{"id":431777,"date":"2026-03-17T14:38:28","date_gmt":"2026-03-17T13:38:28","guid":{"rendered":"https:\/\/climatescience.press\/?p=431777"},"modified":"2026-03-17T14:38:30","modified_gmt":"2026-03-17T13:38:30","slug":"sun-trumps-co%e2%82%82-new-study-shows-solar-activity-drove-most-warming-until-2000","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=431777","title":{"rendered":"Sun Trumps CO\u2082: New Study Shows Solar Activity Drove Most Warming Until 2000"},"content":{"rendered":"<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"687\" height=\"1024\" data-attachment-id=\"431778\" data-permalink=\"https:\/\/climatescience.press\/?attachment_id=431778\" data-orig-file=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0-Sun-Trumps-CO%E2%82%82-New-Study-Shows-Solar-Activity-Drove-Most-Warming-Until-2000.jpg?fit=784%2C1168&amp;ssl=1\" data-orig-size=\"784,1168\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"0 Sun Trumps CO\u2082  New Study Shows Solar Activity Drove Most Warming Until 2000\" data-image-description=\"\" data-image-caption=\"\" data-large-file=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0-Sun-Trumps-CO%E2%82%82-New-Study-Shows-Solar-Activity-Drove-Most-Warming-Until-2000.jpg?fit=687%2C1024&amp;ssl=1\" src=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0-Sun-Trumps-CO%E2%82%82-New-Study-Shows-Solar-Activity-Drove-Most-Warming-Until-2000.jpg?resize=687%2C1024&#038;ssl=1\" alt=\"\" class=\"wp-image-431778\" srcset=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0-Sun-Trumps-CO%E2%82%82-New-Study-Shows-Solar-Activity-Drove-Most-Warming-Until-2000.jpg?resize=687%2C1024&amp;ssl=1 687w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0-Sun-Trumps-CO%E2%82%82-New-Study-Shows-Solar-Activity-Drove-Most-Warming-Until-2000.jpg?resize=201%2C300&amp;ssl=1 201w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0-Sun-Trumps-CO%E2%82%82-New-Study-Shows-Solar-Activity-Drove-Most-Warming-Until-2000.jpg?resize=768%2C1144&amp;ssl=1 768w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0-Sun-Trumps-CO%E2%82%82-New-Study-Shows-Solar-Activity-Drove-Most-Warming-Until-2000.jpg?resize=640%2C953&amp;ssl=1 640w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0-Sun-Trumps-CO%E2%82%82-New-Study-Shows-Solar-Activity-Drove-Most-Warming-Until-2000.jpg?w=784&amp;ssl=1 784w\" sizes=\"auto, (max-width: 687px) 100vw, 687px\" \/><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">Frank Stefani, a researcher at the Helmholtz-Zentrum Dresden-Rossendorf (Institute of Fluid Dynamics), has published work examining the relative roles of solar activity (using the geomagnetic aa index as a proxy) and CO\u2082 in driving global climate changes, particularly sea surface temperatures (SST).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In his most recent paper (published in Atmosphere in 2026), Stefani updates earlier regression analyses comparing the solar aa index and CO\u2082 concentrations (or emissions) against observed global SST data from HadSST4.2. The aa index measures geomagnetic disturbances influenced by solar wind and activity, serving as a long-term proxy for solar variability.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><em><strong>Key findings from the analysis:<\/strong><\/em><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Up to around 2000, the aa index alone predicts SST variations very well\u2014often better than CO\u2082 alone, and comparably to models combining both.<\/li>\n\n\n\n<li>Post-2000 data shows a stronger apparent role for CO\u2082, but Stefani argues that fixing the solar (aa index) contribution based on robust pre-2000 regressions (around 0.04 K\/nT) and then regressing the residual SST against CO\u2082 narrows the estimated Transient Climate Response (TCR)\u2014the warming from a doubling of CO\u2082 under transient conditions\u2014to 1.1\u20131.4 K.