Does Cold Resistance help against extreme cold temperatures in any way, or does it apply to only magical cold damage?
The Creative Director of Paizo (who publish Pathfinder) indicates that damage from environmental effects is supposed to be of the appropriate energy type and thus Resistance X vs cold will allow you to ignore X damage from cold environmental effects, be it lethal or non-lethal.
Apr 12, 2013, 02:20 pm
Can you make a ruling about the effectiveness of cold/fire resistance and evironmental dangers of heat and cold? Does cold/fire resistance negate the dangers of cold/heat? Does it reduce the lethal damage one would take if the fail the associated save? Does one get a bonus to fortitude save for their resistance? Inquiring minds would like to know.
Damage from cold temperatures is cold damage. Damage from hot temperatures is fire damage.
Each resistance ability is defined by what energy type it resists and how many points of damage are resisted. It doesn't matter whether the damage has a mundane or magical source.
While the rules for cold weather do not specify a damage type, common sense dictates that it would be cold damage. Nonlethal is not a damage type - just a property of the damage.
Resistance applies only to effects that deal the kind of damage to which the resistance applies...
The extraordinary ability resistance says
A creature with this special quality ignores some damage of the indicated type each time it takes damage of that kind (commonly acid, cold, electricity, or fire). The entry indicates the amount and type of damage ignored.
That means the special ability doesn't care about the damage's source—that source can be magic or mundane—, but the ability does care that the damage is, in fact, actually damage of the appropriate kind.
Thus, for example, a creature with cold resistance 10 ignores the first 10 points of damage each time the creature's dealt damage by an effect that says the effect deals cold damage. The special ability energy resistance is similar enough, and immunity adds nothing to the conversation.
...And, officially, cold weather deals only lethal and nonlethal damage
I know it seems silly, but the rules for Cold Dangers say that
Cold and exposure deal nonlethal damage to the victim. A character cannot recover from the damage dealt by a cold environment until she gets out of the cold and warms up again. Once a character has taken an amount of nonlethal damage equal to her total hit points, any further damage from a cold environment is lethal damage.
An unprotected character in cold weather (below 40° F) must make a Fortitude save each hour (DC 15, +1 per previous check) or take 1d6 points of nonlethal damage. [...]
In conditions of severe cold or exposure (below 0° F), an unprotected character must make a Fortitude save once every 10 minutes (DC 15, +1 per previous check), taking 1d6 points of nonlethal damage on each failed save. [...]
A character who takes any nonlethal damage from cold or exposure is beset by frostbite or hypothermia (treat her as fatigued). These penalties end when the character recovers the nonlethal damage she took from the cold and exposure.
Extreme cold (below –20° F) deals 1d6 points of lethal damage per minute (no save). In addition, a character must make a Fortitude save (DC 15, +1 per previous check) or take 1d4 points of nonlethal damage.
Emphasis mine. No part of that description says cold weather deals any kind of cold damage.
It's an interesting choice to make cold weather deal mostly nonlethal damage instead of cold damage (or even nonlethal cold damage). It means in less than extreme cold creatures immune to nonlethal damage don't suffer, while those with resistance (or immunity) to cold still do. Thus, for example, a vampire won't typically be destroyed less than extreme cold weather (because its creature type is undead), but a frost giant (that has the subtype cold) has a reason (beyond modesty) to wear furs.
A DM would be wise to consider carefully the ramifications of a house rule that changes the nonlethal damage dealt by cold weather to nonlethal cold damage, lest his ruling encourage nekkid frost giants. Brr.
A GM who thinks this is nonsense can adopt house rules compatible with Pathfinder from Frostburn
The Dungeons and Dragons 3.5 supplement Frostburn under Cold Dangers under Protection from Cold says that
A character with a spell or effect granting cold resistance applies his resistance to both lethal and nonlethal damage from cold temperatures.... (10)
As Pathfinder adopted pretty much as-is the 3.5 rules for Cold Dangers, a GM wanting to allow cold resistance apply to the lethal and nonlethal damage caused by cold weather could do worse than using these rules from Frostburn.
Extreme cold temperatures harm you, by forcing you to roll Fortitude and dealing 1d6 Cold nonlethal damage if you fail. Described here.
However, cold damage reduciton of 6 would negate that damage, and while damage resistance will not make you stop having to test your fortitude, failure does not result in anything. This also seems to be the conclusion on Paizo forums.