### Why extremes are expected to change with a global warming

Filed under: — rasmus @ 5 September 2017

Joanna Walters links extreme weather events with climate change in a recent article in the Guardian, however, some  reservations have been expressed about such links in past discussions.

For example, we discussed the connection between single storms and global warming in the post Hurricanes and Global Warming – Is there a connection?, the World Meteorological Organization (WMO) has issued a statement, and Mike has recently explained the connection in the Guardian.

We still cannot say that single events are caused by climate change for the simple reason that climate change is not a force.

Rather, climate change is a consequence of changed physical conditions. Indeed, one type of climate change could hypothetically consist of storms just becoming more powerful.

I will explain what I mean with climate change below.

If you want to understand the world, then statistics can provide some insights if you have a large number of observations or measurements. This is especially so if you live in a very complex universe with a lot of complicated factors and it is difficult to solve all the equations representing the physics.

To distill information about the climate, you can sort weather data according to different categories, such as magnitude. Then create a table keeping a count of the number of cases that fall into each category, and you will be able to see what magnitudes are common and what range within which you expect them to fall.

You can also plot this type of statistics as a figure known as a histogram.

The histogram is a crude way of showing how frequently you can expect the measurement to fall into each category.

The frequency is proportional to the probability, and you can fit a smooth probability density function (pdf) to the data.

Typical examples of pdfs include the bell-shaped normal distribution for temperature (left panel in the Fig. 1) and the exponential distribution for 24-hr precipitation (right panel i Fig. 1).

What I mean by climate
I usually say that climate is the same as weather statistics (or more precisely, the statistical characteristics of meteorological variables), providing information about what type of weather to expect and its probability.

This statistics, however, will not tell you what one particular outcome will be (i.e. a weather forecast) nor is it a force that influences the outcomes.

The statistics is a mere reflection of (hidden) underlying forces of physics.

Global warming is one kind of climate change caused by an increased greenhouse effect with an impact on both meteorology and the hydrological cycle. It involves physical conditions which set the stage for evaporation, convection, condensation of water vapour, formation of clouds, and precipitation.

Statistical parameters are surprisingly predictable, and weather statistics is systematically influenced by the physical conditions present.

This dependency to physical conditions is evident from how the temperature and precipitation vary from place to place: typically warmer at low latitudes and cooler at higher altitudes; more rain near the coast and less in the interior.

There is also more intense rainfall in the warm tropics than the cooler extra-tropics, and summer precipitation is often more intense than in winter due to different physical conditions.

Typical probability density functions (pdfs) of temperature (left) and precipitation on rainy days (right).

What I mean by climate change
One definition of a climate change is a shift in the pdf describing the temperature, precipitation, or some other variable.

Such a shift in the pdfs is illustrated in Fig. 1 where the grey shading represents the original climate and the red shading a changed climate.

Some variables are strongly affected by changes physical conditions, others are less so. One indicator for their sensitivity to a climate change can be how their character depends on the season, geography, natural variations, or if they exhibit pronounced long-term trends.

Different kinds of extremes
Extremes are often defined as the tails of the distribution (upper or lower parts of the curves in Fig. 1), which are associated with low probability but magnitudes near observed ranges. The magnitude can be either very high (e.g. heat waves, heavy precipitation, intense wind speeds) or low if the pdf has two tails (e.g. freezing temperatures).

The expression “weather extremes” is a catch-all phrase, and not very useful for describing the actual situations. There is a range of different types of extreme weather events, with different nature and different manifestations.

For instance, there are conditions which are present all the time, such as temperature or barometric pressure (there are no days without temperature or pressure). These can be described by one single pdf to indicate their magnitude at any time.

Some conditions are intermittent, such as rain (it doesn’t rain constantly all the time). There are two aspects characterizing intermittent phenomena: how often do these phenomena take place and how intense are they.

For intermittent phenomena, you need two pdfs: one describing their presence (e.g. a Poisson distribution) and one indicating the magnitude when their are present (e.g. Fig. 1).

Some meteorological phenomena are both rare and violent, such as tropical cyclones, mid-latitude cyclones, tornadoes, hail, and lightning.

The more frequent they are, the greater the chance for seeing very extreme events just because you get a larger sample of events over time.

We can use these ideas as a context for Joanna Walters’s article and Hurricane Harvey.

Tropical cyclones
One thing is that global warming may have boosted its force, but will a global warming result in more frequent tropical cyclones?

The oceans are warming, and these hurricanes represent one mechanism that moves the heat from the surface to high levels in the atmosphere where it can escape to space.

We know that the number of tropical cyclones is influenced by several factors: the seasonal cycle, the geography, ocean temperatures and the wind structure in the atmosphere.

According to the IPCC AR5, however, there are little indications of a change in the number of tropical cyclones, although they are becoming more intense (p. 107, TS.5.8.4 Cyclones):

that it is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged, concurrent with a likely increase in both global mean tropical cyclone maximum wind speed and rain rates

I believe the jury is still out on the question of the number of tropical cyclones because the IPCC’s assessment has so far not included studies on the relationship between the number of tropical cyclones and the area of high sea surface temperature, such as the analysis shown in Fig 2 (1).

Fig. 2 shows predictions with a simple model that predicts the number of tropical cyclones (NTC and n) in the North Atlantic based on the area of warm sea surface (A) and the NINO3.4 index. It was created in R using the script tropicalcyclones.R which also retrieves the data. The model was calibrated over the period 1900-1960, and the predictions provide reasonable similar evolution of the North-Atlantic tropical cyclones outside this period. (PDF-version).

The analysis in Fig. 2 shows a crude prediction of the number of tropical cyclones (n) in the North Atlantic based on the area of warm ocean surface (A), and we see a roughly similar trend in these predictions as in the HURDAT2 tropical cyclone record.

One caveat with such empirical studies, however, is that the data record is incomplete and there is a risk that the analysis presents a false picture.

Nevertheless, the IPCC AR5 presents an outlook of increasing extreme precipitation in tropical cyclones making landfall (p. 106, Table TS.2), which is relevant for the flooding connected to Harvey.

Flooding may also become more severe from changes in the landscape, as explained by John Vidal in an article in the Guardian.

I think Joanna Walters’ article about extremes and climate change describes the current situation well, and we should not be too surprised.

A change in the pdf reflects a climate change, and in most cases its range and tails tend to follow the part of the curve that represents the more common conditions.

We must assume that it is only the exceptional cases where the tails of the pdf are unaffected. Furthermore, an increase in the number of tropical cyclones would increase the number of more cases with extreme rainfall.

## References

1. R.E. Benestad, "On tropical cyclone frequency and the warm pool area", Natural Hazards and Earth System Sciences, vol. 9, pp. 635-645, 2009. http://dx.doi.org/10.5194/nhess-9-635-2009

### 277 Responses to “Why extremes are expected to change with a global warming”

1. 151
Brian Dodge says:

Steve Case says: 18 Sep 2017 at 9:15 AM “Dr. Hansen should re-do his study using TMax if he wants to talk about summer temperatures.”

