Dendrochronologia 67 (2021) 125837 Available online 28 April 2021 1125-7865/© 2021 Elsevier GmbH. All rights reserved. Arctic aerosols and the ‘Divergence Problem’ in dendroclimatology Ulf Büntgen a, b, c, d, *, Alexander V. Kirdyanov e, f , Paul J. Krusic a, g , Vladimir V. Shishov h, i , Jan Esper b, j a Department of Geography, University of Cambridge, Cambridge, CB2 3EN, UK b Global Change Research Institute of the Czech Academy of Sciences (CzechGlobe), 603 00, Brno, Czech Republic c Department of Geography, Faculty of Science, Masaryk University, 613 00, Brno, Czech Republic d Swiss Federal Research Institute WSL, 8903, Birmensdorf, Switzerland e V.N. Sukachev Institute of Forest SB RAS, Federal Research Centre, Krasnoyarsk, 660036, Russia f Institute of Ecology and Geography, Siberian Federal University, Krasnoyarsk, 660041, Russia g Department of Physical Geography, Stockholm University, 106 91, Stockholm, Sweden h Mathematical Methods and IT Department, Siberian Federal University, 660075, Krasnoyarsk, Russia i Scientifc Laboratory of Forest Health, Reshetnev Siberian State University of Science and Technology, 660037, Krasnoyarsk, Russia j Department of Geography, Johannes Gutenberg University, 55099, Mainz, Germany A R T I C L E INFO Keywords: Industrial pollution Divergence Problem Boreal forest Carbon cycle Arctic Dimming Considering the importance and complexity of natural (e.g., volcanic eruptions and wildfres) and anthropogenic (e.g., mining, oil and ship- ping industries) aerosol emissions to Arctic warming is particularly timely given the recent temperature extremes recorded at high-northern latitudes (Cohen et al., 2020; Overland and Wang, 2021). Despite our knowledge about the observed and modelled climatic effects of rising Arctic aerosol concentrations (Schmale et al., 2021), which may exhibit regional and seasonal differences and call for diverse research priorities from local to circumpolar scales, we feel that the ecological conse- quences of an aerosol-induced reduction in surface irradiance (i.e., Arctic Dimming) justify more thorough tree-ring investigations in the future. We argue that this is particularly true if the goal is to enhance our understanding of all aerosol generating processes that impact terrestrial vegetation and its ability to assimilate carbon dioxide from the atmosphere. In addition to the exceptional rate of environmental devastation in the vicinity of heavy industrialisation at high-northern latitudes, with Fairbanks and Norilsk just being two extreme cases (Holty, 1973; Bau- duin et al., 2014), the large-scale and long-term effects of aerosol emissions on the functioning and productivity of ecosystems are poorly understood and likely underestimated (Kirdyanov et al., 2020a). Moreover, air pollution from lower latitudes is often accumulates in the Arctic atmosphere (Stohl, 2006; Law and Stohl, 2007; Quinn et al., 2007; Arnold et al., 2016), where it can reside for exceptionally long periods of time. Reduced intensity of scattered incoming solar radiation, particu- larly in the 400–700 nm waveband that is most meaningful to photo- synthesis (Urban et al., 2012), has been demonstrated to reduce the functioning and productivity of taiga and tundra biomes (Stine and Huybers, 2014). The boreal forest, however, not only plays a major role in shaping the Earth’s carbon cycle and climate system (Bradshaw and Warkentin, 2015), but also hosts some of the longest tree ring-based climate reconstructions extending back over the Common Era (Bünt- gen et al., 2020). A better understanding of the possible direct and in- direct effects of Arctic aerosols on net primary production and carbon sequestration is particularly important in light of the current geo-political and commercial race to exploit natural resources north of the Arctic circle. Combined dendrochronological and biogeochemical evidence from Norilsk, the world’s northernmost city with over 100,000 inhabitants, where mining actions and uncontrolled pollutants have expanded * Corresponding author at: Department of Geography, University of Cambridge, Cambridge, CB2 3EN, UK. E-mail address: ulf.buentgen@geog.cam.ac.uk (U. Büntgen). Contents lists available at ScienceDirect Dendrochronologia journal homepage: www.elsevier.com/locate/dendro https://doi.org/10.1016/j.dendro.2021.125837 Received 22 March 2021; Received in revised form 21 April 2021; Accepted 21 April 2021