> Someone living in Truro, for example, in the south of Britain, would on average experience about 25% more solar shortwave radiation (a measure that includes U

> Someone living in Truro, for example, in the south of Britain, would on average experience about 25% more solar shortwave radiation (a measure that includes UV, visible and some infrared light) in a year than someone living in Glasgow or Edinburgh, which are much further north. I'm surprised that the difference is that big, given that the latitude difference between these is actually relatively small. If this difference is correct, is it really just due to the north/south distance, or is this more about weather differences, or is there some other non-obvious factor?