The new figure of 1.7%, down from the WTO's previous estimate of 2.8% in April, marked the first time in 15 years that international commerce was expected to lag the growth of the world economy, the trade body said.
The figures should be a wake-up call for governments, WTO Director-General Roberto Azevedo said in the six-monthly trade outlook report.
The data underlined concerns that, after a long period of growth through globalisation and reliance on global trade, governments are increasingly seeking to protect their own industries and promote domestic producers at the expense of foreign competitors.