The parent company for the WPP media agency networks has cut its forecast from 5.8% to 4.8% growth.
The forecast takes in 70 countries and the revised spend for 2011 is now expected to reach $506 bn (£317 bn).
GroupM has also revised its forecast for digital’s share of the total ad spend this year. It is forecast to move up a point to 17% of global advertising.
Looking to 2012, GroupM’s bi-annual report predicts a 6.8% jump for ad spend to $540.3 bn (£338.4 bn), helped by the London 2012 Olympics and the US presidential election.
GroupM revised its UK ad spend growth prediction for this year downwards from 3.6% to 1.5% last month.
GroupM futures director Adam Smith says: “It’s highly unusual for natural disasters to measurably impact the totality of global advertising. However, the earthquake and subsequent tsunami in Japan was of this rare scale.”
GroupM’s prediction for ad spend in Japan has shifted from a 3% growth to a 5% decrease.