We modelled one plausible estimate of a 10 percent decline in crop yields due to climate change without adaptation. Cropland would need to expand overall by 457 million hectares (increasing the total land gap by 45 percent). Climate change will benefit some crops, at least in the short term, as higher concentrations of carbon dioxide increase the efficiency of photosynthesis. Warmer temperatures will extend the growing season in colder countries and regional shifts in rainfall patterns will make some locations wetter.
Some areas, though, will become drier and hotter. Higher temperatures will harm crops by drying soils, accelerating water loss, and increasing pest damage. Extreme heat events will harm maize, wheat, coffee, and many other crops by interfering with reproduction. Growing seasons in parts of sub-Saharan Africa could become too short or too irregular to support crops, contributing to major food security concerns. The evidence from crop models indicates significant but uncertain capacity to adapt using tailored crop varieties. Uncertainties about local climate change suggest broad “no regrets” strategies. For example, closing yield gaps in Africa and India would increase incomes and provide a buffer against adverse climate impacts, forest protection could increase resilience through improved local hydrology, while safety-net programmes for the rural poor will better equip small farmers to deal with future variability.
Some climate effects, however, are sufficiently clear to emphasize the need for new measures or expanded effort on other menu items.
Farmers need effective regional crop-breeding systems that enable them to select alternative crop varieties specifically adapted to local conditions. Small-scale irrigation and water conservation systems will help farmers cope with rainfall variability. Research organizations and companies must breed new traits to overcome highly likely big climate challenges such as high temperature effects on maize, wheat, rice, and coffee. Finally, governments must help fund adaptation to those major physical changes that are clearly predictable, such as altering production systems in areas that will be affected by sea level rise.