Likelihood (in percent) that future summer average temperatures will exceed the highest summer temperature observed on record (A) for 2050 and (B) for 2090. For example, for places shown in red there is greater than a 90% chance that the summer-averaged temperature will exceed the highest temperature on record (1900–2006).

David. S. Battisti1 and Rosamond L. Naylor2 Higher growing season temperatures can have dramatic impacts on agricultural productivity, farm incomes, and food security. We used observational data and output from 23 global climate models to show a high probability (>90%) that growing season temperatures in the tropics and subtropics by the end of the 21st century will exceed the most extreme seasonal temperatures recorded from 1900 to 2006. In temperate regions, the hottest seasons on record will represent the future norm in many locations. We used historical examples to illustrate the magnitude of damage to food systems caused by extreme seasonal heat and show that these short-run events could become long-term trends without sufficient investments in adaptation. 1 Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195–1640, USA. E-mail: battisti@washington.edu
2 Program on Food Security and the Environment, Stanford University, Stanford, CA 94305–6055, USA. E-mail: roz@stanford.edu The food crisis of 2006–2008 demonstrates the fragile nature of feeding the world’s human population. Rapid growth in demand for food, animal feed, and biofuels, coupled with disruptions in agricultural supplies caused by poor weather, crop disease, and export restrictions in key countries like India and Argentina, have created chaos in international markets (1). Coping with the short-run challenge of food price volatility is daunting. But the longer-term challenge of avoiding a perpetual food crisis under conditions of global warming is far more serious. History shows that extreme seasonal heat can be detrimental to regional agricultural productivity and human welfare and to international agricultural markets when policy-makers intervene to secure domestic food needs. We calculated the difference between projected and historical seasonally averaged temperatures (2) throughout the world by using output from the 23 global climate models contributing to the Intergovernmental Panel on Climate Change’s (IPCC) 2007 scientific synthesis (3). Our results show that it is highly likely (greater than 90% chance) that growing season temperatures by the end of the 21st century will exceed even the most extreme seasonal temperatures recorded from 1900 to 2006 for most of the tropics and subtropics. Presently there are more than 3 billion people living in the tropics and subtropics, many of whom live on under $2 per day and depend primarily on agriculture for their livelihoods (4). With growing season temperatures rising beyond historical bounds, the inevitable question arises: Will people in these regions have sufficient access to food to meet population- and income-driven growth in demand in the future, and thus to achieve food security?

Historical Warnings of Future Food Insecurity with Unprecedented Seasonal Heat