• by Erik Sass , Staff Writer @eriksass1, December 5, 2014

Despite the proliferation of behavioral, video, native, and other new online advertising categories, paid-search marketing still gets the lion's share of digital ad dollars. And in 2015, for the first time, more of those dollars will be going to mobile search than desktop, according to a new forecast from eMarketer.

Even by the standards of the fast-changing digital ad scene, the pace of change is pretty remarkable: over just three years, mobile search will almost triple in dollar revenues, from $5 billion in 2013 to $9 billion this year, and then $13 billion in 2015. In proportional terms, mobile’s share of total paid search revenues will more than double from 24.7% to 50.1% over the same period (the forecast includes spending on search engine optimization).

Looking ahead, eMarketer expects mobile search ad spending to double again to $26 billion in 2018, when it will account for 77% of all paid search spending. To put that dollar figure in perspective, in 2013 total search revenues across all devices came to $18 billion, according to the Interactive Advertising Bureau.

Reflecting the growing importance of mobile search, last month Google announced that it will begin highlighting mobile-friendly sites with a mobile “badge” in its search results. In order to receive the mobile-friendly badge, a Web site must satisfy four main criteria: it must avoid software that is not common on mobile devices, like Flash; use text that is readable without zooming; size content to the screen so users don’t have to scroll horizontally or zoom; and place links far enough apart so that the correct one can be easily tapped.

Last month, I wrote about a study by Searchmetrics that found mobile search results can vary considerably from desktop search. The study analyzed ten thousand keyword searches and found that 36% of Web destination URLs shown in the top 30 mobile search results differed from the same search conducted on a desktop or laptop.