Title: Modeled and Observed Stratospheric Temp..._ Implications for Fingerprint Studies
Author: Richard Delahaye (LLE - Staff)

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AGU Advances	10.1029/2025AV002196

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AGU Advances	10.1029/2025 AV002196

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AGU Advances
COMMENTARY
10.1029/2025AV002196
Modeled and Observed Stratospheric Temperature Changes: Implications for Fingerprint Studies
Peer Review The peer review history for this article is available as a PDF in the Supporting Information.
Key Points:
•		Human fingerprints, marked by tropospheric warming and stratospheric cooling, are evident in Earth's changing atmospheric thermal structure
•		A claim to the contrary in a recent report of the US Department of Energy is incorrect
•		Climate models are capable of capturing the observed reduced cooling of the lower stratosphere in the early 21st century
Supporting Information:
Supporting Information may be found in the online version of this article.
Benjamin D. Santer ^1	, Susan Solomon^2 , David W. J. Thompson^1’^3, and Qiang Fu^4
'School of Environmental Sciences, University of East Anglia. Norwich, UK. 2Department of Earth, Atmospheric, and Planetary Sciences. Massachusetts Institute of Technology. Cambridge, MA, USA, 3Department of Atmospheric Sciences, Colorado State University, Fort Collins, CO, USA. ^4Department of Atmospheric Sciences, University of Washington, Seattle. WA. USA
Abstract Changes in the vertical structure of atmospheric temperature are an important “fingerprint" of human effects on global climate. These changes are mainly driven by human-caused increases in atmospheric levels of CO_2 and other well-mixed greenhouse gases. Key features of this fingerprint are warming of the troposphere, the lowest layer of the atmosphere, and cooling of the stratosphere, the layer above the troposphere. Cooling in the lower stratosphere (from roughly 15-20 km above Earth's surface) also arises from human- caused depletion of stratospheric ozone. While lower stratospheric cooling diminished in the 21st century, largely due to the emerging “healing" of stratospheric ozone levels after the Montreal Protocol, strong cooling of the mid- to upper stratosphere continued unabated. Satellite observations of this distinctive fingerprint are in accord with current state-of-the-art climate model estimates of human-caused temperature changes. The claim to the contrary made in the recent US Department of Energy review of climate science is factually incorrect.
Correspondence to:
B. D. Santer,
bensanter1289@gmail.com
Citation:
Santer, B. D., Solomon, S., Thompson, D. W. J., & Fu, Q. (2026). Modeled and observed stratospheric temperature changes: Implications for fingerprint studies. AGU Advances, 7, e2025AV002196. https://doi.org/10.1029/ 2025AV002196
Received 3 NOV 2025
Accepted 10 FEB 2026
Author Contributions:
Conceptualization: Benjamin D. Santer, Susan Solomon, David W. J. Thompson, Qiang Fu
Data curation: Benjamin D. Santer Formal analysis: Benjamin D. Santer Investigation: Benjamin D. Santer Methodology: Benjamin D. Santer, Susan Solomon, David W. J. Thompson, Qiang Fu
Visualization: Benjamin D. Santer
Plain Language Summary Human-caused changes in carbon dioxide and stratospheric ozone have altered the temperature structure of Earth's atmosphere, warming the lower atmosphere—the troposphere—and cooling the layer above the troposphere (the stratosphere). This canonical “fingerprint” of human effects on climate has been predicted for over 50 years by simple and more sophisticated climate models, and is identifiable with high confidence in satellite temperature data. A recent claim to the contrary in a report by the US Department of Energy is incorrect.
© 2026. The Author(s).
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
1. Introduction
In 2025, the Secretary of the US Department of Energy (DOE) commissioned a “team of independent experts to critically review the current state of climate science." The Secretary. Chris Wright, noted that the conclusions of the review "differ in important ways from the mainstream narrative” (DOE, 2025). We provide below a specific example of one key difference between the DOE report and the “mainstream narrative.” This difference occurs because of a fundamental error in the DOE report: It fails to correctly reflect the scientific understanding of human impacts on temperature at different altitudes in the atmosphere.
In 1967, an early climate modeling study (Manabe & Wetherald, 1967) predicted that increases in atmospheric CO2 would cause the troposphere to warm and the stratosphere to cool. The troposphere extends from the surface to roughly 15 km above the surface, while the stratosphere spans the region from approximately 15 to 50 km. Data from weather balloons and satellites subsequently confirmed this prediction (Ladstadter et al., 2023; Lott et al., 2013; Mears & Wentz, 2016; Steiner et al., 2020; Thorne et al., 2005; Zou & Qian, 2016) (see Figure 1).
The physics responsible for tropospheric warming and stratospheric cooling is well understood (Fels et al., 1980; Goessling & Bathiany, 2016; Jevanjee et al., 2022; Manabe & Wetherald, 1967; Ramaswamy & Schwarzkopf, 2002; Ramaswamy et al.. 2006; Shine et al., 2003; Solomon, 1999; Thompson et al., 2012). The troposphere warms as higher concentrations of CO2 and other well-mixed greenhouse gases enhance the trapping of infrared radiation (Pierrehumbert, 2011). In contrast, elevated CO2 levels lead to increased infrared emission from the stratosphere to space, resulting in stratospheric cooling that increases in magnitude with higher altitude (Fels et al., 1980; Goessling & Bathiany, 2016; Jevanjee et al., 2022; Manabe & Wetherald, 1967; Ramaswamy & Schwarzkopf, 2002; Ramaswamy et al., 2006; Shine et al., 2003; Solomon, 1999; Thompson et al., 2012).
Stratospheric temperatures are also affected by anthropogenic changes in stratospheric ozone, which alter the absorption of ultraviolet radiation. In the lower stratosphere between roughly 15-25 km, where most ozone

