The outline for this post is as follows:
- The Myth and Its Flaw
- Context and Analysis
- Posts Providing Further Information and Analysis
- References
This is the "+References" version of this post, which means that this post contains my full list of references and citations. If you would like an abbreviated and easier to read version, then please go to the "main version" 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 Flaw
Climate models predict that in moist tropical areas, a region of the lower atmosphere will warm more than Earth's surface [19, page 4; 20 - 23; 24, from 31:01 to 31:48]. This region of greater warming is known as the "hot spot" [25, pages 14 and 42; 26; 27, page 6; 28]. The myth claims that a 2006 report of the United States Climate Change Science Program (CCSP) [36, figure 5.7 on page 116] provided evidence against the hot spot's existence [2 - 18]. Many myth advocates resort to deception (or willful avoidance of evidence) in order to defend this myth.
Proponents of this myth include David Evans [2 - 12; 11], Stefan Molyneux [6], Joe Bastardi [116], Steve Milloy [115], Theo Wolters [13], Nicola Scafetta [80, appendix Y on page 53], S. Fred Singer [14, page 378; 81, pages 5 and 6], Christopher Monckton [15; 131], Luboš Motl [119; 120], Anthony Watts [16], Ken Gregory from Friends of Science (via Clive Best) [82], Paul Homewood [17], Tom Nelson [18], EIKE (the European Institute for Climate and Energy) [86], CO2 is Life [84], US Issues [85], Turbulent Eddie [88; 89], No Tricks Zone [83], and 1000frolly [87].
The myth's flaw: The CCSP made no definitive claim on whether the hot spot exists. Instead they noted that issues with data quality and data analysis prevented firm conclusions from being made [36, pages 74, 115 - 116, and 121]. Though lower atmospheric warming was most evident in regions with better data quality [36, page 116], CCSP suggested that other data sources and data analyses should be used to confirm these results [36, pages 14, 42, 120, and 122]. Scientists later examined these data sources, confirming the hot spot's existence (I discuss this further in "Myth: The Tropspheric Hot Spot does not Exist"). Most observational analyses show about as much, or more, "hot spot" warming than was projected by the models that myth advocates abuse. Myth proponents obscure these points by ignoring these later analyses, fabricating images, and evading what the CCSP stated [2 - 18].
Climate models predict that in moist tropical areas, a region of the lower atmosphere will warm more than Earth's surface [19, page 4; 20 - 23; 24, from 31:01 to 31:48]. This region of greater warming is known as the "hot spot" [25, pages 14 and 42; 26; 27, page 6; 28]. The myth claims that a 2006 report of the United States Climate Change Science Program (CCSP) [36, figure 5.7 on page 116] provided evidence against the hot spot's existence [2 - 18]. Many myth advocates resort to deception (or willful avoidance of evidence) in order to defend this myth.
Proponents of this myth include David Evans [2 - 12; 11], Stefan Molyneux [6], Joe Bastardi [116], Steve Milloy [115], Theo Wolters [13], Nicola Scafetta [80, appendix Y on page 53], S. Fred Singer [14, page 378; 81, pages 5 and 6], Christopher Monckton [15; 131], Luboš Motl [119; 120], Anthony Watts [16], Ken Gregory from Friends of Science (via Clive Best) [82], Paul Homewood [17], Tom Nelson [18], EIKE (the European Institute for Climate and Energy) [86], CO2 is Life [84], US Issues [85], Turbulent Eddie [88; 89], No Tricks Zone [83], and 1000frolly [87].
2. Context and Analysis
Section 2.1: Myth proponents offer fabricated images to mislead people
Earth's atmosphere contains multiple layers. The layer closest to the Earth's surface air is known as the troposphere. Climate models predict that tropospheric warming in the tropics should increase with increasing height [19, page 4; 20 - 23; 24, from 31:01 to 31:48]. See "Myth: The Tropospheric Hot Spot is a Fingerprint of CO2-induced Warming" for more on the mechanism behind this increased warming; however, knowing this mechanism is not required for understanding the points made in this blogpost.
The aforementioned tropical warming amplification is called the tropical tropospheric hot spot by many critics of mainstream climate science [25, pages 14 and 42; 26; 27, page 6; 28]. Figure 1 depicts the hot spot (amplification of warming with increasing height in the tropics) in response to warming caused by increased solar activity or in response to warming caused by increased carbon dioxide (CO2):
Figure 1: ECHAM3/LSG model (European Center/Hamburg Model 3 / Large Scale Geostrophic coupled atmosphere-ocean climate model) simulation of the atmospheric response to (a) increased solar forcing (from increased solar output) and (b) increased CO2 forcing (from increased CO2 levels). Colored areas indicate significant responses, with darker blues indicating cooling and darker reds indicating warming. The horizontal axis represents latitude, with the tropics being between roughly 30°N and 30°S. The vertical axis represents altitude, with decreasing atmospheric pressure as altitude increases [1, page 707]. The tropical troposphere lies below 150hPa, while the tropical stratosphere is above 70hPa [37]. Tropical tropospheric warming increases with height in both panels a and b, indicating that the hot spot forms in response to both solar-induced warming and CO2-induced warming. In contrast, strong tropical stratospheric cooling comes with CO2-induced warming, but not solar-induced warming. This figure is taken from a 2001 report of the United Nations Intergovernmental Panel on Climate Change (IPCC) [1, page 707].
