Guest Post by Willis Eschenbach
In the leaked version of the upcoming United Nations Intergovernmental Panel on Climate Change (UN IPCC) Fifth Assessment Report (AR5) Chapter 1, we find the following claims regarding volcanoes.
The forcing from stratospheric volcanic aerosols can have a large impact on the climate for some years after volcanic eruptions. Several small eruptions have caused an RF for the years 2008−2011 of −0.10 [–0.13 to –0.07] W m–2, approximately double the 1999−2002 volcanic aerosol RF.
and
The observed reduction in warming trend over the period 1998–2012 as compared to the period 1951–2012, is due in roughly equal measure to a cooling contribution from internal variability and a reduced 2 trend in radiative forcing (medium confidence). The reduced trend in radiative forcing is primarily due 3 to volcanic eruptions and the downward phase of the current solar cycle.
Now, before I discuss these claims about volcanoes, let me remind folks that regarding the climate, I’m neither a skeptic nor am I a warmist.
I am a climate heretic. I say that the current climate paradigm, that forcing determines temperature, is incorrect. I hold that changes in forcing only marginally and briefly affect the temperature. Instead, I say that a host of emergent thermostatic phenomena act
quickly to cool the planet when it is too warm, and to warm it when it is too cool.
One of the corollaries of this position is that the effects of volcanic eruptions on global climate will be very, very small. Although I’ve demonstrated this before, Anthony recently pointed me to an updated volcanic forcing database, by Sato et al. Figure 1 shows the amount of forcing from the historical volcanoes.
Figure 1. Monthly changes in radiative forcing (downwelling radiation) resulting from historical volcanic eruptions. The two large recent spikes are from El Chichon (1983) and Pinatubo (1992) eruptions. You can see the average forcing of -0.1 W/m2 from 2008-2011 mentioned by the IPCC above. These are the equilibrium forcings Fe, and not the instantaneous forcing Fi.
Note that the forcings are negative, because the eruptions inject reflective aerosols into the stratosphere. These aerosols reflect the sunlight, and the forcing is reduced. So the question is … do these fairly large known volcanic forcings actually have any effect on the global surface air temperature, and if so how much?
To answer the question, we can use linear regression to calculate the actual effect of the changes in forcing on the temperature. Figure 2 shows the HadCRUT4 monthly global surface average air temperature.
Figure 2. Monthly surface air temperatures anomalies, from the HadCRUT4 dataset. The purple line shows a centered Gaussian average with a full width at half maximum (FWHM) of 8 years.
One problem with doing this particular linear regression is that the volcanic forcing is approximately trendless, while the temperature has risen overall. We are interested in the short-term (within four years or so) changes in temperature due to the volcanoes. So what we can do to get rid of the long-term trend is to only consider the temperature variations around the average for that historical time. To do that, we subtract the Gaussian average from the actual data, leaving what are called the “residuals”:
Figure 3. Residual anomalies, after subtracting out the centered 8-year FWHM gaussian average.
As you can see, these residuals still contain all of the short-term variations, including whatever the volcanoes might or might not have done to the temperature. And as you can also see, there is little sign of the claimed cooling from the eruptions. There is certainly no obvious sign of even the largest eruptions. To verify that, here is the same temperature data overlaid on the volcanic forcing. Note the different scales on the two sides.
Figure 4. Volcanic forcing (red), with the HadCRUT4 temperature residual overlaid.
While some volcanoes line up with temperature changes, some show increases after the eruptions. In addition, the largest eruptions don’t seem correlated with proportionately large drops in temperatures.
So now we can start looking at how much the volcanic forcing is actually affecting the temperature. The raw linear regression yields the following results.
R^2 = 0.01 (a measure from zero to one of how much effect the volcanoes have on temperature) "p" value of R^2 = 0.03 (a measure from zero to one how likely it is that the results occurred by chance) (adjusted for autocorrelation). Trend = 0.04°C per W/m2, OR 0.13°C per doubling of CO2 (how much the temperature varies with the volcanic forcing) "p" value of the TREND = 0.02 (a measure from zero to one how likely it is that the results occurred by chance) (adjusted for autocorrelation).
