Global spending on ads for desktops will soon be hit hard by the rise of smartphones, data showed Wednesday.

In 2015, expenditure on desktop advertising made up 19.5 percent of total global ad spending, while the proportion of mobile advertising stood at 10.4 percent, according to research provider Zenith in France.

However, the proportion of mobile advertising is expected to sharply increase to 23.3 percent by 2018, in line with the surge in smartphone users. Meanwhile, the figure for desktop advertising will fall behind at 15.3 percent, the firm said.

Television was the dominant medium for ad spending in 2015, at 36.9 percent of the total, Zenith said.

It also noted that internet ads will grow in dominance over the next three years, while the combined proportion of desktop and mobile advertising is projected to stand at 38.6 percent.