Is an earth plausible without vegetation but a select few city-sized vegetation biomes survive?

Question

I was asked this question over a few beers; what would be the practical considerations for a world in which vegetation has died.

Humans exist in small, self-sufficient biomes representing city-states and each nurtures the remaining vegetation within the biome.

Travel between biomes is conducted in oxygenated vehicles which run periodically at great expense to conduct trade and diplomacy.

What barriers would exist to prevent such a world being believable or viable?

An example consideration

• Could limited plant life produce enough oxygen to sustain a city-sized populace within a biome?

Is such a world plausible?

Answer 1

There is a lot of varying information on oxygen creation from plantlife, mostly because the definition of 'tree' can vary so much. Environment canada suggests 2 mature trees produces enough oxygen to let a family of 4 live, while the new york times puts the figure at an acre of trees will support around 18 people. It also varies by species of tree and age, so it's hard to give firm numbers.

Using the 18 people per acre and 640 acres per square mile, you get around 11k people that can live off of 1 square mile of forest...which is actually around the same population density of chicago. Of course the trees will be competing with people for space, but if you could completely forest over all of chicago, the people there could maintain their oxygen supplies. I imagine if 1 half of the square mile was forest and the other half was city and humans, you could have 5000 people in a square mile breathing off of what the trees create.

Though it's very important to point out that we use oxygen in many other manners...combustion at it's core is consuming oxygen, and so does any of the meat products that we raise and consume. You'll have to have a very 'green' society to make this work...otherwise the population density of your city gets very low.

Answer 2

Well to be honest this is exactly the kind of thing we would expect to see if we start colonizing Mars. People living in domes/caves sealed off from the outside environment and each one growing plants to sustain themselves. Leaving would need suits or enclosed vehicles to protect life.

So the answer is, it is a believable situation.

Answer 3

I agree with bowlturner. It appears to be an opposite situation to terraforming. https://en.wikipedia.org/wiki/Terraforming.

However, terraforming is done with advanced planning, resources, and support from another livable habitat or base (Earth or other base). I think the point where it might be implausible or unfeasible is that your situation is done in a retreat on a populated Earth. If the habitat was so bad as to kill life, was there enough planning to build multiple self sufficient atmospheres? I imagine there was civil and economic turmoil, especially in the cities as it got this bad.

Perhaps, what is more believable is that rather than cities being saved and made self sufficient, new places were built in areas more isolated and less effected by the pollution (due to weather, elevation, etc) so as to give the builders more time. If it were presented as a doomsday scenario that governments had, and they constructed in secrecy, allowing select members of the population to benefit from, I would believe it.