Lets say the EU does geoengineering and then there are crop failures in India the next year. Their fault or not, they are going to get blamed for it and actions taken. The EU would become the scapegoat for any kind of weather/climate issues in future.
This is the trolley problem done at a global scale.
Who cares? Tell them to go pound sand or stop burning so much coal.
Countries are already water seeding. This kind of worry that someone might complain about the eu trying to save itself is so low on the list of things that matter. Let them complain, and the eu can complain about all the other countries geoengineering by burning fossil fuels.
Also what if that complaint comes back in the form of a Nuke as they see it as an act of war?
When things become existential, a lot of things that seems unlikely end up on the table as moral corruption sets in. "Either they go or we do!"
You're a whole lot safer when the people around you can get enough food and water. We already have solutions that don't involve putting entire nations at risk of dying off in large numbers. The problem is that those solutions would eat into the already massive and growing profits of corporations who would sooner put your safety at risk than take even a small hit to their unsustainable growth.
No one would take this as an act of war just like no one takes cyber attacks as an act of war.
We can continue to do it aimlessly, or we can act with purpose.