On the other hand, here on the other side of the Atlantic ... Silicon Valley is not only at a temperate latitude but also downwind (jetstreamwise) of an ocean;

On the other hand, here on the other side of the Atlantic ... Silicon Valley is not only at a temperate latitude but also downwind (jetstreamwise) of an ocean; placing it in the middle of one of our continent's few bastions of reliably non-shitty weather. And there isn't much tech-related stuff happening on the north coast of Alaska or the northern regions of Canada, either. So I daresay there's more to this than just the Arctic Circle.