May 28, 2023

Solar and Space Physics UNIToV

Gruppo di Fisica Solare e Spaziale Università di Roma Tor Vergata

Scientists Develop New Model to Estimate Solar Irradiance Variation Over the Last Five Centuries

Tree rings, ice cores, and cosmogenic isotopes provide clues to past solar activity – and how it may have influenced past climate events

Total solar irradiance, the output of light energy from the Sun that reaches Earth, has long influenced our terrestrial atmosphere on timescales ranging from days to millennia. Using a record of Carbon 14 isotope over the last 500 years, a team of scientists from the University of Rome TorVergata and the National Solar Observatory has reconstructed the area coverage of faculae (plages) and sunspots from 1513 to 2001 using correlation analysis. This study gives scientists an unprecedented look at how solar irradiance varied over a long time scale – and how it may have influenced Earth’s climate events. 

For over 4.5 billion years, Earth has received solar energy from the Sun via energy and particles. The stream of radiative energy, the total solar irradiance (TSI), isn’t constant and varies due to the competitive nature of the Sun’s surface magnetism. Faculae (areas of concentrated magnetism that produce bright light) adds to TSI whereas sunspots (larger areas of magnetism that are cooler and darker) reduce TSI. Understanding the area coverage of these structures helps scientists to estimate the levels of solar irradiance over time. 

The TSI reconstruction by Penza et al. 2022 is shown as a continuous red line; the red bold line is the TSI smoothed over a period of 22 yr with a 2σ uncertainty shown as the orange stripe. Other reconstructions of TSI are reported, obtained with different methods for comparison purposes only. The NRL-TSI data Climate Data Record (green line) is from Coddington et al. (2019). TSI values from Wu et al. (2018) are in magenta. CHRONOS, MC17 TSI values from Egorova et al. (2018) are in blue. The names refer to the grand minima that occurred in the analyzed period, i.e., Spörer, Maunder, Dalton, and Gleissberg.

This work estimated that the change in TSI levels between the Maunder minimum and the present epoch is approximately 2.5 W m−2. This TSI variation would change the global temperatures by about 0.13C, an extremely small variation. It is widely accepted within the scientific community that climate changes prior to the Industrial Revolution in the 1700s can be explained by natural causes, such as TSI variations and volcanic eruptions. Models similar to the one by Penza et al. are used by the Intergovernmental Panel on Climate Change (IPCC) to compile their reports. The present work supports the idea that the Little Ice Age was not a global cooling phenomenon, but rather a regional moderate average cooling (which included the European region).

This study was carried out by a team of researchers from the Department of Physics, University of Rome Tor Vergata (Italy) and from National Solar Observatory (Boulder, USA). 

Reference: Penza, Berrilli, Bertello, Cantoresi, Criscuoli, Giobbi, Total Solar Irradiance during the Last Five Centuries, The Astrophysical Journal, 937:84, 2022