[MrB (Simon)]

The cold is only an issue for DPSS type lasers, which includes the traditional green ones.
When the output of these drops, DO NOT think that because the beam is weak(or gone) it therefore poses less risk to your eyes, it is actually worse!

The DPSS lasers are Diode Pumped Solid State lasers, these use an invisible 1064nm infrared laser diode to pump a frequency doubling crystal. This re-emits the light into the visible spectrum at 532nm. Top quality lasers will have an IR blocking filter on the outlet of the laser(and a heater for the crystals) but often the cheaper lasers omit this filter to save money.
When the temperature drops, the crystal stops lasing and the green beam gets weak or disappears, however the full strength invisible IR beam is still being emitted!

There is a two fold problem with this, the IR diode is usually of higher power rating than the green output because the crystals are not 100% efficient, so say 5mW for a 1mW green(tho likely less), also, with the green (visible) light in your eye your iris contracts and you also would automatically react by looking away. With IR being invisible you get neither of these auto responses so the IR laser could easily be causing damage without you even being aware.

Direct green laser diodes are now here, they are still pricey but not unrealistic(under $100), certainly much, much cheaper than they were only a short time ago.
Direct green lasers do not have reduced output in cold temps as they do not have the temperature sensitive crystals used in the DPSS lasers, they also don't have IR output for the same reason.
Definitely worth spending the extra cash.