I assume you're talking of around 4 degrees warming under business-as-usual conditions?

To pick the most important effect, it's going to impact agriculture severely. Even if irrigation can be managed, untimely heavy rain will still damage crops. And they can't be prevented from affecting crops, unless you build giant roofs.

If you are saying that all these effects can be defended against, I agree. But the key point is that our entire economy is built on a lot of things being extremely cheap. Erecting a giant roof over all sensitive cropland is far less technically challenging than launching a geostationary satellite, but we do the latter and not the former because of the sheer size. It's basically an anchoring effect : now that we expect basic necessities to cost so little, we are unable to cope with a world were they are even slightly more expensive.

If we could overcome these issues and embark on such large scale projects, then agw is an easily solved problem! as you said, it's just an inconvenience.