<\/li>\n\n\n\n<li>This TCR range is at the low end of the IPCC&#8217;s 2021 estimate (1.2\u20132.4 K) and aligns closely with other observationally constrained studies (e.g., Lewis &amp; Curry 2018: 0.9\u20131.7 K; Scafetta 2023: 1.0\u20131.2 K for HadSST4.2).<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Stefani&#8217;s approach refines earlier work (e.g., his 2021 paper), where double regressions gave a broader TCR range (0.6\u20131.6 K), sensitive to including recent data affected by events like strong El Ni\u00f1o periods and low aa values.For projections to 2100, Stefani uses refined aa index forecasts (based on ideas of planetary synchronization of the solar dynamo) and CO\u2082 scenarios assuming constant emissions (30\u201350 Gt\/year, near current levels) plus a linear sink model. Even at higher sensitivities and unabated CO\u2082 growth, warming remains modest (~1 K additional by 2100 in pessimistic cases). Lower sensitivities suggest possible near-term cooling or flattening, with temperatures potentially staying below recent highs (e.g., 2024 peaks).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>This work is discussed in Andy May&#8217;s blog.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Andy May, a retired petrophysicist and climate blogger (andymaypetrophysicist.com), published a detailed review on March 2, 2026, titled &#8220;Stefani on the Sun vs. CO2 as climate drivers&#8221;. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This post analyzes Frank Stefani&#8217;s February 2026 paper in Atmosphere (MDPI): &#8220;Solar and Anthropogenic Climate Drivers: An Updated Regression Model and Refined Forecast.&#8221;May&#8217;s article highlights Stefani&#8217;s findings that solar variability\u2014proxied by the geomagnetic aa index (a measure of solar wind and geomagnetic disturbances, recorded since ~1868)\u2014explains global sea surface temperature (SST) changes (HadSST4.2 dataset) remarkably well from ~1850 to ~2000, often outperforming CO\u2082 alone and matching or exceeding combined solar + CO\u2082 models.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">_____________________________________________________________________________________<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<p class=\"has-large-font-size wp-block-paragraph\"><strong>Stefani on the Sun vs. CO2 as climate drivers<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"723\" height=\"375\" data-attachment-id=\"431783\" data-permalink=\"https:\/\/climatescience.press\/?attachment_id=431783\" data-orig-file=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?fit=1568%2C813&amp;ssl=1\" data-orig-size=\"1568,813\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"0Figure-1_Featured-1\" data-image-description=\"\" data-image-caption=\"\" data-large-file=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?fit=723%2C375&amp;ssl=1\" src=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=723%2C375&#038;ssl=1\" alt=\"\" class=\"wp-image-431783\" srcset=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=1024%2C531&amp;ssl=1 1024w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=300%2C156&amp;ssl=1 300w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=768%2C398&amp;ssl=1 768w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=1536%2C796&amp;ssl=1 1536w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=640%2C332&amp;ssl=1 640w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=1200%2C622&amp;ssl=1 1200w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?w=1568&amp;ssl=1 1568w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?w=1446&amp;ssl=1 1446w\" sizes=\"auto, (max-width: 723px) 100vw, 723px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">From <a href=\"https:\/\/andymaypetrophysicist.com\/2026\/03\/02\/stefani-on-the-sun-vs-co2-as-climate-drivers\/\">Andy May Petrophysicist<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">By <a href=\"https:\/\/andymaypetrophysicist.com\/author\/andymay2014\/\">Andy May<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><a