Russia’s announcement that it would renew its naval blockade on Ukrainian ports has revived concerns about wheat prices and the impact of Russia’s invasion on global hunger.

Russia had previously allowed grains and other agricultural products to pass through the Black Sea thanks to an agreement brokered by the United Nations several months after the invasion. Since then, almost 33 million tons of grains and seed oil products have been exported under this Black Sea Grain Initiative. At a time when the production and availability of food is being disrupted by geopolitical conflict, climate change and other factors the agreement helped reduce global food prices by more than 23 percent, United Nations secretary general António Guterres said this week.