Large-scale urban farming via large rooftop greenhouses could dramatically lower the total cost of growing some foods, especially if you consider the future environmental cost of land-use and fossil fuel emissions from transportation.
I'm not talking about every family having their own little "plot" on their own little roof. I'm talking about large greenhouses covering large buildings.
Still doesn't work? It takes 300-400 sq ft of greenhouse per person to feed them. An apt house roof could feed how many? 20? 50? And 2000 people may live in that building. Make the building taller, now 3000 people life there, and the greenhouse is no larger. That's what 'not scaling' looks like.
We have commercial farming because it takes that to feed us.
Who said anything about eliminating all large-scale rural farms? (And FWIW what I imagine would still very much be commercial farming)
Even barring any future innovation in city planning (better distribution of sunlight, etc), architecture (tiered building design, whatever), and agriculture (crops optimized for greenhouses), we would still benefit from growing food on rooftops, so why wouldn't we?
Oh and by the way, you can use electricity (realistically from a mix of renewable and nuclear power) to keep "sunlight" on in your greenhouses; they don't need to be on rooftops.
I don't disagree that it doesn't scale vertically nearly as obviously as it does horizontally, but why make perfect be the enemy of better?
Its hard enough to keep roofs watertight. Add wet soil for months at a time and the corrosion, leaking, mold etc become a problem.
If you want a farm, put it on a farm. If you want a solar generator, put it in a clean well-lighted place. All this hybridization (rooftop farming, solar roads etc) is not sound engineering.
Every problem you describe sounds like a solvable engineering problem.
We may need to design our buildings to accommodate these kinds of problems, but that doesn't mean they should be dismissed outright -- The potential energy benefits are substantial.
It takes a just a small leap of imagination; we're not talking about magic.
If you take anything away from this discussion, let it be this:
> [Climate change effects] threaten future gains in commodity crop production and put rural livelihoods at risk. Numerous adaptation strategies are available to cope with adverse impacts of climate variability and change on agricultural production. These include altering what is produced, modifying the inputs used for production, adopting new technologies [emphasis mine], and adjusting management strategies. [1]
If the cost for food goes up precipitously (e.g. lots of engineering needed to get modest amounts) then people will starve. Lots of people. That's my takeaway
Cities are way more efficient than spread-out rural towns and villages[1], but we still mostly rely on rural land for food, so they continue to exist. Because rural needs and daily experiences are very different from the average city-dweller, so too are their political beliefs.
The less we need to depend on rural land for food, the more people move into cities, the more efficient everything becomes.
[1] I'd recommend reading the chapter on Dense Cities from Whole Earth Discipline - totally changed my perspective on cities.
Do you believe we should continue mining and burning coal? It's bad, but if we close all the coal mines and factories, a lot of people will lose their way of life.
Large-scale farming (which vastly dominates the rural land mass of the US) has similarly dramatic downsides.
Like I said, I know nothing about the coal industry so I can't offer an informed opinion. Commercial farming covers an order of magnitude more land and employment than energy extraction. There are alternative energies to coal. There are not alternatives to food. Urban agriculture is a logistical impossibility without removing all meat, dairy, corn, wheat, and soy from the world's food supply.
Why must everything be absolute? You can have urban farming and rural farming. Urban farming would obviously have to happen gradually, so start with easier stuff. It's not "impossible". The point is that it will reduce pressure from rural areas which are going to be stressed significantly in the coming decades.
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