Guest Post by Willis Eschenbach
Let me start explaining the link from Picasso to climate science by looking at what Dr. Nir Shaviv called “the most boring graph I have ever plotted in my life”.
This is the graph of the changes in the best estimate of the range of what is called “climate sensitivity” over the last forty years or so.
What is climate sensitivity when it’s at home? To explain that, I’ll have to take a slight detour. First, downwelling radiation.
“Downwelling” in climate science means headed down towards the planetary surface. Downwelling radiation is the total radiation going downwards towards the surface. It is composed of sunshine (shortwave) plus thermal radiation from the atmosphere (longwave). In climate science, this quantity, total downwelling radiation, is called “forcing”, abbreviated “F”
The central paradigm of modern climate science is that if you change the amount of downwelling radiation (forcing), that the surface temperature perforce will change. The claim is that everything else averages out, and if the forcing increases, then surface temperature needs to change to maintain the global energy balance. It has to change. It must.
In short, the central paradigm of modern climate science is the following:
In the long run, global temperature change is proportional to global forcing change.
The putatively constant proportion between the two, which is the temperature change divided by forcing change, is called the “climate sensitivity”.
“Climate sensitivity” is often expressed as the assumed change in temperature given a change of 3.7 watts per square metre (W/m2) in downwelling radiation. The determination of this so-called “climate sensitivity” is a central question arising out of the paradigm that temperature change is proportional to temperature change.
Which leads me to the most boring graph below. It shows the changes over time in the estimate of the value of the climate sensitivity.
Figure 1. Changes over time in the estimate of the climate sensitivity parameter “lambda”. “∆T2x(°C)” is the expected temperature change in degrees Celsius resulting from a doubling of atmospheric CO2, which is assumed to increase the forcing by 3.7 watts per square metre. FAR, SAR, TAR, AR4, AR5 are the UN IPCC 1st, second, third, fourth and fifth Assessment Reports giving an assessment of the state of climate science as of the date of each report
It is worth noting that since 1979, entire new scientific fields like DNA analysis have first been envisioned, then have come into being, and now have reached amazing levels of development … and during that same time, what Dr. Shaviv rightly calls “the most important question in climate” has gone nowhere. No progress at all.
Since 1979, the amount of computing power that we have available, both as individuals and large organizations, has skyrocketed. My trusty PowerMac has more computing ability than most universities had available in 1979. The cost has dropped as well, from $100,000 per “MIPS” (million instructions per second) to less than $1 per MIPS today. And the speed has gone through the roof, with supercomputers running climate models at more than a trillion floating point operations (which have the lovely name of “TeraFLOPs”) every second. The number of people investigating the value of climate sensitivity has also grown over time. And billions and billions of dollars have been spent on trying to answer the question.
So … since the Charney report on climate sensitivity in 1979 we’ve had huge, stupendous increases in:
• Computing power working on the question
• Hours of intensive research applied to the question
• Discussion, debate, and interest in the question
• Money spent on the question
And despite those huge increases in time, work, discussion, and computer power, the investigation of the question of the value of climate sensitivity has gone exactly nowhere. No progress.
How can we understand this scientific oddity? What is the reason that all of that valuable time, money, and effort has achieved nothing? I mean zero. Nada. No movement at all. The most boring graph.
Let me suggest that climate science is the victim of what I call the “Picasso Problem”. Pablo Picasso once said something that has stuck with me for a long time. He said:
“What good are computers? They can only give you answers.”
Now, I wrote my first computer program in 1963, more than half a century ago. I was sixteen. It ran on a computer the size of a small room. I’ve been programming computers ever since then. I’ve written programs to do everything from designing fabric patterns for huge catenary tents, to calculating next year’s tides from this year’s tide tables, to making the plasma-cutting files to guide the cutting of the steel parts for building 25-metre fishing boats, to analyzing the data and doing the math and creating the graphics for this very post. And over the years I’ve made big bucks with my succession of computers.
So when I read that Picasso was dissing computers with that statement, my initial response was to say “Whaa? Computers are great! What is this mad artist on about? I’ve made lots of money with my computer. How can they be no good?”
But upon more mature reflection, I realized that Picasso was right. Here’s what he meant:
Even the best computer can’t give you the right answer unless you ask it the right question.
To me, this was a crucial insight, one that has guided many of my scientific peregrinations—don’t focus too much on the answers. Put some focus on the questions as well.
