(Why? And How? And What? And Whatever.)
Just thinking. Too many scenarios for SHTF to list, and once you know what scenario, I guess you can extrapolate what the effect on us will be. So will just list most likely scenarios. Please note that I’m no political analyst, I don’t have theological training, my meteorology is high school level, and anything and everything else I say is my opinion, not some fixed and immutable law of the world.
WX: Situations with weather at the root (climate changes either way.)
Warming:
If weather warms, the whole weather system becomes more energetic, i.e. it has more energy. More energy equates to more wind, and also to atmospheric interface layers rising higher than they normally would, and oscillating over wider ranges than before. The upshot is more extremes of weather.
Warming will drive current growing zones toward the poles, meaning that regions that formerly were food baskets will now become drier and grow less food. This means that existing food pipelines (via commercial farms, transport, supermarkets) will have to shift one endpoint. There will be financial costs to establish new pipeline wellsprings, ecological costs from eradication of more biodiversity for the purpose of establishing new arable regions, and more ecological costs from completely altered systems emplacing themselves where previously, cleared farm land existed and was in use.
At a local level, what it means is that unless you have some means of controlling your local microclimate, you will find that sure crops begin to fail, necessitating a change in the types of crops you grow. That means you’ll possibly need to learn a whole new set of best practices to get the most out of these new crops. Look one or two temperature zones closer to the equator for what sorts of crops may become your new foods.
The same goes for weeds. If you customarily ate a particular weed as part of your diet, look to see if it grows equally well two zones equator-ward from you, and if not, start researching whatever does, and develop a strategy for switching diets.
Finally, the fauna that lives in particular ecological niches will migrate (if they can) to follow the plants they depend either directly or indirectly on. Grazing animals will follow their feed, which will spread to grow away from the equator following their ideal climate band. Those herbivores that are able to survive in the new location, will be found there soon. Then the predators that used to rely on them as a source of food will either move with them, or switch to a new prey animal.
That “migration” of course doesn’t mean everything will just up and walk. It means the the animals and plants at the cooler edge of the moving band will survive better, while those at the hotter end will perish. Some animals that move freely, will do so, but for most of the rest, it’ll be a generational change. Many long-lived slow-moving species won’t make the change. Expect hunting to be different, foraging to be different.
Cooling:
Global climate change can trigger the other way, too. Almost every process on Earth is balanced on a fairly narrow knife edge of one sort or another. If the energy in the atmosphere increases by just a degree, the total amount of extra energy held in the air alone is a phenomenally large amount, just because there’s lot of air up there. That amount of energy can push many things off their balance point.
One thing that’s happening with global warming is that methane that has been locked up in what used to be permafrost and glacial areas is now able to leach out into the atmosphere. Methane is a greenhouse gas so it may well trigger an even more rapid rise in atmospheric temperature. Which by itself may just speed up the climate band creep described in the previous section, so where’s the cooling come from?
Well, a rapidly-moving climate band will leave a LOT of dead plant material behind it. The way of most things living is that it only takes one really bad event to kill off a forest of trees, a savanna of plants. if it happens at the wrong time, or to a slow-reproducing species, there’s no coming back, just a brown spot of dry fuel for the next fire.
And fire will happen. Once fire happens, (as we’ve already seen with several wildfires) we’re pretty much ineffectual at controlling it. Smoke and ash will cause darkening, and – cooling. Don’t forget that a volcano that is a few hundred yards across, can create enough smoke and ash to darken skies for days, sometimes months, afterwards.
Nuclear strikes also can cause that kind of darkening. The result would be a sudden snap over into extreme cold, draining all the energy out of the atmosphere in a series of destructive winds that would make a typhoon seem like a gentle zephyr by comparison.
If cooling happens, the habitable bands would all shift towards the equator instead, but the point is that just as for the scenario of warming, you’d need to get used to a whole new ecosystem surrounding you, or move to follow your habitable zone.