Monday, July 24, 2017

Myth: The Sun Caused Recent Global Warming and the Tropical Stratosphere Warmed

The outline for this post is as follows:
  1. The Myth and Its Flaws
  2. Context and Analysis (divided into multiple sections)
  3. Posts Providing Further Information and Analysis
  4. References

This is the "main version" of this post, which means that this post lacks most of my references and citations. If you would like a more comprehensive version with all the references and citations, then please go to the "+References" version of this post.

References are cited as follows: "[#]", with "#" corresponding to the reference number given in the References section at the end of this post.

1.  The Myth and Its Flaws

The myth states that the tropical stratosphere, a layer of the middle atmosphere, warmed and that the Sun caused most of the recent global warming. 

John Christy, Jospeh D'Aleo, and James Wallace III are the main proponents of this myth. I will refer to these three proponents as "Christy et al." in this post.

The myth's flaws: in a non-peer-reviewed blogpost/"report", Christy et al. claim the tropical stratosphere warmed, even though Christy knows the tropical stratosphere actually cooled. This distortion allows Christy et al. to:
  1. conceal stratospheric cooling, one of the signs of carbon-dioxide-induced (CO2-induced) global warming,
  2. unfairly criticize government attempts to limit CO2 emissions, and
  3. manufacture false evidence of long-term solar-induced warming, in the form of stratospheric warming.
Christy then cited this misleading blogpost/"report" in his Congressional testimony, using the "report" as evidence that natural factors such as the Sun, but not CO2, caused recent global warming. Christy makes this claim, despite the fact that Christy et al. do not address well-known evidence showing that the Sun did not cause most of the recent global warming. Christy also knows his solar-induced warming hypothesis is wrong, and he supported the hypothesis using indices he objects to. So Christy misled Congress, and likely did so knowingly. In doing so, Christy obscured the fact that increased levels of greenhouse gases such as CO2, not increased solar activity, caused most of the recent global warming.
(I make a more detailed case for CO2-induced global warming in "Myth: Attributing Warming to CO2 Involves the Fallaciously Inferring Causation from a Mere Correlation".)

[Side-note: This myth motivated me to start blogging again; it also helped change the way I view the climate science debate, as I discuss in "John Christy and Atmospheric Temperature Trends". So if you want to blame someone for me blogging again, then blame the three proponents of this myth.] 

2. Context and Analysis

Section 2.1: Solar-induced warming vs. CO2-induced warming

Earth's atmosphere contains multiple layers. The layer closest to the Earth's surface air is known as the troposphere. Above the troposphere is the tropopause, and above the tropopause is the stratosphere. So the order of these atmospheric layers, from highest to lowest, is as follows:
  1. Stratosphere
  2. Tropopause
  3. Troposphere
Please keep this order in mind, because it will be important for understanding Christy et al.'s myth. 

Examining the stratosphere is useful because different factors produce different stratospheric temperature trends. For example:
  • Ozone reduction, due to factors such as human production of ozone-depleting chlorofluorocarbons (CFCs), causes strong stratospheric cooling
  • Carbon-dioxide-induced (CO2-induced) global warming results in strong stratospheric cooling
  • Solar-induced global warming results in mostly stratospheric warming; solar-induced warming does not account for strong stratospheric cooling

(A number of sources explain why increased CO2 cools the stratosphere, though the mechanisms behind this cooling are not crucial to the points made in this blogpost)

So the stratosphere allows scientists to distinguish different causes of global warming: stratospheric warming would be consistent with warming caused by increased solar output, while stratospheric cooling would fit with warming caused by increased CO2 levels. These points are so basic that the United States National Aeronautics and Space Administration (NASA) discusses them in their laymen's level explanation of climate science:

"A second smoking gun is that if the sun were responsible for global warming, we would expect to see warming throughout all layers of the atmosphere, from the surface all the way up to the upper atmosphere (stratosphere). But what we actually see is warming at the surface and cooling in the stratosphere. This is consistent with the warming being caused by a build-up of heat-trapping gases near the surface of the Earth, and not by the sun getting “hotter.” [1]"

These points are also re-affirmed in the following 2006 U.S. Climate Change Science Program document that Christy co-authored:

Figure 1: Summary of factors influencing global climate, and the predicted effects of these factors. The top two rows are the primary non-anthropogenic/natural forcing factors, while the other rows summarize the main anthropogenic (man-made) factors. Some of the listed effects last only a few years (ex: volcanic warming of the stratosphere), while other effects last longer (ex: the effects of well-mixed greenhouse gases last for decades to centuries). Note that CO2-induced global warming would cool the stratosphere, while solar-induced warming would warm the stratosphere [2, table 1 on page 5].

This is where Christy et al.'s myth comes in. In their non-peer-reviewed blogpost (or a "report", as Christy et al. call it), Christy et al. conclude that increased total solar irradiance (TSI) from the Sun caused most of the recent global warming. Christy cites this "report" conclusion in his Congressional testimony. As Christy says in his testimony:

"Indeed, I am a co-author of a report in which we used a statistical model to reproduce, to a large degree, the atmospheric temperature trends without the need for extra greenhouse gases. In other words, it seems that Mother Nature can cause such temperature trends on her own, which should be of no surprise [3; 23, page 36; see: 24, page 10]."

