Vertical farming makes greenhouse cultivation possible in confined urban conditions and provides healthy fruit and vegetables for city dwellers. Agriculture is shifted from conventional cultivation, which requires expansive areas of land, to vertical systems in multistory buildings, also called farmscrapers. With this cultivation method, the plants grow under controlled conditions. To ensure that they receive sufficient nutrients, they are supplied with water, fertilizers and light as well as additional CO₂ for photosynthesis. This usually involves enriching the ambient air, which normally has a CO₂ content of around 0.04 per cent (400 ppm), to levels between 800 and 1,200 ppm. The improved supply of CO₂ increases the rate of photosynthesis, thus promoting plant growth. Vertical farming could become very important in view of a steadily increasing world population.