Scientists can use data from weather balloons (radiosondes) to investigate whether the hot spot exists [29 - 35]. A 2006 report of the United States Climate Change Science Program (CCSP) examined some of this radiosonde data [36, figure 5.7 on page 116]. Myth proponents claim that this CCSP report provides evidence against the hot spot's existence. Myth advocates defend this claim by taking an image from the CCSP report, and comparing this image to model-based temperature projections [2 - 18; 80, appendix Y on page 53; 81, pages 5 and 6; 82 - 87; 89; 111; 115; 116]. This involves comparing temperature trends from the HadAT2 (Hadley Center Radiosonde Temperature) radiosonde analysis with model-based projections supplied by the CCSP [36, figure 1.3 on page 25 and figure 5.7 on page 116]. Figures 2 and 3 show two of these comparisons made by the myth defender David Evans:
Section 2.1: Myth proponents offer fabricated images to mislead people
The aforementioned tropical warming amplification is called the tropical tropospheric hot spot by many critics of mainstream climate science [25, pages 14 and 42; 26; 27, page 6; 28]. Figure 1 depicts the hot spot (amplification of warming with increasing height in the tropics) in response to warming caused by increased solar activity or in response to warming caused by increased carbon dioxide (CO2):
 |
Figure 1: ECHAM3/LSG model (European Center/Hamburg Model 3 / Large Scale Geostrophic coupled atmosphere-ocean climate model) simulation of the atmospheric response to (a) increased solar forcing (from increased solar output) and (b) increased CO2 forcing (from increased CO2 levels). Colored areas indicate significant responses, with darker blues indicating cooling and darker reds indicating warming. The horizontal axis represents latitude, with the tropics being between roughly 30°N and 30°S. The vertical axis represents altitude, with decreasing atmospheric pressure as altitude increases [1, page 707]. The tropical troposphere lies below 150hPa, while the tropical stratosphere is above 70hPa [37]. Tropical tropospheric warming increases with height in both panels a and b, indicating that the hot spot forms in response to both solar-induced warming and CO2-induced warming. In contrast, strong tropical stratospheric cooling comes with CO2-induced warming, but not solar-induced warming. This figure is taken from a 2001 report of the United Nations Intergovernmental Panel on Climate Change (IPCC) [1, page 707]. |
Scientists can use data from weather balloons (radiosondes) to investigate whether the hot spot exists [29 - 35]. A 2006 report of the United States Climate Change Science Program (CCSP) examined some of this radiosonde data [36, figure 5.7 on page 116]. Myth proponents claim that this CCSP report provides evidence against the hot spot's existence. Myth advocates defend this claim by taking an image from the CCSP report, and comparing this image to model-based temperature projections [2 - 18; 80, appendix Y on page 53; 81, pages 5 and 6; 82 - 87; 89; 111; 115; 116]. This involves comparing temperature trends from the HadAT2 (Hadley Center Radiosonde Temperature) radiosonde analysis with model-based projections supplied by the CCSP [36, figure 1.3 on page 25 and figure 5.7 on page 116]. Figures 2 and 3 show two of these comparisons made by the myth defender David Evans:
 |
Figure 2: Evans' image [3] constructed from a 2006 report of the CCSP. The left panel depicts a 1958 - 1999 temperature projection from the Parallel Climate Model ensemble (PCM). The projection is based on the temperature response to increased greenhouse gases such as CO2. Temperature trends are in °C per 42 years [36, figure 1.3 on page 25]. The right panel displays HadAT2 warming/cooling trends versus height for 1979 - 1999. Temperature trends are in °C/decade [36, figure 5.7 on page 116]. The tropics lie between 30°N and 30°S. 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). The tropical troposphere lies below 150hPa, while the tropical stratosphere is above 70hPa [37]. |
 |
Figure 3: Evans' image [12] constructed from a 2006 report of the CCSP. The right panel depicts a 1958 - 1999 temperature projection from the Parallel Climate Model ensemble (PCM). The projection is based on the temperature response to multiple factors including aerosols and increased greenhouse gases such as CO2. Temperature trends are in °C per 42 years, using the same color-scale as the left panel of figure 2 [36, figure 1.3 on page 25]. The left panel displays HadAT2 warming/cooling trends versus height for 1979 - 1999. Temperature trends are in °C/decade, using the same color-scale as the right panel of figure 2 [36, figure 5.7 on page 116]. The tropics lie between 30°N and 30°S. Altitude increases 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) [37]. |
Figure 2's right panel [3] and figure 3's left panel [12] show 1979 - 1999 HadAT2 temperature trends [36, figure 5.7 on page 116]. Figure 2's left panel [3] and figure 3's right panel [12] display 1958 - 1999 model-based projections [36, figure 1.3 on page 25], though Evans' labeling of figure 3 [6, at 6:55; 12; 16] may create the false impression that these are model-based projections for 1979 - 1999. Myth defenders Anthony Watts [16], Nicola Scafetta [80, appendix Y on page 53], Joe Bastardi [116], and Fred Singer [14, page 378; 81, figure 7 on page 6] resort to a similar tactic to create the false impression that HadAT2 data and model-based projections cover the same time-frame, as do others [16; 82 - 87; 115; 119; 120].
