Systemic causes for the worldwide increases in food prices continue to be the subject of debate. Initial causes of the late 2006 price rises included unseasonable droughts in grain producing nations and rising oil prices. Oil prices further heightened the costs of fertilizers, food transport, and industrial agriculture. Other causes of the food crisis may be the increasing use of biofuels in developed countries, and an increasing demand for a more varied diet, meat in particular, across the expanding middle-class populations of Asia. These factors, coupled with falling world food stockpiles have all contributed to the dramatic worldwide rise in food prices. Long-term causes of the food crisis remain a topic of debate. These may include structural changes in trade and agricultural production, agricultural price supports and subsidies in developed nations, diversions of food commodities to high input foods and fuel, commodity market speculation, and climate change.