Dimming of the Mid-20th Century Sun

TL;DR

This study uses measurements of white light faculae from 1874 to 1976 to reconstruct total solar irradiance, revealing a mid-20th-century dimming that may have influenced climate cooling.

Contribution

It provides a new reconstruction of solar irradiance based on faculae, showing a mid-century dimming contrary to previous brightening models.

Findings

The sun dimmed by nearly 0.1% in the mid-20th century.

The dimming correlates with high solar activity levels.

This variation may have impacted climate cooling during 1940-1970.

Abstract

Advances in understanding of the white light faculae measured at the Royal Greenwich Observatory from 1874 to 1976 suggest that they offer a more direct measure of solar brightening by small diameter photospheric magnetic flux tubes than do chromospheric proxies. Proxies such as the area of Ca K plages, the Mg index or the microwave flux include many dark photospheric structures as well as pores and sunspots. Our reconstruction of variation in total solar irradiance,TSI,based on the faculae indicates that the sun dimmed by almost 0.1 percent in the mid- twentieth century rather than brightening as represented in previous reconstructions. This dimmimg at the sun's highest activity level since the seventeenth century is consistent with the photometric behavior observed in somewhat younger sun like stars. The prolonged TSI decrease may have contributed more to the cooling of climate between about 1940 and 1970 than present models indicate.