href=\"https:\/\/www.hzdr.de\/db\/!ContMan.Visi.Card?pUser=262&amp;pNid=698\">Frank Stefani<\/a>, of the Helmholtz-Zentrum Dresden-Rossendorf, Institute of Fluid Dynamics, has published a very interesting&nbsp;<a href=\"https:\/\/www.mdpi.com\/2073-4433\/17\/3\/252\">new paper<\/a>&nbsp;that compares the solar&nbsp;<a href=\"https:\/\/www.emergentmind.com\/topics\/geomagnetic-aa-index\">\u201caa\u201d index<\/a>&nbsp;and CO<sub>2<\/sub>&nbsp;emissions to global SST (sea surface temperatures using the HadSST4.2 dataset) and finds a CO<sub>2<\/sub>&nbsp;sensitivity (TCR or the \u201cTransient Climate Response\u201d) of 1.1 to 1.4K. This is at the low end of the IPCC TCR range of 1.2 to 2.4K (IPCC, 2021, p. 93), but quite close to the values calculated by Lewis and Curry and Nicola Scafetta (Lewis &amp; Curry, 2018), (Scafetta, 2023), and (Lewis, 2023). Scafetta found a plausible range of TCR (versus HadSST4.2) of 1.0K to 1.2K and Lewis &amp; Curry report a range of 0.9K to 1.7K for TCR versus HadCRUT4. The estimates are compared in Table 1.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><em>Table 1. Estimates of TCR, or Transient Climate Response to a doubling of CO<sub>2<\/sub>. Sources: (Stefani, 2026), (Lewis &amp; Curry, 2018), (Scafetta, 2023), and (IPCC, 2021, p. 93).<\/em><\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td colspan=\"5\"><strong>TCR Estimates<\/strong><\/td><\/tr><tr><td>Author<\/td><td>Best Estimate<\/td><td>Range: Low end<\/td><td>Range: High end<\/td><td>Note<\/td><\/tr><tr><td>Stefani<\/td><td>1.26K<\/td><td>1.1<\/td><td>1.4<\/td><td>2026<\/td><\/tr><tr><td>Lewis &amp; Curry<\/td><td>1.2K<\/td><td>0.9<\/td><td>1.7<\/td><td>2018<\/td><\/tr><tr><td>Scafetta<\/td><td>1.1K<\/td><td>1<\/td><td>1.2<\/td><td>2023<\/td><\/tr><tr><td>IPCC AR6<\/td><td>1.8K<\/td><td>1.2<\/td><td>2.4<\/td><td>p. 93<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">All the estimates in table 1 are based on regression models of varying complexity and all attempt to account for the influence of solar variability. The Lewis and Curry estimate does not incorporate a solar activity proxy directly but does use the Atlantic Multidecadal Oscillation (<a href=\"https:\/\/andymaypetrophysicist.com\/2025\/05\/26\/musings-on-the-amo\/\">AMO<\/a>) as an indicator of natural climate variability, which is, in large part, solar variability. Stefani uses the aa index of geomagnetic activity, essentially how disturbed Earth\u2019s magnetic field is by the sun. It is measured in&nbsp;<a href=\"https:\/\/en.wikipedia.org\/wiki\/Tesla_(unit)\">nanoteslas<\/a>&nbsp;(nT).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Nearly every observable form of solar variability is a magnetic phenomenon at its core, including sunspots, flares, and solar wind variability. Thus, the&nbsp;<a href=\"https:\/\/www.ncei.noaa.gov\/products\/geomagnetic-indices\">aa index<\/a>&nbsp;is a good indicator of changes in the sun\u2019s state and output. The aa index as a measure of solar-geomagnetic coupling has been measured consistently since 1868.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Table 1 shows that Stefani\u2019s aa index + CO<sub>2<\/sub>&nbsp;model compares well to Lewis and Curry\u2019s&nbsp;<a href=\"https:\/\/andymaypetrophysicist.com\/2025\/05\/26\/musings-on-the-amo\/\">AMO<\/a>&nbsp;+ CO<sub>2<\/sub>&nbsp;model and Scafetta\u2019s solar proxies + CO<sub>2<\/sub>&nbsp;model. Scafetta uses three estimates of total solar irradiance (TSI) in his study, although he acknowledges that variations in TSI may be only ~20% of the sun\u2019s total influence on Earth\u2019s climate. None of these observation-based models support the high-end IPCC TCR estimate of 2.4K per doubling of CO<sub>2<\/sub>&nbsp;or their best estimate of 1.8K, but all are near the lower end of the IPCC range. The Lewis (2023) correction to the Sherwood (2020) assessment of ECS and TCR relied upon in AR6 is not included in the table. However, after changing Sherwood\u2019s subjective Bayesian assessment of multiple estimates of TCR to an&nbsp;<em>objective Bayesian<\/em>&nbsp;assessment, Lewis calculated a TCR of 1.37 to 1.4 depending upon the assumptions made. This is still close to the other observation-based objective estimates in Table 1.