Buildings and their construction together account for 36 per cent of global energy use and 39 per cent of energy-related carbon dioxide emissions annually, according to the United Nations Environment Program. According to the Green Building Council over the last two decades, built environment emissions have reduced by around 30 per cent. Most of this decrease occurred after 2010 and is largely due to a reduction in operational emissions, most of which are attributable to rapid decarbonisation of the electricity grid in recent years, rather than improvements in the energy efficiency of buildings. Newly constructed buildings are more energy efficient, but 80 per cent of buildings in 2050 have already been built, so a major priority is decarbonising our existing stock. Yet Government policies aimed at improving the efficiency of existing buildings have scaled back dramatically, and insulation installation rates have stalled. Green or sustainable building is the practice of creating healthier and more resource-efficient models of construction, renovation, operation, maintenance, and demolition.