An underground, manmade lake supplies buildings in Helsinki with cold water that acts as an air-conditioner, but with less greenhouse gases.

Summer's in Helsinki, Finland, while short, can be fairly warm. In order to combat the heat, the city has come up with a unique method, using an underground lake.

Instead of buildings blasting their air-conditioning, cold water from an underground source is utilized.

300-feet beneath Esplanade Park located in the center of the city is a 300 feet long manmade cavern.

Water from the cavern gets pumped throughout buildings in the city, acting as an air conditioner.

This system decreases the amount of carbon dioxide and other greenhouse gases released by 80 percent compared to traditional air conditioning systems.

The city also estimates the energy efficiency of the city-wide water cooling system is five times greater than building specific systems.

Other cities around the world, including Toronto and Ithaca, also utilize similar water-based cooling systems.

Helsinki also has a heating system in place for the winter. Thermal energy absorbed from wastewater is pumped through an underground heat station to warm citizens' homes.

The underground heat pump station is reportedly the largest in the world.