How do changes in the Sun affect the Earth's climate? What are the implications for climate change? Observations of sunspots date back to at least the 2nd century BC, and so have speculations that sunspot numbers are related to weather, but scientific evidence is more elusive.
It has been only since the late 1970s, and the availability of irradiance measurements from satellites, that it has been established that the Sun's energy output varies alongside other measures of activity such as sunspots - and thus that the "solar constant" isn't. Jo has been studying the effects of variations in solar radiation on the climate and found that, unexpectedly, solar activity plays a greater role in the climate of middle latitudes than of the tropics. Further investigation reveals that an important factor driving this response is the absorption of solar ultraviolet radiation in the stratosphere.
Over the most recent sunspot cycle, satellite measurements that do exist have shown unpredicted large variations at ultraviolet wavelengths. These have interesting implications for solar effects on stratospheric ozone and for the mechanisms involved in Sun-climate links.
Joanna Haigh CBE FRS is Professor of Atmospheric Physics and co-Director of the Grantham Institute (Climate Change and the Environment) at Imperial College London. She has been fascinated by weather since childhood and she has been lucky enough to follow a career in meteorology. Her particular expertise is in how solar radiation and heat interact with the atmosphere, how these processes are represented in climate models and the physics of climate change.