The International Monetary Fund cut its global growth forecasts for the third time in less than a year on Tuesday, citing a sharp slowdown in China trade and weak commodity prices that are hammering Brazil and other emerging markets. The Fund forecast that the world economy would grow at 3.4 percent in 2016 and 3.6 percent in 2017, both years down 0.2 percentage point from the previous estimates made last October. The updated World Economic Outlook forecasts came as global financial markets have been roiled by worries over China’s slowdown and plummeting oil prices.