So regarding climate science, what is the wrong question, and what is the right question? Once again, please allow me to get side-tractored a bit.
I first got interested in climate science around the turn of the century because of the increase in serial doomcasting regarding some rumored upcoming Thermageddon™. So I started with the basics, by learning how the poorly-named “greenhouse effect” was keeping the earth far warmer than the temperature of the Moon, which is at the same distance from the sun.
However, along the way, I read that the best estimate of the warming over the entire 20th century was on the order of 0.6 degrees Celsius. When I read that, I thought … “Whaa … less than one degree??? All this fuss and the temperature has changed less than one degree?”
I was surprised because of my experience repairing machinery which had a governor, and my experience with solar energy. I viewed the climate as a giant solar-driven heat engine, wherein the energy of the sun is converted into the ceaseless movement of the atmosphere and the ocean working against the brake of friction against the mountains and shores and the endless turbulent losses.
When one analyzes the efficiency or other characteristics of a heat engine, or when one uses tools like the Stefan-Boltzmann equation to convert temperature into the equivalent amount of thermal radiation, you have to use the Kelvin temperature scale (abbreviated “K”). This is the scale which starts at absolute zero. Temperature is a function of the motion of the molecules or atoms involved. And absolute zero is where molecular motion stops entirely.
You can’t use degrees Celsius or Fahrenheit for these calculations, because °C and °F have arbitrary zero points. You have to use the Kelvin scale, it’s the only one that works. Kelvin has the same size units as Celsius, just a different zero point, which is at minus 273.15°C (minus 459.67°F).
Now, the average surface temperature of the Earth is on the order of 14° Celsius, which is 57° Fahrenheit … or 287 Kelvin. And with that average global temperature of 287 Kelvin, the global temperature variation of 0.6 K over the 20th century is a temperature variation of a fifth of one percent.
This was the oddity that shaped my investigation of the climate … during a hundred year period, the temperature had varied by only about one fifth of one percent. This was amazing to me. I’d had lots of experience with governed systems because of my work with electrical generators. These need to be tightly governed so that their speed remains constant regardless of the changing load on the system. And what I’d found in my work with mechanical governors is that it’s quite hard to regulate a mechanical system to within one percent.
Yet despite droughts and floods, despite huge volcanic eruptions, despite constantly changing global cloud cover, despite all kinds of variations in the forcing, despite the hemispheric temperatures changing by ~ 13°C twice over the course of each and every year, despite the globe being balanced on a greenhouse effect which is holding it on the order of ~ 50°C warmer than the moon … despite all of those variations and changes, the average temperature of the Earth didn’t vary by a quarter of one percent over the entire 20th century.
That is amazingly tight regulation. Here’s a real-world example of why I was surprised by that stability.
I was looking at the speedometer today with my truck on “cruise control”. Cruise control in your car is a governor that keeps the speed of the vehicle the same regardless of changes in load on the truck. I set it for 50 miles per hour. Up and down hills it varied by plus and minus one mile per hour. That’s a computer-controlled engine that is speed-regulated to within ±2%, pretty tight regulation … but the Earth’s temperature is far better regulated than that. It stays within less than plus or minus one tenth of a percent.
To me at the time, that thermal stability was a clear sign of the existence of some unknown of natural thermostatic processes that acted in a very efficient manner to maintain the Earth’s temperature within those narrow bounds. So my own quest in the field of climate science was to find out what the natural phenomena were that explained the tight regulation of century-long planetary surface temperatures.
Which left me in a curious position. All of the established climate scientists were, and still are, trying to find out why the temperature is changing so much. They spend time looking at graphs like this, showing the variations in the Earth’s surface temperature:
Figure 2. HadCRUT global average surface temperature anomaly.
On the other hand, because I’m someone with an interest in heat engines and governors, I was trying to find out why the temperature has been changing so little. I spent my time looking at the exact same data as in Figure 2, but expressed in graphs like this:
Figure 3. HadCRUT global average actual surface temperature (the same data shown in Figure 2) and also the approximate average lunar temperature, in kelvin.
And that brings me back, after plowing that distant field, to the question of climate sensitivity and to Picasso’s prescient question, viz: “What good are computers? They can only give you answers.”.
I say that we have made zero progress in four decades of attempting to measure or calculate climate sensitivity because we are using our awesome computer power to investigate why the global temperature changes so much.
For me, this is entirely the wrong question. The question that we should be asking is the following:
Why does the global temperature change so little?
