The forecast for growth this year follows a 5.4% estimated rise in global ad spend in 2018 to $590bn.

Despite this overall growth, the report, based on data from 96 countries, suggests that internet-based advertising will decline by 7.2% outside of the Facebook and Google duopoly.

At a time when the tech giants are under more scrutiny than ever for their data privacy practices, advertising income for Facebook and Google is expected to rise by 22% to $176.4bn this year. This represents a combined share of 61.4% of the online advertising market, up from 56.4% in 2018.

Within internet advertising, mobile spend is expected to increase by 21.9% to $165.7bn globally, with Warc forecasting the channel will overtake TV in Australia, Brazil, Canada, China, France, Germany, India, Italy, Japan, Russia, the UK and the US.

Over half of global ad spend ( 53.3%) will be invested in traditional media in 2019, according to the report. Globally, TV is still the strongest single medium, forecast to attract $195.5bn in investment – a decrease of 1.3% from 2018.

Print advertising continues to decline, with the report expecting a dip of 9.5% this year, while out-of-home, radio and cinema advertising are all forecast to grow.

James McDonald, data editor, Warc, said: "While advertising investment is stable at the top line level – maintaining a 0.7% share of global GDP since 2011 – the market’s undercurrents have changed dramatically in recent years. The amount of ad money available to online publishers beyond Google and Facebook is now in decline, and the repercussions are potentially far-reaching, with several high-profile announcements of job cuts seen among online publishers already this year.

"Print publishers have already been severely hit by the migration of ad dollars online, and while traditional media excluding print have fared admirably to date, their collective take of ad investment is also trending downwards."