Possible links between the solar radius variations and the Earth's climate evolution over the past four centuries

The purpose of this paper is an attempt to investigate whether the effects of solar radius variations have influenced the climate of the Earth over the past four centuries. For this purpose, we first briefly describe the data sets concerning the past indicators which can be accessible for the climate and those available for the solar diameter. The question which is addressed in using such proxies concerns for certain their reliability. Are they of sufficient quality to be handled in computations leading to convincing results? We have divided this study into two parts. The first one begins with the centennial variability, as data concerning the years ranging from AD 1550 to 1880 are certainly not sufficiently accurate to be used on time scales below one year. The second one concerns the decadal variability and deals with the modem epoch, for which the instrumental records are more reliable. Although the approach used is a correlative one and suffers from lack of a precise physical mechanism, that could account for the relationships found between the two studied proxies, it is shown that at least over the last four centuries, warm periods on the Earth correlate well with smaller apparent diameter of the Sun and colder ones with a bigger Sun. Regression analyses are performed on the data demonstrating a high statistical signification, better than one would expect. These results extend the so-called Secchi-Rosa law found for the Maunder Minimum. (C) 2001 Elsevier Science Ltd. All rights reserved.