Based on data received from 59 markets across the Americas, Asia Pacific and EMEA, Carat believes that digital media, with a forecast $17.1bn or 15.7% increase in spend in 2015, is outpacing its previous predictions.
Digital is expected to account for 21.7% of market share, with global mobile spend up 50% and online video rising 21.6%, and for the first time digital is expected to account for more than a quarter of all adspend in 2016.
The upwards trajectory of digital is particularly pronounced in the UK, where the total advertising market is forecast to grow by 6.4%. Digital media spend is forecast to reach just under half (48.2%) of total UK adspend this year, rising to 51.1% in 2016.
A healthy UK advertising market is also driving growth in Western Europe, where adspend is forecast to rise 2.8% this year. However, growth remains stagnant in France and will be just 1.6% in Germany.
The UK advertising industry is expected to benefit from the Rugby World Cup, which England is hosting this autumn, but there are some minor concerns about whether the general election in May will result in a hung parliament and political uncertainty.
Elsewhere, North America is expected to record 4.5% growth although there is wide disparity between the US (4.6%) and Canada (2.5%).
Latin America is the region forecast to post the highest adspend growth (11.1%) this year, while Asia Pacific should record 5.2% growth.
Of that, adspend growth in the region ranges widely from Japan (0.9%) and Australia (1%) to China (7.9%) and India (11.0%).
"Carat's latest advertising forecast gives us increased optimism for the outlook for global advertising spending," said Jerry Buhlmann, CEO of Dentsu Aegis Network.
"With harder times behind us, negative growth markets are pleasingly now a minority, and collectively we can look ahead to 2016 with positive growth predicted for all key markets."
Warc's latest International Ad Forecast, released in December 2014, also concludes that global adspend growth of 4.6% is likely this year. It will be aided by a 14.0%, or $16.8bn, increase in digital advertising expenditure.
Forecast growth of 4.4% and 6.9% for the US and UK respectively are also largely in line with Carat's expectations.
UK adspend in 2014 will be quantified in full as part of the AA/Warc Expenditure Report, which will be released next month.
Data sourced from Carat, Dentsu Aegis; additional content Warc staff