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Stefani found that the solar aa index can successfully predict HadSST4.2 up to 1990-2000 on its own. After 1990 to 2000 the role of CO<sub>2<\/sub>&nbsp;in the regression increases significantly. In figure 1, Stefani\u2019s robust aa index weight of 0.04 K\/nT (that is the HadSST4.2 anomaly temperature in \u00b0C per the aa index in nanoteslas) plus CO<sub>2<\/sub>&nbsp;with a sensitivity of 1.26K per doubling is shown as a thin dark gray line. It is compared to the HadSST4.2 anomaly (shown as black dots). His projected aa index plus CO<sub>2<\/sub>&nbsp;at 1.26K per doubling function to 2100 is shown as a red line. The maximum departure in 2023 and 2024 looks startling, but we need to remember that this follows two strong El Ni\u00f1os (2018-19 &amp; 2023-24) and the Hunga Tonga volcanic eruption. In particular the El Ni\u00f1o from June 2023 to May 2024 was one of the strongest El Ni\u00f1os on record. The&nbsp;<a href=\"https:\/\/www.metoffice.gov.uk\/hadobs\/hadsst4\/\">HadSST4.2<\/a>&nbsp;global anomaly has been falling since September 2024. Thus, a portion of the difference between the aa index plus CO<sub>2<\/sub>&nbsp;function and HadSST4.2 may just be ENSO, the Hunga Tonga eruption, and weather.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"723\" height=\"375\" data-attachment-id=\"431783\" data-permalink=\"https:\/\/climatescience.press\/?attachment_id=431783\" data-orig-file=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?fit=1568%2C813&amp;ssl=1\" data-orig-size=\"1568,813\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"0Figure-1_Featured-1\" data-image-description=\"\" data-image-caption=\"\" data-large-file=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?fit=723%2C375&amp;ssl=1\" src=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=723%2C375&#038;ssl=1\" alt=\"\" class=\"wp-image-431783\" srcset=\"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=1024%2C531&amp;ssl=1 1024w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=300%2C156&amp;ssl=1 300w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=768%2C398&amp;ssl=1 768w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=1536%2C796&amp;ssl=1 1536w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=640%2C332&amp;ssl=1 640w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?resize=1200%2C622&amp;ssl=1 1200w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?w=1568&amp;ssl=1 1568w, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Figure-1_Featured-1.webp?w=1446&amp;ssl=1 1446w\" sizes=\"auto, (max-width: 723px) 100vw, 723px\" \/><figcaption class=\"wp-element-caption\">Figure 1. A plot of Stefani\u2019s regression of the aa index on HadSST4.2 as the dark gray line, HadSST4.2 data are shown as black dots, and the aa index projection to 2100 is shown as a red line. Data source: (Stefani, 2026).<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Stefani\u2019s optimal model projection to 2100 assumes constant emissions of 30-50 Gt of CO<sub>2<\/sub>&nbsp;per year (roughly current levels) plus a simple linear carbon sink model and predicts a global SST increase of 0.6\u00b0C (1.1\u00b0F) compared to the standard HadSST4.2 reference period of 1961-1990. Using pessimistic parameters (high CO<sub>2<\/sub>&nbsp;emissions, a low sensitivity to the aa-index, and a high sensitivity to CO<sub>2<\/sub>) yields a 2100 temperature increase of ~1K over 1960-1990. This is still a benign result.