Can someone please explain to me why exceeding a 2 degree Celsius temperature increase is catastrophic?

I've heard a lot that if we cross this threshold we're doomed. I'm not doubting it – I just want to understand how exactly? It seems like a small amount. I live in the UK and the temperature can range from -10 or colder in the coldest winters, to high 30s in the hottest Summers. If the average temperature was a couple of degrees higher, it might be a bit bothersome, but not really a big deal – in-fact most people would probably appreciate it. I get if you already live somewhere, where it's very hot such that it's difficult to grow food already, that an extra couple of degrees could be problematic, but surely that's a minority of people and is somewhat a distribution of wealth / economic problem – because if they have the money they can import from elsewhere in the world, the majority of where 2 degrees shouldn't make much of a difference to the ability to grow crops or rear livestock? Another issue I hear about is more extreme weather events, but are these really going to be civilization ending? And we may lose some species, and that sucks, but does it really matter that much? In a million years, having transcended into some superior life-form that inhabits every corner of the galaxy, are we really going to miss the polar bears?

As I said, I'm not here to deny global warming or say that we shouldn't be doing anything about it. I'm just trying to understand why 2 degrees is a big deal.