So … what does that mean? Well, it’s a most interesting and unusual result. It strongly confirms a very tiny effect. I don’t encounter that very often in climate science. It simultaneously says that yes, volcanoes do affect the temperature … and yet, the effect is vanishingly small—only about a tenth of a degree per doubling of CO2.
Can we improve on that result? Yes, although not a whole lot. As our estimate improves, we’d expect a better R^2 and a larger trend. To do this, we note that we wouldn’t expect to find an instantaneous effect from the eruptions. It takes time for the land and ocean to heat and cool. So we’d expect a lagged effect. To investigate that, we can calculate the R^2 for a variety of time lags. I usually include negative lags as well to make sure I’m looking at a real phenomenon. Here’s the result:
Figure 5. Analysis of the effects of lagging the results of the volcanic forcing.
That’s a lovely result, sharply peaked. It shows that as expected, after a volcano, it takes about seven-eight months for the maximum effects to be felt.
Including the lag, of course, gives us new results for the linear regress, viz:
R^2 = 0.03 [previously 0.01] "p" value of R^2 = 0.02 (adjusted for autocorrelation) [previously 0.03] Trend = 0.05°C per W/m2, OR 0.18 ± 0.02°C per doubling of CO2 [previously 0.13°C/doubling] "p" value of the Trend = 0.001 (adjusted for autocorrelation). [previously 0.02]
As expected, both the R^2 and the trend have increased. In addition the p-values have improved, particularly for the trend. At the end of the day, what we have is a calculated climate sensitivity (change in temperature with forcing) which is only about two-tenths of a degree per doubling of CO2.
Here are the conclusions that I can draw from this analysis.
1) The effect of volcanic eruptions is far smaller than generally assumed. Even the largest volcanoes make only a small difference in the temperature. This agrees with my eight previous analyses (see list in the Notes). For those who have questions about this current analysis, let me suggest that you read through all of my previous analyses, as this is far from my only evidence that volcanoes have very little effect on temperature.
2) As Figure 5 shows, the delay in the effects of the temperature is on the order of seven or eight months from the eruption. This is verified by a complete lagged analysis (see the Notes below). That analysis also gives the same value for the climate sensitivity, about two tenths of a degree per doubling.
3) However, this is not the whole story. The reason that the temperature change after an eruption is so small is that the effect is quickly neutralized by the homeostatic nature of the climate.
Finally, to return to the question of the IPCC Fifth Assessment Report, it says:
There is very high confidence that models reproduce the more rapid warming in the second half of the 20th century, and the cooling immediately following large volcanic eruptions.
Since there is almost no cooling that follows large volcanic eruptions … whatever the models are doing, they’re doing it wrong. You can clearly see the volcanic eruptions in the model results … but you can’t see them at all in the actual data.
The amazing thing to me is that this urban legend about volcanoes having some big effect on the global average temperature is so hard to kill. I’ve analyzed it from a host of directions, and I can’t find any substance there at all … but it is widely believed.
I ascribe this to an oddity of the climate control system … it’s invisible. For example, I’ve shown that the time of onset of tropical clouds has a huge effect on incoming solar radiation, with a change of about ten minutes in onset time being enough to counteract a doubling of CO2. But no one would ever notice such a small change.
So we can see the cooling effect of the volcanoes where it is occurring … but what we can’t see is the response of the rest of the climate system to that cooling. And so, the myth of the volcanic fingerprints stays alive, despite lots of evidence that while they have large local effects, their global effect is trivially small.
Best to all,
w.
PS—The IPCC claims that the explanation for the “pause” in warming is half due to “natural variations”, a quarter is solar, and a quarter is from volcanoes. Here’s the truly bizarre part. In the last couple decades, using round numbers, the IPCC predicted about 0.4°C of warming … which hasn’t happened. So if a quarter of that (0.1°C) is volcanoes, and the recent volcanic forcing is (by their own numbers) about 0.1 W/m2, they’re saying that the climate sensitivity is 3.7° per doubling of CO2.
Of course, if that were the case we’d have seen a drop of about 3°C from Pinatubo … and I fear that I don’t see that in the records.
They just throw out these claims … but they don’t run the numbers, and they don’t think them through to the end.
