(See the accompanying video for the complete interview.)
Given the some $12 trillion that governments have poured into economies, said Sorrell, the ad economy should be better. Global ad spending is expected to fall 9.8 percent this year, according to the Carat/Aegis Group.
Meanwhile, September, October, November and December are crucial months, said Sorrell.
"As we look forward to next year, we will be cycling easier comparatives," he said. "The numbers that we see have to get better. I think it's steady as you go."
Sorrell highlighted three strategic issues that will become even more important for the ad industry: new markets, new media and consumer insight.
Emerging countries like Brazil, for instance, was one of the only economies in the world to grow in the first half of the year, said Sorrell. BRIC countries make up some 25 percent of WPP's business and Sorrell expects that figure to reach some 33 percent shortly.
Meanwhile, the IOC's decision to let Rio de Janeiro host the 2016 Olympics was a good one, said Sorrell.
"It takes the games obviously from Beijing to Latin America," he said. "And it's the first time that any Latin American country has had a game. I guess the issue in the long-run is when will Africa get the game."
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