In their "report," Christy et al. also claim that CO2 had no observable, significant effect on recent temperature trends. One could test this claim by examining stratospheric temperature to see if there is CO2-induced stratospheric cooling or solar-induced stratospheric warming. A number of scientists already performed this test.

The scientific evidence indicates that ozone depletion and increased CO2 caused stratospheric cooling up to the mid-1990s, as predicted by the scientific community during the 1960s, 1970s, and 1980s. Ozone stabilization (in response to anti-CFC international agreements such as the Montreal Protocol) mitigated stratospheric cooling from the mid-1990s to the present. Post-1997 stratospheric cooling remains in many data-sets, however, especially higher in the stratosphere where CO2-induced cooling is more pronounced (I present some published images of this in a multi-tweet Twitter thread [19]).

This is in agreement with scientific predictions made in the 1970s and 1980s. For instance, since at least the 1960s, scientists have known that CO2-induced stratospheric cooling increases with increasing stratospheric height. In 1980, this point was even acknowledged by scientists working for the fossil fuel company Exxon, consistent with energy industry scientists' acceptance of greenhouse-gas-induced climate change. 

Christy understood these points going to at least 1993. The following quotes from Christy illustrate this point, with the first quote coming from a 1993 scientific paper he co-authored and the second quote coming from his 1997 political testimony:

"The decadal cooling trend of -0.44°C in Fig. 8 is due to a step function—like drop in lower stratospheric temperatures occurring during the El Chichón event. The net downward trend is consistent with ozone depletion observed by the Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) during this period [...], but also qualitatively consistent with CO2 increases [...]. The timing of the cooling relative to the El Chichén eruption supports the view that it might be related to volcanic aerosol-enhanced destruction of ozone [...] [20, page 1203]."

"It is widely thought that the loss of stratospheric ozone, both naturally from volcanic events and from human-generated chemicals, has caused this overall cooling. The increase in greenhouse gases, which will cause stratospheric cooling, is probably a factor as well, though smaller [21]."

Christy re-emphasized these points in a chapter he co-authored for an August 2018 American Meteorological Society (AMS) document:

"After Pinatubo (and perhaps El Chichón), LST [lower stratospheric temperature] declined to levels lower than prior to the eruption, giving a stair-step appearance. Ozone depletion and increasing CO2 in the atmosphere contribute an overall decline [emphasis added], so trends in global LST are clearly negative until approximately 1996. [...] 
Absence of lower stratospheric cooling in the global mean since 1996 is due to recovery of the ozone layer, especially at high latitudes, as the Montreal Protocol and its Amendments on ozone-depleting substances has taken effect [...] [22, page S19].
At higher levels of the stratosphere [...] the observed trend is approximately −0.7°C [per decade] of which 75% is estimated to result from enhanced greenhouse gas concentrations and most of the remaining decline from ozone loss [emphasis added, and citations removed] [...] [22, page S20]."

Christy made a similar point in a September 2019 AMS document, while tacitly admitting that stronger solar output would instead cause stratospheric warming:

"The lack of LST [lower stratopsheric temperature] cooling, despite tropospheric warming, since 1996 is related to the quasi-stabilization of ozone concentrations in this layer as well as the small warming influence of the upper troposphere in the tropics that is included in the LST layer [...]. At higher levels, the temperature decline continues, indicating enhanced radiative cooling associated with continued increases in concentrations of thermally active gases, most notably CO2, and the possible impact of a weak solar cycle [emphasis added, and citations removed] [...] [page S19]. [...] [29, page S19]."

So scientists, including John Christy, observed the stratospheric cooling predicted for multi-decadal CO2-induced warming, but they did not observe the stratospheric temperature trends predicted for multi-decadal solar-induced warming. The contrarian Ross McKitrick, a research colleague of Christy's, often obscures these points.

Section 2.2: The evasions and fabrications of Christy et al. on stratospheric cooling 

Christy et al. do not mention any of the aforementioned evidence in their "report's" 1st edition from August 2016, even though this evidence serves as a useful test for their claims regarding CO2-induced warming and solar-induced warming. Instead they examine temperature trends at, and below, the upper troposphere in the tropics, thereby avoiding the stratosphere. Christy et al. do mention a paper that shows tropical stratospheric cooling, but they fail to mention that the paper shows this cooling. Figure 2 presents some weather-balloon-based atmospheric temperature data from said paper:

Figure 2: Tropical warming/cooling trend versus height for weather balloon measurements (from a latitude of  30°N to 30°S, unless otherwise noted), depicting stratospheric cooling and increasing tropospheric warming with increasing altitude. Pressure decreases from the Earth's surface (near the bottom of the y-axis) to the troposphere to the stratosphere (near the top of the y-axis) [4]. The tropical troposphere lies below 150 hPa, while the tropical stratosphere is above 70hPa [5]. The green line extends to the beginning of satellite era of atmospheric temperature measurements (1979), while the purple line extends to before the satellite era. The inset legend for circles, diamonds, etc. indicates different temperature trends given different data analysis choices. The blue line roughly indicates the warming pattern expected for a moist adiabat [4] (see "Myth: The Tropospheric Hot Spot does not Exist" for more on what a moist adiabat is).