Writing - original draft: Benjamin
D. Santer
Writing - review & editing: Benjamin
D. Santer, Susan Solomon, David
W. J. Thompson, Qiang Fu

Figure 1. Changes in global-mean annual-mean temperature in six atmospheric layers. Results are for the temperatures of the mid- to upper stratosphere (SSU1, SSU2, and SSU3; panels a-c, respectively), as well for lower stratospheric temperature (TLS), total tropospheric temperature (ΤΤΤ) and lower tropospheric temperature (TLT) (panels d-f, respectively). Observed results are from the NOAA/NESDIS group (STAR) for the three Stratospheric Sounding Unit layers and from the average of three observational groups for TLS, ΤΤΤ, and TLT. Model results are synthetic satellite temperatures from 32 realizations of historical climate change performed with nine different climate models. Approximate altitude ranges of the weighting functions for these layers are given in brackets (Karl et al., 2006; Thompson et al., 2012). All results are anomalies relative to climatological means over 1986 to 2025. See Supporting Information S1 for further details.

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resides (Salawitch et al., 2023), increases in ozone-depleting substances led to the destruction of ozone, which caused strong cooling over the last 3-4 decades of the 20th century (Solomon, 1999). When ozone stopped decreasing after roughly 2000, observed lower stratospheric cooling diminished or even switched sign to weak warming.
This post-2000 change in lower stratospheric temperature was expected. It was due to effective controls on ozonedepleting substances implemented under the Montreal Protocol and its amendments and adjustments, enabling emerging recovery of ozone levels (Solomon et ål., 2016, 2017; Wang et al., 2025). In the lower stratosphere, the contribution of ozone recovery to temperature trends offset or even exceeded the CO2-induced cooling. In the mid- to upper stratosphere, however, where the radiative signature of CO_2 increases is largest (Thompson

Figure 2. Total global-mean atmospheric temperature changes over 25-year periods. Results are for six different atmospheric layers, arranged vertically by height of the layer with respect to Earth's surface (panels a-f). The total temperature change is the least-squares linear trend per year X 25 years, calculated over 2001 to 2025 for the HISTex realizations and satellite observations and over 25-year non-overlapping segments of pre-industrial control runs. The latter provide estimates of the natural internal variability of atmospheric temperature trends inferred from nine different CMIP6 models. The same nine models were used to calculate the multi-model average synthetic Stratospheric Sounding Unit and MSU atmospheric temperature trends from 32 realizations of HISTENT runs with anthropogenic and natural external forcing. Trends from individual HISTeN realizations are also shown (in gray dots). The spread of temperature trends in these 32 individual realizations is influenced by inter-model differences in the applied external forcings and the climate responses to those forcings, as well as by inter-model differences in the amplitudes, patterns, and timescales of intrinsic variability. It is also influenced by temperature trend differences between individual realizations of a single model (see Table S1 in Supporting Information S1), which arise from the effects of intrinsic variability. The y-axis location of the HISTEN trends and observed trends is arbitrary.

et al., 2012), the observed cooling remained substantial after 2000, ranging from —1.1 to —1.4°C over 2001 to 2025 (see Figures 2a-2e) (Casas et ål., 2022; Maycock et al., 2018; Santer et al., 2023, 2025; Steiner et al., 2020).

