Businesses such as restaurants and retailers often choose to leave their doors open during the summer months, hoping to lure potential customers inside. But these businesses contribute to CO2 in the atmosphere and help increase the risk of blackouts.

According to New York-based energy giant Con Edison, throughout the course of a summer, an average store can waste upwards of 4,200 kWh of electricity — releasing a whopping 2.2 tons of carbon dioxide into the atmosphere — simply by leaving the air conditioning on while windows and doors are open. And during the summer, when a city’s power grid is already overtaxed, this practice could also increase the risk of widespread brownouts and blackouts.

As grist.com reports, in New York City alone, air conditioning in commercial spaces accounts for about 10 to 20% of all of the energy used in the Big Apple and up to 10 million metric tons of greenhouse gas emissions released each year. If all 10,000 of the city’s businesses shuttered their windows and doors when running the A/C, they could save about 22,000 extra tons of carbon dioxide emissions.

Business owners in New York have been progressive in implementing energy efficient measures, however. More businesses are closing their doors during the summer and the city recently passed Local Law 88. LL 88, as it often is referred to, is comprehensive. It will require upgrades to lighting in hallways, fire stairs, lobbies, storerooms, boiler and mechanical rooms and other areas that are not residential units.