Notes and Data
For the value of the forcing, I have not used the instantaneous value of the volcanic forcing, which is called “Fi“. Instead, I’ve used the effective forcing “Fe“, which is the value of the forcing after the system has completely adjusted to the changes. As you might expect, Fi is larger than Fe. See the spreadsheet containing the data for the details.
As a result, what I have calculated here is NOT the transient climate response (TCR). It is the equilibrium climate sensitivity (ECS).
For confirmation, the same result is obtained by first using the instantaneous forcing Fi to calculate the TCR, and then using the TCR to calculate the ECS.
Further confirmation comes from doing a full interative lagged analysis (not shown), using the formula for a lagged linear relationship, viz:
T2 = T1 + lambda (F2 – F1) (1 – exp(-1/tau)) + exp(-1/tau) (T1 – T0)
where T is temperature, F is forcing, lambda is the proportionality coefficient, and tau is the time constant.
That analysis gives the same result for the trend, 0.18°C/doubling of CO2. The time constant tau was also quite similar, with the best fit at 6.4 months lag between forcing and response.
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In this case it’s the Sato paper, which provides a dataset of optical thicknesses “tau”, and says:
The relation between the optical thickness and the forcings are roughly (See “Efficacy …” below):
instantaneous forcing Fi (W/m2) = -27 τ
adjusted forcing Fa (W/m2) = -25 τ
SST-fixed forcing Fs (W/m2) = -26 τ
effective forcing Fe (W/m2) = -23 τ
And “Efficacy” refers to
Hansen, J., M. Sato, R. Ruedy, L. Nazarenko, A. Lacis, G.A. Schmidt, G. Russell, et al. 2005. Efficacy of climate forcings. J. Geophys. Res., 110, D18104, doi:10.1029/2005/JD005776.
Forcing Data
For details on the volcanic forcings used, see the Sato paper, which provides a dataset of optical thicknesses “tau”, and says:
The relation between the optical thickness and the forcings are roughly (See “Efficacy …” below):
instantaneous forcing Fi (W/m2) = -27 τ
adjusted forcing Fa (W/m2) = -25 τ
SST-fixed forcing Fs (W/m2) = -26 τ
effective forcing Fe (W/m2) = -23 τ
And “Efficacy” refers to
Hansen, J., M. Sato, R. Ruedy, L. Nazarenko, A. Lacis, G.A. Schmidt, G. Russell, et al. 2005. Efficacy of climate forcings. J. Geophys. Res., 110, D18104, doi:10.1029/2005/JD005776.
(Again, remember I’m using their methods, but I’m not claiming that their methods are correct.)
Future Analyses
My next scheme is that I want to gin up some kind of prototype governing system that mimics what it seems the climate system is doing. The issue is that to keep a lagged system on course, you need to have “overshoot”. This means that when the temperature goes below average, it then goes above average, and then finally returns to the prior value. Will I ever do the analysis? Depends on whether something shinier shows up before I get to it … I would love to have about a dozen bright enthusiastic graduate students to hand out this kind of analysis to.
I also want to repeat my analysis using “stacking” of the volcanoes, but using this new data, along with some mathematical method to choose the starting points for the stacking … which turns out to be a bit more difficult than I expected.
Previous posts on the effects of the volcano.
Prediction is hard, especially of the future.
Pinatubo and the Albedo Thermostat
Dronning Maud Meets the Little Ice Age
New Data, Old Claims about Volcanoes
Volcanoes: Active, Inactive and Interactive
Stacked Volcanoes Falsify Models
Greg Goodman says:
September 24, 2013 at 2:45 am
Youkillmeandyoudomegood: says “The Kiehl-Trenberth budget “396″ (W/m2) surface radiation value ”
What does that “value” represent? Surface upward IR would presumably include 0.7*S-B black body emission, 0.3*reflected solar, reflected atmospheric backscatter/re-emission.
Not the same as “blind theoretical calculation using Stefan-Boltzman law.”
Let’s stop presuming and see what K. Trenberth really says: “…we have taken the surface skin temperature from the NRA at T62 resolution and 6-h sampling and computed the correct global mean surface radiation from (I) [R = εσT^4] as 396.4 W m−2. (a href=”http://www.cgd.ucar.edu/staff/trenbert/trenberth.papers/TFK_bams09.pdf”>here, page 315)
So Trenberth himself says he applied the Stefan-Boltzman law on measured surface temperature and that it is the way how he obtained the 396 W figure.
