>It's not hard to install AC in Europe

Its orders of magnitude harder. When I lived in the USA, I could just pick up a $200 window unit and have it installed within minutes. Every single person had air conditioning. Now I live in Finland where the windows are the worst designed windows I've ever seen. They are thin, tall windows that open vertically on hinges like doors. So rain gets in, and its impossible to install a window AC or even a box fan. You're forced to either install a mini split ($1000+) or central air. And neither options are available for renters. Really, the #1 priority should be trying to bring American style sliding windows to Europe. Then everything else can fall into place downstream of that.

That's exactly what I wrote though. You CAN install a normal split. You are blocked because as a renter you don't have the power to.

My point is that we are not in an AC crisis, we just need to change the laws so that owners are forced to provide, however they want, summer comfort in the same way they must provide winter comfort.

Unlike energy autonomy, green transition, or defense issues, the "AC issue" is actually easy to tackle for governments and I'm betting it will happen pretty soon because that's an easy win that costs nothing to governments and governments loves popular measures that cost nothing and and give them the good role.

I just moved to Portugal and had zero issues installing a portable unit to help me survive the heatwave. For the hinged windows you just grab an installation kit that works with them and you're good to go. The only problem is that the portable AC I got is not a window unit (& it's single-hose), but I wanted to have it before the heatwave started and don't care too much about few percentage points in lost efficiency as long as it keeps me and my pets alive. Total cost was €320 with the installation kit for a 12000BTU unit.

Can sliding windows be properly insulated? In general cold is a bigger deal in Europe than warmth, and will continue to be so.

German style tilting windows close as tightly as the regular (or door-like as you say) do. UK has windows sliding up, but is also famous for being drafty as the windows are never tight. I suppose good sliding windows can exist though?

I have myself pondered the problem with regular windows and a movable AC. My apartment has old school 4-pane windows with 2 layers both having their own window handles, so 8 independent small windows for each opening. They do look great in an old building but I don't see any reasonable way to set up AC with these. Thankfully no need yet as the apartment has never reached 30C inside, but we'll see what the future brings.

You can just buy plastic that you attach to the frame around the window with a hole for the hose. Its reasonable air tight, but we typically get air from outside for ventilation anyway.

Sliding windows are terrible though. Why would you want those?