The Publicis owned media agency says it expects global ad income to drop 10.2% to $443.7bn (£271.5bn) this year, hit by the “worst recession since the Great Depression”.
However, the media agency has raised its growth forecast for next year, from 0.4% to 0.9%, its first 2010 upgrade in 18 months.
Zenith adds it expects the market will continue to “improve steadily” over the next three years and will reach “normal” 5% growth in 2012.
Despite global increases, the agency says Western European and US ad markets will continue to decline next year, falling to $106.2bn (£64.9bn) and $153.3bn (£93.8bn) from $106.7bn (£65.3bn) and $156.9bn (£96bn) respectively.
Television ad spend is forecast to fall 7.6% to $171.5bn (£104.9bn) this year, but will see its market share increase from 38.2% to 39.2% as people turn to the “cheap but absorbing form of entertainment” in the recession. The medium is expected to grow to $175bn (£107.1bn) next year.
Spending on newspapers and magazines is expected to drop to $101.9bn (£62.3bn) and $45.1bn (£27.6bn) this year and again to $97.8bn (£59.8bn) and $43.1bn (£26.4bn) respectively in 2010.
Online is the only medium that has grown this year, up from $49.3bn (£30.2bn) last year to $54bn (£33bn), and is forecast to grow again to $60bn (£36.8bn) in 2010.
The agency says the internet to overtake newspapers to become the world’s second-largest advertising medium by 2015.
The sunnier forecast from Zenith tells a similar story to a recent study by Nielsen that showed that the decline in advertising spending is slowing.