Looks like Pear trellis rust (European pear rust)- Gymnosporangium fuscum. I live in Toronto, Canada and until recently it didn't exist here (it was only in a few spots on the west coast of Canada and California. As I have just recently moved into a home with a pear tree in the yard I was looking forward to eating its fruit in a few weeks. But then I noticed this blight on the leaves and have no idea what can be done or what the effect will be on the tree and its fruit.
I have very similar on my pear tree. Unfortunately, my clever book says real control is only achieved if there are no Junipers in the vicinity as this is a two hosts pathogen.
Hi - I had this "blight" on both my pear trees last year, for the first time - the fiery yellow spots were on every leaf so it was therefore not feasible to remove affected leaves. It did not affect the crop of pears, however, which were quite o.k. The spots eventually developed into powdery blisters about the size of a 5p piece, and when the leaves fell in the autumn I collected them up and burnt them. This year the trees are perfectly OK, without any sign of yellow spots, and a decent crop of pears forming. So I wouldn't worry too much, but it is probably wise not to let any affected leaves lie around on the ground.