After much thought and even more research, I say the reason that global average temperature changes so little is that temperature is NOT proportional to forcing as is generally believed. As a result, the so-called “climate sensitivity” is not a constant as is assumed … and since it is not a constant, trying to determine its exact value is a fool’s errand because it has none. That’s why we can’t make even the slightest advance on measuring it … because it’s a chimera based on a misunderstanding of what is happening.
Instead, my hypothesis is that the temperature is maintained within narrow bounds by a variety of emergent phenomena that cool the earth when it gets too hot, and heat it up when it gets too cool. I have found a wide variety of observational evidence that this is actually the case. See the endnotes for some of my posts on my hypothesis.
But hey, that’s just my answer. And I freely agree that my answer may be wrong … but at least it is an answer to the right question. The true mystery of the climate is its amazing thermal stability.
Finally, how did an entire field of science get involved in trying to answer the wrong question? I say that it is the result of the 1988 creation of the Intergovernmental Panel on Climate Change (IPCC) by the United Nations.
In 1988, the field of climate science was fairly new. Despite that, however, the UN was already convinced that it knew what the problem was. Typical bureaucratic arrogance. As a result, in the UN General Assembly Resolution 43/53 from 1988, the Resolution which set up the IPCC, it says that the UN General Assembly was:
Concerned that certain human activities could change global climate patterns, threatening present and future generations with potentially severe economic and social consequences,
Noting with concern that the emerging evidence indicates that continued growth in atmospheric concentrations of “greenhouse” gases could produce global warming with an eventual rise in sea levels, the effects of which could be disastrous for mankind if timely steps are not taken at all levels,
And in response, it jumped right over asking if whether or not this was scientifically correct, and went straight to taking action on something that of course, the General Assembly knew nothing about. The Resolution says that the General Assembly:
… Determines that necessary and timely action should be taken to deal with climate change within a global framework;
Calls for action always make bureaucrats happy. So the IPCC, an expressly political “Intergovernmental” organization, became the defacto guiding light for an entire field of science … which turned out to be a huge mistake.
Now, up until that time, and since that time as well, every other field of science has managed to make amazing strides in understanding without any global “Intergovernmental” panel to direct their efforts. We’ve had astounding successes with our usual bumbling catch-as-catch-can scientific method, which involves various scientists working fairly independently around the planet on some scientific question, sometimes cooperating, sometimes competing, without needing or wanting anyone to “summarize the science” as the IPCC claims to do.
And given the lack of progress shown by the “Most Boring Graph” at the top of this post, I’d say that the world should never again put a bunch of United Nations pluted bloatocrats in charge of anything to do with science. If we had set up an “Intergovernmental Panel on DNA Analysis” when the field was new, you can be certain that long ago the field would have gone uselessly haring down blind alleys lined by nonsensical claims that “97% of DNA scientists agree” …
Over at Dr. Judith Curry’s excellent blog, someone asked me the other day what I didn’t like about the IPCC. I replied:
Here are some of the major reasons. I have more.
First, it assumes a degree of scientific agreement which simply doesn’t exist. Most people in the field, skeptics included, think the earth is warming and humans may well have an effect on it. But the agreement ends there. How much effect, and how, and for how long, those and many other questions have little agreement.
Second, it is corrupt, as shown inter alia by the Jesus Paper.
Third, it generally ignores anything which might differ from climate science revealed wisdom.
Fourth, it is driven by politics, not by science. Certain paragraphs and conclusions have been altered or removed because of political objections.
Fifth, in an attempt to be inclusive of developing countries, it includes a number of very poor scientists.
Sixth, any organization that ends up with Rajendra Pachauri as its leader is very, very sick.
Seventh, they’ve ignored actual uncertainty and replaced it with a totally subjective estimate of uncertainty.
Eighth, it lets in things like the Hockeystick paper and the numerous “Stick-alikes” despite them being laughably bad science.
Ninth, it makes “projections” that have little to no relationship to the real world, like Representative Concentration Pathway 8.5 (RCP 8.5).
Tenth, it generally excludes skeptics of all types, either directly or because skeptics know better than to associate with such an organization.
Eleventh, anyone making “projections” that go out to the year 2100 is blowing smoke up your fundamental orifice.
Twelveth, it is far, far too dependent on untested, unverified, unvalidated climate models.
Thirteenth, the IPCC generally thinks without thinking about it that warming is bad, bad, bad … which is the opposite of the actual effects of the warming since the Little Ice Age.
