weaning off fossil fuels completely is going to be a long complicated process. for now we will need to use fossil fuels to build greener infrastructure.

Possibly. Industrial processes are very energy intense.

For example, melting steel takes a certain amount of energy per mass to liquify, and since you're trying to liquify it, you need that energy quickly, otherwise it'll just get warm but stay solid. Nuclear could do it, maybe even wind if all other energy sinks (e.g. houses, apartments, etc) aren't using too much of that renewable energy when the melt is occurring.

We do our best, but once the process starts, it must be completed no matter where the energy is coming from, otherwise it was just a waste of time and money.