Been done (by others). Improved our knowledge of the interactions between water vapor, clouds, and aerosols.
By the way, Hansen et al looked at Northern hemisphere temperatures, which is a somewhat larger dataset than just the Eastern US.

“In contrast to the widespread global warming, the central and south central United States display a noteworthy overall cooling trend during the 20(th) century, with an especially striking cooling trend in summertime daily maximum temperature (Tmax) (termed the U.S. “warming hole”). Here we used observations of temperature, shortwave cloud forcing (SWCF), longwave cloud forcing (LWCF), aerosol optical depth and precipitable water vapor as well as global coupled climate models to explore the attribution of the “warming hole”. We find that the observed cooling trend in summer Tmax can be attributed mainly to SWCF due to aerosols with offset from the greenhouse effect of precipitable water vapor.”

https://openi.nlm.nih.gov/detailedresult.php?img=PMC4221782_srep06929-f2&req=4
Attribution of the United States “warming hole”: aerosol indirect effect and precipitable water vapor.
Yu S, Alapaty K, Mathur R, Pleim J, Zhang Y, Nolte C, Eder B, Foley K, Nagashima T – Sci Rep (2014)

2. 152
jgnfld says:

Re. “The heat in this case is generated by my body, not any “absence of cooling” produced by my clothing. The clothing simply prevents heat from escaping, it doesn’t generate any heat on its own. If my body didn’t produce any heat, then no amount of clothing could warm me. Duh!”

“Duh” indeed. The greenhouse effect “simply prevents heat from escaping” as well though in this case the heat originates in the Sun. And like clothing in the winter, preventing heat from escaping, er, well, produces warming in the affected local environment.

In the one case the local environment is the area around your body under your clothes. In the other case the affected area is the planet under the atmosphere. The fundamental radiation budget ideas are exactly the same.

True, like a dead body, if the Sun “didn’t produce any heat, then no amount of [greenhouse effect] could warm me.” But it’s totally irrelevant as well. FYI, the Sun does, actually, shine. And the greenhouse effect is an important component of the resulting radiation budget.

So again, my suggestion is you try out your ideas that “the absence of cooling cannot produce warming” on the next subzero day by walking around nude for a few hours to check out your ideas.

3. 153

V: Even if less volcanic activity were somehow able to increase warming (which makes no sense as far as I’m concerned)

BPL: Your personal incredulity proves nothing. We have sunlight coming in; we can alter Earth’s temperature if we can increase or decrease the sunlight reaching the ground. This is so elementary it’s hard to believe you’re not trolling.

Gavin et al., I recommend putting Victor in the borehole with the other fanatics. When he’s here he wastes an incredible amount of other peoples’ time.

4. 154
CCHolley says:

Victor @149

“You are wrong. You just choose to focus on the least important one, volcanism and ignore the greenhouse gas forcing and solar irradiance.”

No, I never ignored either issue, as should be clear from my previous comments. But in this case it’s the effects of volcanic eruptions (and their absence) that is being discussed. Your objection is a straw man, sorry.

Nope. Not a straw man at all.

You clearly stated: “So no matter how you want to argue this, you are still left with a dramatic runup in temperature for which there is no explanation based on the current state of climate science.”

Volcanism, which you appear to be obsessed with, was a minor influencer of the period in question. The temperature rise is clearly understood as mostly driven by CO2 forcing. Your statement is completely false and the point of your volcano discussion is completely absurd. A red herring.

Working hard on your denialism. Or more likely intentional obfuscating.

5. 155
Astringent says:

Victor @150 The climatic effect of an eruption doesn’t just depend on VEI. Unsurprisingly it’s more complex. Eruptions with low VEI can produce as much sulphate as eruptions with larger VEI. The location of an eruption can also effect the way in which aerosols are dispersed and the effect on climate. A better measure of the effect of aerosols than counting eruptions on Wikipedia might be to look at Total Visible Optical Depth which measures the ‘dimming’ of the sun caused by the aerosols. Not hard to find and fairly un-ambiguously shows that, irrespective of event frequency, VOD was lower in the first part of the last century.

6. 156

Trigger warning: this comment responds to Victor’s ongoing confusion. If you’re heartily sick of it, please just ‘scroll on by.’

Victor, #!50–

“I really can’t believe how hard it is for people here to get it. I’m truly astonished. I expected more from this group.”

Back at you, V. I’m quite astounded at how stubbornly obtuse you are being. It’s certainly indicative of your lack of intellectual humility that you assume, apparently without any qualms, that you’ve ‘got it’ and everybody else is clueless.
Point 1:

Disabling the cooling system would NOT produce any warming, because the warming is produced from the computer system itself. The cooling system functions as a control of that warming — that’s it. Disabling the cooling system could never produce any warming over and above the warming produced by the system it’s designed to cool.

“(A theoretical hint: you are stumbling over “generated.” It’s the wrong conceptual framing.)” Well, duh! That’s my point. Absence of cooling cannot generate warming. It can only allow temperatures to rebound from a previous level.

Victor, do you dare try the experiment? Because if you are running a desktop, I guarantee you that disabling the cooling system–say, by cutting the leads to the cooling fan–will most certainly “produce warming” as measured by a thermometer placed inside the unit, and ultimately as manifested by component failure.

You are of course correct that the heat is not ‘generated’ by the absence of the cooling fan; and in fact no *additional* heat is being generated by the normal working of the system. Yet quite predictably, temperature *will* rise, far beyond anything the computer has ever ‘experienced’ before, because the rate at which the computer is losing heat to the environment has drastically decreased. That thermal energy is manifested inside the desktop case as rising temperature.

The situation with the climate system is not quite perfectly analogous, since we are talking about aerosols reflecting incoming solar radiation: the effective energy input from the sun actually *does* change, since more volcanic aerosols reflect away more incoming energy. However, the basic logic of a cooling influence modulating temperature in a variable equilibrium with a relatively constant energy input (‘warming influence’, ie., insolation at the top of the atmosphere) does apply.

Point 2:

I’m still puzzling over what mental model leads you to assert that:

Absence of cooling cannot generate warming. It can only allow temperatures to rebound from a previous level.

There seem to be at least two confusions. First, since every object in the universe that isn’t at absolute zero radiates energy, there is never (barring that exception) an ‘absence of cooling.’ And the earth system specifically is always radiating to space. That is in fact how (in broad strokes) the greenhouse effect works: GHGs reduce radiative efficacy, leaving more accumulated heat in the system, which then warms up, once again increasing radiative efficacy, ultimately resulting in a new and warmer equilibrium.

