Clouds, solar irradiance and mean surface temperature over the last century

TL;DR

This study investigates the complex relationships between clouds, solar irradiance, and surface temperature over the last century, highlighting the significant influence of solar activity, especially UV radiation, on global temperature changes.

Contribution

It extends previous work by analyzing data from 1900 to the present, revealing a strong correlation between solar irradiance and temperature, and quantifying the solar contribution to recent global warming.

Findings

Solar irradiance correlates with surface temperature, especially with a 22-year cycle.

Cloud cover shows a decadal correlation with opposite phases for high and low clouds.

Solar effects account for nearly all temperature increase before 1956, but less than 14% after 1956.

Abstract

The inter-relation of clouds, solar irradiance and surface temperature is complex and subject to different interpretations. Here, we continue our recent work, which related mainly to the period from 1960 to the present, back to 1900 with further, but less detailed, analysis of the last 1000 years. The last 20 years is examined especially. Attention is given to the mean surface temperature, solar irradiance correlation, which appears to be present (with decadal smoothing) with a 22-year period; it is stronger than the 11-year cycle correlation with one year resolution. UV in the solar radiation is a likely cause. Cloud data are taken from synoptic observations back to 1952 and, again, there appears to be a correlation - with opposite phase for high and low clouds - at the 20-30y level. Particular attention is devoted to answering the question, 'what fraction of the observed increase in mean Global temperature (~0.7^oC) can be attributed to solar, as distinct from man-made, effects?' We conclude that a best estimate is 'essentially' all from 1900 to 1956 and <14% from 1956 to the present.