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">A word on Transient Climate Response<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The transient climate response is the modeled warming due to increasing the atmospheric CO<sub>2<\/sub>&nbsp;concentration by 1% each year until it doubles, which would take about 70 years. This is different from the commonly cited value of ECS, which is the equilibrium climate sensitivity, or the final warming due to a sudden doubling of CO<sub>2<\/sub>. ECS is an untestable number, since it would take over 1,000 years for the atmosphere to completely come to equilibrium after CO<sub>2<\/sub>&nbsp;suddenly doubles. Given the implausible scenario, ECS can never be tested, except in a climate model. Thus, it is not a scientific quantity per Karl Popper (Popper, 1962). TCR on the other hand is very realistic and could be tested given enough time and effort.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Conclusions<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The paper is a welcome addition to the growing group of observation-based estimates of climate sensitivity to CO<sub>2<\/sub>. It is appropriate that Stefani chose to create his model around HadSST4.2. SSTs are more stable than air temperatures on land and they respond mainly to changes in insolation, whether due to cloud cover changes or changes in the sun itself. The changes in SST due to the greenhouse effect are smaller for the reasons discussed in my&nbsp;<a href=\"https:\/\/andymaypetrophysicist.com\/2026\/02\/27\/is-the-ocean-surface-a-boundary-condition\/\">previous post<\/a>. I recommend the paper, it is interesting, significant, and a good read.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\">Works Cited<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">IPCC. (2021). Climate Change 2021: The Physical Science Basis. In V. Masson-Delmotte, P. Zhai, A. Pirani, S. L. Connors, C. P\u00e9an, S. Berger, . . . B. Zhou (Ed.).,&nbsp;<em>WG1.<\/em>&nbsp;Retrieved from&nbsp;<a href=\"https:\/\/www.ipcc.ch\/report\/ar6\/wg1\/\">https:\/\/www.ipcc.ch\/report\/ar6\/wg1\/<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Lewis, N. (2023, May). Objectively combining climate sensitivity evidence.&nbsp;<em>Climate Dynamics, 60<\/em>, 3139-3165.&nbsp;<a href=\"https:\/\/doi.org\/10.1007\/s00382-022-06468-x\">https:\/\/doi.org\/10.1007\/s00382-022-06468-x<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Lewis, N., &amp; Curry, J. (2018). The Impact of Recent Forcing and Ocean Heat Uptake Data on Estimates of Climate Sensitivity.&nbsp;<em>Journal of Climate, 31<\/em>, 6051-6071. DOI:&nbsp;<a href=\"https:\/\/doi.org\/10.1175\/JCLI-D-17-0667.1.\">https:\/\/doi.org\/10.1175\/JCLI-D-17-0667.1.<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Popper, K. R. (1962).&nbsp;<em>Conjectures and Refutations, The Growth of Scientific Knowledge.<\/em>&nbsp;New York: Basic Books. Retrieved from&nbsp;<a href=\"http:\/\/ninthstreetcenter.org\/Popper.pdf\">http:\/\/ninthstreetcenter.org\/Popper.pdf<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Scafetta, N. (2023). Empirical assessment of the role of the Sun in climate change using balanced multi-proxy solar records.&nbsp;<em>Geoscience Frontiers, 14<\/em>(6). Retrieved from&nbsp;<a href=\"https:\/\/www.sciencedirect.com\/science\/article\/pii\/S1674987123001172\">https:\/\/www.sciencedirect.com\/science\/article\/pii\/S1674987123001172<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Sherwood, S. C., Webb, M. J., Annan, J. D., Armour, K. C., J., P. M., Hargreaves, C., . . . Knutti, R. (2020, July 22). An Assessment of Earth\u2019s Climate Sensitivity Using Multiple Lines of Evidence.&nbsp;<em>Reviews of Geophysics, 58<\/em>.&nbsp;<a href=\"https:\/\/doi.org\/https:\/\/doi.org\/10.1029\/2019RG000678\">https:\/\/doi.org\/https:\/\/doi.org\/10.1029\/2019RG000678<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Stefani, F. (2026). Solar and Anthropogenic Climate Drivers: An Updated Regression Model and Refined Forecast.&nbsp;<em>Atmosphere, 17<\/em>(3).