Philippine activists warn about possible riots. Aid agencies across Asia worry how they will feed the hungry. Governments dig deeper every day to fund subsidies. A sharp rise in the price of rice is hitting consumer pocketbooks and raising fears of public turmoil in the many parts of Asia where rice is a staple. Part of a surge in global food costs, rice prices on world markets have jumped 50 percent in the past two months and at least doubled since 2004. Experts blame rising fuel and fertilizer expenses as well as crops curtailed by disease, pests and climate change. There are concerns prices could rise a further 40 percent in coming months. The higher prices have already sparked protests in the Philippines, where a government official has asked the public to save leftover rice. In Cambodia, Prime Minister Hun Sen ordered a ban on rice exports Wednesday to curb rising prices at home. Vietnamese exporters and farmers are stockpiling rice in expectation of further price increases.