A slowdown in China, Russia and Brazil will take the steam out of global advertising this year, media buyer Zenith Optimedia said on Monday, as it trimmed its forecast for growth in spending on advertising by 0.2 percentage points to 4.0 percent.

The agency, owned by Publicis, said the world could no longer rely on emerging markets to set the pace, and it expected North America, Europe and Japan to contribute more to growth this year than newer markets, for the first time since 2006.

Growth in ad spending would accelerate to 5.0 percent in 2016, boosted by the Olympics in Brazil and the U.S. presidential election, Zenith Optimedia said.

Next year will also see mobile internet advertising overtake newspaper advertising for the first time, accounting for 12.4 percent of global adspend, while newspapers will take 11.9 percent, it said.

"We are now witnessing the fastest transition of ad budgets in history as marketers and agencies scramble to catch up with consumers' embrace of the mobile way of life," said Zenith Optimedia Chief Executive Steve King. 

Reuters (Reporting by Paul Sandle, editing by Louise Heavens)