Figure 2 shows tropospheric warming lower in the atmosphere at atmospheric pressures greater than 150 hPa, along with stratospheric cooling higher in the atmosphere, at pressures of 70 hPa and less. Christy et al. also cite three other weather balloon analyses (RAOBCORE, RICH, and RATPAC) and two satellite-based analyses (UAH and RSS), each of which show tropospheric warming and stratospheric cooling in the tropics. 

So the observations from Christy et al.'s cited sources match the atmospheric pattern one would expect for CO2-induced warming, but not solar-induced warming, as indicated in figure 1. Christy should know this, since he co-authored a 2006 report showing this pattern of tropospheric warming and stratospheric cooling in weather balloon analyses and satellite analyses. Yet Christy et al. conveniently avoid addressing this pattern, even though in a 2017 AMS document Christy again depicts this tropospheric warming and stratospheric cooling.

Christy et al. remain at pressure levels of 150 mb and greater (equivalent to a pressure of 150 hPa and greater), keeping them at or beneath the upper troposphere. This allows them to avoid the stratospheric cooling present in figure 2 above 150 hPa; thus Christy et al. evade this evidence against their solar-induced warming hypothesis. Figure 3 shows the highest atmospheric layer Christy et al. examine in their "report's" 1st edition, at an atmospheric pressure of 150 mb:

Figure 3: A portion of table XXIII-1 from the 1st edition of Christy et al.'s "report." In this portion of the table, Christy et al. use weather balloon data from 150 mb, weather balloon data from 200 mb, and mid-troposphere temperature (TMT) satellite data as indicative of tropical upper tropospheric temperature. The numbers on the right indicate the "r bar squared" values for these data-sets [6, page 59].

So instead of addressing stratospheric cooling, Christy et al. avoid the cooling by making sure to stay below the stratosphere in their "report's" 1st edition. This sort of evasion is common among "skeptics" of man-made, CO2-induced climate change. Thus Christy et al.'s evasion does not shock me, despite the fact that it involves Christy willfully evading points he has known since at least 1993, as I discussed in section 2.1. What shocks me is what they did in their "report's" 2nd edition: Christy et al. make stuff up.

In their "report's" 2nd edition from April 2017, they re-label 150 mb as the tropical stratosphere on at least three different occasions, and thus knowingly mislead their audience. Christy et al. use their misrepresentation to make it look as if the tropical stratosphere warmed, as shown in figure 4 below:

Figure 4: This is figure VIII-3 from the 2nd edition of their "report" [7, page 25]. This (supposedly) shows tropical stratospheric data from three weather balloon data-sets [7, page 24].

Then they claim that CO2 has no observable impact on this stratospheric warming trend:

"For comparison to the rest of the results presented in this report, Tropical Stratospheric 150 mb Balloon Data is shown next in Figure VIII-3. Interestingly, the 1977 shift is still evident. But not surprisingly, the overall model explanatory power is lower [...]. Nevertheless, no impact of CO2 is evident [...] [7, page 24]."

Hilariously, Christy et al. fail to completely cover their tracks, since they say 150 mb is part of the tropical troposphere, not the tropical stratosphere, elsewhere in the "report's" 2nd edition:

Figure 5: A portion of table XIII-1 from the 2nd edition of Christy et al.'s "report." In this portion of the table, Christy et al. use weather balloon data from 150 mb, weather balloon data from 200 mb, and mid-troposphere temperature (TMT) satellite data as indicative of tropical tropospheric temperature. They call 150 mb the lower troposphere [2, page 63]; this conflicts with their "report's" 1st edition, in which they claim 150 mb is part of the tropical upper troposphere, as shown in figure 3. 150 mb should be part of the upper, not lower, troposphere since 150 mb is higher in the atmosphere 200 mb and figure 5 notes that 200 mb is part of the tropical upper troposphere [2, page 63]. So figure 5 contradicts atmospheric physics and an earlier figure from the "report's" first edition.

They also state that their solar-induced warming model does not explain the 150 mb stratospheric temperature very well. This represents their tacit admission that they failed to adequately explain tropospheric temperature, since the 150 mb data they refer to is tropospheric temperature, not stratospheric temperature. 150 mb (which is equivalent to 150 hPa) represents the border between the tropical lower tropopause and the tropical upper troposphere, not the tropical stratosphere:

"We present an overview of observations in the [tropical tropopause layer] [...]. We present a synthesis definition with a bottom at 150 hPa [...] and a top at 70 hPa [...] [5]."

And even the paper cited by Christy et al. states that 150 hPa is around the tropical tropopause region that is associated with a transition from tropospheric warming to stratospheric cooling. This transition is shown in figure 2 above, which comes from said paper. This paper also shows strong, tropical stratospheric cooling, as shown in figure 2 and figure 6 below:

Figure 6: Temperature in the lower stratosphere at 50 hPa, relative to a baseline [4].

The strong, tropical stratospheric cooling displayed in figures 6 and 2 contrasts with Christy et al.'s made-up stratospheric warming shown in figure 4; so Christy et al. misrepresent tropospheric warming as being stratospheric warming. This is ironic since for years Christy (falsely) claimed that the tropical troposphere had not warmed, yet Christy now attempts to exploit the tropospheric warming that he long denied.

