The glass skyscraper was once a symbol of America’s mighty economic power. Perhaps it still is, but to many people nowadays, the glass skyscraper is the epitome of unsustainable architecture. Glass skyscrapers are incredibly inefficient because of all the heat that escapes through the windows, which mean heating systems have to work incredibly hard to keep the interior of buildings at a comfortable temperature. The mayor of New York City, Bill de Blasio, even identifies skyscrapers with all-glass façades as the primary cause of greenhouse emissions in New York. That’s why the mayor has announced plans to introduce a bill that bans the construction of glass skyscrapers, forming part of efforts to reduce citywide greenhouse emissions by 30 percent. Under Bill’s bill, existing glass buildings will also have to be retrofitted to meet stricter new carbon emission standards.