From CO2Science: A number of studied have documented connections between solar forcing and climate change on multiple time scales. Ogurtsov et al. (2020) recently added to this growing body of literature by searching for a solar-climate link in the region of Northern Fennoscandia.
Paper Reviewed: Ogurtsov, M., Veretenenko, S.V., Helama, S., Jalkanen, R. and Lindholm, M. 2020. Assessing the signals of the Hale solar cycle in temperature proxy records from Northern Fennoscandia. Advances in Space Research 66: 2113-2121.
In conducting their study the researchers utilized eight summer proxy temperature reconstructions based on a combination of tree-ring width, maximum latewood density, tree-height increment, pollen spectra and instrumental data, along with a “new improved version of the instrumental record of sunspot number” as an indicator of solar activity, to search for a solar-climate link over the period 1700-2000.
After conducting a series of statistical procedures on these data Ogurtsov et al. report finding a statistically significant negative correlation between solar forcing and climate in six of the eight summer temperature records on a time scale relevant to the Hale cycle (ca 22 years), which inverse relationship was confirmed in two additional larger-scale analyses using the sunspot record and (1) a high latitude warm season proxy of the whole Northern Hemisphere and (2) a sea surface temperature reconstruction of the North Atlantic. The addition of these latter two records for comparison, in the words of the authors, “showed that the climatic imprint of ca 22-year Hale solar cycle is real and expands not only to Northern Fennoscandia but to more extensive regions of the Northern Hemisphere as well.”
Nevertheless, correlation does not prove causation. There must be a physical mechanism explaining the solar-driven temperature changes. And although discerning that mechanism (or mechanisms) was beyond the scope of their analysis, Ogurtsov et al. opine “galactic cosmic ray flux looks like the most probable physical agent,” providing several explanations and citations from the literature to back up their theory.
