One of the biggest, if not THE biggest user of petroleum is transportation. Cars, planes, trucks, ships: they use petroleum-based fuels, adding tremendously to air pollution and global warming. So buying whatever one can locally helps reduce one of the worst wastes of this valuable nonrenewable resource and helps keep the world healthier, to boot. Thus, getting your yarns from local sources is one way to help.
But where? Up here in the Frozen North, there aren't too many sheep, and musk oxen, though available, produce really expensive (tho' ever-so-wonderful) wool.
Ah, but there are lots of dogs. Rummaging around in my trunkful o' yarn the other day, I happened to discover a bag of soft doggy wool that I had saved many years ago from my Shetland sheepdog, Piccolo. She has long since gone to that squirrel-chasing forest in the sky, but her fur remains behind, possibly to keep me warm. I have a neighbor who mixes dog wool with angora rabbit wool and makes the most lovely soft and fuzzy hats with the blend. She says the dog wool is a bit slippery (and takes a few washes to reduce that wet-dog smell), but that it works fine in blends.
There's a book out there called Knitting with Dog Hair, and I found a couple of websites for businesses that specialize in knitting or spinning pet hair. One of them, VIP Fibers, even has free patterns. Dog hair is also called chiengora (chien = dog in French). If your interest is in spinning rather than knitting, here's some guidelines for spinning chiengora.