a) Urban Farming commonly produces leafy greens and water rich produce like tomatoes and cucumbers. This is commonly known as 'horticulture'. The horticulture to 'farmland farming' ratio is already less than 1:10.
A larger part of horticulture are crop that grow pretty well on the fields and that are commonly not produced under glass in CES (controlled environment systems). These are crops like Kale, Cabbage, Beans, Peas, Potatoes, Carrots etc. The ratio of CES to horticulture is also well above 1:10. So in summary even if we'd take all the CES production into the cities, it would be well below 1%
b) Viewed from the other side, from the available area. Even in a relatively boring and unpopular city like for example Dortmund/Germany it is extremely hard to find available plots that would be suitable for UF. If the plot is in a residential zone the square meter price is 200-400€. Commercial zone: 80-100€. Agricultural (outside city boundaries): 3-5€.
So inner city plots are waaay more expensive than agricultural land.
We are currently trying to find roundabout three acres of inner city space for an urban farm. With the help of the municipality. It is going to become very hard to find something. To find anything...
Heck, even if you'd simply assume that you can take _all_ of the city space and farm on it, it is still just a small fraction of agriculture. Cities are dense. Cities only cover relatively little of the overall available area.
You don't need to farm the inner city but it certainly helps to do it nearby. You can definitely benefit from doing it on the rural outskirts of cities
For every statement that in hindsight is hilarious because we've surpassed it by miles, there's thousands and thousands of statements that are wrong because of their sheer optimism.
