Has global warming modified the relationship between sunspot numbers and global temperatures?

TL;DR

This study investigates how the relationship between sunspot activity and global temperatures has evolved from 1880 to 2016, revealing a stable lead of solar activity over temperature changes, but with disturbances caused by rising CO2 emissions since the 1960s.

Contribution

The paper introduces a combined wavelet coherence and cointegration approach to uncover a stable, yet disturbed, relationship between solar activity and global temperatures over time.

Findings

Sunspot numbers lead temperature changes by over two years.

The relationship between sunspots and temperatures is stable over time.

Increasing CO2 emissions since the 1960s have disturbed this relationship.

Abstract

We study time evolution of the relationship between sunspot numbers and global temperatures between 1880 and 2016 using wavelet coherence framework. The results suggest that the relationship is stable in time. Changes in the sunspot numbers precede changes in the temperatures by more than two years as suggested by the wavelet phase differences. This leading position of the sun activity is stable in time as well. However, the relationship has been disturbed by increasing $CO_2$ emissions since 1960s. Without controlling for the effect of possible global warming, or more precisely the positive connection between increasing $CO_2$ emissions and the global temperatures, the findings would have been quite different. Combination of the cointegration analysis and wavelet coherence framework has enabled uncovering a hidden relationship between the solar activity and global temperatures, and possibly explaining equivocal results in the topical literature.