GURPS After the End 2: The New World talks about a cold climate in the new world but really only reiterates some information from Basic Set: Campaigns about snow. Where's the acid snow? Where's the Day After Tomorrow-equse storms so cold that they freeze you when you are exposed to them? Well, the author most likely had a limit on space and left some things up to the GM to explotrate ...so this is me. Extrapolating. My own post-apocalyptic campaign is going to be a "cold" apocalypse - because let's be honest, they are scarier than the Mad Max-style dusty everywhere endings.)
So a few assumptions first:
- The average temperature is between 2 and 20 degrees colder than the average temperature on record for the region. Even a mild drop of a mere 2 degrees can cause terrible winters. The last Ice Age we had was a drop of only 12 degrees...
- The remaining populous knows how to deal with cold extremes. This could be as simple as requiring everyone to take Survival (Arctic) and other useful cold travel skills like Skiing, Skating, etc. The GM could also allow a better default for Survival (Arctic) giving the equivalent of a Dabbler Perk for a single skill. Thus in "snowpocalypse" campaigns Survival (Arctic) defaults to Per-2 instead of Per-5. The latter would be a campaign switch.
- Most precipitation is going to be ice, hail, snow, sleet, etc.
- The growing season is going to be short (perhaps 3 to 4 months) and cold-resistant crops (e.g., carrots, kale, or spinach) will be prominent. Domesticated animals that can more easily survive the cold or forage on their own will also be more prominent (e.g., sheep).
Detailed Winter Survival
Surviving in the cold is a matter of being able to keep warm. This is glossed over for After the End, but in the spirit of "Survival at the End" a more detailed approach may be appealing to some. Winter survival depends on the same things that surviving in other climates do, but more of it. When building shelters you must make them as windproof and rainproof as possible. Insulators such as emergency blankets, rocks, etc. to reflect body heat or a fire can make all the difference. When building a shelter (see here) the GM can allow a Survival (Arctic) to act as a complementary skill for the purposes of increasing your HT or HT-based Survival (Arctic). A well-made shelter can be the difference between life and death.
Composition of meals can also make the difference. In normal climates an adult needs around 2,500 calories a day to maintain a healthy weight - in a arctic climate this doubles. Thus the GM could fairly argue that a character needs an additional 1-3 meals per day (or double portions per meal) in cold climates. Since the very act of digestion expends energy this could also help combat the cold. In game terms the GM could decide that such a diet is effectively the Hungry quirk (GURPS Power-Ups 6: Quirks, p. 23) and a level of Temperature Tolerance (Cold). Thus, for the equivalent of an extra meal per day the subject gains +2 to HT rolls to resist losing FP or LFP to cold effects.
Starting a fire in the snow is hard. In most cases you'll first need to clear the area of snow - at least 2 to 3 feet from the outmost edge fire. If this is not possible due to either the depth of snow, packed ice underneath, or similiar circumstances a fire bed must be created. A fire bed can be anything from a "raft" of wood, an automobile hood, or other objects of "flat nature." The idea is that the fire needs to sit far enough above the snow that it won't contact the snow-melt and thus have the possibility of drowning the coalbed. Once you have a fire going you'll need to have a way to shield it from snowfall or other precipitation (building under a tree or similiar structure). The last thing you want is your fire to go out...
The good news about surviving in the cold is that as long as you have a fire and something to boil water in you can process all the water you need. In an emergency you can also eat snow, but this is a hotly contested point! Eating snow will bring your core temperature down and that can be deadly in the cold. On the other hand, eating snow while physically exerting yourself can lower your temp some, but not dangerously. Being dehydrated is probably worse!
After the End 2 (p. 12) has a few entries for storms, here's a few new ones and some modifications:
"Acid Snow": Use the rules for Acid Rain, except that corrosion damage gains the cyclic modifier (another point of damage per minute for up to 10 minutes). Acid snow also sticks around for a while just like normal snow and wandering into a patch can be dangerous!
"Rad Snow": As for Fallout Rain, but use the rules for Acid Snow.
Like a normal blizzard but dumping 0.5" to 1" of snow per 5-10 minutes (optionally, roll 3d6) in subzero temperatures. Unlike a normal blizzard those caught out in must make an HT (or HT-based Survival (Arctic) roll every hour. Failure results in 1-point of injury. Critical failure causes 1d instead. GMs can increase the frequency of rolls to every 30 minutes for temperatures of -20°F or higher, 10 minutes for temperatures -40°F or higher, and 1 minute for temperatures and -60°F or higher. Such blizzards last 1d hours and eventually dissipate.
Picking Over the Bones
Surviving in the cold sucks. It's probably more miserable than just about any other climate other than the desert. Even then the heat takes a day or two to kill you - you can die from exposure in just a few hours. I also think that having water everywhere (and in a form that might kill you) is more subtly dangerous. There's a reason why the Viking's idea of the end of the world was heralded by several years of severe winter and cold afterall.