• by Gavin O'Malley , Staff Writer @mp_gavin, June 20, 2016

Illustrating this point, Zenith now expects the ad medium to overtake desktop by 2017 -- a full year ahead of the Publicis unit’s previous forecast.

Worldwide, brands will blow $99.3 billion on mobile advertising, next year -- beating out the $97.4 billion they’ll drop on desktop ads -- according to Zenith’s new Advertising Expenditure Forecast.

What changed?

Simply put, mobile growth is refusing to slow at expected rates. 

After 95% growth, last year, Zenith now expects to see growth of 46% this year, followed by 29% growth in both 2017 and 2018.

By 2018, therefore, mobile will make up 58% of the total ad market.

Bolstering mobile’s position, desktop continues its steady decline. Desktop advertising actually peaked back in 2014 -- at $98.9 billion -- and then shrank by 0.2% in 2015, to $98.7 billion.

Thanks to mobile’s rise, traditional display ads like banners are expected to shrink by 3.1%, this year. What’s more, while Zenith expects to see some growth in display over the next two years, it will barely be enough to make up for the ground lost, this year.

“Banner ads are much less effective on mobile devices than on desktops,” Zenith notes in its new report. “Consumers find them more intrusive, and are more likely to click on them by accident than by design.”

As such, online video and social media will be the sole sources of growth for display advertising over the next three years.

Specifically, online video advertising will grow by 20.1% a year on average between 2015 and 2018, while social media will grow 23.6%.