I wouldn't say we haven't solved it. The solution are straightforward, but they represent an scale of project that most people don't understand at all. However

I wouldn't say we haven't solved it. The solution are straightforward, but they represent an scale of project that most people don't understand at all. However, there are examples of humans doing projects at such scale before. Most notably, the totality of the infrastructure we built to extract and refine the amount of fossil fuels we do today. The gigantic offshore rigs, the thousands of miles of pipelines, the refineries, etc. Doable, but can't happen overnight without everyone dropping everything and working on only this.