Some myth proponents [2; 4; 5; 8; 15], including Evans [2; 4; 5; 8], also compare the CCSP's 1979 - 1999 HadAT2 trends [36, figure 5.7 on page 116] with 1890 - 1999 model-based projections from a 2007 report of the United Nations Intergovernmental Panel on Climate Change (IPCC) [38, figure 9.1 on page 675]. These myth proponents focus on panels c and f from this IPCC figure shown below [2; 4; 5; 8; 15]:
 |
Figure 4: Atmospheric temperature change in °C/century from 1890 to 1999 in the Parallel Climate Model ensemble (PCM) in response to (a) increased solar forcing (from increased solar output), (b) volcanic activity, (c) well-mixed greenhouse gases such as CO2, (d) tropospheric and stratosopheric ozone changes, (e) sulfate aerosols, and (f) the sum of all the aforementioned factors. Darker blues represent cooling and darker reds represent warming. The horizontal axis indicates latitude, with the tropics being between roughly 30°N and 30°S. The vertical axis indicates altitude, with decreasing atmospheric pressure as altitude increases [38, figure 9.1 on page 675]. The tropical troposphere lies below 150hPa, while the tropical stratosphere is above 70hPa [37]. |
Thus myth proponents compare 1979 - 1999 HadAT2 trends with model-based projections for 1890 - 1999 [2; 4; 5; 8; 15; 119; 120; 131] or for 1958 - 1999 [2 - 4; 6, at 6:55; 7; 9 - 13; 14, page 378; 15 - 18; 80, appendix Y on page 53; 81, pages 5 and 6; 82 - 87; 89; 111; 115; 116]. This comparison makes no sense, since 21-year HadAT2 data would likely show less total warming than 42-year and 110-year model-based projections, even if the climate models in question were accurate. The color-scales also differ between the HadAT2 images [36, figure 5.7 on page 116] vs. the model-based projections [36, figure 1.3 on page 25; 38, figure 9.1 on page 675]. For instance, a warming trend of ~0.2°C/decade would appear yellow on the HadAT2 image [36, figure 5.7 on page 116]. In contrast, that same rate of warming would be ~0.8°C of total warming on the 1958 - 1999 CCSP model-based image and would appear dark orange (almost red) [36, figure 1.3 on page 25], not yellow. For the IPCC's 1890 - 1999 image, this amount of warming would be ~2.1°C and thus would be beyond the image's color-scale [38, figure 9.1 on page 675]. Comparing these three graphs is therefore misleading, since the same level of warming would be a different color in all three images.
Thus Evans' figures 2 and 3 use both a misleading color-scale and a misleading time-frame that renders their model-data comparisons invalid. This is rather ironic, since Evans complains that scientists use misleading color-scales for their hot spot graphs [2, page 11].
So why do myth proponents engage in this misguided comparison? Is the CCSP to blame? No, because unlike myth defenders, the CCSP compared 1979 - 1999 HadAT2 trends with 1979 - 1999 model-based trends using the same color-scale for both trends [36, figure 5.7 on page 116], as shown in figure 5 below:
 |
Figure 5: Temperature projections for 1979 - 1999 for four climate model ensembles: (A) Community Climate System Model ensemble (CCSM3.0), (B) Parallel Climate Model ensemble (PCM), (C) Geophysical Fluid Dynamics Laboratory Global Coupled Climate Model ensemble (GFDL-CM2.1), and (D) Goddard Institute for Space Studies EH ensemble (GISS-EH) [36, page 104 and figure 5.7 on page 116]. The projections are based on the temperature response to 20th century (20CEN) changes in multiple factors, including aerosols and increased greenhouse gases such as CO2 [36, page 94]. Panel (E) displays displays HadAT2 warming/cooling trends versus height for 1979 - 1999. Temperature trends are in °C/decade [36, figure 5.7 on page 116]. The tropics lie between 30°N and 30°S. Atmospheric 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). The tropical troposphere lies below 150hPa, while the tropical stratosphere is above 70hPa [37]. |
Yet myth defenders do not display the CCSP's 1979 - 1999 model-based projections from figure 5. Instead myth proponents display images (such as figures 2 and 3) that remove the 1979 - 1999 model-based projections, and replace them with CCSP or IPCC model-based projections for 1959 - 1999 [2 - 4; 6, at 6:55; 7; 9 - 13; 14, page 378; 15 - 18; 80, appendix Y on page 53; 81, pages 5 and 6; 82 - 87; 89; 111; 115; 116] or 1890 - 1999 [2; 4; 5; 8; 15]. Myth proponents therefore present a fabricated image that exaggerates the difference between HadAT2 and the model-based trends. If myth proponents know they are doing this, then they are deceptive. If myth defenders do not know they are doing this, then they are willfully ignorant, since they did not look up the original source of their image (the 2006 CCSP report), even though that source is freely available online [36, figure 5.7 on page 116]. So if someone presents you with comparisons like figures 2 and 3, and acts as if those comparisons are credible, then that person is misleading you.
The myth proponent Joanne Nova (and presumably her partner David Evans, another myth advocate) know they are excluding the models in figure 5 when they present figures 2 and 3 [108; 109]. The blogger ItsNotNova (who may also go by the name "Nice One") called Nova and Evans out on this in 2013 [108; 110]. Yet Nova and Evans post their fabricated images anyway, without a retraction or correction [2 - 12], and thus willfully exclude the models in figure 5. So Nova and Evans deceptively offer fabricated images in order to defend the myth.
