More Words, Deeper Hole

Continental interiors in general tend to be unsuitable for comfortable human habitation. Once you get away from bodies of water, the temperature swings start getting unreasonable - further south, the bad patch is in the summer when it gets blisteringly hot, and as you go north it shifts to the bitter cold winters, with a nice stretch running along the US/Canada border where one conveniently gets *both*.

Sometimes I think the climate of the planet would be greatly improved if we dug kilometer-wide trenches north-to-south over the whole planet at intervals of about 10 kilometers, and filled them with water. Then everybody would get the benefits of a maritime climate, without having to crowd the seacoasts.