“Air conditioning,” Eva Horn once wrote, “is one of the oldest dreams of mankind. It means creating a world without heat or cold, rain or snow, without suffocating humidity or dusty winds.” However, when considering the challenges facing the current era, air conditioning yields a significant feedback loop: the hotter it is outside, the more air conditioners are put to use; the more air conditioners are put to use, the more their hydrofluorocarbons are emitted; the more their hydrofluorocarbons are emitted, the larger the seasonal hole in the ozone layer becomes, thus warming the climate. "One of the oldest dreams of mankind," in other words, exacerbates a seemingly inescapable system failure.

However, a new paper from Nature Communications hints at the possibility of an air conditioning system which pulls carbon dioxide from the air, thus reversing the products have typically waged against the environment. According to CityLab, the concept is called 'crowd oil,' and it is "still theoretical and faces many challenges." 

Though the concept provides an ideal solution, air conditioners would still have to produce heat, and that heat would have to go somewhere. “When you run an air conditioning system, you don't get anything for nothing,” says materials chemist Geoffrey Ozin of the University of Toronto, co-author on the new paper from Nature Communications. “If you cool something, you heat something, and that heat goes into the cities.”