> What is weird is that Harbin is super populated and not that far north (it’s a couple of degrees south of Seattle).

Latitude has quite a bit of influence on climate but insolation isn't the whole story. Winds generally blow east to west at those latitudes. Harbin's air flow is from the interior of Asia, vs the North Pacific for Seattle and Ketchikan.

Seattle - https://en.wikipedia.org/wiki/Mediterranean_climate

Harbin - https://en.wikipedia.org/wiki/Humid_continental_climate#Hot/...