
Willis,
Solomon is wrong to attribute the “pause” to volcanic eruptions since there is no big eruption since 1998. But I’m afraid you also got it wrong.
As mentioned before, your 14 W/m^2 is not comparable to 3.7 W/m^2/K. The latter is climate sensitivity without feedback. It is not necessarily due to CO2 forcing. Actually any forcing will do. The forcing attributed to CO2 is 1.66 W/m^2 since pre-industrial era according to IPCC. This CO2 forcing is a global radiative imbalance at TOA. Radiative balance is incoming radiation minus outgoing radiation. What you calculated are changes in surface down welling radiation locally at Mauna Loa. Not comparable to CO2 forcing.
The radiation absorbed by the atmosphere will warm the surface since it is tightly coupled with mid-troposphere temperature. Your 14 W/m^2 should have warming effect on the surface. And if you look at your Figure 2 closely, you will see an increase in temperature 1990-93. This is a local effect since the temperature and forcing are both local. Globally, there’s drop in temperature 1991-93 from Figures 4 & 5 presumably due to Mt. Pinatubo eruption.
“After Pinatubo the El Nino index fell.”
What about the 1991/1992 El Nino?:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml
“But that doesn’t mean that the El Nino pump somehow explains the variations of the planetary temperature.”
The highest global temperatures do tend to be during an El Nino and not after, unless there is a lot of stratospheric aerosols at the time of course.
“The El Nino pump RESPONDS to high temperatures, it doesn’t cause them. The pump just kicks in whenever too much heat builds up in the tropical Pacific..”
It is a build of of heat in the Pacific, and it responds to a drop in solar forcing, whether that be stratospheric aerosols causing dimming at the surface, or a large enough drop in the solar wind speeds to effect global teleconnections, as in the very clear examples of 1997/98 and 2009/10:
http://snag.gy/nf9SK.jpg
Hi Willis,
I don’t think AOD generates anywhere near the loss of net solar energy that you have calculated. This is mostly because the AOD is a measure of how much the intensity of an incident light beam is diminished along the original direction of that beam. Most of the light that is scattered by volcanic aerosols is “forward scattered” at relatively shallow angles away from the original direction, very little is actually reflected at backward angles. (A bit is also absorbed by the aerosol particles themselves, causing a bit of warming, as we can see in the satellite temperature history for the stratosphere in the period following each major eruption.) Forward scattering dominates for all particles in the atmosphere that are larger than about 50 nanometers (and volcanic aerosols are much larger than 50 nm).
So even though the direct intensity of the sun is reduced by the amount you calculate, most of that reduction is not actually lost to space…. most is just converted into diffuse light, and a little is absorbed and converted to heat within the atmosphere. The actual reduction in solar energy reaching Earth is far lower than you calculated. NASA GISS multiplies tau by 23 to estimate the average global reduction in watts per square meter.
You can see the effect of forward scattering by looking at the sky when there is a bit of smoke/haze in the air; you will see that the sky at all angles anywhere near the sun is very bright, and much brighter than it would be on a perfectly clear day. That bright sky surrounding the sun is due to forward scattered light. It is much like the difference between a sand blasted light bulb and a clear light bulb; the total light exiting the bulb is the same, but it is more diffuse for the bulb with an irregular surface. I have read that diffuse light is actually quite good for plant growth, because more leaf area is illuminated, since there are no dark shadows cast by one leaf on another when light is arriving over a wide range of angles.
People seem to use the word ‘aerosol’ in a vague fashion. I can never be sure what they mean. Is an aerosol everything that spews into the atmosphere? Particulate matter and gas? To my mind they are totally different. A gas is not a blackbody and only ‘works’ in specific wave bands ie. absorption/emission lines. A particle is a blackbody and emits/absorbs in the broadband. The radiation physics are totally different.
Doublings? Either I’m confused, or you misstated something slightly.
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.
Did you mean almost four times? Four doublings of 3.7 is 59.2; four times (two doublings) is 14.8.
Or am I just missing something in my current decaffeinated state?