The second, and more puzzling, confusion, is the concept that “It can only allow temperatures to rebound from a previous level.” Here’s the idealized model equation, according to me at least:

Energy content = Warming rate – Cooling rate

Clearly, if there is a warming rate (from whatever cause), but an ‘absence of cooling’, the energy content will be determined solely by the warming rate associated with the incoming energy (again, from whatever source.)

According to you, that shouldn’t happen–which seems to indicate that you are working from some other model. Care to share? Maybe we can sort out the source of your confusion.

Point 3:

Coming at your statement from another angle, it seems to privilege the (otherwise unspecified) ‘previous level’, since the implication is that that ‘level’ will somehow once and forever control the possible temperature that the system can achieve. That would seem to imply a really remarkable system ‘memory’, and I have no idea what mechanism you think exists that would give this result. Again, care to share?

Finally, a thought experiment on this point. Let’s assume a planet–I’m mischievously going to call it “Nibiru”–orbiting a sun Far, Far Away. Nibiru has an atmosphere rather similar to Earth’s, but with a stratosphere just jam-packed with SO2 particulates. (I have no idea where they come from, but hell, this is a thought experiment–maybe there’s a local population of Maxwell demons which find the creation of them amusing.) So a very large fraction of the incoming solar radiation is immediately reflected away, resulting in a relatively low surface temperature as compared with Earth.

One day a small meteor made almost entirely of Unobtanium smacks into the Nibiruvian atmosphere and vaporizes. Stunningly, it turns out that Unobtanium is immediately fatal to the demons (despite their magical powers). The SO2 concentration begins to fall, and reaches Earthly levels within a couple of years. Now we have a planet which looks, from a radiative point of view, just like Earth.

So: what, in your view, keeps temperatures from rising to Earthly levels? Remember:

“Absence of cooling cannot generate warming. It can only allow temperatures to rebound from a previous level.”

In our thought experiment, the meteor impact created an ‘absence of cooling’. Yet the result was atmospheric parameters identical to Earth’s, and everything we know says that the result should be Earthly temperatures. How do you explain this contradiction?

7. 157
Victor says:

144 Barton Paul Levenson says:

V 137: if you want to insist that some event is caused by the absence of something then you let yourselves in for this sort of ridicule

BPL: Copious bleeding would follow the absence of skin. Infection would follow the absence of an immune system. Death would follow an absence of oxygen. Is it that great a leap to “an absence of sun screening makes the Earth warmer?” Are you really this out of it, or are you pretending?

Yes, if you peeled off some skin you would bleed. But that is not what caused the bleeding. Blood is produced within the body, not outside it. Your skin prevents the already existing blood from leaving the body. When skin is removed, bleeding ensues. That does NOT mean the bleeding is due to the absence of skin. For example, if you apply a tourniquet to your arm and then remove some skin from your hand, there will be no (or very little) bleeding.

The absence of an immune system is not what produces an infection, which is produced by bacteria entering the system. The immune system destroys or inactivates those bacteria. If you were in a totally sterile environment, the absence of an immune system would NOT produce an infection.

Similarly it is not the absence of oxygen which produces death. Many organisms can survive in an oxygen-free environment.

A good way to think of this is by recalling how a vacuum is produced: NOT by the absence of air from within, but by positive air pressure impinging from without. That’s probably the clearest example of what I’ve been trying to get across, because for so many years the cause of a vacuum was thought to be the absence of something.

You and the others are producing straw man arguments under the assumption that I’ve been denying the regulatory effect of volcanic aerosols. In other words, you are reading through the lens of your own bias. I totally agree that volcanic aerosols can have a cooling effect by blocking out some degree of solar irradiance. In that sense, they have a regulatory effect roughly comparable to the way skin prevents bleeding, the immune system prevents infection, and oxygen prevents asphyxiation. And yes, once that regulatory effect is removed, temperatures can rise. But the absence of that regulatory effect is by no means what produces the rise in temperature any more than the absence of air produces a vacuum — you’ve been confusing colloquialisms with scientific understanding. The best it can do is allow the temperature to rise to the level it would have attained had the aerosols not been present earlier.

8. 158
Victor says:

154
CCHolley says: “You clearly stated: “So no matter how you want to argue this, you are still left with a dramatic runup in temperature for which there is no explanation based on the current state of climate science.”

Volcanism, which you appear to be obsessed with, was a minor influencer of the period in question. The temperature rise is clearly understood as mostly driven by CO2 forcing. Your statement is completely false and the point of your volcano discussion is completely absurd. A red herring.”

According to the explanation offered at the Skeptical Science site I referenced earlier, the two major causes of warming during the period in question were “1. Increasing solar activity; and 2. Low volcanic activity (as eruptions can have a cooling effect by blocking out the sun).” Greenhouse gases are mentioned only as one of some “other factors.” Additionally, let me call your attention to the following graph, also from Skeptical Science: https://static.skepticalscience.com/images/co2_temp_broad.gif

Greenhouse gases are represented by the green line, temperatures by the red line. As you can see, the green line rises only very gradually during the period in question (ca. 1910-1940), while the red line rises abruptly. Given the striking difference it’s very hard to see how the former could have caused the latter.

“The scientists who brushed aside Callendar’s claims were reasoning well enough. (Subsequent work has shown that the temperature rise up to 1940 was, as his critics thought, mainly caused by some kind of natural cyclical effect, not by the still relatively low CO2 emissions. . .” from Spencer Weart, “The Discovery of Global Warming” https://history.aip.org/climate/co2.htm

“Working hard on your denialism. Or more likely intentional obfuscating.”

The need to embellish your disagreement with personal insults speaks to your own insecurity and does nothing to enhance your argument.

9. 159
Victor says:

Before everyone jumps all over me, I need to clarify what I meant when discussing a vacuum. A vacuum is indeed produced by removing the air from a container, so what I wrote was, strictly speaking, incorrect. What I meant to say was that the EFFECTS of a vacuum are produced by external air pressure, not simply by removing air. Thus when one struggles to open a vacuum sealed container due to “suction” it is not the vacuum inside the container that one is struggling against, but the air pressure external to the container. The more air one removes, the stronger is the external pressure, just as the more aerosols removed from the atmosphere as the effects of a volcanic eruption dissipates, the warmer the atmospheric temperature becomes.

10. 160
Al Bundy says:

Kevin McKinney: So, what about Tmin? It can often be a highly relevant number for summer heat stress.

AB: True. For example, humans can tolerate very high temperatures as long as they are given the opportunity to cool down. Perhaps small, highly insulated windowless sleeping rooms might become a standard feature for houses in the future. Heck, I bet such rooms would be one of the best ways to reduce carbon emissions today, especially if said rooms had internet. Why heat or cool your whole house or provide exterior views when you’re sitting in front of a screen?

