The figures, contained in WARC’s latest International Ad Forecast, represent cuts in the expected combined growth rate of printed, online, television, outdoor and radio advertising spend of 0.5% in 2012 and 1.5% in 2013.
Taking into account forecast inflation, the report predicts that global ad spend will rise by just 1.8% and 1.6% this year and next.
UK ad spend, adjusted for inflation, is now expected to grow in 2013 by just 0.5% to £15.6bn rather than by 2.5%.
Advertising expenditure in newspapers will show a decline of 1.9% while ad spend in magazines is expected to decrease by 1.1%, the revised forecast shows.
Spend on internet advertising is still expected to achieve healthy growth in 2013 although the figure has been downgraded from 11.6% to 9%.
Warc’s data editor Suzy Young said that global events such as the London 2012 Olympics, the Diamond Jubilee, the US presidential election and Euro 2012 had boosted advertising spend around the world but that 2013 would "suffer by comparison" with advertisers having less spending incentives.
She added: "I think this is still a very optimistic outlook for the UK and I wouldn’t be surprised if that figure is downgraded again. It really depends on our GDP growth. If we keep seeing ongoing fluctuation then confidence in the markets will continue to remain extremely fragile."
Based on WARC's quarterly Expenditure Report, the forecast covers 12 international markets including the US, the UK, Russia, India, Brazil, Germany and Canada.
The fastest growing ad markets in 2013 are expected to be Russia (+14%) and China (+12.5%) follwoed by Brazil (+9.5%) and India (9%), accroding to the report.
Meanwhile growth in US ad spend is predicted to slow to 2.5% by the end of 2012 compared to an earlier forecast of 4.1%.