Motivation The need for action is pressing in order to feed the expanding human population, expected to increase by almost one billion people per decade for the next three decades at least. Much of this increase will occur in developing countries in the low-latitude regions of the world. To meet the associated food demand, crop yields will need to increase, consistently, by over 2% every year through this period. Most research on agriculture and climate change has focused on potential impacts on regional and global food production, yet few studies have considered how global warming may affect food security. Food security has been defined as access by all people at all times to enough food for an active, healthy life. (World Bank, 1986).

The World Food Summit, convened in 1996 by the Food and Agriculture Organization of the United Nations in Rome, highlighted the basic right of all people to an adequate diet and the need for concerted action among all countries to achieve this goal in a sustainable manner (FAO, 1996). The overall world production changes mask a disparity in response to climate change between developed and developing countries. The largest negative changes are predicted to take place in developing regions, although the extent of decreased production varies greatly from country to country, depending on the specific nature and degree of the local change in climate. The welfare effects of climate change on individual countries will not only depend upon changes in domestic yields, but also on changes in world prices, and the country's relative strength as an exporter and importer. Cereal-price increases resulting from climate-induced reductions in yield are estimated to range between 24 and 145%.The combination of production declines in developing countries and increases in prices due to climate change would increase the number of people at risk of hunger.

Furthermore, the results show that adaptation strategies do little to reduce these disparate effects. This is due to the fact that developed countries have many more resources to utilize in adaptation strategies than do developing countries. Globally, both minor and major levels of adaptation can help restore world production levels (especially when CO2 physiological effects are included), compared to climate change scenarios with no adaptation. Low level adaptation largely offsets the negative climate change effects on yields in developed countries, thus improving their comparative advantage in world markets.

However, developing countries are predicted to benefit little from this level of adaptation, and may experience a negative change of -9% to -12% in cereal production. More intensive adaptation may effectively eliminate the overall global reduction of cereal yields. Whereas under low adaptation cereal price increases range from 10 to almost 100%, under more intensive adaptation the compounding price responses range from a decline of 5% to an increase of 35%. Not only do preliminary analyses of direct effects of global warming indicate greater adverse effects in poor countries, but these same countries are less able to achieve the changes required for adapting. Less developed countries also tend to have less developed capital markets, with access for farmers being a pervasive and chronic problem for many.

High interest rates are common even where loans for the agricultural sector can be obtained.If the needed adjustments require investment, these factors will slow or eliminate farmers' ability to adapt. Alternative assumption -lowering of trade barriers, low economic growth, and low population growth- were tested both in the absence and in the presence of climate change. Without climate change, the combination of full trade liberalization and low population growth would have beneficial effects on the world food system, whereas the effects of low economic growth would be detrimental.

With climate change, the beneficial effects of full trade liberalization and low population growth would be equal to or even exceed the otherwise adverse effects of climate change. Therefore, there may be much to be gained from altering the conditions of trade and development as a strategy for helping to mitigate potentially negative climate change impacts.In the absence of such measures, cereal production would tend to diminish, particularly in the developing world, while prices and population at risk of hunger would increase due to climate change. The unequal distributional aspects of climate change are further supported by differences in income level (poor peasants have a higher degree of risk aversion, they are likely to use fewer purchased inputs and to be less able to make large purchases of equipment; the premium put on assuring minimal levels of production of needed food crops may inhibit rapid shifts in farming systems), access to credit and possibility for diversification (monoculture producers in vulnerable areas -tropical developing countries- will be more heavily affected). Given a presumption of adverse effects in tropical areas, developing countries can expect a slowdown of growth and a decrease in agricultural incomes.

Given the large percentage of the labour force engaged in agriculture in low income countries, this effect is likely to increase overall income inequality within countries. Urban-rural disparities would also increase with resulting increases in urban migration and overcrowding. How, then, may climate change alter the ability of the world's growing population to gain access to food? For subsistence farmers and people who now face a shortage of food, lower yields and yield quality, when and if they occur, may result not only in measurable economic losses but also, indeed, in malnutrition and possibly famine. A compendium of recent work on this topic is found in Downing (1995) Vulnerability to famine is a complex concept that integrates environmental, social, economic, and political aspects.

Groups most vulnerable to climate change in regard to food security may be those who are most exposed to the risk of climate change impacts on crop productivity and changes in commodity prices, with the least capacity to cope with unfavorable changes in agricultural conditions and to access food, and therefore, prone to suffer the severest consequences of famine, malnutrition, and debility. Groups vulnerable to hunger in the present, and likely to be vulnerable to climate change effects in the future, include rural smallholder farmers, pastoralists, wage laborers, urban poor, refugees, and other destitute groups. Of these, the most vulnerable to the negative effects of climate change are probably rural subsistence farmers, landless wage earners, and urban poor: they have little food security now and therefore are susceptible to even small changes in agroclimatic circumstances or economic status (Bohle et al., 1994).

For households that both raise food and work off the farm, climate change may affect the time for crop planting, but this may conflict with critical off-farm employment. In the Basic Linked System, the number of people at risk of hunger was defined as those people in developing countries (excluding China) with an income insufficient to either produce or procure their food requirements. The BLS estimates that with climate change, declines in yields in low-latitude regions are projected to require that net imports of cereals increase under all scenarios tested.Higher grain prices will affect the number of people at risk of hunger. For the climate change scenarios without adaptation, their estimated number increases 1% for each 2-2.5% increase in prices.

The number of people at risk of hunger grows by 10-60% in the scenarios tested, resulting in an estimated increase of between 60 million and 350 million people in this condition, by 2060. With less agricultural production in developing countries and higher prices for foodstuffs on international markets, the estimated number of people at risk of hunger will inevitably increase. The largest increase occurs with a global mean surface temperature rise of 50C and with no beneficial physiological effects of CO2 on crop growth and yield.The smallest change, a decline of 2%, is seen to occur with a 40C warming, full CO2 physiological effects on yields, and high levels of farmer adaptation. As a consequence of climate change and adaptation level 1, the number of people at risk of hunger increases by 40-300 million (6-50%) from the reference scenario of 641 million people.