Victor uses VEI…. and I’ll use Wiki.. “Under the VEI, ash, lava, lava bombs and ignimbrite are all treated alike.” ” It is, however, not obviously related to the amount of SO2 emitted by the eruption. ” “. This is clearly demonstrated by two eruptions, Agung (1963) and El Chichón (1982). Their VEI classification separates them by an order of magnitude in explosivity, although the volume of SO2 released into the stratosphere by each was measured to be broadly similar, as shown by the optical depth data for the two eruptions.”[7]”

What’s an order of magnitude difference amongst friends, eh, Vic?

11. 161
Victor says:

#155 Astringent says:

“A better measure of the effect of aerosols than counting eruptions on Wikipedia might be to look at Total Visible Optical Depth which measures the ‘dimming’ of the sun caused by the aerosols. Not hard to find and fairly un-ambiguously shows that, irrespective of event frequency, VOD was lower in the first part of the last century.”

Thanks for this clarification. After digging a bit via Google, I found this very interesting report from the IPCC: https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-7-2.html

Here’s the relevant graph: https://www.ipcc.ch/publications_and_data/ar4/wg1/en/fig/figure2-18.jpeg

As should be clear, we see very low values for VOD during the period in question (1910-1940), so you certainly do have a point. I stand corrected.

However, I must insist that there is no way any lack of volcanic activity at any level could raise temperatures to a point higher than what could be expected from a rebound from levels produced by any previous eruptions. As I’ve already gone into this issue I won’t repeat myself here. (See above)

12. 162
Dan H. says:

CCHolly @48,

I think Steve was referring to high summertime temperatures, not the average. Check out how high and low temperatures have changed during the summer months in the U.S. The low temperatures have increased dramatically over the past century. High temperatures have increased since the cooler 1970s, but are similar to the early 20th century. There has actually been a decrease in the percentage of days above 95F in most areas of the country. An average does not pick up on these subtleties.

https://www.epa.gov/climate-indicators/climate-change-indicators-high-and-low-temperatures

13. 163

V 157: it is not the absence of oxygen which produces death. Many organisms can survive in an oxygen-free environment.

BPL: Try it yourself some time.

V: …a vacuum is produced: NOT by the absence of air from within, but by positive air pressure impinging from without.

BPL: Where in God’s name did you get that idea? That’s about as wrong a statement as I’ve ever heard. A vacuum is produced by outside pressure? Is English your first language?

14. 164
jgnfld says:

The absence of cooling cannot lead to warming.

The absence of gases cannot lead to any vacuum effects.

Good Lord. Definitely bore hole time.

15. 165
mike says:

trolls getting fed. just sayin…

16. 166
Dan H. says:

BPL @ 163,
It is called the Venturi principle.

17. 167

DH 166: It is called the Venturi principle.

BPL: Right, the principle by which pressure lessens in a fast-flowing pipe when it goes through a choke point. Where, exactly, is the choke point in Earth’s atmosphere? And how does the atmosphere resemble flow in a pipe? Show your work.

18. 168
Thomas says:

163 BPL: Try it yourself some time.

Oh if only! The world’s average IQ would jump a whole point!!!

19. 169
20. 170
CCHolley says:

Victor @158

According to the explanation offered at the Skeptical Science site I referenced earlier, the two major causes of warming during the period in question were “1. Increasing solar activity; and 2. Low volcanic activity (as eruptions can have a cooling effect by blocking out the sun).” Greenhouse gases are mentioned only as one of some “other factors.”

However, for the Skeptical Science link for which you referenced under the “advanced” tab you will find the following quote which is representative of the current scientific understanding:

“CO2 and the Sun played the largest roles in the early century warming, but other factors played a part as well. For example, human aerosol emissions caused a slight cooling, ozone and other greenhouse gases caused a slight warming, low volcanic activity resulted in a slight warming, and natural cycles like the Atlantic Multidecadal Oscillation (AMO) may have contributed to the warming as well.”

Greenhouse gases are represented by the green line, temperatures by the red line. As you can see, the green line rises only very gradually during the period in question (ca. 1910-1940), while the red line rises abruptly. Given the striking difference it’s very hard to see how the former could have caused the latter.

It might be hard to understand if the effect of adding CO2 to the atmosphere were linear, but it is not, it is logarithmic. Model runs duplicate the warming. Also as stated before, the rise to 1940 is somewhat an illusion due to the inflated wartime temperature record.

The need to embellish your disagreement with personal insults speaks to your own insecurity and does nothing to enhance your argument.

Strictly an observation. If you consider that an insult, then YOU must be insecure.

21. 171
CCHolley says:

Dan H @162

I think Steve was referring to high summertime temperatures, not the average. Check out how high and low temperatures have changed during the summer months in the U.S. The low temperatures have increased dramatically over the past century. High temperatures have increased since the cooler 1970s, but are similar to the early 20th century. There has actually been a decrease in the percentage of days above 95F in most areas of the country. An average does not pick up on these subtleties.

I think you are reading the charts wrong.

Figure 1 shows heat index with the exception of the dust bowl anomaly going up.

Figure 2 shows unusually hot summer temperatures going up.

Figure 3 shows unusually cold winter temperatures going down.

Figure 4 shows a map of weather stations with change in trends of unusually hot days (95th percentile not 95 degrees). Visually you might conclude that there are more stations with less, but figure 2 would tell you that overall the trend is slightly up.

Figure 5 shows a map of weather stations with change in trends of unusually cold days. Visually this clearly shows a significant decrease in cold days. Only a small handful of stations have more.

Figure 6 shows the number of record daily highs going up and the number of record daily lows going down.

22. 172
Victor says:

Yes, I admit it. I was so eager to make my point that I misleadingly confused a vacuum with the effect produced by it. I recognized my blunder shortly after I made it, and immediately corrected myself. (See above.)

I was moreover reminded by Astringent that there is a difference between the total number and intensity of volcanoes and the VOD index, which is the more meaningful measure as far as cooling aerosols are concerned. I looked into this and admitted that he was right and my earlier assessment had been misleading. (Once again, see above.)

However, with regard to the principal point I’ve been arguing, i.e. that a lack of volcanic activity cannot have contributed, to any significant degree, to the extreme global warmup we see from ca. 1910 through ca. 1940, I must say I’m astonished at the inability (or unwillingness) of anyone responding here to grasp that very basic point. Lots of energy has been devoted by commenters here expounding on the nature of heat and cooling and it’s all been a huge waste of time as there is little to nothing in any of this I would disagree with. Of course, an elimination of the cooling system in my computer would cause it to “heat up.” But strictly speaking this is simply a colloquial expression which, taken literally, is incorrect — as I’m sure everyone here recognizes. The true source of heat is the computer itself, NOT the removal of the cooling system. Is that really so hard to understand?

If I cool my room with an air conditioner for several hours and then turn it off, the room will heat up for sure, but the source of the heat is certainly NOT the absence of air conditioning, but the temperature of the surrounding environment. Which should tell us that the temperature in the room cannot rise above the temperature of the surrounding environment simply because the air conditioner has been turned off.