And as I think about, it must not necessarily be a wrong approach if we would assume the energy for the surface evaporation is chiefly provided by the solar irradiation and atmospheric mid-IR backradiation – which seems to me even quite likely after all. In such case we in fact at all don´t need to postulate much lower water emissivity than 1, the Trenberth surface radiation value would be more or less correct and only remaining major problem with the budget would be that it overestimates the TOA insolation some 4 W/m^2 if compared to TSI average measured by SORCE-TIM instrument last decade, which doesn’t seem to be a result of a systematic error.
Jim S, I already commented on why glaciation does not disprove Willis ‘governor’.
September 22, 2013 at 10:43 am
No one is claiming climate had been perfectly stable for 4.3 billion years and that this is thanks to tropical storms.
[R = εσT^4] , what’s ε ?
[Emissivity, the amount of radiation emitted/absorbed by a substance. For first-order calculations it can be taken as 1 for the surface of the planet. Use 0.9 or so if you want more accuracy. It doesn’t affect the energy based calculations for balances and the like, because it scales both incoming and outgoing the same. -w.]
“And I confess that I’m reluctant to abandon that interpretation.”
Joe, the point is that the start of month, end of month thing only matters if you have tau=2*step as in your exaggerated example. Paul_K reported specific figures and the error is minimal in the context of this data and tau of about 6 or 7 steps.
There was another thread awhile back that discussed in part the effects of volcanoes. I see it written by you. One thought that I had at that time was perhaps the severity or lack of it depends on where the solar cycle is when the volcano erupts. Could it be that the major solar and atmospheric mechanisms that are at work at the time of the eruption, end up modifying the effects of the volcano by either enhancing or diminishing the effect?
There is another thought that came to me several weeks. I mentioned it once before and I still am wondering about the ‘why’ of what it appears to show. The reason that it might fit into some of the conversation here has to do with comments that mention governors, or modulators. This chart from SIDC shows the excess ssn count between the hemispheres…http://sidc.oma.be/sunspot-index-graphics/wnosuf.php
When the North is dominant it looks like it corresponds closely with the cooling trend of our planet, and when the South is dominant it corresponds closely with the warming trends. How could this be? Is it possible that there is a slight directional change in the output or focus of the Sun from this? Is this a governor/modulator mechanism?
Damn, you guys are cold. There a blog around here where they’ll actually talk to laymen?
Greg Goodman: “You may have an interesting point. But how about you post a graph produced by you code so that we can see what the effect is without every man jack of us having to do it just to see your point?”
I apologize for failing to respond; I somehow missed your comment before. Yes, I probably should have gone to the trouble of figuring out to post a drawing. But with so many folks here saying so many abstruse things, I guess my mental picture of the readership is of a bunch guys who have R consoles already open and waiting for code to be slapped into them.
In any event, I believe we’ve been overtaken by events; Paul_K graciously gave an explanation above (and I followed up).
As to the “spin up” issue, the approach I’d take would be to use the above routine’s y0 as one of the parameters the modeling routine tweaks. Although I assume that such an approach could be costly in some situations, I don’t think it would ordinarily present a problem in the case of a simple single-order, scalar system.
Again, my apologies for ignoring your comment.
http://www.drroyspencer.com/wp-content/uploads/UAH_LT_1979_thru_August_2013_v5.6.png
There is the link Willis, which shows the Mt. Pinatubo eruption had a much greater influence on the climate then you try to convey. Note this was in the face of an El Nino at that time.
Again Willis it is impossible to come up with what you came up with due to all the variables of the climate system, let alone the variability of each individual volcanic eruption.
If everyone would look at the link I just provided ,you will see it is at odds with the data Willis has given. This was in the face of an El Nino making it even more meaningful.
Willis I also have some very recent studies that support my view of much greater solar variabilty then what Leif and yourself try so hard to convince is otherwise.
@Willis Eschenbach.
I can’t comment on your ACFs becauase the time axes has no units.
You don’t understand why ACFs are important? Let me explain.
The ACF is a measure of lag in a system as measured in this contect. Climaye temperature data shows persistance. This means that there is correlation between samples at long time intervals. It is well known, eg Luck & Lederer and others, McIntyre, Tol for example.