Section 2.2: Myth proponents rely on a CCSP report that undermines their myth
Though myth proponents' figures 2 and 3 exaggerate the difference between the models and HadAT2, CCSP's figure 5 still shows some differences between the model-based projections and HadAT2. Since this post focuses on the tropospheric hot spot, I will focus on the differences in the troposphere. CCSP suggest some reasons for this models vs. HadAT2 discrepancy, though myth proponents usually conveniently leave out the CCSP's reasoning [2 - 18; 80, appendix Y on page 53; 81, pages 5 and 6; 82 - 87; 89; 111; 115; 116; 119; 120; 131]:
"Taken together these results imply that any residual systematic errors in the homogenized radiosonde products will likely lead to a spurious cooling bias.
[...]
Another noticeable difference is that the HadAT2 data show a relative lack of warming in the tropical troposphere, [...] where all four models simulate maximum warming. This particular aspect of the observed temperature-change pattern is very sensitive to data adjustments [...]. Tropospheric warming in the observations is most obvious in the [northern hemisphere] extra-tropics, where our confidence in the reliability of radiosonde records is greatest.
[...]
[...]
Another noticeable difference is that the HadAT2 data show a relative lack of warming in the tropical troposphere, [...] where all four models simulate maximum warming. This particular aspect of the observed temperature-change pattern is very sensitive to data adjustments [...]. Tropospheric warming in the observations is most obvious in the [northern hemisphere] extra-tropics, where our confidence in the reliability of radiosonde records is greatest.
[...]
Systematic, historically varying biases in day-time relative to night-time radiosonde temperature data are important, particularly in the tropics [...]. These are likely to have been poorly accounted for by present approaches to quality controlling such data [...] and may seriously affect trends [36, pages 74, 115 - 116, and 121]."
To elaborate on these points further: for years scientists have known that radiosonde analyses contain spurious cooling in the tropical troposphere [27, page 19; 34; 35; 41 - 46]. Accounting for this spurious cooling, along with internal climate variability, explains most of the difference between models vs. radiosonde analyses with respect to tropical tropospheric warming [34; 47; 118, slide 30]. Neither internal variability nor the spurious cooling imply a flaw in the climate models [49; 48, page 188; 49, page 4], as I discuss in "Myth: Santer et al. Show That Climate Models are Very Flawed". The HadAT2 acknowledges this [78; 114].
The spuriously cool radiosonde trends resulted from changes in radiosonde equipment during the 1980s [44 - 46; 90; 91]; these changes made radiosondes more prone to direct heating by the Sun, such that the radiosondes were no longer just measuring air temperature [45; 90; 91]. This is what CCSP refers to when they mention "historically varying biases in day-time relative to night-time radiosonde temperature data [36, page 121]." So radiosonde-based tropospheric warming trends that begin in 1979 will be spuriously low, due to artificially warm radiosonde readings from the 1980s [44 - 46; 90; 91; 118, slide 30]. However, radiosonde trends that begin in 1958 will be less prone to this problem, as depicted in the 2005 HadAT2 figure below:
 |
Figure 6: Top two panels: HadAT2 warming/cooling trend (in K/decade, equivalent to °C/decade) versus height. Crosses indicate trends statistically distinguishable from 0 [39, figure 11]. The tropics lie between 30°N and 30°S. 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). The tropical troposphere lies below 150hPa, while the tropical stratosphere is above 70hPa [37]. Bottom two panels: Estimate of some of the uncertainty (in K/decade, equivalent to °C/decade) at atmospheric pressure levels corresponding to the top panel images [39, figure 11]. |
Figure 6 displays the hot spot (greater warming in the upper troposphere than near the surface in the tropics) from 1958 - 2002, but not from 1979 - 2002. This lack of a hot spot from 1979 - 2002 is likely because of the aforementioned 1980s changes in radiosonde equipment in the tropics [44 - 46; 90; 91]. Figure 6 also shows tropospheric warming and less uncertainty from 1979 - 2002 in the northern hemisphere extra-tropics at latitudes north of 30°N. This supports the CCSP's claim that "tropospheric warming in the observations is most obvious in the [northern hemisphere] extra-tropics, where our confidence in the reliability of radiosonde records is greatest [36, page 116]."
HadAT2 scientists published figure 6 in 2005 [39, figure 11], before the 2006 CCSP report. And the HadAT2 team explicitly states that when citing the HadAT2 analysis, people should cite the 2005 paper that includes figure 6 above [50]. Yet I know of no myth proponent who shows the 1958 - 2002 image from figure 6 [2 - 18; 80, appendix Y on page 53; 81, pages 5 and 6; 82 - 87; 89; 111; 115; 116; 119; 120; 131], likely because myth advocates are either unaware of this image or they believe it would deflate their "no hot spot" narrative. After all, including this pre-1979 data reduces the difference between HadAT2 vs. the model-based projections [34, figure 2; 78], which runs contrary to the result myth proponents likely want.
So myth defenders instead focus almost exclusively on the 1979 - 1999 HadAT2 image from figures 2 and 3 [2 - 18; 80, appendix Y on page 53; 81, pages 5 and 6; 82 - 87; 89; 111; 115; 116; 119; 120; 131]. David Evans, the most prominent myth defender, even claims that the HadAT2 panel from figures 2 and 3 is the only data there is [12]. Evans' partner Joanna Nova, another myth proponent, concurs, claiming that HadAT/HadAT2 "was the only dataset the CCSP used [113]." Evans also suggests that the CCSP may have tried to nefariously conceal the data:
"This important and pivotal data was not released publicly by the climate establishment until 2006, and then in an obscure place [...]. [...] The weather balloon data showing the atmospheric warming pattern was finally released in 2006, in the US Climate Change Science Program [...] This is the only data there is. [By the way], isn’t this an obscure place to release such important and pivotal data – you don’t suppose they are trying to hide something, do you [12]?"
