It is obvious that for man-made (MMF) fibres very little land is needed, compared to natural fibres of vegetable or animal origin.
For MMF from synthetic polymers almost no land is needed, while these fibres represented in 2016 68% of the total global fibre production. For cellulosic man-made fibres, like viscose, only about 3 to 4% of the land used for natural fibre production is needed. 27% of the land is needed for cotton, representing about one third of global fibre production, and 69% of the land is needed for wool representing only 1% of the global fibre production. Needless to say that synthetic man-made fibres cannot be abandoned in favour of natural fibres. There is just not enough land available, for an exclusive switch to wool or cotton, without leading to global famine or ecological catastrophes.
For viscose fibres, having beech and eucalyptus wood as raw material, land unsuitable for food production can be used, in combination with 50 to 400% higher fibre yield. The concept of sustainability is rooted in forestry. It entails forests being managed in a way that enables perpetual functionality, not only in terms of raw material supply, but as the habitat of flora and fauna, protection against erosion and landslides, and as a recreational retreat and as an aquifer.
Today, arable farm land is and will be in the future, more than ever before vital to sustain food production for the world population, and not for production of fibres to clothe the world population.
In view of this, the global population will depend on man-made fibres.