An influence of solar spectral variations on radiative forcing of climate

Current understanding suggests that radiative forcings over the course of an 11-year solar cycle are in phase with related influences on climate. Recent satellite data have revealed, however, that there seems to be a surprising spectral component to solar variability, at least in the declining phase of the current solar cycle: UV radiation decreases strongly while visible radiation increases. Joanna Haigh and colleagues now show that these spectral variations — when incorporated into a radiative-photochemical model — lead to decreases in ozone below 45 kilometres and increases above. As a consequence of the ozone changes, radiative forcing of surface climate is out of phase with solar activity. This finding, although based on a short record from a potentially anomalous solar cycle, suggests that a major revision to our current understanding of solar forcing of climate may be in order.