The Frostbelt, the inverse of the Sunbelt, refers to the Northern US, and the North-East in particular. Briefly popular in the 1970s, which saw severe winter weather, falling population, and energy shortages across the region. As the 'Rust-belt' (North-Central Midwest) and more prosperous coastal North-East have diverged since the 70s, the term 'Frostbelt' has lost much of its popularity and is now rarely used-as opposed to the more durable 'Sunbelt'.