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In the following, we compare simulated and observed atmospheric temperature changes over six different broad atmospheric layers. The six layers are those sampled by the primary satellite instruments used to measure atmospheric temperatures: the Stratospheric Sounding Unit (SSU) (Zou & Qian, 2016) and the Microwave Sounding Unit and Advanced Microwave Sounding Unit (MSU/AMSU). SSU supplies mid- to upper stratospheric temperatures (SSU3, SSU2, and SSU1; Figures la-lc), while MSU/AMSU provides lower stratospheric temperature (TLS), total tropospheric temperature and lower tropospheric temperature (TLT; Figures Id-lf, respectively) (Mears & Wentz, 2016; Spencer et al., 2017; Zou et al., 2023).

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This is not a formal “fingerprint” study. Fingerprinting relies on the analysis of spatial or spatio-temporal patterns to identify forced signals embedded in the background noise of intrinsic variability (Hasselmann, 1979; Hegerl et al., 1996; Lucarini & Chekroun, 2024; Santer et al., 1995). The results presented below, however, are directly relevant to the credibility of a study that performed fingerprinting with latitude-altitude temperature-change patterns (Santer et al.. 2023). The finding of a human fingerprint in Santer et al. (2023) is challenged in the DOE report.
2.		Temperature Trend Results
The new DOE report (DOE, 2025) claims that: “An important element of the expected general fingerprint of anthropogenic climate change is simultaneous warming of the troposphere and cooling of the stratosphere. The latter feature is also influenced by ozone depletion and recovery. The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2021) acknowledged that cooling had been observed but only until the year 2000. The stratosphere has shown some warming since, contrary to model projections.”
We agree that “simultaneous warming of the troposphere and cooling of the stratosphere” is an important fingerprint of human-caused climate change. This fingerprint has been unambiguously identified in observations in many different scientific studies (Lott et al., 2013; Santer et al., 1996, 2013, 2023, 2025; Tett et al., 1996; Thorne et al.. 2002). As noted above, it is also true that because of the recovery of stratospheric ozone in the 21st century, the lower stratosphere has showed muted cooling or even warming since 2000 (Solomon et al., 2016. 2017; Wang et al., 2025). It is not true, however, that reduced post-2000 cooling of the lower stratosphere in observations is “contrary to model projections"—see, for example. Figure 4 in Santer et al. (2021) and results in Figure 3D of Santer et al. (2023). All current satellite estimates of lower stratospheric temperature change over 2001 to 2025 are within the range of results from state-of-the-art model simulations of historical climate change (compare colored symbols and gray dots in Figure 2d).
Consistency between modeled and observed global-mean temperature trends over 2001 to 2025 holds for all stratospheric layers—not just for the lower stratosphere. The observed and simulated post-2000 cooling in the mid- to upper stratosphere, from approximately 25 to 50 km above the surface, is significantly larger than in model estimates of natural variability (Figures 2a-2c). Even over the period of ozone recovery, therefore, detection of human-caused cooling of the mid- to upper stratosphere (relative to intrinsic variability) far exceeds the five-sigma “gold standard” for particle discovery in physics.
In their summary of the "Stratospheric cooling” section of the DOE report, the authors state that: “A combination of tropospheric warming and stratospheric cooling is a commonly cited “fingerprint” of anthropogenic climate change. Stratospheric warming since 2000 coincides with continued surface and tropospheric warming, a pattern that is not found in climate model simulations and is not apparently consistent with the anthropogenic fingerprint."
This claim is incorrect, as Figure 2 clearly shows. The large post-2000 cooling of the mid- to upper stratosphere and simultaneous warming of the troposphere is common to simulations and observations. In all stratospheric and tropospheric layers (including the lower stratosphere), the observed global-mean temperature changes after 2000 are within the range of model results (Figure 2). Model-data consistency holds not only for the 2001 to 2025 period characterized by ozone recovery, but also for the first 15 years of the full gap-free satellite record (19862000), a time of pronounced ozone depletion (see Figure Sl in Supporting Information Sl).
In summary, our focus here has been on global-mean temperature trends in six atmospheric layers during the early 21st century. Over 2001 to 2025, simulated and observed global-mean changes reveal a common signal of simultaneous tropospheric warming, mid- to upper stratospheric cooling, and relatively small temperature changes in the lower stratosphere (Figure 2). This signal is spatially coherent, as is evident in the full latitudealtitude patterns of atmospheric temperature change (Figure 3). The results shown here are fully consistent with prior research that has identified a human fingerprint in the vertical structure of atmospheric temperature change (Santer et al., 2023, 2025). Our results do not support a specific claim made in the DOE CWG report—that observed atmospheric temperature changes are "not apparently consistent” with an anthropogenic fingerprint (DOE, 2025).

