No mention of permafrost? Yes, the _air_ will be more habitable, but if the _ground_ is a boggy mess, you’re not going to be doing much with this newly habitable land.
The further away from the equator you go, the more your sunlight becomes a fickle seasonal creature hitting you at odd angles in varying intensity. Temperature isn't the only variable affecting the growing season and agricultural productivity.
Remove it: overheat the planet. It will turn to mud. Anything built on it will subside or sink. Massive amounts of trapped organic matter will turn to methane.
Eventually, I presume the area would settle into a new climatic zone, with neither permafrost nor mud. Emphasis on "eventually".