Trade tensions and higher interest rates are slowing the global economy, though for now there are no signs of a sharp downturn, the OECD said on Wednesday, lowering its outlook for next year.

The Organization for Economic Cooperation and Development forecast that global growth would slow from 3.7 percent this year to 3.5 percent in 2019 and 2020. It had previously projected 3.7 percent for 2019.

The global growth slowdown would be worst in non-OECD countries, with many emerging-market economies likely to see capital outflows as the Federal Reserve gradually raised interest rates. The OECD cut its outlook for countries at risk such as Brazil, Russia, Turkey and South Africa.

Rising interest rates could also spur financial markets to reconsider and thus reprice the risks to which investors are exposed, triggering a return to volatility, the OECD said.

"We're returning to the long-term trend. We're not expecting a hard landing; however, there's a lot of risks. A soft landing is always difficult," OECD chief economist Laurence Boone told Reuters.

"This time it is more challenging than usual because of the trade tensions and because of capital flows from emerging markets to countries normalizing monetary policy," she added.

A full-blown trade war and the resulting economic uncertainty could knock as much as 0.8 percent off global gross domestic product by 2021, the OECD calculated.

Though at the source of the current tensions, the U.S. economy was expected to fare better than most other major economies, albeit because of costly fiscal stimulus.

The OECD left its forecasts for the United States in 2018 and 2019 unchanged, projecting growth in the world's biggest economy would slow from nearly 3.0 this year to slightly more than 2.0 percent in 2020 as the impact of tax cuts waned and higher tariffs added to business costs.

Trimming its outlook for China, the OECD forecast the country's growth would slow from 6.6 percent to a 30-year low of 6.0 percent in 2020 as authorities tried to engineer a soft landing in the face of higher U.S. tariffs.

The outlook for the euro area was also slightly darker than in September, with growth seen slipping from nearly 2.0 percent this year to 1.6 percent in 2020 despite loose monetary policy over the period.