Impacts of climate change on food production David B. Lobell Aug 6, 2008 dlobell@stanford.edu

Future CO2 for several emission scenarios A1b 2 x pre-industrial B1

Projections for average global temperatures IPCC, 2007

Average climate model projections of soil moisture change by 2080 IPCC, 2007

What will this mean for the crops we depend on? Photosynthesis: CO2 + H20  sugar + O2 Most photosynthesis is called C3, but some plants have developed a mechanism to avoid photorespiration by concentrating CO2 in the leaf interior. This makes them more productive in very hot and sunny conditions, and less sensitive to changes in CO2 C3 crops: wheat, rice, soybean, barley, and most others C4 crops: maize (corn), sorghum, millet, sugarcane.

Measuring the CO2 fertilization effect FACE: Free-air CO2 enrichment (Long et al. 2006)

Summary so far 1) Higher CO2 will help crop yields, more so for C3 crops than C4 crops

Direct effects of climate change The main effects of warming: -faster rates of development (see below) -faster rates of photosynthesis and respiration -higher rates of evapotranspiration (important in dry regions) -fewer frosts (important in cold regions) “birth” “adolescensce” “adulthood” “death” In a cooler year, this process can take ~10 days longer than in warmer year, which means 10 or more days to photosynthesize

Direct effects of climate change -So warming can have some positive and some negative effects. -The net balance differs depending on crop and location -Overall, crops in most regions prefer cooler temperatures Average Global Yields vs. temperatures, 1961-2002 Yield Change (%) Temperature Change (ºC)

Summary so far Higher CO2 will help crop yields, more so for C3 crops than C4 crops Warming will reduce yields in most locations Precipitation changes will be important in some areas, but projections of future precipitation are very uncertain.

Human responses to climate change Farmers and scientists are not dumb In response to these pressures, people are likely to adapt. Two main types of adaptations Trade Management changes

Human responses to climate change Trade Cool nations “win” Warm nations “lose” One example of estimated impacts for 2x CO2 (from Cline 2007)

Human responses to climate change 2) Management changes Red = no management changes Green = “adaptation” IPCC, 2007

Summary so far Higher CO2 will help crop yields, more so for C3 crops than C4 crops Warming will reduce yields in most locations Precipitation changes will be important in some areas, but projections of future precipitation are very uncertain. Adaptation will help to reduce impacts on global food production, assuming that poorer countries can afford to import food, that the right investments are made in new technologies, and that farmers implement adaptations quickly enough to avoid big losses. (Three big assumptions) In tropical countries, impacts could be quite large (up to 50% losses) even in 20 years For the globe, impacts are most likely small until ~2050 or 2xCO2. But if CO2 levels go much higher than 550 ppm, then effects could be quite large.

Future CO2 for several emission scenarios A1b 2 x pre-industrial B1