Iceland has a much more temperate climate than its latitude (~65 degrees) would suggest, thanks to the North Atlantic Current bringing relatively warm water/air so far up north.
There is a lot of geothermal activity (geysers, volcanoes) in Iceland, because it lies on the boundary between the Eurasian plate and the North American one. They generate a lot of heat, at least locally. I'm curious and haven't made any calculations (I wouldn't even know where to begin) but does this activity influence the climate in Iceland in a meaningful way? E.g. without the geothermal activity, would the mean annual temperature drop, and if so, by how many degrees?