How much has the Sun influenced Northern Hemisphere temperature trends? An ongoing debate

• Published in: Research in astronomy and astrophysics Vol. 21; no. 6; pp. 131 - 68
• Main Authors: Connolly, Ronan, Soon, Willie, Connolly, Michael, Baliunas, Sallie, Berglund, Johan, Butler, C. John, Cionco, Rodolfo Gustavo, Elias, Ana G., Fedorov, Valery M., Harde, Hermann, Henry, Gregory W., Hoyt, Douglas V., Humlum, Ole, Legates, David R., Lüning, Sebastian, Scafetta, Nicola, Solheim, Jan-Erik, Szarka, László, Loon, Harry van, Velasco Herrera, Víctor M., Willson, Richard C., Yan, Hong, Zhang, Weijia
• Format: Journal Article
• Language: English
• Published: Beijing National Astronomical Observatories, CAS and IOP Publishing Ltd 01.08.2021; IOP Publishing; Center for Environmental Research and Earth Science(CERES),Salem,MA 01970,USA; Independent scientists,Dublin,Ireland%Center for Environmental Research and Earth Science(CERES),Salem,MA 01970,USA%Independent scientists,Dublin,Ireland%Retired,formerly Harvard-Smithsonian Center for Astrophysics,Cambridge,MA 02138,USA%Independent researcher,Malm?,Sweden%Retired,formerly Armagh Observatory,College Hill,Armagh BT61 9DG,Northern Ireland,UK%Comisión de Investigaciones Científicas de la Provincia de Buenos Aires,Argentina; Grupo de Estudios Ambientales,Universidad Tecnológica Nacional,Colon 332,San Nicolás,Buenos Aires,Argentina%Laboratorio de Física de la Atmósfera,Facultad de Ciencias Exactas y Tecnología,Universidad Nacional de Tucumán,Av.Independencia 1800,4000 Tucumán,Argentina; Department of AOP Physics,University of Oxford,Oxford,UK; Instituto de Física del Noroeste Argentino(Consejo Nacional de Investigaciones Cientficas y Técnicas-Universidad Nacional de Tucumán),4000 Tucumán,Argentina%Faculty of Geography,Lomonosov,Moscow State University,Leninskie Gory St.1,Moscow 119991,Russia%Helmut-Schmidt-University,Hamburg,Germany%Center of Excellence in Information Systems,Tennessee State University,Nashville,TN 37209 USA%Independent scientist,Berkeley Springs,WV,USA%Emeritus Professor in Physical Geography,Department of Geosciences,University of Oslo,Norway%College of Earth,Ocean,and the Environment,University of Delaware,Newark DE 19716-2541,USA%Institute for Hydrography,Geoecology and Climate Sciences,Hauptstraβe 47,6315 ?geri,Switzerland%Department of Earth Sciences,Environment and Georesources,University of Naples Federico Ⅱ,Complesso Universitario di Monte S.Angelo,via Cinthia,21,80126 Naples,Italy%Retired,formerly Department of Physics and Technology,UiT The Arctic University of Norway,9037 Tromsφ,Norway%ELKH Institute of Earth Physics and Space Science,9400 Sopron,Csatkai utca 6-8,Hungary%Retired,formerly National Center for Atmospheric Research,Boulder,Colorado,USA%Instituto de Geofisica,Universidad Nacional Autónoma de México,Ciudad Universitaria,Coyoacán,04510,México D.F.,México%Active Cavity Radiometer Irradiance Monitor(ACRIM),Coronado,CA 92118,USA%State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi'an 710061,China%Department of Mathematics and Physics,Shaoxing University,Shaoxing,China
• Subjects: (Sun:) solar terrestrial relations; (Sun:) sunspots-Sun: faculae; 19th century; Air temperature; Anthropogenic factors; Climate change; Estimates; Glaciers; Global temperatures; Global warming; Human influences; Intergovernmental Panel on Climate Change; Irradiance; Northern Hemisphere; plages; Sea surface temperature; Solar activity; Solar irradiance; Sun: activity; Surface temperature; Surface-air temperature relationships; Temperature; Temperature trends; Tree rings; Trends; Urbanization; Variability; Weather stations; Northern Hemisphere; Sun:faculae; (Sun:)solar terrestrial relations; plages; Sun:activity; (Sun:)sunspots
• ISSN: 1674-4527
• DOI: 10.1088/1674-4527/21/6/131

In order to evaluate how much Total Solar Irradiance (TSI) has influenced Northern Hemisphere surface air temperature trends, it is important to have reliable estimates of both quantities. Sixteen different estimates of the changes in TSI since at least the 19 th century were compiled from the literature. Half of these estimates are “low variability” and half are “high variability”. Meanwhile, five largely-independent methods for estimating Northern Hemisphere temperature trends were evaluated using: 1) only rural weather stations; 2) all available stations whether urban or rural (the standard approach); 3) only sea surface temperatures; 4) tree-ring widths as temperature proxies; 5) glacier length records as temperature proxies. The standard estimates which use urban as well as rural stations were somewhat anomalous as they implied a much greater warming in recent decades than the other estimates, suggesting that urbanization bias might still be a problem in current global temperature datasets – despite the conclusions of some earlier studies. Nonetheless, all five estimates confirm that it is currently warmer than the late 19 th century, i.e., there has been some “global warming” since the 19 th century. For each of the five estimates of Northern Hemisphere temperatures, the contribution from direct solar forcing for all sixteen estimates of TSI was evaluated using simple linear least-squares fitting. The role of human activity on recent warming was then calculated by fitting the residuals to the UN IPCC’s recommended “anthropogenic forcings” time series. For all five Northern Hemisphere temperature series, different TSI estimates suggest everything from no role for the Sun in recent decades (implying that recent global warming is mostly human-caused) to most of the recent global warming being due to changes in solar activity (that is, that recent global warming is mostly natural). It appears that previous studies (including the most recent IPCC reports) which had prematurely concluded the former, had done so because they failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with Northern Hemisphere temperature trend estimates. Therefore, several recommendations on how the scientific community can more satisfactorily resolve these issues are provided.