Effects of climate change on agriculture

• 1. Introduction

  ›

  Effects of climate change on agriculture represent one of the most consequential intersections of planetary science and human survival. Between 1961 and 2021, global agricultural productivity could have been 21% greater than it actually was, if it had not been hampered by a warming world. That figure sits in the background of every harvest, every food price spike, every aid shipment to a drought-stricken region. What forces are slowly eroding the world's capacity to feed itself? How do warming temperatures, shifting rainfall, and a sky increasingly thick with carbon dioxide quietly reshape the fields that feed eight billion people? And who bears the heaviest burden when those fields begin to fail?

  The stakes are not abstract. In 2021, between 720 million and 811 million people were classified as undernourished globally. Among them, 200,000 were at a catastrophic level of food insecurity. Climate change is projected to add between 8 and 80 million more people to that count by 2050. The range is wide because the future depends on choices being made right now, choices about emissions, adaptation, trade, and investment. The answers will be written in crop yields and food prices for decades to come.

• 2. When the Weather Turns

  ›

  Australia's farmers are very likely to suffer losses during El Nino weather conditions, a pattern that illustrates how deeply agriculture is tied to climate variability. Extreme weather has always threatened harvests, but climate change is tilting the odds in a dangerous direction. The 2003 European heat wave led to 13 billion euros in uninsured agricultural losses. In West Africa, climate-intensified extreme weather has already decreased millet yields by 10-20% and sorghum yields by 5-15%. In Southern Africa, climate change intensified the 2007 drought, triggering acute food insecurity in Lesotho.

  In Europe, heat extremes grew more frequent between 1950 and 2019, while cold extremes declined. The severity of heatwave and drought effects on European crop production tripled over a 50-year period, from losses of 2.2% during 1964-1990 to losses of 7.3% in 1991-2015. Floods add a separate layer of damage. In May 2019, floods shortened the corn planting season in the Midwestern United States, cutting the projected yield from 15 billion bushels to 14.2 billion. In China, research published in 2023 found that extreme rainfall had cost the country about 8% of its rice output over the two preceding decades, a loss considered comparable to those caused by extreme heat over the same period.

  One of the more alarming possibilities is synchronized crop failures, where extreme climate events strike multiple major producing regions simultaneously. Analysis of historic data has already found synchronized climate events associated with up to 20% yield losses. If every region with a synchronized growing season were to experience crop failure at the same time, losses to the four major crops could reach 17-34%. A ban on staple crop exports from Russia, Thailand, and the United States alone would place around 200 million people, 90% of them from Sub-Saharan Africa, at risk of starvation.

• 3. The Four Crops That Feed the World

  ›

  Corn (maize), rice, wheat, and soybeans sit at the center of every serious assessment of agricultural risk from climate change. The three cereals together account for half of total human calorie intake, and together with soybeans, they account for two thirds. These are the crops that researchers have studied most intensively, and the findings are sobering.

  Maize is considered the most vulnerable to warming of the four. One meta-analysis concluded that every 1 degree Celsius of global warming reduces maize yields by 7.4%. Maize is also a C4 plant, meaning it gains little benefit from elevated carbon dioxide. Under the high-emission SSP5-8.5 scenario, the most advanced models project a global decline in maize yields of 24% by 2100. When temperatures rise above 36 degrees Celsius, corn pollen loses its vitality entirely.

  Wheat tells a more complicated story. Temperature changes alone are expected to reduce annual wheat yields by 6% per degree Celsius of global warming, but precipitation and the carbon dioxide fertilization effect benefit wheat more than other crops. Updated modelling results published in November 2021 indicated that under the highest-warming scenario, global wheat yields could actually increase by 18% by 2100. In Iran, however, scenarios modelling a temperature increase of up to 2.5 degrees Celsius and a rainfall decrease of up to 25% project wheat yield losses of as much as 45% in temperate areas and over 50% in hot-arid areas.

