Little Green Acorns

I don't want to turn this blog into a Glyn Davies-style gardening column, but.... I noticed that the oak tree at the bottom of our garden in Llwynypia has thrown off hundreds of small green acorns - enough to feed a sty of pigs, it felt like when I was picking them up off the lawn. This is the fifth summer since we moved into the house, but the first time this has happened. Two years ago we had the tree surgeons in to trim and lop. Anyone with any ideas as to why it's this year we have had the acorns? (Yes, I know, blame global warming....)