If your plan involves moving the entirety of food production to areas of the globe that are currently permafrost and have no comparable ecosystems to where we are currently farming, you are going to have a bad time. You can't just bootstrap a healthy, thriving set of soil conditions, food webs, etc in a couple years. These things normally take thousands or even tens of thousands of years on geological timescales. Just look at how long it takes deciduous forests to reach their apex state: thousands of years.