If global average atmospheric temperature is, let’s say, 0 degrees Celsius, and there is a major volcanic eruption with a high VOD index, then we would expect the temperature to go down somewhat, due to the cooling effect of the aerosols produced. Let’s say it goes down by .1 degree. And since most such aerosols tend to dissipate after a year or so, let’s say that during the period of dissipation, the temperature increases as a result to approximately its original level of 0. Is there any reason to believe the temperature could rise above that level simply due to the absence of any additional eruptionsm, as though the lack of such eruptions were capable of generating additional heat?

So if we take some measurements after that eruption and determine that the temperature has in fact risen to .4 degrees Celsius, it would seem impossible to claim that this increase, or indeed any part of it, is due to a lack of subsequent eruptions. We are, it seems to me, forced to conclude that the rise in temperatures must have some other cause.

If someone sees a flaw in this reasoning, by all means point that out. But please don’t accuse me of being an idiot or a “denier” because I’ve refused to admit that my computer will heat up if the cooling fan turns off. I’ve never made such a ridiculous claim, and if you think I have then you need some remedial training in language comprehension.

23. 173
Victor says:

164 jgnfld says:

“The absence of cooling cannot lead to warming.

The absence of gases cannot lead to any vacuum effects.

Good Lord. Definitely bore hole time.”

Please don’t put words into my mouth. Of course the absence of cooling can, under certain conditions, lead to warming. If you had understood what I wrote you would not assume that this is what I meant. It’s not a question of what “leads to” warming, but what “produces” warming. What I asserted, and I was very clear about that, was that the absence of cooling cannot produce additional warming. This is so basic it boggles the mind to think that anyone following a science blog could fail to get it. Sure, turning off the air conditioner can “lead to” the room getting warmer. But it could never produce that additional warmth, which is produced by the environment, NOT the absence of an air conditioner.

24. 174
Hank Roberts says:

> V … a vacuum

He’s talking about the device with which he cleans his house.
The fan removes air from inside it, then the atmosphere pushes the dirt into the bag.
‘s obvious.

Victor, that’s hardware, not climate.

25. 175

V 172: I must say I’m astonished at the inability (or unwillingness) of anyone responding here to grasp that very basic point.

BPL: Probably because that “very basic point” is dead wrong. Sorry, but reality is as it is, not as we would have it.

26. 176
jgnfld says:

@173 Re. “Sure, turning off the air conditioner can ‘lead to’ the room getting warmer. But it could never produce that additional warmth, which is produced by the environment, NOT the absence of an air conditioner.”

The local environment at the Earth’s surface–which “produces” no heat at all (that’s the Sun’s job)–is itself getting warmer due to our changing the radiation budget with greenhouse gas emissions. So yes, turning off that air conditioner–i.e., reducing aerosols–will in fact lead to measuring higher temps than previously. You see, the radiation budget operating at the time the air conditioner is stopped is not the same radiation budget that operated when the air conditioner was turned on.

I must say I’m astonished at your inability (or unwillingness) to grasp that very, very basic point.

27. 177
zebra says:

For those feeding Victor:

I understand that responding to trolls has its purposes. However, I am disappointed in the extent to which people “play along” when someone like V is engaging in junior-high word games.

If Victor were a serious student, and we wanted to educate him, would not the first step be to establish, and demand the use of, proper terminology? If Victor isn’t willing to maintain the discipline of precision that scientists, or those wishing to become scientists or engineers, must practice, then he can’t claim to be debating at their level.

I still don’t know what the heck he is talking about.

Victor, if you have a hypothesis or a conjecture about some climate phenomenon, please state it, formally, in scientific language.

28. 178
Timothy Wilhoit says:

Dan H. @ 162

I’ve seen graphs (apparently from Steve Goddard’s site) showing lower readings for daytime highs in CONUS spanning over the last century. I had a look on NOAA’s site to get more information about the U.S. Historical Climatology Network. They had an article addressing concerns about poor siting at some of their stations. After investigation they discovered:

“…the sign of the bias is counterintuitive to photographic documentation of poor exposure because associated instrument changes have led to an artificial negative (“cool”) bias in maximum temperatures and only a slight positive (“warm”) bias in minimum temperatures.”

https://www.ncdc.noaa.gov/ushcn/station-siting

Instrument changes (to electronic sensors) over the last 25 years has lead to an overall “cool” effect. The adjusted numbers are better but with some residual “cool” effect. The so-called skeptic crowd are happy to use these figures (the unadjusted ones, I’m sure) to create a false impression of cooling in CONUS in the last century. That’s why they like using the average high temperatures, not high/low averages.

Although they seem happy hammering other people for co-mingling data, they don’t have a problem doing it themselves.

29. 179
Victor says:

#177 Zebra: “Victor, if you have a hypothesis or a conjecture about some climate phenomenon, please state it, formally, in scientific language.”

Glad to. Let’s assume an average global temperature of 0 degrees Celsius and a subsequent volcanic eruption whose aerosols cool that temperature to -.1 degrees. Assuming that these aerosols will dissipate over time, we can expect the temperature to rise to approximately its initial level (0 degrees) eventually — all other things being equal, natch. With me so far?

Now let’s assume that there are no other volcanic eruptions over the next 30 years. And during that time the average global temperature rises by, say, .5 degrees. As I understand it, you believe that the aforementioned absence of volcanic activity can be seen as causing at least some part of this additional rise in temperature over and above the initial 0 degree level. If that is indeed the case, can you please explain how such a rise in temperature can be due to what amounts to NO influence whatsoever? Or would you be willing to admit that there must be some cause other than the lack of volcanic activity?

30. 180
zebra says:

Victor #179,

Sorry, you have not offered a hypothesis or conjecture.

You have, however, illustrated my point: You trying to engage in a “definition debate”, which is what people do when they are in middle school or high school. It consists of saying “my point is valid because ’cause’ is/should be defined this way”. (Nyah nyah nyah is often added at the end.)

But in science, people agree to what words mean before having a debate. If someone says “x is caused by a lack of volcanic activity”, we don’t argue about the definition of “cause”. We ask for a scientific statement that meets the criteria for a hypothesis. You have yet to provide such a statement.

If all you want to do is discuss the philosophy of cause and effect, we can do that without reference to GMST. But if you want to discuss GMST, you have to base it on actual physical effects and the theoretical constructs in physics (thermodynamics, and so on) that are relevant.

Which is it?

31. 181
Dan H. says:

CCHolley,

No, I am reading them just fine. Figure 2 shows an increase, if you selectively choose the rather cool decade of the 1970s. Compared to the much warmer 1930s or 50s, there is little change. This is apparent in Figure 1 also, with little difference in heat waves spanning the entire 120 years, except to say that the 1930s were much hotter, and the 1960s and 70s were much colder. Contrarily, the low temperatures are much higher than at any point in the temperature record. Addistionally, I agree with your interpretation that Figure 4 shows a decrease in unusually hot summer days. Further confirming my previous statement.

