London—U.S. ad spending will increase 4.1% this year over last year, according to marketing intelligence company Warc. Next year, U.S. ad spending will slow to 3.3% growth, “when there will be no quadrennial boost from the presidential elections and the Olympics,” Warc said in a statement. Ad spending in China will see the greatest increase this year, up 14.8% over last year, followed by Russia, which will see an ad spending increase of 13.6%. Warc's ad forecast is based on a weighted average of ad spending predictions from ad agencies, media companies and analysts.