Date Published: May 31, 2019
Publisher: Public Library of Science
Author(s): Deepak K. Ray, Paul C. West, Michael Clark, James S. Gerber, Alexander V. Prishchepov, Snigdhansu Chatterjee, Young Hoon Jung.
Crop yields are projected to decrease under future climate conditions, and recent research suggests that yields have already been impacted. However, current impacts on a diversity of crops subnationally and implications for food security remains unclear. Here, we constructed linear regression relationships using weather and reported crop data to assess the potential impact of observed climate change on the yields of the top ten global crops–barley, cassava, maize, oil palm, rapeseed, rice, sorghum, soybean, sugarcane and wheat at ~20,000 political units. We find that the impact of global climate change on yields of different crops from climate trends ranged from -13.4% (oil palm) to 3.5% (soybean). Our results show that impacts are mostly negative in Europe, Southern Africa and Australia but generally positive in Latin America. Impacts in Asia and Northern and Central America are mixed. This has likely led to ~1% average reduction (-3.5 X 1013 kcal/year) in consumable food calories in these ten crops. In nearly half of food insecure countries, estimated caloric availability decreased. Our results suggest that climate change has already affected global food production.
Previous assessments of climate change impact on crop yields commonly combine future climate scenarios and process-based crop models to project future yields for a limited number of crops for 2050 or later [1–4]. At higher levels of warming, strong yield losses are predicted in lower latitudes especially for maize and wheat crops . Although these results provide insights into long-term future changes, there are large uncertainties in both the modeled climate projections  and in the crop model parameters [6–8]. Hence, the distant time horizon, small number of crops, and coarse resolution limit the results’ utility for stakeholders and policy makers to develop goals and strategies.
The Intergovernmental Panel for Climate Change—Assessment Report (AR) 5  (IPCC AR5) on climate change impact on crop yield/production notes that between the AR4 and AR5 the required connection of climate change impact to food security impact was missing. Our study directly addresses this by translating the potential impact of recent climate change on crop yields (Fig 1) to consumable food calories change in each country (Table 1, S4 Table). While translating crop production change to consumable food caloric change, we accounted for the current dietary consumption pattern of individual crops per country, including bookkeeping for directly and indirectly consumed calories in each country . We found that out of the studied 53 countries with a hunger index of serious, alarming, or seriously alarming  in 2008, 27 countries (or ~51%) had decreased consumable calories due to mean climate changes (~ -0.4% in these ten crops or ~ -0.3% across all food calories consumed across all 53 countries studied–S4 Table). Though we detected subnational level crop yield and production changes (Fig 1), determining consumable food caloric changes at that level would require data not available globally: subnational dietary patterns, evaluation of the climate change impact in the entire food supply chain  and socio-economic conditions . These individual issues should be explored in future studies to understand mean climate change impacts on local scale food security.