I have no argument with your interpretation of the other figures, except to say that they have nothing to do with high summer temperatures. Yes, winter temperatures have increased. This is true in not just the average, but the decrease in especially cold days.

That is my entire point with using an average, and claiming that everything associated with the average is increasing. This is simply not true as the figures indicate. The large increase in low temperatures is driving the average higher.

32. 182
jgnfld says:

Let’s see. First you assume there is no global warming from the greenhouse effect caused by the warming from additional greenhouse gasses being added to the atmosphere between time one and time two, and then you conclude that if your assumption is true, there is no global warming.

GREAT–and quite typical–example of denier “logic”!

The GWPF published a study last year which made the same assumption and quite unsurprisingly came to the same conclusion.

Try real logic: Aerosols (in general) cool and greenhouse gases warm. One must establish the radiation budgets at time one and at time two to attribute what is going on. It is quite possible for man-released greenhouse gasses to contribute over 100% of warming over time if there is concurrent cooling going on or for aerosols to contribute over 100% of cooling over time if there is concurrent warming going on if one looks at both factors simultaneously. Example: If there is .1 degree of cooling from aerosol additions from time one to time two and there is .5 degree of warming overall, unless something else is going on, you must conclude that greenhouse gases warmed the atmosphere .6 degrees and so man caused greenhouse gas additions caused 120% of the warming while aerosols caused 20% of the cooling. 120%-20%=100%.

And you really do need to look at warming factors and cooling factors simultaneously. See IPCC AR5 Summary for Policy Makers Section C and Figure SPM 5 in that section.

http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_SPM_FINAL.pdf

33. 183
Victor says:

#180 Zebra says:

“Sorry, you have not offered a hypothesis or conjecture.

You have, however, illustrated my point: You trying to engage in a “definition debate”, which is what people do when they are in middle school or high school. It consists of saying “my point is valid because ’cause’ is/should be defined this way”. (Nyah nyah is often added at the end.)”

How would YOU define it, Zebra?

“But in science, people agree to what words mean before having a debate. If someone says “x is caused by a lack of volcanic activity”, we don’t argue about the definition of “cause”. We ask for a scientific statement that meets the criteria for a hypothesis. You have yet to provide such a statement.”

What terms would you like me to define? It all seems pretty obvious to me.

“If all you want to do is discuss the philosophy of cause and effect, we can do that without reference to GMST.”

There was nothing remotely associated with philosophy in the hypothetical I posed. Simple logic is fundamental in both philosophy and science.

“But if you want to discuss GMST, you have to base it on actual physical effects and the theoretical constructs in physics (thermodynamics, and so on) that are relevant.”

I thought that’s what I was doing. What physical effects have I omitted? And what theoretical constructs do you have in mind?

I think you’re bluffing, Zebra. I don’t think you have a clue as to what constitutes a valid scientific hypothesis. I posed two very straightforward questions. Why don’t you try answering them instead of dodging the issue by blowing smoke.

34. 184
Victor says:

182 jgnfld says:

“Let’s see. First you assume there is no global warming from the greenhouse effect caused by the warming from additional greenhouse gasses being added to the atmosphere between time one and time two, and then you conclude that if your assumption is true, there is no global warming.”

Wow! Whose post were you reading? I assumed nothing whatever about the greenhouse effect, which is irrelevant to the hypothetical I presented. I also made no reference to global warming. Do you understand the meaning of the phrase “all other things being equal”?

“Try real logic: Aerosols (in general) cool and greenhouse gases warm. One must establish the radiation budgets at time one and at time two to attribute what is going on.”

Yes, aerosols cool and greenhouse gases warm. Why did you think I needed to be reminded of that? Radiation budget is irrelevant to the point I was making. All that was needed was the (hypothetical) temperatures.

“It is quite possible for man-released greenhouse gasses to contribute over 100% of warming over time if there is concurrent cooling going on or for aerosols to contribute over 100% of cooling over time if there is concurrent warming going on if one looks at both factors simultaneously.”

This looks like a tautology. In any case, I see no reason not to agree. What’s your point?

“Example: If there is .1 degree of cooling from aerosol additions from time one to time two and there is .5 degree of warming overall, unless something else is going on, you must conclude that greenhouse gases warmed the atmosphere .6 degrees and so man caused greenhouse gas additions caused 120% of the warming while aerosols caused 20% of the cooling. 120%-20%=100%.”

You are seeing what you want to see and hence pursuing a straw man. I said nothing whatever about greenhouse gases. I was talking about the effects of volcanic aerosols.

“And you really do need to look at warming factors and cooling factors simultaneously.”

That’s what I was doing.

“See IPCC AR5 Summary for Policy Makers Section C and Figure SPM 5 in that section.

Thanks for that link. Very instructive:

“Volcanic forcing is not included as its episodic nature makes it difficult to compare to other forcing mechanisms.” From caption accompanying Figure SPM.5, “Radiative forcing by emissions and drivers.” Nowhere in that document could I find any reference to any warming effect due to a lack of volcanic activity.

I posed a question at the end of my hypothetical. Why don’t you cut to the chase and see if you can come up with an answer?

35. 185
nigelj says:

Victor @172

“However, with regard to the principal point I’ve been arguing, i.e. that a lack of volcanic activity cannot have contributed, to any significant degree, to the extreme global warmup we see from ca. 1910 through ca. 1940, I must say I’m astonished at the inability (or unwillingness) of anyone responding here to grasp that very basic point.”

You are simply completely wrong. A lack of volcanic activity below the norm (this is the important thing) for 1910 – 1940 means less dust than normal, which means more solar warming for a few years so temperatures increased a bit. Volcanic activity was not the only factor causing warming through this period, the solar cycle itself was positive, and CO2 emissions were starting to get significant.

So anyway a reduction over time in cooling can lead to warming in a sense, if some fundamental thing changes like less dust in the atmosphere. Warming is just a change in temperature from some causal factor.

36. 186
CCHolley says:

Dan H. @181

That is my entire point with using an average, and claiming that everything associated with the average is increasing. This is simply not true as the figures indicate. The large increase in low temperatures is driving the average higher.

I don’t think anyone claimed that everything associated with the average was increasing. However, the increasing average does show that the climate is warming.

Never said the other information was not interesting. The fact that extremely cold winter days are declining rapidly verses the number of extreme summer temperature days is, in fact, as predicted by theory. The heat retention of CO2 forcing should result in winters warming faster than summers. So there is no surprise in the data you reference.

37. 187
CCHolley says:

I assume Victor’s whole discussion on vulcanism is to put doubt on our understanding of what caused the early century warming. Then, in his logic it follows that there could be some other unknown cause such as long term natural variation that could also be applied to the current warming trend.

