As for your starving person example, ask that person to choose between breathing and eating? Eventually that is what it will come down to if we keep clearing our air filtration system.
I forget the exact numbers but from a Nova program, they were highlighting "man made trees". Scientists have been studying how trees clean our air for decades and finally came up with a semi-viable alternative. They discovered it was the flickering of the leaves that allowed the trees to work more efficiently. However, the stats weren't promising. Just from 1 adult's exhalation of CO2, in one day, takes a mature tree a year to remove. So for 1 adult, you need 365 mature trees just to neutrailize our breath. Now add to that all the other emissions each of us produce and you see where we're heading....yet we keep cutting them down. Plus not all trees absorb CO2. Some release it plus you have to factor in when a tree dies naturally, and begins to rot in the forest, it releases all the CO2 it absorbed in its lifetime. Plus only mature trees, 15 yrs or older, absorb CO2. Now what we do (in our infinite wisdom) is cut down trees to clear land for building homes, so more people can be born so we cut down more trees etc etc etc. Take a regular sized apartment building for example. The amount of trees cut down to make room for the building cleaned the air of 1 person's exhalations. So what do we do? Put 120 people on that land....where are the trees to clear all THEIR exhalations? No where that's where......
Ok, so never mind the tree loss, and we have megafarms running way more efficently than in olden times. But to gain that efficiency, we are using tractors, combines, processing plants all of which emit CO2. Now a team of horses produces CO2 as well, the ratio compared to a modern tractor I can't tell you but I doubt it is even close. (plus the horse's "exhaust" can be used as fertilizer, not so with a tractor's exhaust).
I think the starving man question is the key to our future. Sure, his immediate need is for food, but we can't only think in immediate needs. That is guaranteeing our demise as a species. Our planet can only sustain us for so long, its resources aren't infinite. I used this example once before:
Put 1 flea on CG while he's riding and he doesn't even notice.
Put 1,000,000 fleas on him and he won't be going anywhere and will probably die in a day (a flea weighs about a gram so 1M is 1,000 Kilos). He'd probably die of blood loss since fleas consume a fair amount of blood. Same as our planet: we can't keep consuming its resources wholeheartedly, there's nothing happening to replenish them....in fact, we are doing things to reduce the reserves more rapidly without any real benefit (just think of how much energy and resources have been wasted on say, WWII......never mind the wars in Iraq and Afghanistan.....and don't even get me started on things like NASCAR lol (not that I'm saying we should stop all non-essential things like NASCAR but there WILL come a point where we won't have any choice....)
I forget where I heard this but it is 100% true:
The cleanest method of travel is the trip not taken......(basically what they are saying is don't travel somewhere just for the sake of travel)