&nbsp;<a href=\"https:\/\/doi.org\/10.3390\/atmos17030252\">https:\/\/doi.org\/10.3390\/atmos17030252<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<div data-wp-interactive=\"core\/file\" class=\"wp-block-file\"><object data-wp-bind--hidden=\"!state.hasPdfPreview\" hidden class=\"wp-block-file__embed\" data=\"https:\/\/climatescience.press\/wp-content\/uploads\/2026\/03\/Complete_Resume_2020_Andy_May-no-address.pdf\" type=\"application\/pdf\" style=\"width:100%;height:600px\" aria-label=\"Embed of Complete_Resume_2020_Andy_May-no-address.\"><\/object><a id=\"wp-block-file--media-ee9dc874-91f1-430b-8f9f-b15e1b6d758f\" href=\"https:\/\/climatescience.press\/wp-content\/uploads\/2026\/03\/Complete_Resume_2020_Andy_May-no-address.pdf\">Complete_Resume_2020_Andy_May-no-address<\/a><a href=\"https:\/\/climatescience.press\/wp-content\/uploads\/2026\/03\/Complete_Resume_2020_Andy_May-no-address.pdf\" class=\"wp-block-file__button wp-element-button\" download aria-describedby=\"wp-block-file--media-ee9dc874-91f1-430b-8f9f-b15e1b6d758f\">Herunterladen<\/a><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Frank Stefani, a researcher at the Helmholtz-Zentrum Dresden-Rossendorf (Institute of Fluid Dynamics), has published work examining the relative roles of solar activity (using the geomagnetic aa index as a proxy) and CO\u2082 in driving global climate changes, particularly sea surface temperatures (SST).<\/p>\n<p>In his most recent paper (published in Atmosphere in 2026), Stefani updates earlier regression analyses comparing the solar aa index and CO\u2082 concentrations (or emissions) against observed global SST data from HadSST4.2. The aa index measures geomagnetic disturbances influenced by solar wind and activity, serving as a long-term proxy for solar variability.<\/p>\n","protected":false},"author":121246920,"featured_media":431778,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_coblocks_attr":"","_coblocks_dimensions":"","_coblocks_responsive_height":"","_coblocks_accordion_ie_support":"","_crdt_document":"","advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[1],"tags":[691829997,691841915,691820968,691820785],"class_list":{"0":"post-431777","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","6":"hentry","7":"category-uncategorized","8":"tag-carbon-dioxide-co","9":"tag-frank-stefani","10":"tag-sea-surface-temperatures-sst","11":"tag-solar-activity","13":"fallback-thumbnail"},"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0-Sun-Trumps-CO%E2%82%82-New-Study-Shows-Solar-Activity-Drove-Most-Warming-Until-2000.jpg?fit=784%2C1168&ssl=1","jetpack_likes_enabled":true,"jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/paxLW1-1Ok9","jetpack-related-posts":[{"id":330517,"url":"https:\/\/climatescience.press\/?p=330517","url_meta":{"origin":431777,"position":0},"title":"The Solar Cycles: A New Physical Model","author":"uwe.roland.gross","date":"05\/29\/2024","format":false,"excerpt":"Dr. Frank Stefani and colleagues from Helmholtz-Zentrum Dresden \u2013 Rossendorf and the Institute for Numerical Modelling, University of Latvia, have proposed a new physically consistent model of solar variability. It proposes that the known solar cycles, from the eleven-year Schwabe cycle to the 193-year De Vries cycle are related to\u2026","rel":"","context":"In \"193-year De Vries cycle\"","block_context":{"text":"193-year De Vries cycle","link":"https:\/\/climatescience.press\/?tag=193-year-de-vries-cycle"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2024\/05\/0solar-cycle-nasa.webp?fit=1200%2C675&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2024\/05\/0solar-cycle-nasa.webp?fit=1200%2C675&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2024\/05\/0solar-cycle-nasa.webp?fit=1200%2C675&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2024\/05\/0solar-cycle-nasa.webp?fit=1200%2C675&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2024\/05\/0solar-cycle-nasa.webp?fit=1200%2C675&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":429506,"url":"https:\/\/climatescience.press\/?p=429506","url_meta":{"origin":431777,"position":1},"title":"Stefani