This is a fallacy, of course.

We do not have the best records for this period for both temperatures and forcings. Although attribution studies can be done based on the best information available at the time, they remain highly uncertain. However, based on current work, the most likely major causes are CO2 and solar forcings. Volcanism played a role, but it was relatively minor. Nevertheless, the fact that there is uncertainty in the attribution for this period does not mean our understanding of climate is incomplete. On the contrary. We know what drives climate. Radiative forcings are well understood and for the amount of warming that appears to have occurred, changes in radiative forcing must be responsible. This regardless of whether or not we can identify with precision which ones played exactly what role. Natural unforced variation although not particularly well understood simply cannot drive this level of warming and there is no evidence that such long term variations of significant impact exist.

So, to say that any lack of understanding for the period in question casts doubt on AGW theory is absurd. First, if there were some unknown cause for warming of the first half of the past century, the possibility would have to based on some evidence and be explainable by physics. It isn’t enough to just say because we don’t know with high certainty what exactly caused what part of the warming that another possibility exists. Science does not work that way. Second, the physics of the greenhouse effect are well known. We can use physics to calculate that the climate sensitivity for CO2 is about one degree with an additional one degree from water vapor feedback. So for a low climate sensitivity, one must show that high negative feedbacks exist. Of course there is no viable theory attempting to explain such feedbacks nor is there any evidence to suggest any exist.

Victor’s volcano discussion is just one big fat red herring and nothing more.

38. 188
Victor says:

176 jgnfld says:

“The local environment at the Earth’s surface–which “produces” no heat at all (that’s the Sun’s job)–is itself getting warmer due to our changing the radiation budget with greenhouse gas emissions. So yes, turning off that air conditioner–i.e., reducing aerosols–will in fact lead to measuring higher temps than previously. You see, the radiation budget operating at the time the air conditioner is stopped is not the same radiation budget that operated when the air conditioner was turned on.”

What, exactly, are you trying to say? What on Earth does the “radiation budget” have to do with the workings of an air conditioner?

Look, I’ll make it REAL easy for you. Your room is hot. You turn on the air conditioner for a few hours, which cools it down. You then turn the air conditioner off, and, over time, the room warms up again. Now listen carefully, because this is very important: turning off the air conditioner can never raise the temperature of the room to a point higher than it would have been had the a.c. never been turned on at all. So forget about the “radiation budget,” or the effect of greenhouse gases, because they have nothing to do with it. Let me repeat: turning off the air conditioner can never raise the temperature of the room to a point higher than it would have been had the a.c. never been turned on at all.

And obviously the same goes for volcanic aerosols: the dissipation of volcanic aerosols over time can never raise the temperature of the Earth to a point higher than it would have been had there never been any volcanic eruptions at all. Sorry, but I can’t make it any simpler than that. If you still don’t understand it, then there is no hope for you.

39. 189

V 188: turning off the air conditioner can never raise the temperature of the room to a point higher than it would have been had the a.c. never been turned on at all.

BPL: You have sunlight coming in, and atmospheric back-radiation from greenhouse gases. Mask the inputs for a while with volcanic aerosols. When the aerosols go away again, the temperature can rise above what it was, because the atmospheric back-radiation has increased in the mean time.

You’re welcome.

40. 190
zebra says:

Victor #183,

A hypothesis about GMST would be one sentence or so, without long narratives about hypotheticals or air conditioners.

It would have some quantitative prediction, like:

“If all other variables do not change their behavior, if volcanic activity declines to near zero for a 20-year period, there would be no statistically significant change in the rate at which GMST is increasing during that period.”

Is that what you are saying? If not, what??

The hypothesis is really a shorthand way of describing the experiment (or calculation or modelling) that you intend to perform; it establishes the parameters and what you will be measuring. (Saying “no change” is really a formality; you may think there will be a change, but testing for statistical significance makes more sense with that wording.)

So far, you haven’t come close to anything like this.

41. 191
jgnfld says:

@188

Let me make it real easy for you: It depends on the radiation budgets operating when you turn your AC on and and when you turn it off.

If you turn it on in the morning when the temps inside and out are, say, 25C and turn it off in the afternoon when the temps are 35C outside, darned if the room doesn’t warm up to 35C, or even 40C+ if there is greenhouse heating through south facing windows.

Alternatively, if you turn on the AC when it is 35C out (and possibly 40C+ inside the room if there are south facing windows) and turn it off when it is 25C out and the sun is down, darned if the room doesn’t cool off to near 25C (not completely to 25C due to daylight heating stored in the thermal mass of the house being released).

In your AC arguments, you are assuming something that does not exist: A constant outdoor temperature and no other factors like changing solar insolation through the windows in the room. That is, you are assuming a constant radiation budget at times one and two. That doesn’t happen in the real world.

Equivalently, in your Earth arguments you are assuming the same thing. But there simply is no constant radiation budget on Earth between points separated by years. Importantly, over multiple decades, the greenhouse effect is dominant over volcanism at least under our present conditions but other things are going on as well.

You are simply trying to assume away greenhouse heating. Fine, do it. It just means your arguments are completely foolish.

42. 192

V 188: the dissipation of volcanic aerosols over time can never raise the temperature of the Earth to a point higher than it would have been had there never been any volcanic eruptions at all.

BPL: Can you write that down as an equation?

43. 193
Dan H. says:

CCHolley,
Yes, the theory states that warming should be most prevalent under the coldest conditions; the high latitudes, wintertime, and summer lows. The previous argument was concerning summertime highs, which have not shown any significant change.

44. 194
Victor says:

187 CCHolley

Thanks, CC, for your very thoughtful and obviously sincere response. But first things first. Before getting into the larger significance of the issues I’ve raised, I would appreciate it if you would either acknowledge or contest my claim that a lack of volcanic activity could not possibly be even partially responsible for the extreme run-up of global temperatures recorded between ca. 1910 and 1940. At best, one might want to argue that the dissipation of aerosols from previous eruptions could have been responsible for a rebound from some earlier cooling event, but the rebound would have been caused by the dissipation of cooling aerosols, NOT by a lack of subsequent volcanic activity. And a rebound is certainly not sufficient to provide a cause for the original heat level, assuming it was so high as to contribute to the early 20th century warming, however indirectly. Do you agree, or is there something you see in the evidence that I do not?

“I assume Victor’s whole discussion on vulcanism is to put doubt on our understanding of what caused the early century warming. Then, in his logic it follows that there could be some other unknown cause such as long term natural variation that could also be applied to the current warming trend.

This is a fallacy, of course.”

The argument you present is circular. It is the evidence that must be considered when we evaluate any hypothesis. Yet for you, the many uncertainties in interpreting the evidence don’t really matter, because the hypothesis has to be valid in any case. Why? because of “the physics.” Yet it is “the physics” that the evidence is expected to confirm — and in many cases does not.

