Global online traffic will quadruple by 2015 as the number of gadgets linked to the Internet climbs to 15 billion, according to a forecast by networking colossus Cisco.

Cisco's fifth annual Visual Networking Index Forecast, released Wednesday, predicted that nearly three billion people, more than 40 percent of the expected world population, will be using the Internet by the year 2015.

"The explosive growth in Internet data traffic, especially video, creates an opportunity in the years ahead for optimizing and monetizing visual, virtual and mobile Internet experiences," said Cisco vice president Suraj Shetty.

Personal computers generated 97 percent of consumer Internet traffic last year, but the share will drop to 87 percent in the next four years as more people turn to smartphones, tablets, and Web-enabled televisions, Cisco said.

Online video traffic, including data rich 3-D and high-definition transmissions, was projected to be 14 times greater in 2015 compared to last year.

By then, a million minutes of video will traverse the Internet every second, according to the Cisco forecast.

Mobile data traffic was expected to increase by a magnitude of 26 times in the same period.