In succession to our paper dedicated to Ed Spiegel, we proceed to establish a proportionality relation between the solar-cycle variation of the sky-brightness and that of the global warming. The increase of the optical depth appearing in the sky brightness may cause the solar-cycle global warming of a few degrees from the minimum to the maximum.

We wish to dedicate this paper to Douglas, in celebration of his 60th birthday anniversary.

Introduction

Solar magnetism not only controls the solar activity but also influences significantly the structure of the convection zone (Gough, 2001). On the other hand, the influence of solar activity on terrestrial meteorology such as found in tree rings, etc., has long been the subject of discussion (Eddy, 1976) but without finding the definitive causal relation explaining the physics involved. Recently, however, Sakurai (2002) analysed data of the sky background brightness observed with the Norikura coronagraph over 47 years (1951–1997) and found a clear 11.8-year periodicity as well as the marked annual variation, both exceeding the 95 per cent confidence level.

The annual variation is apparently meteorological, e.g., the famous Chinese yellow soil particles (rising up to 100 thousand feet high! – old Chinese sayings). The solar-cycle variation is also considered to be caused by increased aerosol formation (Sakurai, 2002); but if the solar activity changes the chemistry in the upper atmosphere; the observed time lag of 2 to 4 years of the sky-brightness variation relative to sunspot maximum is somewhat enigmatic.