It is well known that the ACF of temperature does not conform to an 1st Order ARMA process. The fall off in the early lags is too great and the persistence in long lags is too great to be accounted for by the behaviour of a single capacitance. There has been musch speculation about representing the temperature series as a Hurst process, which is of course non-linear. Alternatively, the ACF can be approximated by a multi-compartment model and given the quality of the data it is difficult to distinguish between the two.
Persistance has a very important role in system dynamics, especially in non-linear systems and cannot be ignored. It is a fundamental property of a system and is often only minimally represented, if at all, in the use of standard entropic measures such as R^2. This is not an appropriate measure to characterise a system and unless one is very precise in one’s definitions..
You told me to grab some data and do an analysis. Thank you, I already have. See:
http://judithcurry.com/2012/02/19/autocorrelation-and-trends/
I wrote this after Luck et al presented their analysis. I was somewhat unconvinced and did the calculations as a reality check. Since this was for a blog, not a journal, I have gone to some length to explain the principles of the analysis in a simple way as I am aware that signal processing is a black art to many people.. I am perfectly happy to discuss the underlying mathematics with anyone and I am well aware that there are several approximations in the analysis, as there are of course in Luck et al’s
.I would add that estimation of persistance from ACFs with a strong seasonal signal is not straightfoward. Low pass filtering the signal will give wildly incorrect results. Highly precise multi-notch filtering is highl problematic. The method that I used is one that is used in some biomedical signals where one is looking for subtle persistances in the presence of wide variability. It also has its limitations, bit I go to some length to establish the effect of the method on the ACF.
Since you told me to put up or shut up, I wrote an essay on the difference between statistical and physical modelling and emphasised how one could be mislead into thinking that a non-linear system is linear, again, in a very simplistic way. It didn’t see the light of day on WUWT, but I am sure that you can recover the document from Anthony Watts.
.
I
http://books.google.com/books?id=vUtSluaODqYC&pg=PA45&lpg=PA45&dq=the+11+year+solar+cycle+continued+during+the+maunder+minimum&source=bl&ots=g4qt3JnWMQ&sig=URAhIGZWdOjfuRpPj4w6ZRNnSx8&hl=en&sa=X&ei=Y-09UtWKFuaHygHOiYCYDg&ved=0CC8Q6AEwATgK#v=onepage&q=the%2011%20year%20solar%20cycle%20continued%20during%20the%20maunder%20minimum&f=false
I hope this link works. t will be a very interesting read for you Willis.
Willis read pages 43-46 if nothing else when you have time.
Willis – If you’re still monitoring this thread: It could be interesting to see if there’s a volcano effect on diurnal temperature range (DTR).
http://australianclimatemadness.com/2011/09/12/another-paper-suggests-cosmic-ray-influence-on-clouds/
Don’t know quite what it would mean if there was or wasn’t one, but it could be interesting…..
—–
Yhanks for replying to my previous query. I want to do a bit of checking on what you said about RCS but haven’t been able to put the time into it yet (I too have been and am on holiday in the UK).
Typos – “Thanks”, “ECS”.
On another note there was a large eruption in Guatemala 2 days ago…http://thewatchers.adorraeli.com/2013/09/23/violent-eruption-and-series-of-major-pyroclastic-flows-at-santa-maria-guatemala/
The earth is very active recently with above normal count of quakes and a 7.7 quake in Pakistan this morning that is rated a 9 on the shake index. Pakistan has been severely rattled.
Willis Eschenbach says:
September 24, 2013 at 8:58 am
“Unfortunately, as a result of that error, your entire argument collapses.”
You’re right. As I thought about it again there is in fact no need to postulate much lower water emissivity than 1 (Trenberth even uses emissivity value 0.9907) – the energy for the surface evaporation can easily be provided both by the solar irradiation and atmospheric mid-IR radiation. So the Trenberth surface radiation value can be more or less correct after all.
I appologize for the confusion, some wrong ideas fortunately don’t live long.
