Over 50% of the world's population now lives in cities, and the figure is set to rise to 75% by 2050. While the world's cities only cover 2% of the global land area, they account for a staggering 70% of greenhouse-gas emissions and share the burden of responsibility for global climate change. These facts make the development of sustainable solutions for urban cities a requirement and place various demands on future cities. Some of the requirements include energy-saving and efficient street and traffic lighting, water and wastewater management, and the reduction of CO2 emissions from motor vehicles. Flagship cases where major achievements towards becoming smart cities have already been taken include Barcelona, Singapore, Stockholm and Seoul.