The forecast, revised down from a 3.3 percent forecast made in April, means 2015 will be the fourth year in a row with trade growth of less than 3 percent, half the annual average in 1990-2008 before the financial crisis hit.

The WTO's forecast implies growth will quicken this year, from 2.5 percent growth in 2014. But its expectations have repeatedly proved overly optimistic as hopes of global economic recovery have receded.

There were still big potential risks to its latest numbers.

"These include a sharper-than-expected slowdown in emerging and developing economies, the possibility of destabilizing financial flows from an eventual interest rate rise by the US Federal Reserve, and unanticipated costs associated with the migration crisis in Europe," the WTO said in a statement.

The Chinese slowdown already caused the WTO to cut its 2015 forecast for growth in Asian imports to 2.6 percent, down from a 5.1 percent projection in April, and Asian exports to 3.1 percent from the previous 5.0 percent forecast.

China's falling demand was one major reason why global trade shrank in the first two quarters of 2015, contracting from the previous quarter by an average of 0.7 percent. Falling demand in Brazil and oil and commodity prices also contributed.

However, year-on-year global growth for the year to date is still positive, at 2.3 percent from the same period of 2014.

In 2016, world trade is expected to grow by 3.9 percent, a revision of the WTO's previous forecast of 4.0 percent.

That rebound is predicated on Asian import growth bouncing back from 2.6 percent in 2015 to 4.3 percent, as well as Latin America flipping from a 5.6 percent import contraction this year to 5.7 percent import growth in 2016.

The WTO forecasts covered trade in goods, but not trade in services.