Solar Radiation in the Arctic during the Early Twentieth-Century Warming (1921–50): Presenting a Compilation of Newly Available Data

Abstract

The early twentieth-century warming (ETCW), defined as occurring within the period 1921–50, saw a clear increase in actinometric observations in the Arctic. Nevertheless, information on radiation balance and its components at that time is still very limited in availability, and therefore large discrepancies exist among estimates of total solar irradiance forcing. To eliminate these uncertainties, all available solar radiation data for the Arctic need to be collected and processed. Better knowledge about incoming solar radiation (direct, diffuse, and global) should allow for more reliable estimation of the magnitude of total solar irradiance forcing, which can help, in turn, to more precisely and correctly explain the reasons for the ETCW in the Arctic. The paper summarizes our research into the availability of solar radiation data for the Arctic. An important part of this work is its detailed inventory of data series (including metadata) for the period before the mid-twentieth century. Based on the most reliable data series, general solar conditions in the Arctic during the ETCW are described. The character of solar radiation changes between the ETCW and present times, in particular after 2000, is also analyzed. Average annual global solar radiation in the Russian Arctic during the ETCW was slightly greater than in the period 1964–90 (by about 1–2 W·m−2) and was markedly greater than in the period 2001–19 (by about 16 W·m−2). Our results also reveal that in the period 1920–2019 three phases of solar radiation changes can be distinguished: a brightening phase (1921–50), a stabilization phase (1951–93), and a dimming phase (after 2000).