Crop-growing skyscrapers

By 2050, close to 80% of the world's inhabitants are expected to live in urban areas. Even on the most cautious reading of today's demographic trends, the global population will have grown by roughly three billion over the same span. Should farming carry on as it is practised now, feeding them all would demand about a billion hectares of new land - a territory some 20% larger than Brazil. The trouble is that, worldwide, upwards of 80% of the soil well suited to crops is already under cultivation, and careless management has ruined perhaps 15% of it over time. What, then, can be done to secure enough food for everyone on the planet?
Growing food indoors is hardly a fresh idea - glasshouses have been turning out cucumbers and similar crops for many years. What has changed is the sudden pressure to expand the method far enough to feed an extra three billion mouths. Meeting that demand, many argue, will take a completely rethought form of indoor cultivation, built on the latest technology. The 'Vertical Farm' is one such scheme. Picture a tall, many-floored building whose interior is kept under tight environmental control and given over to crops. Sitting right inside cities, such buildings would slash the distances food must be carried before reaching the people who eat it. A vertical farm would have to be productive, cheap to put up and safe to run. Get it right, its backers argue, and the payoff is considerable: districts renewed, a steady and varied supply of wholesome food produced in every season, and, in time, the healing of the natural systems that ordinary field agriculture has worn away.
Learning to cultivate most of the crops we now regard as commonplace took our species something like 10,000 years. In the process, much of the ground we farmed was spoiled, and lush natural landscapes were often reduced to near-desert. Over the same stretch we became a city-based species: today around 60% of all people are stacked up in urban housing. So while most of us enjoy a roof over our heads, the plants that feed us are left at the mercy of the open air, and all we can do is trust that the weather holds. More and more often, though, a fast-shifting climate ensures it does not. Each year great floods, prolonged dry spells, hurricanes and fierce monsoons exact their price, wiping out crops by the millions of tonnes.
Those who back vertical farming point to a whole range of possible benefits. Harvests, for one, could come the whole year through, since the plants would sit in precisely regulated conditions tuned for ideal growth. Nothing would be lost to the weather - no ruined crops from drought, flood or pests. Because everything could be raised organically, there would be no call for herbicides, pesticides or fertilisers of any kind. Many of the infectious illnesses people pick up where farming and humans meet would become far less common. And though running it would draw a certain amount of power, the farm could feed electricity back into the grid, generating methane from the composting of plant and animal parts that no one eats. The need for tractors, ploughs and long shipping routes would vanish too, cutting the use of diesel dramatically.
One serious weakness, though, is the crops' dependence on electric light. Deprived of it, the plants closest to the windows would catch more of the sun and shoot up faster than the rest, so the whole operation would lose efficiency. A single-storey greenhouse at least enjoys daylight falling straight from overhead, yet plenty of them still call for lamps to top it up.
In a building of many floors, where no daylight reaches from overhead, the demand climbs far higher still. Producing that much light could prove ruinously costly, at least until cheap renewable power becomes available - and for now that looks more like a distant hope than anything we can expect soon.
One version already worked out sets the plants on stacked shelves running along rails, so that shifting the shelves brings each plant enough sunlight. In a single-storey greenhouse lit from above, the arrangement is up and running and performs well; whether it could work at all without that overhead daylight, however, remains an open question.
What vertical farming represents is a bid to tackle the very real difficulty of feeding a population that keeps growing. For now, though, much more work is needed before its environmental cost - above all its hunger for energy - can be brought to an acceptable level. Our food may well be grown inside skyscrapers one day, yet most specialists hold at present that we are far likelier simply to use the roofs that city buildings already offer.

Question 1 - 7

Complete the sentences below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

Certain crops, such as ﻿, have long been raised under cover.

Placed within ﻿ themselves, vertical farms would shorten the journeys food makes to reach buyers.

Waste matter from crops and livestock could be converted into methane, enabling a vertical farm to produce ﻿.

With farm machinery no longer needed, much less ﻿ would be burned.

One drawback is that the plants cannot do without ﻿ light.

In one approach, crops are set out on movable ﻿.

The likeliest outcome, many think, is that crops will be raised on the ﻿ of urban buildings.

Certain crops, such as ﻿, have long been raised under cover.

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