Other research also shows tropical stratospheric cooling, providing further evidence against Christy et al.'s claim of tropical stratospheric warming. Christy et al.'s solar-induced warming model likely could not explain this stratospheric cooling, since solar-induced warming does not account for strong, long-term stratospheric cooling. Christy knows this since he co-authored a document explaining this point, as I discussed with respect to figure 1. Yet despite this knowledge, Christy chooses not to include stratospheric temperature data from above 150 mb. It is as if Christy is willfully ignoring evidence against his solar-induced warming model.

Christy not only ignores evidence from other researchers, but Christy also ignores his own published research. For example, Christy co-authored a paper which states that 100 mb (100 hPa) lies within the tropical tropopause:

"Figure 1 shows these temperature trends as a function of pressure (altitude) from the surface (~1000 hPa) to the tropopause (~100 hPa/17 km) [8, page 1696]."

Since the tropopause is beneath the stratosphere, then this means that any pressure level beneath 100 mb must be beneath the tropical stratosphere and thus must not be part of the tropical stratosphere. Since 150 mb is beneath 100 mb (see figure 2 above), then 150 mb is not part of the tropical stratosphere. Thus Christy's co-authored paper implies that 150 mb is not part of the tropical stratosphere, contrary to the 2nd edition of Christy et al.'s "report".

Christy's published research also shows tropical cooling at 150 mb and 100 mb. So Christy is clearly aware of data on cooling above 150 mb, but he chooses not to include this data. And Christy has known about man-made stratospheric cooling since at least 1993, as I showed in section 2.1. Furthermore, Christy co-runs the University of Alabama in Huntsville (UAH) satellite data analysis, and this UAH analysis shows stratospheric cooling, including cooling in the tropics. Figure 7 shows depicts this UAH cooling trend, along with satellite-based cooling trends from Remote Sensing Systems (RSS) and the National Oceanic and Atmospheric Administration Center for Satellite Applications and Research (NOAA/STAR):

Figure 7: (A),(B) 1979 - 2016 near-global (A) and tropical (B) lower stratospheric cooling trends predicted by climate models and observed in satellite data analyses. Trends are presented as an average of all the trend values for a given trend length. (C),(D) Ratio between the near-global (C) and tropical (D) stratospheric cooling trend predicted by the climate models vs. the stratospheric cooling trend observed in the satellite data analyses [10, figure 3 on page 378].

Yet remarkably, in Christy et al.'s "reports" Christy chooses not to mention his UAH stratospheric temperature analysis, even though he chooses to mention his UAH tropospheric temperature analysis. UAH's stratospheric cooling data would have argued against Christy's solar-induced warming hypothesis, which may be why Christy decided not to mention his UAH analysis.

Section 2.3: Christy knows that Christy et al.'s argument depends on their untenable temperature correction

So given section 2.2's evidence against Christy et al.'s solar-induced warming hypothesis, how do Christy et al. attempt to support their hypothesis? To do this, Christy et al. claim to subtract out warming caused by the Sun and an ocean cycle known as the El Niño-Southern Oscillation (ENSO). Christy et al. then state that no significant tropospheric and surface warming remained after this subtraction. Thus recent global warming was likely caused by the Sun and ENSO.

Christy et al.'s aforementioned reasoning fails, since Christy et al. use flawed, cumulative indices to correct for solar-induced and ENSO-induced warming. These indices are "cumulative" because the indices assume that the Earth accumulates energy from solar-induced and ENSO-induced warming, such that a warmer Earth does not radiate more energy. For example, Christy et al.'s cumulative ENSO index assumes that when Earth's troposphere warms during an El Niño year, the energy in the troposphere simply accumulates and is passed on to the next year.

But this conclusion violates basic physics, as the climate scientist Timothy Osborn points out: a warmer Earth would radiate more energy into space (as per the Stefan-Boltzmann law), instead of all the energy just accumulating. Scientists can observe this increased radiation during a warm El Niño; the radiation increase occurs largely because El Niño increases cloud cover and these clouds then reflect the solar radiation Earth would otherwise absorb. This cloud-based mechanism compensates for less emission of radiation by clouds during El Niño. So increased radiation during warm El Niño events debunks the implausible physics implied by Christy et al.'s cumulative indices.

Given this defect in Christy et al.'s cumulative indices, scientists rarely (if ever) use Christy et al.'s indices for ENSO and for total solar irradiance (TSI). In fact, I know of no peer-reviewed scientific paper that uses Christy et al.'s cumulative indices. Scientists instead use non-cumulative indices to account for solar-induced and ENSO-induced warming. Some researchers accumulate ENSO measures intra-annually, across months within a year. This however, yields very different results from Christy et al.'s inter-annual accumulation across multiple years in figure 8 below. It is one thing to say that released energy from ENSO temporarily accumulates for months; it is quite another thing to say that energy accumulates and remains for years or decades. Even Christy's sources apply non-cumulative solar and ENSO indices, as does Christy in his peer-reviewed work. These non-cumulative indices are compatible with Earth radiating more energy as Earth warms, in contrast to Christy et al.'s cumulative indices. 