  Rice presents a third pattern. Temperature changes alone reduce global rice yields by 3.2% per degree Celsius of warming, but climate effects on rice in East Asia had been a net positive as of 2021. As of that year, global projections for rice were less consistent than those for wheat and maize, and less able to identify a clear trend. The 2024 comprehensive review by Yuan et al. summed it up plainly: under high-emission scenarios without adaptation, the combined effects of rising temperatures, altered precipitation, and increased evapotranspiration are projected to reduce yields of all four staple cereals by approximately 5-10% by mid-century.

• 4. The Fertilization Mirage

  ›

  Higher concentrations of atmospheric carbon dioxide do stimulate plant growth. In C3 plants such as wheat, oats, and rice, CO2 fertilization usually more than doubles the initial stimulation of photosynthesis, increasing carbon assimilation and vegetative growth. Elevated CO2 also causes partial stomatal closure, reducing water loss and improving water-use efficiency under drought stress. This has been demonstrated in Free-Air CO2 Enrichment (FACE) trials designed to mimic predicted future atmospheric conditions.

  However, the benefits come with a significant catch. Changes in atmospheric carbon dioxide reduce the nutritional quality of the very crops it helps grow. Food crops could see a reduction of protein, iron, and zinc content of 3-17%, projected at the carbon dioxide levels expected by 2050. A 2014 meta-analysis found that crops and wild plants exposed to elevated CO2 had lower concentrations of magnesium, iron, zinc, and potassium. Doubling CO2 levels results in an average 8% decline in the concentration of minerals. At those same conditions, plants contain 6% more carbon, 15% less nitrogen, 9% less phosphorus, and 9% less sulfur. The increase in carbon comes largely from calorie-providing starch and simple sugars, while the nitrogen decrease translates directly into lower protein content.

  Some two billion people live in countries where citizens receive more than 60% of their zinc or iron from crops like wheat, rice, peas, and soybeans. Deficiencies of these nutrients already cause an estimated loss of 63 million life-years annually. The CO2 fertilization effect also cancels out most of itself: a 2016 estimate found that ozone increases alone caused yield losses of 5±1.5% in the four major crops, which nearly cancelled out the fertilization effect of 6.5±1.0%. For C4 crops like maize, which accounts for a large share of global calories, CO2 fertilization has little effect to begin with.

• 5. Pests, Pathogens, and Shifting Boundaries

  ›

  Historically, cold temperatures at night and in winter months killed off insects, bacteria, and fungi before they could spread too widely. A warmer world removes that check. The warmer, wetter winters are promoting fungal plant diseases like wheat rust (stripe and brown/leaf) and soybean rust to travel northward. A 1 degree Celsius increase in global temperature could result in a 10-25% decline in crop yields due to pest growth alone, according to some estimates.

  Currently, pathogens result in losses of 10-16% of the global harvest, and this level is likely to rise. Soybean rust is one notable example: it can kill off entire fields in a matter of days. Insect pests are also gaining territory. The potato tuber moth and Colorado potato beetle are predicted to spread into areas currently too cold for them. The Mountain Pine Beetle epidemic in British Columbia, Canada killed millions of pine trees partly because winters were not cold enough to slow the growing larvae. The 2019-2022 locust infestation focused on East Africa was considered the worst of its kind in many decades.

  The fall armyworm, Spodoptera frugiperda, is a highly invasive pest capable of massive damage to maize crops. Its recent spread to countries in sub-Saharan Africa has been linked to climate change, and it is expected to spread further. Around 9% of agricultural production depends in some way on insect pollination, and wild bumblebees are known to be particularly vulnerable to recent warming. Bacteria like Salmonella and fungi that produce mycotoxins grow faster as the climate warms, adding food safety risks on top of yield losses.

