Bluebells

In the afternoon we had to be at Amber Nook just to finish off the cleaning.  While I was around the outside I spotted these.  They must have lost their calendar!   We haven't really had winter yet and here are plants thinking its Spring.

Something has to be wrong!  I am not sure what triggers Bluebells to start sprouting.  I doubt it is a period of dormancy and a cold period as it isn't that long ago we were clearing the the seedheads away..  It can't be day length because firstly no part of the plant should be above the ground and the days certainly aren't lengthening.  The only idea I have come up with is ground temperature it might be higher than required for true dormancy.   However it's OK as climate change isn't happening is it?