Unless you're somewhere really really really cold your Pi's going to be fine. User James Adams (listed as the Pi Foundation's Director of Hardware Engineering) on the raspberrypi.org forums states the following in relation to the BCM2835 used in earlier Pis:
Theoretically the operating temp. range is determined by the range of
the component with the smallest range.
The Samsung eMMC and Samsung LPDDR2 are all rated for -25 to +80
degrees C, so the range is -25 to +80. (BCM2835 and ana SW are greater
range than this, caps are -25 to +85).
However that is the max range for the silicon die – so a user would
have to take into account the heat generated when in use and make sure
this does not cause the temp. to exceed 80C.
Those figures should hold fine for the Pi 2, so you're looking at a minimum of -25 degrees C. If your Pi's that cold I hope that you have a large hat and some mittens.
There are anecdotal reports (the link to the original writeup has rotted) of Pis working down to -110 degrees C in nitrogen, which is reassuring for anyone living in chillier climes.