Of course, Evans' paranoia is baseless. The CCSP cites other data sources, in addition to HadAT2 [36, page 52], contrary to what Nova claims. And contrary to what Evans claims, the 1979 - 1999 HadAT2 analysis does not reflect all of the data, as shown by the 1958 - 1979 data in figure 6 (and figure 7 below). Furthermore, scientists made no attempt to conceal the data, since figure 6 was available before the 2006 CCSP report. The CCSP report even cites [36, pages 52, 149, 153, 155, and 162] the 2005 paper [39] from which figure 6 was taken, along with citing [36, pages 52 and 151] another 2005 paper [40] that presented a radiosonde-based image as well (see figure 7 below). So Evans is also wrong when he insinuates that the CCSP tried to conceal the data [12]. If he read the CCSP report more closely, then he would know better than to make such uninformed, paranoid claims.
By 2005 scientists made some progress in accounting for the solar-induced bias in 1980s radiosonde temperature readings; this progress involved the use of various data analysis methods and different corrections for known artifacts/errors in the data [40, figure 4]. These corrections are known as homogenization and the artifacts are known as heterogeneities [29 - 32; 36, page 6; 39; 40; 50] (I discuss homogenization in more detail in section 3.1 of "John Christy, Climate Models, and Long-term Tropospheric Warming", with examples of scientists validating homogenization techniques). Current radiosonde-based analyses likely still contain heterogeneities that cause the analyses to under-estimate tropical tropospheric warming [34; 118, slide 30]. And even back in 2006, the CCSP mentioned the need for homogenization that corrects heterogeneities [36, page 6].
A research team at the United Kingdom Met Office used homogenization to generate the HadAT2 analysis [39; 50] shown in figures 2, 3, and 5. Another team at the National Oceanic and Atmospheric Administration (NOAA) used alternative homogenization methods to generate a radiosonde analysis known as RATPAC (Radiosonde Atmospheric Temperature Products for Assessing Climate) [40]. Figure 7 depicts a 2005 RATPAC image:
 |
Figure 7: RATPAC warming/cooling trend versus height from 1979 - 2004 (in K/decade, equivalent to °C/decade) [40, figure 4]. The tropics lie between 30°N and 30°S. 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). The tropical troposphere lies below 150hPa, while the tropical stratosphere is above 70hPa [37]. |
Evans and other myth proponents conveniently avoid displaying figure 7 [2 - 18; 80, appendix Y of page 53], even though the RATPAC team published figure 7 in 2005 [40], before the 2006 CCSP report [36]. This further rebuts Evans' paranoid idea that scientists may have tried to conceal the radiosonde data [12].
While RATPAC figure 7 partially homogenizes for the 1980s solar-induced bias [40, figure 4], HadAT2 images from figures 2, 3, and 5 do not adequately address this 1980s heterogeneity [36, figure 5.7 on page 116; 39, figure 11]. Thus the RATPAC figure [40, figure 4] displays more tropical tropospheric warming than do the HadAT2 figures [36, figure 5.7 on page 116; 39, figure 11]. This confirms CCSP's statement that for the tropical troposphere, "the observed temperature-change pattern is very sensitive to data adjustments [36, page 115]." To account for this, the CCSP recommended that:
- Scientists compare tropospheric warming trends from different sources, such as radiosondes and satellites [36, page 122].
- Multiple, independent research groups develop homogenized analyses in order to ensure that the results are not due to flaws in a particular homogenization method [36, pages 14, 42, 120, and 122].
- Scientists should use other climate variables to test for the predictions implied by different data sources [36, page 122].
The 2005 RATPAC figure 7 and 2005 HadAT2 figure 6 illustrate point 2: in comparison to the HadAT2 team [39, figure 11], the RATPAC team made more progress in homogenizing the 1980s solar-induced heterogeneity [40, figure 4]. And the HadAT2 team acknowledges that scientists should compare the HadAT2 analysis to satellite analyses and other radiosonde analyses, to make sure the HadAT2 result is robust [50]. So the HadAT2 research team accepts points 1 and 2 from CCSP [78; 114].