Christy may not even believe his claims regarding the cumulative ENSO index, since in subsequent research he used a non-cumulative ENSO index to argue that ocean cycles such as ENSO had a negligible effect on post-1979 tropospheric warmingSimilarly, Christy may not believe his claims regarding his cumulative TSI index, since in the same subsequent research Christy wrote:

"The amplitude of the 11-year [solar] cycle has diminished since the peak in 2000 and, in our residual time series, there is indeed a slight slowdown in the rise after 1998. One may arbitrarily select an accumulation period of TSI [emphasis added], so that a peak occurs near 1998 so the TSI coincides with (explains) variations in [lower tropospheric temperature] (e.g., a 22-year TSI trailing average peaks in 2000, though other averaging periods do not), but this would compromise the independence between the predictors and predictand [emphasis added] [the predictor is the factor used to predict the predictand] [17, page 514]."

So in his peer-reviewed work, Christy admits that:
  1. A cumulative TSI is arbitrary, since it involves arbitrarily selecting a period over which TSI accumulates.
  2. A cumulative TSI compromises the relationship between TSI and the temperature trends one uses TSI to predict.

And in this same paper, Christy also admits that CO2 caused significant tropospheric warming; thus Christy contradicts his claim that there is no evidence that CO2 had an observable, significant effect on recent temperature trends. So Christy's published research contradicts his cumulative-index-based, blog article claims. Christy admits to significant CO2-induced global warming when communicating with informed scientists in his peer-reviewed papers, but he claims that there is no evidence of this significant CO2-induced warming when he speaks with non-experts he can fool with Christy et al.'s non-peer-reviewed blog articles. Thus Christy willfully misleads the public, as I discuss further in sections 3.5 and 3.6 of "John Christy Fails to Show that Climate Models Exaggerate CO2-induced Warming".

Strangely, Christy et al. seem to use a non-cumulative CO2 index for their work [7, page 8], as pointed out by Brandon R. Gates [12]. By using a non-cumulative CO2 index, Christy et al. avoid passing CO2's impact from year to subsequent year. In contrast, Christy et al. use cumulative solar and ENSO indices, allowing them to pass the solar and ENSO impacts from year to subsequent year. This double-standard makes it easier for Christy et al. to (incorrectly) argue that the Sun and ENSO caused recent warming, while CO2 did not.

In fact, Christy et al. cite Hoyt and Schatten's 1993 paper for their cumulative solar index, even though this 1993 paper uses a non-cumulative solar index. This 1993 paper also notes that solar irradiance and northern hemisphere temperature diverged in recent decades ("recent decades" before 1993) in a way consistent with CO2-induced warming. This suggestion from 1993 does not fit well Christy et al.'s claim that the Sun, not CO2, is responsible for much of the post-1970s global warming trend. Moreover, Hoyt+Schatten later recognized deficiencies in a data-set used in their 1993 paper, as did other scientists. Schatten then went on to co-author subsequent papers showing a decrease in TSI during post-1970s warming. Thus this research rebuts Christy et al. solar-induced warming hypothesis, and undermines the outdated 1993 analysis Christy et al. used to support their position.

And since 1993, things have only gotten worse for Christy et al.'s solar-induced warming hypothesis. To see why, let's contrast Christy et al.'s cumulative TSI index with two non-cumulative TSI indices based on either satellite measurements or sunspot numbers:

Figure 8: Cumulative TSI and cumulative ENSO index used by Christy et al. [6, page 18].

Figure 9: Non-cumulative TSI from the NOAA's Climate Data Record (CDR), based on satellite observations. The peaks and troughs represent the 11 year solar cycle. Data sources are SORCE TIM (Solar Radiation and Climate Experiment, with Total Irradiance Monitor), ACRIM (Active Cavity Radiometer Irradiance Monitor) and PMOD (Physikalisch-Meteorologisches Observatorium Davos) [13].

Figure 10: Monthly sunspot numbers from 1979 to 2018, as a proxy-based estimate of TSI [18].

(Christy et al. remain obscure about their source for their TSI estimate. They cite a 1993 paper, but they do not make clear where they get the subsequent 20+ years of post-1980s TSI data, beyond referencing ACRIM, Willie Soon, and an unspecified paper from Lean et al.. This last citation may refer to the Lean et al. analysis in figure 9 above, or an earlier analysis from Lean that shows no post-1970s solar-cycle-corrected increase in TSI. However, I suspect Christy et al. instead rely on a cumulative form of Scafetta+Willson's TSI estimate, since Christy and Soon cite Scafetta's work. 
Scafetta+Willson's non-cumulative analysis has a post-1970s increase in TSI. It also differs from figure 9, other TSI-based analyses {such as those based on sunspots, as in figure 10 above}, and Christy et al.'s figure 8. So even if Christy et al. accumulated Scafetta+Willson's TSI estimate instead of accumulating the estimate from figure 9, one could not treat Scafetta+Willson's non-cumulative analysis as being an equivalent defense of Christy et al.'s cumulative analysis. I discuss some of the debilitating problems with Scafetta+Willson's analysis in section 2.4.)

