<Li> Ravallion--Unusually high mortality with unusually severe threat to food intake of some segments of a population . </Li> <Li> Cuny--A set of conditions that occurs when large numbers of people in a region cannot obtain sufficient food, resulting in widespread, acute malnutrition . </Li> <P> Food shortages in a population are caused either by a lack of food or by difficulties in food distribution; it may be worsened by natural climate fluctuations and by extreme political conditions related to oppressive government or warfare . The conventional explanation until 1981 for the cause of famines was the Food availability decline (FAD) hypothesis . The assumption was that the central cause of all famines was a decline in food availability . However, FAD could not explain why only a certain section of the population such as the agricultural laborer was affected by famines while others were insulated from famines . Based on the studies of some recent famines, the decisive role of FAD has been questioned and it has been suggested that the causal mechanism for precipitating starvation includes many variables other than just decline of food availability . According to this view, famines are a result of entitlements, the theory being proposed is called the "failure of exchange entitlements" or FEE . A person may own various commodities that can be exchanged in a market economy for the other commodities he or she needs . The exchange can happen via trading or production or through a combination of the two . These entitlements are called trade - based or production - based entitlements . Per this proposed view, famines are precipitated due to a breakdown in the ability of the person to exchange his entitlements . An example of famines due to FEE is the inability of an agricultural laborer to exchange his primary entitlement, i.e., labor for rice when his employment became erratic or was completely eliminated . </P> <P> According to the Physicians for Social Responsibility (PSR), global climate change is additionally challenging the Earth's ability to produce food, potentially leading to famine . </P>

What is one of the main causes for famine in the world today