The main issue with permafrost is instability. If you build on permafrost, when it melts you’ll lose everything that’s not anchored to bedrock. Imagine the ground 3ft below the surface of your street suddenly collapsing, like a sinkhole. At the very least that would ruin the road, the water and sewer pipes, the electricitu and telecom lines, etc. Melting permafrost also releases A LOT of methane, a much more potent greenhouse gas than CO2. (Runaway global warning, anyone?) Lastly, after the permafrost melts, the soil that is left isn’t necessarily suitable for agriculture: it washes away easily and is prone to waterlogging.

Of course, these challenges can be overcome with time and money. It might become worth doing once the current arable land turn into deserts. But the scope of it is huge. We’ll have to invent a whole new type of agriculture.