Climate Change and Agriculture: What Research Shows About Food Security Risks

Climate change poses documented and growing risks to agricultural systems that provide the food supply for global populations. Research on how rising temperatures, shifting precipitation patterns, more frequent drought and flood events, and increased atmospheric carbon dioxide are affecting crop yields, livestock production, fisheries, and food security has grown rapidly alongside the urgency of the climate challenge. Understanding what the evidence shows about agriculture's vulnerability and adaptation capacity is essential for policy responses that protect food security in a warming world. Crop yield research represents one of the most extensively studied dimensions of climate and agriculture. Studies using field experiments, historical yield data, and crop models find that yields for major staple crops including wheat, rice, maize, and soybeans decline as temperatures rise above crop-specific thresholds. For maize, a degree Celsius increase in average growing season temperature is associated with yield declines of approximately 7 percent in recent meta-analyses, with variation depending on geography, growing conditions, and adaptation measures. Wheat and rice show similar sensitivities to temperature increases at critical developmental stages including flowering. These yield sensitivities are not uniformly distributed: some higher-latitude regions may initially benefit from warmer temperatures as growing seasons lengthen, while tropical and subtropical regions that are already near crop temperature optima face the most severe impacts. Elevated atmospheric carbon dioxide, which drives climate change, also has direct effects on plant physiology. Higher CO2 concentrations stimulate photosynthesis in some crops, a fertilization effect that can partially offset temperature-related yield losses. However, research on food composition under elevated CO2 finds that higher CO2 reduces protein and micronutrient concentrations in crops including wheat and rice, raising nutritional quality concerns that are additional to yield effects. The net effect of CO2 on agricultural systems is complex and context-specific. Extreme weather events are becoming more frequent and severe as a consequence of climate change, and their effects on agriculture are documented in research. Drought reduces crop yields through water stress at critical growth stages. Flooding damages crops directly and through waterlogging of soils. Heat waves at critical reproductive stages can cause crop failure even when growing season temperatures are otherwise manageable. Research on the relationship between extreme weather frequency and agricultural production finds increasing variance in yields, which undermines the predictability that food systems and markets require. Agricultural adaptation to climate change is an active research area. Crop breeding that develops heat-tolerant and drought-tolerant varieties, changes in planting dates to avoid critical weather periods, diversification of crops and cropping systems, irrigation infrastructure, and cover crops and other soil health practices are adaptation strategies with documented effectiveness in specific contexts. Research on adaptation potential finds that some combination of these approaches can significantly reduce projected yield losses, but that full offset of climate impacts is unlikely without more fundamental technological innovation. Food security for the most vulnerable populations is the dimension of climate and agriculture research that researchers emphasize as most urgent. The populations most at risk from climate-related agricultural disruption are those in tropical and subtropical regions with limited economic and institutional capacity to adapt, who also are often those with the fewest historical contributions to greenhouse gas emissions. Research on climate change and food security finds that the combination of yield losses, increased food price volatility, and reduced nutritional value of crops could increase the number of people experiencing food insecurity substantially by mid-century under high-warming scenarios. Livestock agriculture is affected by climate change through multiple pathways. Higher temperatures reduce feed conversion efficiency and animal productivity and increase disease risk and mortality during heat events. Pasture and feed crop availability is affected by the same temperature and precipitation changes that affect crop agriculture. Research on livestock systems under climate change finds that heat stress already reduces productivity in many regions and that warming will increase this stress substantially, with tropical and subtropical livestock systems facing the most severe challenges. Fisheries and aquaculture are also affected by climate change through ocean warming, acidification, and deoxygenation. Research on marine fisheries finds that warming is causing range shifts in commercially important fish populations, moving them toward higher latitudes and depths. Acidification reduces the ability of marine organisms including shellfish and coral to form calcium carbonate shells and skeletons, threatening aquaculture production and the marine ecosystems that support wild fisheries. Research on freshwater fisheries finds similar disruption from warming temperatures and altered stream flows. The research on climate change and agriculture supports the conclusion that the risks to food security are real, growing, and unevenly distributed, with the greatest vulnerabilities in the communities with the least capacity to adapt. Responses require both mitigation of greenhouse gas emissions to limit the ultimate magnitude of climate change and adaptation investments to reduce the vulnerability of agricultural systems and the communities that depend on them to the changes that are already locked in by past emissions.