Temperature increase is due to the greenhouse effect. This is caused by an increase in the amount of card on dioxide (caused by humans), it traps in the heat. This causes the oceans to get warmer. Warm water takes up more space than cold water, this leads to erosion of coastlines and destruction of natural habitats.
It also causes ice caps to melt, not only does this increase ocean volume it increases the amount of fresh water in the ocean. This changes how our oceans flow. (Plus the decreased ice caps causes the earth to heat up more - ice and snow don't absorb much of the sun's radiation. With the ice and snow lessening it's taking in more radiation).
The effect of all this is climate change. It will effect different parts of the world in different ways.
Droughts will probably lengthen (this means famines by the way).
Monsoons are less predictable. With monsoons increasing in the volume or length (this means flooding and the displacement of huge numbers of people). They may become shorted or contain less rain (causes agricultural difficulty with means less food and the displacement of huge numbers of people.)
As for Britain and Ireland. Remember that crap weather you mentioned OP? That'll get crapper - the extreme weather events (wind, snow, rain and heat) they'll become more frequent and more extreme. (This has an effect of agricultural production.)
Plus all the displaced people need to move somewhere. They will be in need of food and shelter. Immigration will increase and countries will have to adapt to this.
So that's what is not to like. It doesn't mean it'll just be a bit warmer and it certainly doesnt mean the end or even less 'crap weather'.