Despite Finland’s relatively cool temperatures, climate changes have made heat waves more common in Northern Europe, and the demand for cooling buildings in summer is increasing. Instead of installing air conditioners for individual buildings, Helsinki is pioneering a vast network of underground infrastructure that pumps cold water from lakes and seas into local buildings. Beneath an unassuming park in downtown Helsinki sits a reservoir containing nearly 9 million gallons of water that is recycled and cooled by waste energy after it is used for cooling, replacing the need for air conditioning in the city and cutting carbon pollution by 80%. Read more about this undertaking in this article from Fast Co. Exist.