on the Sun vs. CO2 as climate drivers","author":"uwe.roland.gross","date":"03\/04\/2026","format":false,"excerpt":"Frank Stefani, of the Helmholtz-Zentrum Dresden-Rossendorf, Institute of Fluid Dynamics, has published a very interesting new paper that compares the solar \u201caa\u201d index and CO2 emissions to global SST (sea surface temperatures using the HadSST4.2 dataset) and finds a CO2 sensitivity (TCR or the \u201cTransient Climate Response\u201d) of 1.1 to\u2026","rel":"","context":"In \"Atlantic Multidecadal Oscillation (AMO)\"","block_context":{"text":"Atlantic Multidecadal Oscillation (AMO)","link":"https:\/\/climatescience.press\/?tag=atlantic-multidecadal-oscillation-amo"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Screenshot-2026-03-04-124010.png?fit=1200%2C623&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Screenshot-2026-03-04-124010.png?fit=1200%2C623&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Screenshot-2026-03-04-124010.png?fit=1200%2C623&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Screenshot-2026-03-04-124010.png?fit=1200%2C623&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2026\/03\/0Screenshot-2026-03-04-124010.png?fit=1200%2C623&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":393316,"url":"https:\/\/climatescience.press\/?p=393316","url_meta":{"origin":431777,"position":2},"title":"Climate Oscillations 12: The Causes &amp; Significance","author":"uwe.roland.gross","date":"08\/06\/2025","format":false,"excerpt":"While internal variability may play a role in our observed oscillations, it is possible that gravitational forces and changes in solar output provide the pacing of the oscillations. Since all climate oscillations clearly influence the others through a mechanism named \u201cteleconnections,\u201d if the pacing of a few of the oscillations\u2026","rel":"","context":"In \"astronomical periods\"","block_context":{"text":"astronomical periods","link":"https:\/\/climatescience.press\/?tag=astronomical-periods"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/08\/0AQNPLSWo_KzxXKVbW7IbL7_vsFYRwpeEDr7n4wOji7EYEkkB1n0lKGSzzfQRN21EEW2YTvQtJVQSWUfh7fwAwOb_zqmvvqK2jdNxixoG7mgswXaDvyZS-6qY2mUTFO5a-1.jpeg?fit=1200%2C1200&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/08\/0AQNPLSWo_KzxXKVbW7IbL7_vsFYRwpeEDr7n4wOji7EYEkkB1n0lKGSzzfQRN21EEW2YTvQtJVQSWUfh7fwAwOb_zqmvvqK2jdNxixoG7mgswXaDvyZS-6qY2mUTFO5a-1.jpeg?fit=1200%2C1200&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/08\/0AQNPLSWo_KzxXKVbW7IbL7_vsFYRwpeEDr7n4wOji7EYEkkB1n0lKGSzzfQRN21EEW2YTvQtJVQSWUfh7fwAwOb_zqmvvqK2jdNxixoG7mgswXaDvyZS-6qY2mUTFO5a-1.jpeg?fit=1200%2C1200&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/08\/0AQNPLSWo_KzxXKVbW7IbL7_vsFYRwpeEDr7n4wOji7EYEkkB1n0lKGSzzfQRN21EEW2YTvQtJVQSWUfh7fwAwOb_zqmvvqK2jdNxixoG7mgswXaDvyZS-6qY2mUTFO5a-1.jpeg?fit=1200%2C1200&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2025\/08\/0AQNPLSWo_KzxXKVbW7IbL7_vsFYRwpeEDr7n4wOji7EYEkkB1n0lKGSzzfQRN21EEW2YTvQtJVQSWUfh7fwAwOb_zqmvvqK2jdNxixoG7mgswXaDvyZS-6qY2mUTFO5a-1.jpeg?fit=1200%2C1200&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":254638,"url":"https:\/\/climatescience.press\/?p=254638","url_meta":{"origin":431777,"position":3},"title":"Jupiter, Earth and Venus\u2018 tropical alignments point to the mean solar cycle length","author":"uwe.roland.gross","date":"04\/25\/2023","format":false,"excerpt":"The Earth\u2019s axial precession doesn\u2019t drive the orbit period of major solar system bodies such as Jupiter and Venus. Our finding shows the reverse; that Earth\u2019s axial precession is driven by Jupiter and Venus\u2019 entrainment of the Lunar orbit, which is the proximate cause of precession by its tidal action\u2026","rel":"","context":"In \"axial precession\"","block_context":{"text":"axial