Can changes in cloudiness cause larger UV changes than ozone depletion?
Long-term trends in cloud type and amount are largely unknown due to the relatively short data record of comprehensive cloud observations, and the high variability of clouds on inter-annual and longer time scales. Some evidence exists showing that, at least over the time span of satellite-based ozone measurements, changes in cloud cover have been much less important than stratospheric ozone reductions in causing surface UV changes. • Are the risks of ultraviolet (UV) exposure at the beach less on a cloudy day? Not necessarily. The effect of clouds on UV radiation is as varied as the clouds themselves. Fully overcast skies lead to reductions in surface UV irradiance. On average, scattered or broken clouds also cause reductions, but short-term or localised UV levels can be larger than for cloud-free skies if direct sunlight is also present. Clouds tend to randomise the directions of the incoming radiation (because of scattering) so that a hat may provide less protection on a cloudy day r
