Changes in the global production of major crops are important drivers of food prices, food security and land use decisions. Average global yields for these commodities are determined by the performance of crops in millions of fields distributed across a range of management, soil and climate regimes. Despite the complexity of global food supply, here we show that simple measures of growing season temperatures and precipitation--spatial averages based on the locations of each crop--explain about 30% or more of year-to-year variations in global average yields for the world's six most widely grown crops. For wheat, maize, and barley, there is a clearly negative response of global yields to increased temperatures. Based on these sensitivities and observed climate trends, we estimate that warming since 1981 has resulted in annual combined losses of these three crops representing roughly 40 MT or $5 billion per year, as of 2002. While these impacts are small relative to the technological yield gains over the same period, the results demonstrate already occurring negative impacts of climate trends on crop yields at the global scale.

A concept note about setting up an international program for studying the effects of the emergence of biofuels on global poverty and food security. 

The recent global expansion of biofuels production is an intense topic of discussion in both the popular and academic press. Much of the debate surrounding biofuels has focused on narrow issues of energy efficiency and fossil fuel substitution, to the exclusion of broader questions concerning the effects of large-scale biofuels development on commodity markets, land use patterns, and the global poor. There is reason to think these effects will be very large. The majority of poor people living in chronic hunger are net consumers of staple food crops; poor households spend a large share of their budget on starchy staples; and as a result, price hikes for staple agricultural commodities have the largest impact on poor consumers. For example, the rapidly growing use of corn for ethanol in the U.S. has recently sent corn prices soaring, boosting farmer incomes domestically but causing riots in the streets of Mexico City over tortilla prices. Preliminary analysis suggests that such price movements, which directly threaten hundreds of millions of households around the world, could be more than a passing phenomenon. Rapid biofuels development is occurring throughout the developed and developing world, transforming commodity markets and increasingly linking food prices to a volatile energy sector. Yet there remains little understanding of how these changes will affect global poverty and food security, and an apprehension on the part of many governments as to whether and how to participate in the biofuels revolution.

We propose an international collaborative effort to:

• Understand and quantify the effects of expanding biofuels production on agricultural commodity markets, food security, and poverty;
• Develop training programs and policy tools to harness the benefits and mitigate the damages from such expansion on both local and global scales; and
• Build an international network of scholars and government officials devoted to studying and managing biofuels development and its social consequences

Most research on the agricultural impacts of climate change has focused on the major annual crops, yet perennial cropping systems are less adaptable and thus potentially more susceptible to damage. In regions where perennial crops are economically and culturally important, improved assessments of yield responses to future climate are needed to prioritize adaptation strategies. These impact assessments, in turn, must rely on climate and crop models that contain often poorly defined uncertainties. We evaluated the impact of climate change on six major perennial crops in California: wine grapes, almonds, table grapes, oranges, walnuts, and avocados. Outputs from multiple climate models were used to evaluate climate uncertainty, while multiple statistical crop models, derived by resampling historical databases, were used to address crop response uncertainties. We find that, despite these uncertainties, climate change in California is very likely to put downward pressure on yields of almonds, walnuts, avocados, and table grapes by 2050. Without CO2 fertilization or adaptation measures, projected losses range from 0 to >40% depending on the crop and the trajectory of climate change. Climate change uncertainty generally had a larger impact on projections than crop model uncertainty, although the latter was substantial for several crops. Opportunities for expansion into cooler regions were identified, but this adaptation would require substantial investments and may be limited by non-climatic constraints. Given the long time scales for growth and production of orchards and vineyards (30 years), climate change should be an important factor in selecting perennial varieties and deciding whether and where perennials should be planted.