precession","link":"https:\/\/climatescience.press\/?tag=axial-precession"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/04\/0-period-of-rotation.jpg?fit=1200%2C675&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/04\/0-period-of-rotation.jpg?fit=1200%2C675&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/04\/0-period-of-rotation.jpg?fit=1200%2C675&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/04\/0-period-of-rotation.jpg?fit=1200%2C675&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/04\/0-period-of-rotation.jpg?fit=1200%2C675&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":288673,"url":"https:\/\/climatescience.press\/?p=288673","url_meta":{"origin":431777,"position":4},"title":"Climate, CO2, and the Sun","author":"uwe.roland.gross","date":"11\/26\/2023","format":false,"excerpt":"From Watts Up With That? By Andy May In my\u00a0previous post\u00a0on multiple regression of known solar cycles versus HadCRUT5, I simply threw the solar cycles, ENSO, and sunspots into the regression blender and compared the result to various models that included CO2. Before reading this post, it is a good\u2026","rel":"","context":"In \"CO2\"","block_context":{"text":"CO2","link":"https:\/\/climatescience.press\/?tag=co2"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/11\/0sub4_hero.jpg?fit=1200%2C531&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/11\/0sub4_hero.jpg?fit=1200%2C531&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/11\/0sub4_hero.jpg?fit=1200%2C531&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/11\/0sub4_hero.jpg?fit=1200%2C531&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2023\/11\/0sub4_hero.jpg?fit=1200%2C531&ssl=1&resize=1050%2C600 3x"},"classes":[]},{"id":329595,"url":"https:\/\/climatescience.press\/?p=329595","url_meta":{"origin":431777,"position":5},"title":"Data Reveal That US Heat Wave Index, Japan Drought Coincide With Solar Activity","author":"uwe.roland.gross","date":"05\/22\/2024","format":false,"excerpt":"In 1962, Japanese meteorologist Hirohide Saito found the instability of summer temperature of Hokkaido (northern part of Japan) during the solar minimum. In 1967 Japanese meteorologist Junkichi Nemoto published the following graph, below, showing that drought in Japan occurs at the solar minimum as well as at the solar maximum.","rel":"","context":"In \"drought\"","block_context":{"text":"drought","link":"https:\/\/climatescience.press\/?tag=drought"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2024\/05\/00min-iss-e1598005412889.webp?fit=1200%2C775&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2024\/05\/00min-iss-e1598005412889.webp?fit=1200%2C775&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2024\/05\/00min-iss-e1598005412889.webp?fit=1200%2C775&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2024\/05\/00min-iss-e1598005412889.webp?fit=1200%2C775&ssl=1&resize=700%2C400 2x, https:\/\/i0.wp.com\/climatescience.press\/wp-content\/uploads\/2024\/05\/00min-iss-e1598005412889.webp?fit=1200%2C775&ssl=1&resize=1050%2C600 3x"},"classes":[]}],"_links":{"self":[{"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/posts\/431777","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/users\/121246920"}],"replies":[{"embeddable":true,"href":"https:\/\/climatescience.press\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=431777"}],"version-history":[{"count":11,"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/posts\/431777\/revisions"}],"predecessor-version":[{"id":431791,"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/posts\/431777\/revisions\/431791"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/climatescience.press\/index.php?rest_route=\/wp\/v2\/media\/431778"}],"wp:attachment":[{"href":"https:\/\/climatescience.press\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=431777"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/climatescience.press\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=431777"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/climatescience.press\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=431777"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}