But this anyway somehow doesn’t seem to collapse the argument that the water cycle cools Earth surface by taking the latent and specific heat from it and transporting it up to the atmosphere and not much by cooling the surface by subsequent rain, nor it seems to collapse the argument that Earth climate system doesn’t seem to have effective surface temperature “homeostasis” or “thermostat” mechanisms able to counter the effects of solar and GCM activity changes – which seem being partially dependent on the solar activity. It even very much looks like the surface temperature anomalies are driven by this changes both on short and longtime scales, because the amount of absorbable incoming solar energy reaching the surface changes with changes of this factors both directly and indirectly – affecting the low-cloudiness, changing albedo, factor, which can have even considerably higher magnitude than just changes of the TSI.
But I’m really not sure what is exactly your “heretic” idea, maybe you mean only purely terrestrial forcing factors? So I appologize if it is a misunderstanding.
In any case I fully agree that the effects of volcanic erruptions are likely overestimated and in my opinion they can even have a phase where the ejected particles cause dimming when still in the air, but after eventually settling down having opposite forcing effect by at least intermittently lowering the albedo of the surfaces where it settled down (especially at high albedo surfaces as snow or ice) – which can at least partially offset the previous dimming effect. (Just an instant idea)
happycrow says:
September 24, 2013 at 8:20 am
happycrow says:
September 24, 2013 at 10:54 am
Russ, I did a search for your “earlier idea”. I find only two comments from “happycrow”, the two I show above …
And far from being cold, new ideas get discussed here all the time.
You got to post them first, though …
Give it another shot.
w.
Look at the data for the recent Mt. Pinatubo eruption, volcanic influences are NOT over estimated.
Willis you have the data(I presented) it is in black and white ,unless you don’t believe satellite temperature data..
Willis some day give us your explanation or explanations for why the climate changes abruptly at times ,while at other times it is more stable and yet at other times it fips from a glacial regime to an inter glacial regime.
You say it is not the sun, not co2, not volcanic activity, etc.etc. so what is it?
Mark Wright: Which begs the question, apart from cooling from volcanoes, what else at the scale of ESNO events is causing it to be warmer and cooler?
If La Nina causes an upwelling of colder water, a tropical governor will cause it to be warmed by additional solar. When El Nino hits this energy will be dumped to the atmosphere. Hence frequency and amplitude of El Nino/Nina cycle has the means to cause heat gain or loss to the climate system. Notwithstanding the tropical a governor action. In fact because of the latter.
tumetuestumefaisdubien1 says:
September 24, 2013 at 11:43 am
Ladies and gentlemen, I give you the action of a true seeker and scientist. When you are wrong, say so, digest the implications and move on. Tume, if I might call you that, well done.
That’s one reason that I enjoy writing for the web, any illusions I entertain have a short half-life in the hot glare of public discussion.
Curiously, the water cycle of “evaporation, condensation, rain, and repeat” cools the earth in lots of ways. In addition to reflecting sunlight from their top surface as cumulus clouds do, and transporting heat from the surface directly to the upper troposphere where it radiates easily to space, thunderstorms cool the surface in a variety of other ways, particularly (but not exclusively) over the ocean.
1. Wind driven evaporative cooling. Once the thunderstorm starts, it creates its own wind around the base. This self-generated wind increases evaporation in several ways, particularly over the ocean.
. a) Evaporation rises linearly with wind speed. At a typical squall wind speed of 10 mps (20 knots), evaporation is about ten times higher than at “calm” conditions (conventionally taken as 1 mps).
. b) The wind increases evaporation by creating spray and foam, and by blowing water off of trees and leaves. These greatly increase the evaporative surface area, because the total surface area of the millions of droplets is evaporating as well as the actual surface itself.
. c) To a lesser extent, surface area is also increased by wind-created waves (a wavy surface has larger evaporative area than a flat surface).
. d) Wind created waves in turn greatly increase turbulence in the boundary layer. This increases evaporation by mixing dry air down to the surface and moist air upwards.
. e) As the spray rapidly warms to air temperature, which in the tropics is often warmer than ocean temperature, evaporation also rises above the sea surface evaporation rate.
2. Wind driven albedo increase. The white spray, foam, spindrift, changing angles of incidence, and white breaking wave tops greatly increase the albedo of the sea surface. This reduces the energy absorbed by the ocean.