Fourteenth, the IPCC was given the wrong task at its inception. Rather than setting out to find what actually controls the climate, it was given the task of finding out how much CO2 we could emit before it became dangerous. That tasking assumed a whole host of things which have never been established.
Fifteenth … aw, heck, that’s enough. I have more if you are interested.
So … that’s the climate Picasso Problem. The field of climate science is trying to use computers to find an answer to the wrong question, and as a result, the field is going nowhere.
Here, we’re still in haze and smoke from the Camp Fire, and the number of fatalities is over seventy. I’m wearing an N95 mask when I go outside. Here’s the latest smoke map … Anthony Watts is up in Chico, in the bright red spot at the top, over 100 micrograms per cubic metre of smoke. I’m near the coast to the west of Santa Rosa, north of San Francisco, where it’s much better but still bad.
Keep a good thought over the fire victims, it’s hard times for all.
My best wishes to every one,
PS—As usual, I ask that when you comment, please quote the exact words you are discussing, so we can all understand both who and what you are replying to.
FURTHER READING: These are some of my posts explaining my hypothesis regarding why the global temperature is so stable, and providing evidence for the hypothesis
The Thermostat Hypothesis 2009-06-14
Abstract: The Thermostat Hypothesis is that tropical clouds and thunderstorms actively regulate the temperature of the earth. This keeps the earth at a equilibrium temperature.
Which way to the feedback? 2010-12-11
There is an interesting new study by Lauer et al. entitled “The Impact of Global Warming on Marine Boundary Layer Clouds over the Eastern Pacific—A Regional Model Study” [hereinafter Lauer10]. Anthony Watts has discussed some early issues with the paper here. The Lauer10 study has been controversial because it found that…
The Details Are In The Devil 2010-12-13
I love thought experiments. They allow us to understand complex systems that don’t fit into the laboratory. They have been an invaluable tool in the scientific inventory for centuries. Here’s my thought experiment for today. Imagine a room. In a room dirt collects, as you might imagine. In my household…
Further Evidence for my Thunderstorm Thermostat Hypothesis 2011-06-07
For some time now I’ve been wondering what kind of new evidence I could come up with to add support to my Thunderstorm Thermostat hypothesis (q.v.). This is the idea that cumulus clouds and thunderstorms combine to cap the rise of tropical temperatures. In particular, thunderstorms are able to drive…
It’s Not About Feedback 2011-08-14
The current climate paradigm believed by most scientists in the field can be likened to the movement of balls on a pool table. Figure 1. Pool balls on a level table. Response is directly proportional to applied force (double the force, double the distance). There are no “preferred” positions—every position…
Estimating Cloud Feedback From Observations 2011-10-08
I had an idea a couple days ago about how to estimate cloud feedback from observations, and it appears to have panned out well. You tell me. Figure 1. Month-to-month change in 5° gridcell actual temperature ∆T, versus gridcell change in net cloud forcing ∆F. Curved green lines are for…
Sun and Clouds are Sufficient 2012-06-04
In my previous post, A Longer Look at Climate Sensitivity, I showed that the match between lagged net sunshine (the solar energy remaining after albedo reflections) and the observational temperature record is quite good. However, there was still a discrepancy between the trends, with the observational trends being slightly larger…
Forcing or Feedback? 2012-06-07
I read a Reviewer’s Comment on one of Richard Lindzen’s papers today, a paper about the tropics from 20°N to 20°S, and I came across this curiosity (emphasis mine): Lastly, the authors go through convoluted arguments between forcing and feed backs. For the authors’ analyses to be valid, clouds should…
A Demonstration of Negative Climate Sensitivity 2012-06-19
Well, after my brief digression to some other topics, I’ve finally been able to get back to the reason that I got the CERES albedo and radiation data in the first place. This was to look at the relationship between the top of atmosphere (TOA) radiation imbalance and the surface…
The Tao of El Nino 2013-01-28
I was wandering through the graphics section of the TAO buoy data this evening. I noted that they have an outstanding animation of the most recent sixty months of tropical sea temperatures and surface heights. Go to their graphics page, click on “Animation”. Then click on “Animate”. When the new…
Emergent Climate Phenomena 2013-02-07
In a recent post, I described how the El Nino/La Nina alteration operates as a giant pump. Whenever the Pacific Ocean gets too warm across its surface, the Nino/Nina pump kicks in and removes the warm water from the Pacific, pumping it first west and thence poleward. I also wrote…
Slow Drift in Thermoregulated Emergent Systems 2013-02-08
In my last post, “Emergent Climate Phenomena“, I gave a different paradigm for the climate. The current paradigm is that climate is a system in which temperature slavishly follows the changes in inputs. Under my paradigm, on the other hand, natural thermoregulatory systems constrain the temperature to vary within a…
