[H]ow do you propose Europe protect not only people from the heat, but [all these other things]?

Why does it have to be framed as all-or-nothing? I agree that using air conditioning to reduce the number of people who die from the heat does nothing to help with the problem of jellyfish, but how is that relevant, exactly?

Your AC isn't going to work when your power plants are stuffed with jellyfish and have to shut down.