3. Cold rain and cold wind. As the moist air rises inside the thunderstorm’s heat pipe, water condenses and falls. Since the water is originating from condensing or freezing temperatures aloft, it cools the lower atmosphere it falls through. It also cools the surface when it hits. In addition, the falling rain entrains a cold wind. It is cooled by the evaporation of the falling drops This cold wind blows radially outwards from the center of the falling rain, cooling the surrounding area.
4. Increased reflective area. White fluffy cumulus clouds are not tall, so basically they only reflect from the tops. On the other hand, the vertical pipe of the thunderstorm reflects sunlight along its entire length. This means that thunderstorms shade an area of the ocean out of proportion to their footprint, particularly in the late afternoon.
5. Modification of upper tropospheric ice crystal cloud amounts (Lindzen 2001, Spencer 2007). These clouds form from the tiny ice particles that come out of the smokestack of the thunderstorm heat engines. It appears that the regulation of these clouds has a large effect, as they are thought to warm (through IR absorption) more than they cool (through reflection).
6. Enhanced nighttime radiation. Unlike long-lived stratus clouds, cumulus and cumulonimbus generally die out and vanish as the night cools, leading to the typically clear skies at dawn. This allows greatly increased nighttime surface radiative cooling to space.
7. Delivery of dry air to the surface. The air being sucked from the surface and lifted to altitude is counterbalanced by a descending flow of replacement air emitted from the top of the thunderstorm. This descending air has had the majority of the water vapor stripped out of it inside the thunderstorm, so it is relatively dry. The dryer the air, the more moisture it can pick up for the next trip to the sky. This increases the evaporative cooling of the surface.
In part because they utilize such a wide range of cooling methods, cumulus clouds and thunderstorms are extremely good at reducing the surface temperature of the earth. Together, they form the governing mechanism for the tropical temperature.
Pass. Not sure I understand that.
The currently accepted paradigm for the evolution of the climate is that changes in temperature are a linear function of the changes in forcing. I say the earth’s temperature is not set by the forcing, but by interlocking thermostatic mechanisms. In other words, I say the earth has a thermostat.
Mmmm … interesting question about fallen particles. Most of the stuff that is injected into the stratosphere is not ash, but chemical compounds, especially the reflective sulfates. It is these which circle the globe fairly rapidly, stay airborne, and lower the incoming sunlight.
Not sure what effect sulfates would have on the ice, however. And while the ash is darker than snow, it’s far from black like soot, take a look at the pictures of the ash-falls after big explosions.
All the best,
w.
Willis: I repeated my calculations to correct for the fact that the oceans only cover 70% of the surface and added in the heat capacity of the air. WIth a 50 m mixed layer ocean and atmosphere, a -1 W/m2 forcing causes temperature to drop at an initial rate of 0.2 degC/yr, or about 0.01 degC per month.
A no-feedbacks climate sensitive of 1.2 degC for 2XCO2 is sometimes described as a Planck feedback of -3.2 W/m2/degC*. Once the temperature has dropped 0.1 degC, the reduction in outgoing blackbody radiation will cancel 0.32 W/m2 of current (negative) volcanic forcing. Therefore any temperature drop quickly begins to diminish the net radiative forcing associated with volcanic aerosols (which also dissipate). However, the system is out of equilibrium for several years after an eruption. No lagged relationship between forcing and temperature is an equilibrium relationship.
* If you believe in positive feedback and a climate sensitivity of 2.4 degC for 2XCO2, the “effectiveness of the Planck feedback” is reduced to -1.6 W/m2/degC, enough to still begin to counter the volcanic forcing, but half as quickly. The higher climate sensitivity allows larger temperature swings.
Since you believe overall feedback is negative, a climate sensitivity of 0.6 degC for 2XCO2 would double the “effectiveness of the Planck feedback” to -6.4 W/m2/degC. An 0.1 degC temperature drop will negate 0.64 W/m2 of volcanic forcing and severely limit the amount of cooling.
You don’t have to reject the conventional linear relationship between forcing and temperature change simply because you believe volcanos have less impact than natural variation on temperature or because you believe feedback is negative. The Planck feedback IS negative (-3.2 W/m2/degC) and it could be made more negative by clouds. The conventional explanation is that water vapor feedback cancels about half of the Planck feedback. If all of the Planck feedback were negated by positive feedbacks, one has a run-away greenhouse effect.