Since ancient times, and particularly since the observation of variations in sunspot numbers, it has been speculated that changes in solar activity may influence the climate on Earth. This idea has captured the imagination of many, both scientists and non-scientists, but the subject has historically been viewed with some mistrust by the meteorological community despite many statistical analyses suggesting solar signals in climate records. This was mainly because there was little quantitative evidence of any variation in the output of solar radiation and so no obvious physical mechanism for the supposed influence. Since the availability of solar radiation measurements from earth-orbiting satellites, however, it has been established that the Sun’s output isn’t constant. Furthermore, the political and economic importance of differentiating natural from human factors as causes of climate change implies a real need to establish how much, and to understand by what means, the Sun may be contributing to global warming. This talk will outline the chequered history of solar-climate studies, assess what is known about variations in the Sun and review the evidence for a solar influence on climate. It will conclude with a discussion of recent research that is trying to unravel some of the complex physical mechanisms involved.

Joanna Haigh is Professor of Atmospheric Physics at Imperial College London. Her scientific interests include radiative transfer in the atmosphere, climate modelling and radiative forcing of climate change. She has published widely on these topics in the scientific literature and also contributed to numerous items in the written and broadcast popular media. She has been Vice-President of the Royal Meteorological Society, Editor of the Quarterly Journal of the R.Met.S., a Lead Author on the Intergovernmental Panel on Climate Change and acted on many UK and international scientific panels. She is a Fellow of the Institute of Physics and of the R.Met.S. and in 2004 she received the Institute of Physics Charles Chree Medal and Prize for her work on solar variability and its effects on climate.