Air Conditioning Nairobi, Refrigerating The Planet 2013-03-11
I’ve mentioned before that a thunderstorm functions as a natural refrigeration system. I’d like to explain in a bit more detail what I mean by that. However, let me start by explaining my credentials as regards my knowledge of refrigeration. The simplest explanation of my refrigeration credentials is that I…
Dehumidifying the Tropics 2013-04-21
I once had the good fortune to fly over an amazing spectacle, where I saw all of the various stages of emergent phenomena involving thunderstorms. It happened on a flight over the Coral Sea from the Solomon Islands, which are near the Equator, south to Brisbane. Brisbane is at 27°…
Decadal Oscillations Of The Pacific Kind 2013-06-08
The recent post here on WUWT about the Pacific Decadal Oscillation (PDO) has a lot of folks claiming that the PDO is useful for predicting the future of the climate … I don’t think so myself, and this post is about why I don’t think the PDO predicts the climate…
The Magnificent Climate Heat Engine 2013-12-21
I’ve been reflecting over the last few days about how the climate system of the earth functions as a giant natural heat engine. A “heat engine”, whether natural or man-made, is a mechanism that converts heat into mechanical energy of some kind. In the case of the climate system, the…
The Thermostatic Throttle 2013-12-28
I have theorized that the reflective nature of the tropical clouds, in particular those of the inter-tropical convergence zone (ITCZ) just above the equator, functions as the “throttle” on the global climate engine. We’re all familiar with what a throttle does, because the gas pedal on your car controls the…
On The Stability and Symmetry Of The Climate System 2014-01-06
The CERES data has its problems, because the three datasets (incoming solar, outgoing longwave, and reflected shortwave) don’t add up to anything near zero. So the keepers of the keys adjusted them to an artificial imbalance of +0.85 W/m2 (warming). Despite that lack of accuracy, however, the CERES data is…
Dust In My Eyes 2014-02-13
I was thinking about “dust devils”, the little whirlwinds of dust that you see on a hot day, and they reminded me that we get dulled by familiarity with the wonders of our planet. Suppose, for example, you that “back in the olden days” your family lived for generations in…
The Power Stroke 2014-02-27
I got to thinking about the well-known correlation of El Ninos and global temperature. I knew that the Pacific temperatures lead the global temperatures, and the tropics lead the Pacific, but I’d never looked at the actual physical
Albedic Meanderings 2015-06-03
I’ve been considering the nature of the relationship between the albedo and temperature. I have hypothesized elsewhere that variations in tropical cloud albedo are one of the main mechanisms that maintain the global surface temperature within a fairly narrow range (e.g. within ± 0.3°C during the entire 20th Century). To…
An Inherently Stable System 2015-06-04
At the end of my last post , I said that the climate seems to be an inherently stable system. The graphic below shows ~2,000 climate simulations run by climateprediction.net. Unlike the other modelers, whose failures end up on the cutting room floor, they’ve shown all of the runs ……
The Daily Albedo Cycle 2015-06-08
I discussed the role of tropical albedo in regulating the temperature in two previous posts entitled Albedic Meanderings and An Inherently Stable System. This post builds on that foundation. I said in the latter post that I would discuss the diurnal changes in tropical cloud albedo. For this I use…
Problems With Analyzing Governed Systems 2015-08-02
I’ve been ruminating on the continuing misunderstanding of my position that a governor is fundamentally different from simple feedback. People say things like “A governor is just a kind of feedback”. Well, yes, that’s true, and it is also true that a human being is “just…
Cooling And Warming Clouds And Thunderstorms 2015-08-18
Following up on a suggestion made to me by one of my long-time scientific heroes, Dr. Fred Singer, I’ve been looking at the rainfall dataset from the Tropical Rainfall Measuring Mission (TRMM) satellite. Here’s s the TRMM average rainfall data for the entire mission to d…
Tropical Evaporative Cooling 2015-11-11
I’ve been looking again into the satellite rainfall measurements from the Tropical Rainfall Measurement Mission (TRMM). I discussed my first look at this rainfall data in a post called Cooling and Warming, Clouds and Thunderstorms. There I showed that the cooling from th…
How Thunderstorms Beat The Heat 2016-01-08
I got to thinking again about the thunderstorms, and how much heat they remove from the surface by means of evaporation. We have good data on this from the Tropical Rainfall Measuring Mission (TRMM) satellites. Here is the distribution and strength of rainfall, and thus …
Where the Temperature Rules The Sun
I’ve held for a long time that there is a regulatory mechanism in the tropics that keeps the earth’s temperature within very narrow bounds on average (e.g. ± 0.3°C over the 20th Century). This mechanism is the timing and amount of the daily emergence of the cumulus cloud field, and the timing and emergence of thunderstorms.