Figures 9 and 10 show an 11-year cycle in solar output. Once one takes this cycle into account, there is not a post-1979 increase in TSI. Yet Christy et al. transform this lack of an increase into a cumulative TSI increase, as shown in figure 8. They perform this transformation using the faulty method Christy critiqued above: arbitrarily selecting an accumulation period, thus compromising the relationship between TSI (the predictor) and temperature trends (the predictand). Christy et al. then use this manufactured TSI increase, from their defective cumulative TSI index, to argue that the Sun caused much of the recent global warming.

When scientists use non-cumulative indices to correct for solar-induced warming and ENSO-induced warming, most of the post-1950s tropospheric and surface warming remained, contrary to the claims Christy et al. made in their blogpost/"report". Christy himself showed this in his published research. Thus these non-cumulative indices provide another line of evidence against Christy et al.'s solar-induced warming model.

Section 2.4: The collapse of Christy et al.'s solar-induced warming hypothesis, and confirmation of CO2-induced warming

So let's summarize some of the relevant lines of evidence against Christy et al.'s solar-induced warming hypothesis and/or evidence in favor of the CO2-induced warming hypothesis:
  1. Significant global warming remains even after correcting for TSI.
  2. The relationship between solar output and global warming fails a number of statistical tests and model-based tests.
  3. Solar output has not correlated well with recent global warming. An indirect test of this is cosmic ray exposure, since TSI should limit the ability of cosmic rays to reach Earth. Yet Earth's cosmic ray exposure did not significantly decrease during this global warming, providing further evidence that TSI did not significantly increase during post-1970s warming. Solar flux also decreased, consistent with decreasing TSI. Nicola Scafetta attempts to get around this by claiming TSI increased from 1970 - 2000 and decreased post-2000. He states that these TSI changes correlate with 1970 - 2000 surface warming and a nearly stable 2000 - 2018 temperature trend, while claiming this temperature pattern conflicts with model-based estimates of CO2-induced, man-made warming. Scafetta's argument fails since statistically significant warming occurred from 2000 - 2018, at a rate roughly on par with, or greater than, 1970 - 2000 warming, as I discuss in a separate Twitter thread [25]. And Scafetta fails in his attempt to use the El Niño-Southern Oscillation (ENSO) to explain away this post-2000 warming, as per "Myth: El Niño Caused Post-1997 Global Warming". Thus, by Scafetta+Willson's own reasoning, the post-2000 significant warming trend undermines their TSI analysis, just as a post-2000 stable trend would have supported their analysis. This is consistent with Scafetta's history of false predictions on temperature trends, as covered in "Myth: No Global Warming for Two Decades", along with sections 2.2 and 2.5 of "Myth: Attributing Warming to CO2 Involves the Fallaciously Inferring Causation from a Mere Correlation". Scafetta's TSI estimate also conflicts with a number of other estimates based on satellite data, sunspot records, etc., and it relies on the outdated Hoyt+Schatten 1993 analysis discussed in section 2.3.
  4. Increased solar output would warm days more than nights, since the Sun shines during the day. This would increase the diurnal temperature range (DTR), which measures the difference between daily maximum temperature vs. daily minimum temperature; however, regional differences also affect DTR. In contrast, CO2-induced warming should decrease the DTR, by warming nights more than days. CO2 increases also impact clouds, and these cloud changes can then influence DTR. DTR decreased from the 1950s, consistent with CO2-induced warming and arguing against a large contribution from solar-induced warming.
  5. The stratosphere cooled, in accordance with CO2-induced global warming but not solar-induced warming. The tropopause also rose, consistent with stratospheric cooling caused by ozone depletion and increased CO2, along with increasing geopotential height due to thermal expansion of the troposphere.
  6. Increased CO2 contributed to the observed cooling of the mesosphere and thermosphere, atmospheric layers above the stratosphere, consistent with CO2-induced global warming.
  7. The regional pattern of warming and precipitation matches what one would expect from CO2-induced warming, instead of warming caused by other factors, such as increasing levels of solar-radiation-absorbing aerosols and increasing solar output.
  8. CO2-induced warming melts sea ice, affecting ocean heat uptake in a way that results in more warming in the winter than in the summer. This reduces the magnitude of the northern hemisphere seasonal cycle (SC, a.k.a. the magnitude of the annual cycle; in the upper troposphere SC instead increases, though the discussion here will focus on surface SC). Augmented sulfate aerosol levels also decrease SC, while causing global cooling by reflecting solar radiation. So if solar-induced global warming occurred via a reduction in sulfate aerosols leading to an increase in absorbed solar radiation, then SC should increase. But in reality global warming occurred from the 1960s to the 1990s, with SC decreasing and sulfate aerosol levels/emissions increasing. Global warming then continued post-1990s, with SC stabilizing and then increasing as sulfate aerosol levels/emissions stabilized and then decreased. This observed pattern thus conflicts with the sulfate-aerosol-based solar-induced warming hypothesis. The observed pattern instead fits with a scenario in which post-1960s greenhouse-gas-induced warming more than offset the cooling effect of sulfate aerosols, as per figure 12 below, with changes in both aerosols and greenhouse gases impacting SC.    
  9. CO2 absorbs energy in particular wavelengths and emits energy in particular wavelengths, as predicted by scientists over century ago, shifting Earth's energy balance (the amount of energy the Earth takes up vs. the amount of energy the Earth releases). Climate sensitivity states how much warming results from CO2's effect on Earth's energy balance. Scientists estimate climate sensitivity in a number of ways, such as examining how much warming occurred with CO2 increases in the distant past. Scientists can then use these climate sensitivity estimates to determine how much of the recent global warming was caused by increased CO2 levels. The vast majority of the climate sensitivity estimates imply that CO2 caused most of the recent global warming; for instance, even deeply flawed studies with low climate sensitivity estimates, involved CO2-induced warming being roughly equivalent to the observed warming trend (I discuss this more in section 3.4 of "John Christy Fails to Show that Climate Models Exaggerate CO2-induced Warming" and in "Christopher Monckton and Projecting Future Global Warming, Part 1").

