(CNN Money) — The explosion of Internet video viewing on smartphones and tablets is costing wireless carriers tens of billions of dollars each year — and that growing tab is going to land in your cell phone bill. The amount of data downloaded to mobile devices doubled this year compared to last. Video was the largest contributor to that growth, according to Cisco’s Visual Networking Index. Cisco (CSCO, Fortune 500) expects that trend to continue, with mobile data downloads more than doubling every year through at least 2014. By that time, mobile Internet traffic will have grown to 17 times 2010’s levels. Over the next four years, total mobile video traffic will expand to 197 million gigabytes — or about 13 billion YouTube videos.