That's what I thought... But if it's winter in the north then it's summer in the south, so you'd expect them to average in a way that you wouldn't see such stark differences between say January and July. In July it's winter in the south, summer in the north. Intuitively I'd assume they'd average. Temps would still be rising year over year, but you wouldn't see a difference between months. A couple people have answered that it has to do with the earths tilt and the fact that there's more landmass in the north. Seems plausible I guess.