By Sylvia Rowley at Green Futures

Behind closed doors in cities around the world lies a great untapped resource: unused space. But not, perhaps, for long. Every day, thousands of spare rooms, flats and even entire houses are put online for travellers and tourists to rent on an informal, short-term basis.

Airbnb, the behemoth of this burgeoning industry, now has listings in 14,457 cities. Dubbed the ‘eBay for space’, it has enabled 1.6 million stays since it was founded in 2008. Alongside competitors such as Crashpadder and the high-end portal Onefinestay, it’s part of a wider trend of renting, swapping, sharing and trading things with each other when we’re not using them.

This peer to peer consumption has “immense potential” to reduce our environmental impact, according to Prashant Vaze, author of The Economical Environmentalist, because often it means we use existing resources more efficiently.

Crashpadder says that the carbon footprint of the average stay through its site is 80% smaller than a night at a three to five star hotel, because very little extra energy is used for a guest in a spare room.

And it’s not just homes. Car owners, too, are saving energy and lining their pockets, with lending schemes likeWhipCar [see 'How to make a city flow']. Given that an average car requires around four tonnes of CO2 to make, says Vaze, this shift has the potential to cut road-related emissions considerably.

Although peer to peer consumption is expanding at a storming pace (Airbnb grew at a rate of 800% last year, with half of guests travelling on business) it remains relatively niche. In London, for example, there are 1,423 rooms on Airbnb, but nearly 750,000 in hotels. A spokesman for the British Hospitality Association said he does not see it as a serious threat to the hotel industry.

This article originally appeared in Green Futures, the magazine of independent sustainability experts Forum for the Future.

Image courtesy of  micmol on flickr