A +50 change means the hottest regions, that already reach up to 50 degrees, would hit boiling point for extended periods of the year. Some if those are by the sea, which would continuously boil, filling the atmosphere with steam and cause a new greenhouse effect boost and a wave of heating that would push temperatures even higher.

The problem is there are certain thresholds that cause new greenhouse effects to kick in and push temperatures even higher. For example, if temperatures rise enough to melt the Methane frost layers, they'll melt and probably kick global temperatures up another 5 or 6 degrees all by themselves. If we trigger enough of these knock on effects in a chain, well end up with an unlivable atmosphere. That's the extreme scenario, but it is not impossible.