• by Joe Mandese  @mp_joemandese, June 18, 2013

The global ad economy now is expected to expand only 3.5% this year, according to the latest quarterly forecast released this morning by Publicis’ ZenithOptimedia Group. The update, which is down four-tenths of a point from ZO’s last projection of a 3.9% rate of growth, puts 2013 even with a relatively lackluster 2012 in terms of global ad spending growth.

ZO cited continuing economic and political volatility for its downgrade -- especially the slow recovery of the Eurozone and North Korea’s saber-rattling, but actually upgraded its outlooks for 2014 and 2015 by 0.1 and 0.2 points, respectively.

The U.S. remains the world’s largest advertising market by a wide margin, accounting for about a third of all ad spending, and despite its maturity, ZO predicts it will contribute to 29% of the $73 billion it estimates will be added to the world’s ad economy through 2015.

“After the U.S., however, the biggest contributors are all much younger and more dynamic markets,” ZO Head of Forecasting Jonathan Barnard writes in the report released early this morning. “China comes second, accounting for 18% of additional ad dollars over this period, followed by Argentina (7%), Indonesia (6%) and Russia (4%). Between them these five markets will contribute 64% of the extra expenditure in the global ad market between 2012 and 2015.”

Geography aside, the Internet will account for the biggest stimuli in global advertising expansion, especially the hyper-accelerated mobile sector.

“The recovery in 2014 and 2015 will be led by Internet advertising, the principal engine of ad spend growth,” Barnard notes, estimating that overall Internet ad spending will expand an average of 15% annually through 2015, and will contribute two-thirds of all of the incremental growth in the ad economy though that period.

“This growth is being driven by digital innovations - such as better measurement of exposure to advertising, greater localization, and integration with mobile devices - and online video and social media, which continue to grow at about 30% per year,” he details, noting that mobile will actually expand “five times faster than desktop Internet.”

“Mobile is, by some distance, the fastest-growing segment of internet advertising,” the report concludes, estimating that mobile ad spending will expand 67% this year, and an average of 51% annually through 2015, due to the rapid consumer adoption of smartphones and tablets.

“By contrast, we forecast desktop Internet advertising to grow by 10% a year,” Barnard noted. “Here we count as mobile all Internet ads delivered to smartphones and tablets, whether display, classified or search.”