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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
  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 tropical stratosphere, a layer of the middle atmosphere, warmed and 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. 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.


[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



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

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 a source 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 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]."

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, though post-1997 stratospheric cooling remains in many data-sets, especially higher in the stratosphere where CO2-induced cooling is more pronounced. This is in agreement with scientific predictions made in the 1970s and 1980s.

Christy et al. do not mention any of this in their "report's" 1st edition. Instead they examine temperature at, and below, the upper troposphere in the tropics. 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 beneath 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 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.

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-warming hypothesis. Figure 3 shows the highest atmospheric layer Christy et al. examine, 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. So Christy et al.'s evasion does not shock me. 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, 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 is ironic 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. abuse tropospheric warming in an attempt to make it look like the stratosphere warmed. 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 cooling above 150 mb, but he chooses not to include this data. 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 analysis that shows tropical stratospheric cooling, 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.

So given this 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.

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, 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. 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. Even Christy's sources applied non-cumulative solar and ENSO indices, as did Christy in his peer-reviewed work. These non-cumulative indices are compatible with Earth radiating more energy as Earth warms.

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 down all of CO2's impact from year to subsequent year. In contrast, cumulative solar and ENSO indices, allowing them to pass all of 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 a 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.

And since 1993, things have only gotten worse for Christy et al.'s solar-warming hypothesis. To see why, let's contrast Christy et al.'s cumulative total solar irradiance (TSI) index with a non-cumulative TSI index:

Figure 8: Cumulative TSI and cumulative MEI 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 9 shows 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. turn this lack of an increase into a cumulative TSI increase, as shown in figure 8. And Christy et al. 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 used 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". Thus these non-cumulative indices provide another line of evidence against Christy et al.'s solar-induced warming model.

So let's summarize some of the relevant lines of evidence against Christy et al.'s solar-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.
  4. The stratosphere cooled, in accordance with CO2-induced global warming but not solar-induced warming.
  5. Observed cooling of the mesosphere and thermosphere, atmospheric layers above the stratosphere, fits with CO2-induced global warming.
  6. CO2 absorbs 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 energy absorption. 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 the increased CO2 (I discuss this more in "Christopher Monckton and Projecting Future Global Warming, Part 1").

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 figure below illustrates this for point 1:


Figure 10: Relative global temperature from 1979 - 2010 for three surface temperature records (GISS, NCDC and CRU) and two lower tropospheric temperature records (RSS and UAH), after correction for TSI, volcanic effects, and ENSO [9].

Christy et al. should be aware of the six aforementioned points; NASA even discusses these issues when educating non-experts about climate science. For instance, NASA explains points 4 and 5 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); I discuss Christy et al.'s debunked NOAA conspiracy theory 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?


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"
They do this on behalf of ICECAP, an organization that uses Christy et al.'s blogposts/"reports" to attack the US Environmental Protection Agency's attempts to regulate CO2 emissions. It is unfortunate the Christy peddled these 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]." 

This greatly differs from testimony Christy gave in a 2007 court case. As stated in court documents from that 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]." 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 likely (>66% 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. 

Make of that what you will, in light of Christy's response to the evidence and the following oft-repeated point:

"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]."

"A skeptic will question claims, then embrace the evidence. A denier will question claims, then reject the evidence [16]."  




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"
  3. http://climatefeedback.org/scientists-reactions-us-house-science-committee-hearing-climate-science/
  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"
  11. http://climate.nasa.gov/causes/
  12. https://twitter.com/brandonrgates/status/900493496481488896
  13. "A solar irradiance climate data record"
  14. "United States District Court for Vermont, Case No. 2:05-cv-302"
  15. "How the growth of denialism undermines public health"
  16. https://twitter.com/neiltyson/status/732191219883900928?lang=en