(I make a more detailed case for CO2-induced global warming in "Myth: Attributing Warming to CO2 Involves the Fallaciously Inferring Causation from a Mere Correlation".)

The aforementioned points, along with other lines of evidence, show that increased CO2 (not increased solar activity) caused most of the post-1950s and post-1970s global warming. The figures below illustrates this for point 1:

Figure 11: Relative global temperature from 1979 - 2010 for three surface temperature records (GISS, NCDC a.k.a. NOAA, and CRU) and two lower tropospheric temperature records (RSS and UAH), after an adjustment that removes the influence of TSI, volcanic effects, and ENSO [9].

Grant Foster, a co-author of this figure, updated its analysis with data through 2018. His results showed similar pattern of global warming, even after correction for ENSO, volcanic effects, and changes in solar irradiance.

Figure 12: Relative global surface temperature trend from 1850 - 2017 (observations), with the contribution of various factors to this temperature trend (colored lines). The gray line is the sum of each of the depicted colored lines. The surface temperature trend takes into account changes in sea surface temperature measuring practices during the 1930s and 1940s, which I elaborate more on in "Myth: Karl et al. of the NOAA Misleadingly Altered Ocean Temperature Records to Increase Global Warming". The authors of this figure adapted it from the results of their 2019 paper [26 - 28].

This figure displays global warming acceleration post-1998. Post-1998 acceleration also appears in global surface temperature trend analyses such as ERA5 (which is endorsed by the contrarians Judith Curry and Ryan Maue), NASA's GISTEMP, NOAA's global analysis, NCEP-2, and 20CR, consistent with other sources on accelerating climate change. For further discussion of accelerating warming, see section 2.1 of "Myth: The IPCC's 2007 ~0.2°C/decade Model-based Projection Failed and Judith Curry's Forecast was More Reliable". 

Christy et al. should be aware of the eight aforementioned points since those points are well-known; NASA even discusses these issues when educating non-experts about climate science. For instance, NASA explains points 5 and 6 as follows:

"But several lines of evidence show that current global warming cannot be explained by changes in energy from the sun: 
If the warming were caused by a more active sun, then scientists would expect to see warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere, and a warming at the surface and in the lower parts of the atmosphere. That's because greenhouse gases are trapping heat in the lower atmosphere [11]."

And the United States National Oceanic and Atmospheric Administration (NOAA) has noted as much as well. Yet Christy et al. conveniently side-step the aforementioned points, even though these points argue against their solar warming hypothesis. In fact, Christy et al. insinuate that the NOAA is engaged in deceptive data manipulation with regard to global warming (Christy's co-author D'Aleo regularly smears the NOAA in this way and Christy also peddles paranoid conspiracy theories about the scientific community); I discuss Christy et al.'s debunked NOAA conspiracy theory in "Myth: Karl et al. of the NOAA Misleadingly Altered Ocean Temperature Records to Increase Global Warming" and in section 3.8 of part 2 of "John Christy and the Tropical Tropospheric Hot Spot".

So who is more likely to be deceptive: the NOAA and NASA who seek to educate non-experts on climate science, or Christy et al. who willfully conceal relevant evidence from non-experts?

Section 2.5: A political/religious ideology motivates Christy et al.'s distortions and Christy's shifting position

In conclusion, Christy et al. non-peer-reviewed blogposts/"reports":
  • exclude data relevant to testing their solar-induced warming hypothesis
  • distort evidence in a way that suits their preferred conclusion
  • rely on a litany of misrepresentations
  • offer claims inconsistent with other claims made in the "reports"
  • conflict with Christy's published research

They do this on behalf of ICECAP, an organization that uses Christy et al.'s blogposts/"reports" to attack the United States Environmental Protection Agency's (EPA's) attempts to regulate CO2 emissions. Christy's co-authored these blogposts with ICECAP's founder Joseph D'Aleo. D'Aleo uses his religious and political ideology to discount the negative effects of CO2-induced, man-made climate change, as does Christy and Christy's UAH colleague Roy Spencer.

This may provide further context as to why ICECAP incorporates D'Aleo and Christy's blogposts/"reports" into their political attacks on EPA regulation of CO2 emissions. It may also explain why Christy uses these "reports" to attack emissions regulations. This fits with Christy's history of objecting to climate models being used to inform policy, even as he makes (failed) objections to model-based predictions; I give more examples of his failed, politically expedient objections in "John Christy and Atmospheric Temperature Trends".

