Photo source: AZoCleanTech By Naveed Qazi, Sustainability Analyst I n our world, more than half of the population now lives in cities, and the United Nations projects that this figure will reach about 68 per cent by 2050. The question is no longer whether cities should become sustainable, but how sustainability can be achieved across rapidly expanding urban areas. The answer lies not only in new technologies and smarter planning but also in ideas that are nearly two thousand years old and remain remarkably relevant. Cities such as Copenhagen, Singapore, Curitiba, Stockholm, and Freiburg demonstrate that economic growth, environmental protection, and a high quality of life can coexist, although rising living costs remain an ongoing challenge. Copenhagen's extensive cycle-track network, district heating system, and CopenHill waste-to-energy facility integrate sustainable mobility, clean energy, and public recreation. Singapore's Supertree Grove, vertical greening, and NEWater p...