• 6. Land, Water, and the Ground Beneath

  ›

  Approximately 2.4 billion people live in the drainage basin of the Himalayan rivers. In India alone, the Ganges provides water for drinking and farming for more than 500 million people. In the Indus River watershed, mountain water resources contribute to up to 60% of irrigation outside of the monsoon season, and an additional 11% of total crop production. Glaciers have been retreating since 1850, and that retreat is expected to continue. Global warming of 1.5 degrees Celsius will reduce the ice mass of Asia's high mountains by about 29-43%.

  Beyond glacial retreat, climate change is reshaping the water cycle in ways that simultaneously threaten both floods and droughts. Under the probable mid-range climate change scenario, SSP2-4.5, precipitation events globally will become larger by 11.5%, yet the time between them will increase by an average of 5.1%. The 2020-2023 Horn of Africa drought has been primarily attributed to a great increase in evapotranspiration exacerbating the effect of persistent low rainfall, conditions that would have been more manageable in the cooler preindustrial climate.

  On the coasts, low-lying areas such as Bangladesh, India, and Vietnam face major losses of rice cropland if sea levels rise as expected by the end of the century. Vietnam relies heavily on its southern tip, where the Mekong Delta lies, for rice planting. A one-metre rise in sea level will cover several square kilometres of rice paddies there. An estimated 15% of the US coastline already has the majority of local groundwater below sea level, making saltwater intrusion into freshwater wells a present-day concern.

  Soil itself is under pressure. Increased erosion in agricultural landscapes from anthropogenic factors can cause losses of up to 22% of soil carbon in 50 years. Warmer conditions could cause the soil microbe population size to increase dramatically, by 40-150%. A 2005 study reported that temperatures in Siberia had increased by three degrees Celsius on average since 1960, more than anywhere else on Earth, raising conflicting expectations for Russian agriculture: a northward extension of farmable land but also possible productivity losses and increased drought risk.

• 7. Who Bears the Cost

  ›

  Global agricultural productivity growth has improved food security for hundreds of millions of people, and the Green Revolution increased yields per unit of land area by between 250% and 300% since 1960. Yet between 1961 and 2021, global productivity could have been 21% greater without the counteracting role of climate change. The burden of that lost potential falls unevenly.

  Over 70% of people in the Asian region depend on agriculture for their livelihood; it employs nearly 60% of the workforce and provides 22% of the gross domestic product of the area. In India, agriculture makes up 52% of employment. Latin American production is concentrated: Brazil, Mexico, and Argentina alone contribute 70-90% of the total agricultural output in the region. In Mexico, only 21% of farms are irrigated, leaving 79% dependent on rainfall, making them especially exposed to the erratic spring rains that have plagued Central America from 2009 to 2019.

  A 2016 modelling study suggested that by mid-century, the most intense climate change scenario would reduce per capita global food availability by 3.2%, with 529,000 people projected to die between 2010 and 2050 as a result, primarily in South Asia and East Asia. Two-thirds of those deaths would be caused by the lack of micronutrients from reduced fruit and vegetable supply, not outright starvation. One estimate suggests that warming of 3 degrees Celsius relative to late 20th century temperatures would cause labour capacity in Sub-Saharan Africa and Southeast Asia to decline by 30-50%, with some workers potentially exposed to dangerous heat stress on up to 250 days per year. That lost labour capacity could push crop prices up by around 5%, a cost passed directly to the most food-insecure populations.

  The IPCC Sixth Assessment Report from 2022 confirmed that nearly all of the 8 to 80 million additional people at risk of hunger by 2050 will be concentrated in Sub-Saharan Africa, South Asia, and Central America. A 2025 systematic review found that without effective adaptation measures, climate change could reduce global agricultural food production by up to 14% by 2050. A 2026 joint report by the Food and Agriculture Organization and the World Meteorological Organization identified 25 degrees Celsius as a critical temperature threshold beyond which crop yields begin to decline significantly, with effects on harvests and food prices persisting for up to a year.