You saw the film The Day After Tomorrow. This is that. Not like in the movie, but still…
Warming causes melting of ice, adding fresh water into the North Atlantic, which interferes with a major current system that at present warms Europe.
Consequence: The planet warms dangerously, while at the same time, large parts of Europe become much cooler, to the extent that people may not be able to live there in the manner they do now, or produce very much food there. Gibraltar would have a climate similar to the coast of Maine, and Berlin would have a climate similar to the Northwest Territories or northern Hudson Bay.
The models have predicted this, but it now seems that they’ve under-predicted it. It appears to be happening faster, and more furiously, than expected.