Since 2005, other scientists applied points 1, 2, and 3, leading to numerous lines of evidence supporting the hot spot's existence (I discuss this further in "Myth: The Tropspheric Hot Spot does not Exist"). For example, scientists generated re-analyses that incorporate data from diverse sources, including radiosondes and satellites [57; 58]. Evans himself cites re-analysis results [3; 9; 59], as does the myth proponent Anthony Watts [16]. John Christy [61, pages 4 - 7; 62; 63, pages S16 and S17] and Judith Curry [60; 121], two critics of mainstream climate science, also cite a re-analysis known as ERA-I (European Centre for Medium-Range Weather Forecasts Interim re-analysis) [57; 58; 64]. Figure 8 below compares some of ERA-I's results to model-based projections:
 |
Figure 8: ERA-I and model-based warming/cooling trends versus height, represented as the trend at a particular pressure level divided by the near-surface temperature trend at that latitude. The results at a particular latitude represent the average of the temperature response in both hemispheres at that latitudinal distance from the equator. The model-based results depict an average response from an ensemble of models included in the Coupled Model Intercomparison Project 5 (CMIP5). Results displayed are for 1979 - 2005 for (a) ERA-I, (b) the model-based temperature response to multiple factors including aerosols and increased greenhouse gases such as CO2, and (c) the model-based temperature response to increased greenhouse gases. Also displayed are (d) the model-based temperature response from 2006 - 2100 under Representative Concentration Pathway 8.5 (RCP8.5) [53, figure 1], in which humans continue to release large amounts of CO2 [54 - 56]. The tropics lie between latitudes 0° and 30°. 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). The tropical troposphere lies below 150hPa [37]. |
In comparison to the model-based projections, ERA-I shows less warming amplification in the lower troposphere [53, figure 1; 79, figure 3c]. This is likely because ERA-I under-estimates lower tropospheric warming, as admitted by the ERA-I team [64; 65, section 9] and other researchers [66, section 2]. This was addressed in ERA5 [99, which is defined in 100; 122; 124 {generated using 125}], the update to ERA-I [122; 126 - 128; 130]. ERA-I also clearly shows a hot spot, with upper tropospheric warming being greater than near-surface warming in the tropics [53, figure 1a; 79, figure 3c]. ERA-I therefore provides one line of evidence for the hot spot, as shown in a number of studies [53, figure 1a; 64, figure 23 on page 348 and section 10.2.2 on page 351; 67, figure 7; 68, figure 1; 69, figure 4; 79, figure 3c]. Thus scientists made progress on the hot spot by following the aforementioned points 1 and 2 from the CCSP [36, pages 14, 42, 120, and 122]: scientists incorporated diverse data sources into multiple, homogenized analyses such as ERA-I [57; 58]. Consistent with this ERA-I result, other studies confirm that climate models fairly accurately represent the ratio of upper tropospheric warming to near-surface warming [30, sections 4 and 5; 33, figure 3; 42, RSS results in table 4 of 42 are spuriously low due to heterogeneities corrected in the RSS results presented in 20, 75, and 76; 75; 77; 79, figure 3c; 129, figures 2a and 2b], as I discuss in section 2.2 of "Myth: Santer et al. Show that Climate Models are Very Flawed".
Strangely, Judith Curry holds ERA-I in high esteem [60; 121], though she also disputes the hot spot's existence [51; 52]. Maybe she is unaware that her favored re-analysis supports the position she disputes? Curry is not the only critic of mainstream climate science who fails (intentionally or unintentionally) to acknowledge evidence undermining their position. For instance, John Christy adamantly disputes the hot spot's existence [25; 26; 70 - 74], despite the hot spot in the ERA-I analysis [53, figure 1a; 64, figure 23 on page 348 and section 10.2.2 on page 351; 67, figure 7; 68, figure 1; 69, figure 4] he cites [61, pages 4 - 7; 62; 63, pages S16 and S17] (in "John Christy and Atmospheric Temperature Trends", I summarize other cases of Christy misrepresenting climate science in politically expedient ways).
Section 2.3: Subsequent evidence rebuts myth's proponents claims and confirms the hot spot's existence
Myth proponents also avoid evidence of the hot spot. Proponents perform this evasion by almost exclusively focusing on their fabricated figures 2 and 3, with their misleading comparisons of 1979 - 1999 HadAT2 data with model-based projections for 1958 - 1999 or for 1890 - 1999 [2 - 18; 80, appendix Y on page 53; 81, pages 5 and 6; 82 - 87; 89; 111; 115; 116; 119; 120; 131]. It's almost as if some myth defenders think atmospheric science stopped with one HadAT2 image from a 2006 CCSP report...
In contrast to the antics of myth advocates, one need not focus solely on HadAT2 to the exclusion of other observational analyses. So I will compare these other analyses with the model-based projections that myth defenders misuse. The model-based projections in question are:
- Group 1 : three of the models for 1979 - 1999 presented by the CCSP in figures 5A, 5B, and 5D above (excluding the outlier model in figure 5C)
- Group 2 : the outlier model for 1979 - 1999 presented by the CCSP in figure 5C above
- Group 3 : the 1958 - 1999 CCSP projection in the right panel of figure 3
- Group 4 : the 1890 - 1999 IPCC projection in figure 4f
(I examine comparisons to more recent CMIP5 models in "Myth: Santer et al. Show That Climate Models are Very Flawed" and in figure 8 above)
I exclude figure 2A and figure 4c from the above groups, because these figures depict only the impact of changes in greenhouse gases [36, figure 1.3 on page 25; 38, figure 9.1 on page 675], while observational analyses would include the impact of greenhouses and other factors. So I will focus on model-based projections that include the impact of greenhouse gases and other factors [36, figure 1.3 on page 25, page 94, and figure 5.7 on page 116; 38, figure 9.1 on page 675]. Excluding figures 2A and 4c will not matter too much for my comparison belows, because tropical upper tropospheric warming in figures 2A and 4c is only slightly greater than tropical upper tropospheric warming in model groups 3 and 4, respectively [36, figure 1.3 on page 25; 38, figure 9.1 on page 675].