Where the Temperature Rules The Total Surface Absorption
Reflecting upon my previous post, Where The Temperature Rules The Sun, I realized that while it was valid, it was just about temperature controlling downwelling solar energy via cloud variations. However, it didn’t cover total energy input …
Dear Dr. McKitrick,
I’d be happy to address your concerns in the peer-reviewed literature. I think that would be the appropriate place to respond.
That said, a brief response is necessary to some of the points you made. It would be unfortunate if readers of your blog post were unaware of our prior research – research which addresses many of the issues you have raised.
This is the only response I will make on Dr. Curry’s website.
1. We routinely consider “ANTHRO only” fingerprints – see, e.g., the discussion on page 7 of the Supplementary Material of the 2018 Santer et al. Science paper. That discussion explains why the “ANTHRO only” and HIST+8.5 fingerprints yield very similar results. In my opinion, it is not unreasonable to expect other scientists to read such background information, particularly since it is cited in the Nature Climate Change paper you are critiquing.
2. You suggest – incorrectly – that we never evaluate the adequacy of model-based estimates of internal variability. We routinely make such evaluations. Examples are given in Fig. S7 of the 2018 Santer et al. Science paper and in Figs. 9 and 10 of the 2011 Santer et al. JGR paper.
3. Readers of your blog post might infer that we are unconcerned with differences between modeled and observed tropospheric warming rates. That is not the case. Many of our publications have attempted to understand the causes of differences between simulated and observed warming rates in the early 21st century. In the 2017 Santer et al. Nature Geoscience paper, we find that a large error in model climate sensitivity – Dr. Christy’s preferred hypothesis for model-versus-data warming rate differences – does not explain the temporal structure of these differences.
4. The pattern comparison statistic we use in our “fingerprint” work is an uncentered spatial covariance. It is not a correlation.
5. Even if one ignores all pattern information and considers global-mean changes alone, the amplitude of observed tropospheric temperature changes remains large relative to model-based estimates of internal variability (see, e.g., Fig. 1E in the 2017 Santer et al. Scientific Reports paper). This holds even for University of Alabama tropospheric temperature data.
6. Whether we do or do not remove residual long-term drift from control run data has minimal impact on our results. We only detrend once (over the final 200 years of each control run). We do not detrend each L-year chunk we are processing when we estimate time-dependent S/N ratios.
7. It is true that “rebound” of tropospheric temperature from the cooling caused by Pinatubo contributes to observed warming over the satellite era. You neglect to mention that our group has studied volcanically induced “rebound” of tropospheric temperature since 2001 (see, e.g., Santer et al. 2001, JGR; Santer et al. 2014, Nature Geoscience). The rebound effect is relatively small over the entire 40-year satellite tropospheric temperature record. Additionally, it is impermissible to focus solely on “rebound” from the eruptions of El Chichon in 1982 and Pinatubo in 1991, and to ignore the cooling effects of early 21st century volcanic eruptions. The climate effects of post-2000 volcanic forcing have been studied in a number of publications (e.g., Solomon et al., Science, 2011; Ridley et al., GRL, 2014; Santer et al., GRL, 2015). The effect of these post-2000 eruptions is to reduce S/N ratios for analysis periods sampling temperature changes in the early 21st century.
8. In other fingerprint detection work, we have tested not only against model-based estimates of internal variability, but also against “total” natural variability (internally generated plus variability forced by changes in solar irradiance and volcanoes). See, e.g., the 2013 Santer et al. “vertical fingerprint” paper in PNAS. For changes in the vertical structure of atmospheric temperature, we can detect an anthropogenic fingerprint even against this larger “total” natural variability.
9. The control run distributions of noise trends are Gaussian (at least for tropospheric temperature).