Letter to the Editor

Reconstruction of annual solar irradiance over the last three millennia

¹ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
² Technical University of Braunschweig, Universitätspl. 2, 38106 Braunschweig-Nordstadt, Germany
³ School of Space Research, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea
⁴ Space Physics and Astronomy Research Unit and Sodankyä Geophysical Observatory, Oulu, Finland

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 12 February 2026
Accepted: 30 April 2026

Abstract

Solar irradiance measurements are limited, spanning only the last few decades, requiring reconstructions to assess solar variability on longer timescales and its impact on Earth’s climate. We present the first physics-based reconstruction of total solar irradiance (TSI) at annual resolution over the last three millennia. The reconstruction is obtained by extending the SATIRE-T model beyond the telescopic era using recently published, annually resolved sunspot number series derived from cosmogenic isotope records. This yields a continuous, physics-based TSI record extending from the satellite era back over the last three millennia, with an annual resolution throughout the pre-telescopic period. Over this full interval, the reconstructed TSI exhibits a maximum difference of 1.04_−0.2^+0.14 W m⁻², defined as the difference between the maximum and minimum of the 50-year running mean values.