3.		
80°S 40’S	0’	40°N 80’N

80°S 40°S	0’	40°N 80’N

C/decade

Figure 3. Simulated and observed latitude-height profiles of atmospheric temperature trends over 2001 to 2025 (in °C/decade). Trends were calculated from zonal-mean temperatures for the six atmospheric layers shown in Figure 1. Trends are plotted at the approximate heights of the maxima of each weighting function peak (indicated by dotted blue horizontal lines) and were smoothly interpolated in the vertical. Model results are for simulations of historical climate change (HISTENf) performed with nine different CM1P6 models (panels a-i). If more than one HISTEM realization was available for an individual model, the result in panels (a)-(i) is for the ensemble-mean trends. The CMIP6 multi-model average is also shown (MMA; panel j). Satellite observations are for Stratospheric Sounding Unit data combined with two different observed MSU/AMSU data sets (panels k and 1; see in Supporting Information Sl). Stippling in panel (j) denotes latitude bands and layers at which the local S/N ratio exceeds 2—that is, where the CMIP6 MMA trend over 2001 to 2025 is two times greater than the between-model standard deviation of the trend. There is no stippling in panel J at the peak of the TLS weighting function. This is because lower stratospheric temperature changes over 2001 to 2025 are small due to the effects of ozone recovery.

Implications
The DOE report was released in July 2025, on the same day as the US Environmental Protection Agency (EPA) released a proposal to rescind the 2009 "endangerment finding”—the finding that provides the EPA with the legal authority to regulate emissions of greenhouse gases. The DOE report is referenced 16 times in the July 2025 EPA proposal, including on the issue of attributing climate change to human causation (Storrow et al., 2025). As our analysis clearly illustrates, the DOE report is not a reliable source of information on the vertical structure of changes in atmospheric temperature, which is a key piece of evidence for human effects on global climate.
Scientific concerns have also been raised regarding other aspects of the treatment of climate change detection and attribution in the DOE report (Dessler & Kopp, 2025). Far from being “unsettled” science, attribution science has for decades routinely examined the natural explanations of climate change highlighted in the DOE report, such as fluctuations in solar irradiance, volcanic activity, and natural internal variability. These natural factors cannot explain the observed changes in Earth's climate. Human influence provides the explanation that is fully consistent with observations, theory, and modeling, as the US National Academies reaffirmed in September 2025 (National Academies of Sciences et al., 2025).
Following a lawsuit alleging failure of the DOE to follow proper Federal Advisory Committee procedures, the author team of the DOE report was dissolved in early September (Waldman, 2025). The DOE report itself, however, has not been retracted or corrected. It is still available on the DOE website, and is still being publicly referenced by DOE Secretary Wright as a credible source of information on climate science. It is not. and it should not inform legal decisions on the scientific basis for the 2009 endangerment finding.

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The eventual fate of the DOE CWG report is currently unclear. But we view it both important and with precedent (Piecuch, 2025) to rebut an incorrect scientific claim made in the DOE report. Setting the record straight in the peer-reviewed literature is particularly important when demonstrably incorrect scientific claims are made in official government reports.

Acknowledgments
We acknowledge the World Climate Research Programme's Working Group on Coupled Modeling, which is responsible for CMIP. and we thank the climate modeling groups for producing and making available their model output. For CMIP, the US Department of Energy's Program for Climate Model Diagnosis and Intercomparison (PCMDI) provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. DWJT acknowledges the support of the National Science Foundation Climate and Large- scale Dynamics program. QF acknowledges support from the Calvin Professorship in Atmospheric Sciences. The authors are grateful to three reviewers for constructive comments.

Conflict of Interest
The authors declare no conflicts of interest relevant to this study.
Data Availability Statement
Observational satellite temperature data used in the paper (MSU/AMSU and SSU) and synthetic satellite temperature data from CMIP6 simulation output are available at: https://doi.org/10.5281/zenodo.18507593 (Santer, 2026a). The Matplotlib codes for plotting Figures 1-3 are provided at: https://doi.org/10.5281/zenodo. 18508640 (Santer. 2026b).
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