Huge opportunities exist for cutting greenhouse gas emissions and generating employment. In some countries the built environment is responsible for up to 40% of total energy use. A worldwide transition to energy-efficient buildings would create millions of jobs, as well as "greening" existing employment for many of the estimated 111 million people already working in the construction sector. Investments in improved energy efficiency in buildings could generate an additional 2-3.5 million green jobs in Europe and the United States alone, with the potential much higher in developing countries.