It is unfortunate that Christy peddled his shoddy blogposts/"reports" to Congress in 2017:

"Indeed, I am a co-author of a report in which we used a statistical model to reproduce, to a large degree, the atmospheric temperature trends without the need for extra greenhouse gases. In other words, it seems that Mother Nature can cause such temperature trends on her own, which should be of no surprise [3; 23, page 36; see: 24, page 10]." 

This differs from Christy's 1993, 1997, and 2018 claims on man-made stratospheric cooling (see section 2.1), in which Christy admitted that the Montreal Protocol's limits on human release of ozone-depleting gases resulted in stabilization of ozone levels and a reduction in man-made cooling of the lower stratosphere. Christy's above quoted claims to Congress also greatly differ from testimony he gave in a 2007 court case:

"Plaintiffs’ own expert, Dr. Christy, agrees with the IPCC’s [Intergovernmental Panel on Climate Change] assessment that in the light of new evidence and taking into account remaining uncertainties, most of the observed warming over the last fifty years is likely to have been due to the increase in GHG [greenhouse gas] concentrations. [...]. Christy agrees that the increase in carbon dioxide is real and primarily due to the burning of fossil fuels, which changes the radiated balance of the atmosphere and has an impact on the planet’s surface temperature toward a warming rate [14]." 

Yet in his aforementioned 2017 Congressional testimony, Christy says that atmospheric temperature trends can largely be explained "without the need for extra greenhouse gases [3; 23, page 36; see: 24, page 10]." So from 2007 to 2017, Christy's public acceptance of strong greenhouse-gas-induced warming went away, even though more evidence of greenhouse-gas-induced warming accumulated over this same time-period. The IPCC went in the opposite direction as Christy in response to the evidence: the IPCC moved from saying in 2007 that it was very likely (>90% chance) that greenhouse gas increases caused most of the warming, to saying in 2013 that it was very likely (>90% chance) that greenhouse gas increases caused most of the warming and that it was extremely likely (>95% chance) that human activities caused most of the warming.

So in response to new evidence, the IPCC expressed increased confidence in the evidence-based claims, while Christy expressed reduced confidence to the point that he no longer accepted the evidence-based claims. That contrasts with Christy's colleague Roy Spencer, who stated in 2019 that his best guess agreed with the IPCC assessment that humans caused most of the post-1950s global warming. Make of that what you will, especially in light of the following oft-repeated points:

"It is, however, important not to confuse denialism with genuine scepticism, which is essential for scientific progress. Sceptics are willing to change their minds when confronted with new evidence; deniers are not [15]."

"Arguing with science denialists is usually a waste of time. They masquerade as ordinary colleagues who adhere to the overarching goal of science, i.e. to find the best approximations of truth in the matter under consideration. The crucial difference is that your colleagues will accept a scientific statement if provided with sufficiently strong reasons to do so. In contrast, climate science denialists, like other pseudoscientists, tend to be driven by motives that make them impossible to convince, however strong the arguments they are presented with [emphasis added] [16, section 5]."  

3. Posts Providing Further Information and Analysis

4. References

  1. "Is the Sun causing global warming?"
  2. "Executive Summary: Temperature trends in the lower atmosphere - Understanding and reconciling differences"
  4. "Atmospheric changes through 2012 as shown by iteratively homogenized radiosonde temperature and wind data (IUKv2)"
  5. "Tropical Tropopause Layer" [doi:10.1029/2008RG000267]
  6. "On the Existence of a “Tropical Hot Spot" & The Validity of EPA’s CO2 Endangerment Finding" []
  7. "On the Existence of a “Tropical Hot Spot” & The Validity of EPA’s CO2 Endangerment Finding, Abridged Research Report, Second Edition" []
  8. "A comparison of tropical temperature trends with model predictions"
  9. "Global temperature evolution 1979–2010"
  10. "Comparing tropospheric warming in climate models and satellite data"
  13. "A solar irradiance climate data record" [cataloged in: "NOAA Climate Data Record (CDR) of Total Solar Irradiance (TSI), NRLTSI Version 2", DOI: 10.7289/V55B00C1; depiction of trend in:]
  14. "United States District Court for Vermont, Case No. 2:05-cv-302"
  15. "How the growth of denialism undermines public health"
  16. "Dealing with climate science denialism: experiences from confrontations with other forms of pseudoscience"
  17. "Satellite bulk tropospheric temperatures as a metric for climate sensitivity"
  18. (from the SIDC [Solar Influences Data Analysis Center], using the SILSO [Sunspot Index and Long-term Solar Observations]:
  20. "Precision lower stratospheric temperature monitoring with the MSU: Technique, validation, and results 1979–1991"
  21. "Testimony of John R. Christy, Committe on Environment and Public Works; Department of Atmospheric Science and Earth System Science Laboratory, University of Alabama in Huntsville, Huntsville AL 35899; 10 July 1997" (
  22. "State of the climate in 2017"
  23. Full Committee Hearing - "Climate Science: Assumptions, Policy Implications, and the Scientific Method" (Wednesday, March 29, 2017 - 10:00am) []
  24. "U.S. House Committee on Science, Space & Technology, 29 Mar 2017, Testimony of John R. Christy"
  26. "A limited role for unforced internal variability in twentieth-century warming"
  27. []
  28. []
  29. "State of the climate in 2018"

No comments:

Post a Comment