Each of the model groups has tropical tropospheric amplification extending between tropical latitudes 30°N and 30°S, or 20°N and 20°S [36, figure 1.3 on page 25 and figure 5.7 on page 116; 38, figure 9.1 on page 675]. Thus I will focus on these latitudes, because these are also the same latitudes available for each observational analysis I will cite. I will also focus on an atmospheric pressure level of around 250hPa - 300hPa (equivalent to an altitude of roughly 9km to 11km [36, figure 5.7 on page 116; 92, page 1; 93, slide 29]), since this region contains some of the greatest tropical tropospheric amplification in each of the model groups [36, figure 1.3 on page 25 and figure 5.7 on page 116; 38, figure 9.1 on page 675].
For the tropical upper troposphere from 30°N - 30°S, at an atmospheric pressure of ~250hPa - ~300hPa, and an altitude of ~9km - ~11km, the models project roughly the following warming trends in K per decade [36, figure 1.3 on page 25 and figure 5.7 on page 116; 38, figure 9.1 on page 675]:
- Group 1 : 0.2 - 0.3 (from 1979 - 1999) [36, figure 5.7 on page 116]
- Group 2 : 0.4 - 0.6 (from 1979 - 1999) [36, figure 5.7 on page 116]
- Group 3 : 0.19 - 0.29 (from 1958 - 1999) [36, figure 1.3 on page 25]
- Group 4 : 0.08 - 0.1 (from 1890 - 1999) [38, figure 9.1 on page 675]
Unfortunately, I cannot cite observational analyses covering all of these time periods because, for example, satellite-based analyses go back to only late 1979 [20; 41; 42; 75; 97] and relatively reliable radiosonde-based analyses go back to only 1958 [29 - 34; 40]. This should not be a problem for myth defenders, since they compare observational analyses on one time-frame with model-based analyses on a different time-frame [2 - 18; 80, appendix Y on page 53; 81, pages 5 and 6; 82 - 87; 89; 111; 115; 116; 119; 120; 131], as I discussed in section 2.1. To address this issue and to avoid cherry-picking short time periods that are not statistically robust [65, figure 3; 105, page 194; 117], I will present observational evidence covering the longest feasible time periods available in the literature.
I discuss evidence that the hot spot exists in "Myth: The Tropspheric Hot Spot does not Exist". In that blogpost I cite multiple lines of evidence, including {in brackets I place the corresponding sections in which I discuss those lines of evidence}:
- satellite-based estimates that depend on global positioning system radio occultation (GPS RO) {section 2.2}
- satellite-based estimates that depend on microwave emissions (using microwave sounding units or MSUs) {section 2.3}
- radiosonde estimates based temperature detectors {section 2.4}
- radiosonde estimates that infer temperature indirectly from wind measurements {section 2.4}
- re-analyses {section 2.5}
I elaborate on each of these sources in "Myth: The Tropspheric Hot Spot does not Exist", so I will not mention all the details again here. Instead I will present warming trends from analyses within each class of evidence.
GPS RO, late 2001 - 2017 tropical upper tropospheric warming trend in K per decade from 30°N - 30°S, 10km altitude, and an atmospheric pressure of ~260hPa [94, figure 4; 122, figure 11]:
Satellite-based MSU, 1979 - 2017 tropical mid-to-upper tropospheric warming trends in K per decade from 20°N - 20°S [20, figure 4B; 95, page S18]
(I consider the UAH results to be unreliable for reasons I mention in section 2.3 of "Myth: The Tropspheric Hot Spot does not Exist"):
With the exception of the "Weng and Zou" results mentioned a bit later [96], these MSU-based estimates do not target a specific altitude or atmospheric pressure level, but instead present a weighted average of results across a broad vertical swath of the atmosphere [20; 41; 42; 75; 97]. Thus these MSU-based analyses would be expected to show less warming than the predicted warming maximum at 250hPa - 300hPa. The altitude-weighted MSU-based estimates represent a mid-to-upper tropospheric analysis known as TTT, which I discuss further in section 2.3 of "Myth: The Tropspheric Hot Spot does not Exist". Figure 9 below shows the relative contribution of different atmospheric altitudes to the TTT temperature trend:
Satellite-based MSU, late 1978 - 2004 tropical mid-to-upper tropospheric warming trend in K per decade between from 30°N - 30°S [98, figure 8]:
GPS RO, late 2001 - 2017 tropical upper tropospheric warming trend in K per decade from 30°N - 30°S, 10km altitude, and an atmospheric pressure of ~260hPa [94, figure 4; 122, figure 11]:
- >0.30
(I consider the UAH results to be unreliable for reasons I mention in section 2.3 of "Myth: The Tropspheric Hot Spot does not Exist"):
- UW : ~0.17
- NOAA/STAR : ~0.21
- RSS : ~0.19
- UAH : ~0.12
With the exception of the "Weng and Zou" results mentioned a bit later [96], these MSU-based estimates do not target a specific altitude or atmospheric pressure level, but instead present a weighted average of results across a broad vertical swath of the atmosphere [20; 41; 42; 75; 97]. Thus these MSU-based analyses would be expected to show less warming than the predicted warming maximum at 250hPa - 300hPa. The altitude-weighted MSU-based estimates represent a mid-to-upper tropospheric analysis known as TTT, which I discuss further in section 2.3 of "Myth: The Tropspheric Hot Spot does not Exist". Figure 9 below shows the relative contribution of different atmospheric altitudes to the TTT temperature trend:
 |
| Figure 9: Relative weight of different atmospheric layers for the temperature trend in the mid-to-upper troposphere TTT analysis [112]. The tropical troposphere lies below 150hPa [37], equivalent to an altitude below ~14km [36, figure 5.7 on page 116; 92, page 1; 93, slide 29]. The main point of this image is the curved black line that bounds that solid yellow "TTT" region on the bottom left. The curved black line represents the relative contribution of each altitude to TTT, in the form of a horizontal histogram, with the x-axis measuring the relative weight [112] as per a weighting function [20; 41; 42; 75; 97]. For example, the curved black line is farther right at 4km than at 12km, indicating that an altitude of 4km contributes more to the TTT temperature trend than does an altitude of 12km [112]. |
- UMD : ~0.20 - ~0.24
Satellite-based MSU, 1979 - 2009 tropical upper tropospheric warming trend in K per decade, at an atmospheric pressure of 300hPa, ~9km altitude, and between latitudes 30°N and 30°S [96, figure 13 and section 4.3]
(I consider these results to be unreliable, as I discuss in section 2.3 of "Myth: The Tropspheric Hot Spot does not Exist"):
- Weng and Zou : ~0.8 - ~1.0
Radiosonde, 1958 - 2014 tropical upper tropospheric warming trends in K per decade between latitudes 20°N - 20°S, at an atmospheric pressure of 300hPa, and ~9km altitude [34, figure 3]
(I consider that HadAT2 results to be less reliable for reasons I went over in section 2.2 above):
- IUKv2 : ~0.25 - ~0.33 [32, figures 1 and 2; 34, figure 3]
- RATPAC : ~0.20 - ~0.25
- RICH : ~0.21 - ~0.26
- RAOBCORE : ~0.21 - ~0.26
- HadAT2 : ~0.16 - ~0.21 [34, figure 3]
Re-analyses, 1979 - 2017 (unless otherwise noted) tropical upper tropospheric warming trends in K per decade between latitudes 30°N and 30°S, at an atmospheric pressure of 300hPa, and an altitude of ~9km
(I consider the 20CR results to be irrelevant, and the NCEP and NCEP-2 results to be less reliable, for reasons I explain in section 2.5 of "Myth: The Tropspheric Hot Spot does not Exist"; CFSR [104 {generated using 99, which is defined in 100}] is also a clear outlier, MERRA runs only until about 2015 or 2016 [102 {generated using 99, which is defined in 100}] {MERRA-2 extends through 2017 [101 {generated using 99, which is defined in 100}]}, and 20CR extends to only 2013 or 2014 [104 {generated using 99, which is defined in 100}]):
(I consider the 20CR results to be irrelevant, and the NCEP and NCEP-2 results to be less reliable, for reasons I explain in section 2.5 of "Myth: The Tropspheric Hot Spot does not Exist"; CFSR [104 {generated using 99, which is defined in 100}] is also a clear outlier, MERRA runs only until about 2015 or 2016 [102 {generated using 99, which is defined in 100}] {MERRA-2 extends through 2017 [101 {generated using 99, which is defined in 100}]}, and 20CR extends to only 2013 or 2014 [104 {generated using 99, which is defined in 100}]):
- ERA5 : ~0.18 [123 {generated using 99, which is defined in 100}; 124 {generated using 125} ]
- MERRA-2 : ~0.22 (1980 - 2017) [101 {generated using 99, which is defined in 100}]
- JRA-55 : ~0.19 (same trend for 1958 - 2017) [102; 106 {generated using 99, which is defined in 100}]
- ERA-I : ~0.27 [101 {generated using 99, which is defined in 100}]
- MERRA : ~0.30 [102 {generated using 99, which is defined in 100}]
- NCEP-2 : ~0.17 [103 {generated using 99, which is defined in 100}]
- NCEP : ~0.20 (~0.16 for 1958 - 2017 ; ~0.13 for 1948 - 2017) [103; 106; 107 {generated using 99, which is defined in 100}]
- CFSR : ~0.49 [104 {generated using 99, which is defined in 100}]
- 20CR : ~0.28 [104 {generated using 99, which is defined in 100}]
UAH [20, figure 4B; 95, page S18] and NCEP-2 [103 {generated using 99, which is defined in 100}] display unusually low warming rates in comparison to the other observational analyses. This likely stems from flaws in the UAH analysis and NCEP / NCEP-2 analyses, as I discuss in sections 2.3 and 2.5 of "Myth: The Tropspheric Hot Spot does not Exist", respectively. Other than UAH, NCEP / NCEP-2, and HadAT2 (the last of which I discussed in section 2.2 above), almost all of the observational analyses have warming trends within the range of, or greater than, the model-based projections for groups 1, 3, and 4. Model group 2 is the outlier, with a warming rate greater than almost all of the observational analyses. But this does not help myth proponents much, since myth proponents did not use group 2; they instead used groups 3 and 4 [2 - 18; 80, appendix Y on page 53; 81, pages 5 and 6; 82 - 87; 89; 111; 115; 116; 119; 120; 131]. And it would be unjustified cherry-picking for myth advocates to focus on group 2's model, to the exclusion of the group 1 models that were presented in the same figure as group 2's model.
(I discuss comparisons to more recent CMIP5 model-based projections in "Myth: Santer et al. Show That Climate Models are Very Flawed" and in figure 8 above)
No comments:
Post a Comment