You, like so many other supporters of the mainstream view, treat “the physics” as though it were some rock solid truth that could not possibly be in error. Sorry, but that’s not how science works. The “physics” on which the mainstream climate view is based is not simply a matter of the usual laws, such as thermodynamics, on which mainstream science correctly relies — it is far more complex than that, with many uncertainties. It is, therefore, a theory, not a law, a theory which can be validated only through testing on the basis of real evidence, not the manipulation of mathematical formulas, statistical or otherwise.

The early 20 th century run-up in temperature presents a challenge for mainstream climate science because it is IN FACT not at all easy to explain. And as I’ve noticed time and again, when “mainstream” climatologists are forced to come up against evidence that challenges their theories, they fall back on very dubious speculations that in at least some cases, make very little sense. I’ve referred to these as “ad hoc explanations,” i.e., explanations literally pulled out of a hat, with no organic relation to the overall theory, but nevertheless handy as a sort of dodge. The “lack of volcanic activity” explanation is a perfect example, but there are others as well.

Enough said for now. I’ll be posting more on this issue presently.

45. 195
Victor says:

Children children children. We seem to be having a bit of a reading comprehension problem. I’ll respond to BPL, since his attempt is brief and to the point. But the same logic applies to everyone else.

BPL: “You have sunlight coming in, and atmospheric back-radiation from greenhouse gases. Mask the inputs for a while with volcanic aerosols. When the aerosols go away again, the temperature can rise above what it was, because the atmospheric back-radiation has increased in the mean time.”

Nice example. But the temperature rise you describe as due to an increase in back-radiation would have happened in any case, regardless of whether the inputs had initially been masked by volcanic aerosols. The volcanic activity is therefore irrelevant. It is certainly not the cause of the temperature rise, which you yourself attribute to background radiation.

46. 196

Another crack at helping Victor out here–I’ll do that (one hopes!) by staying within the conceptual frame he puts forth. He wrote:

Let’s assume an average global temperature of 0 degrees Celsius and a subsequent volcanic eruption whose aerosols cool that temperature to -.1 degrees. Assuming that these aerosols will dissipate over time, we can expect the temperature to rise to approximately its initial level (0 degrees) eventually — all other things being equal, natch. With me so far?

Now let’s assume that there are no other volcanic eruptions over the next 30 years. And during that time the average global temperature rises by, say, .5 degrees. As I understand it, you believe that the aforementioned absence of volcanic activity can be seen as causing at least some part of this additional rise in temperature over and above the initial 0 degree level. If that is indeed the case, can you please explain how such a rise in temperature can be due to what amounts to NO influence whatsoever? Or would you be willing to admit that there must be some cause other than the lack of volcanic activity?

(I’ve bolded what I take to be the crucial bit.)

The problem with this is that the question as posed is unanswerable, because we don’t have all the necessary information: specifically, we don’t know what the volcanic influence was during the initial period (ie., prior to the first eruption.)

On one hand, we might assume that there has been none for sufficient time prior to the posited eruption for aerosols to fall to zero. In that (counterfactual) case, Victor’s question is indeed a poser: he has assumed that ‘everything else is equal’. So we would have a temperature rise that literally, given the assumptions posited, can have no cause whatever–now *everything* potentially causal is equal, not just ‘everything else.’

On the other hand, we might assume that there has been some lower, but non-zero ‘background level’ of volcanic aerosols-let’s arbitrarily make it 2 on a scale of 10, for ease of discussion. In this case, everything makes sense (at least qualitatively speaking): you have temperature dropping when aerosol forcing increases from 2 to (let’s say) 8, then rising again as the aerosols clear. During the subsequent period, you have aerosol forcing of 0, by Victor’s assumption, and sure enough, the temperature rises higher than it had previously been, when the forcing was 2. I wouldn’t say that it’s due to “NO influence whatsoever,” though, because I consider 0 to be a number.

To be boringly explicit, I’d see the second case as a cartoon model of reality, and the first as a case of assumptions containing a masked impossibility. I call it an “impossibility” mostly because of the logical contradiction exposed above, but also because, though I couldn’t find the VOD data (referred to above) graphed in a reasonable amount of time spent searching, I really doubt that VOD *ever* drops to zero for any length of time. (Ie., I have the impression that there’s a volcano eruption with *some* small explosivity pretty much all the time.)

I did find an oldish paper (2000, I think) from Alan Robock which bears on this point, and supports my idea. See plate 6, which gives optical depth values for various volcanic indices, graphed from 1850 to the mid-’90s or so. Visually–insert usual caveats about Mk. 1 eyeball here–you can certainly see that the period from the early teens to ca. 1960 was quiet, but not quite non-zero for most indices (some can’t be distinguished visually from zero.)

All in all, the graph seems much in line with my case 2–except of course with real numbers instead of arbitrary ones.

Robock, 2000:

http://climate.envsci.rutgers.edu/pdf/ROG2000.pdf

P.S.:

Tangentially related, but illustrating that SO2’s effects are not the same in different layers of the atmosphere (effects of ‘effusive versus explosive eruptions’), and darned interesting in its own right, a paper out in June:

https://www.sciencedaily.com/releases/2017/06/170621133451.htm.

47. 197
CCHolley says:

Dan H. @193

Yes, the theory states that warming should be most prevalent under the coldest conditions; the high latitudes, wintertime, and summer lows. The previous argument was concerning summertime highs, which have not shown any significant change.

Steve Case @143 was questioning TMax i.e. the highest recorded temperature for a given year. And with the tone of his post, he was implying that this somehow casts doubt on warming. When you look at this in context of the whole, it is trivial. That is my point. The data, no matter how you look at it shows warming as expected.

48. 198
Brian Dodge says:

“…concerning summertime highs, which have not shown any significant change.”
Says who?
http://onlinelibrary.wiley.com/doi/10.1029/2012GL053361/full
“[21] Figure 2 displays globally averaged time series and trends for warm spell event length (HWD) and peak of the hottest event (HWA). All three indices show increasing trends for both aspects, however yearly values and trend magnitude vary.

49. 199
Al Bundy says:

Victor: the dissipation of volcanic aerosols over time can never raise the temperature of the Earth to a point higher than it would have been had there never been any volcanic eruptions at all.

AB: So? Methinks you’re trying to “win” via legalistic parsing. You’re admitting that your original point was goop in a way that you hope makes it look like your point wasn’t goop. Kind of like tripping and then doing a somersault and returning to a standing position while raising your arms triumphantly and saying, “Ta-da!”

Dude, you tripped, which is no big deal, but that “Ta-da!” just makes you look foolish.

50. 200
jgnfld says:

@194

“The volcanic activity is therefore irrelevant.”

No. It forms part of the radiation budget at any particular time and therefore can be of little or great relevance at that time depending on releases of ash, sulfates, etc. You just can’t escape that.

It’s just like any other factor in the global equation you refuse to produce.