Rome - Extreme heat events currently threaten the livelihoods and health of over a billion people, causing half a trillion work hours to be lost annually, with the prospect for damage to livestock herds and crop yields set to soar higher in the future. Agricultural workers and agrifood systems are on the frontlines, absorbing the greatest impacts from extreme heat.
The frequency, intensity and duration of extreme heat events have risen sharply over the past half century, with worrying impacts on agrifood systems and landscapes, according to "Extreme heat and agriculture," a new report from the Food and Agriculture Organization of the United Nations (FAO) and the World Meteorological Organization (WMO).
Extreme heat refers to situations where daytime and nighttime temperatures rise above their usual ranges for a protracted period, leading to physiological stress and direct physical damages to food crops, livestock, fish, trees and human beings.
The report examines how extreme heat ripples through agricultural systems and how heatwaves can interact with other climatological variables, including rain, solar radiation, humidity, wind and drought - to trigger compound effects that wreak havoc on individuals and entire ecosystems.
"This work highlights how extreme heat is a major risk multiplier, exerting mounting pressure on crops, livestock, fisheries and forests, and on the communities and economies that depend upon them." said FAO Director-General QU Dongyu.
"Extreme heat is increasingly defining the conditions under which agrifood systems operate," said WMO Secretary-General Celeste Saulo. More than simply an isolated climatic hazard, it acts "as a compounding risk factor that magnifies existing weaknesses across agricultural systems."
The joint FAO-WMO report's sections describe the physical science of extreme heat, the vulnerabilities, observed and projected impacts on agriculture, adaptation strategies, case studies, and offer policy recommendations.
Plants, animals, fish, trees and humans
The impact of extreme heat events is relative to the context of when and where they occur. The report cites how in the spring of 2025, a part of Kyrgyzstan's Fergana mountain range endured a protracted stretch of 30.8 degrees Celsius, 10 degrees higher than usual. This caused a thermal shock on fruit and wheat crops, contributing to a locust outbreak, heightened evaporation that reduced irrigation capacity, and eventually a 25 percent decline in cereal harvests.
Rising average global temperatures and more frequent and intense extreme heat events narrow the "thermal safety margin" species rely on for biological processes that support photosynthesis, cellular regeneration, reproduction and ultimately staying alive. Extreme heat intensity roughly doubles at 2 degrees Celsius of global warming, and quadruples at 3 degrees, relative to 1.5 degrees increase in average global temperatures, according to the report.
For the most common livestock species, stress begins at above 25 degrees Celsius, and a bit lower for chickens and pigs, which are unable to cool themselves by sweating. Above that threshold, animals begin to suffer, initially seeking shade, drinking more water, eating and moving less, while if exposure persists, they begin to suffer from digestive tract breakdowns, organ failure and cardiovascular shock. Even when not lethal, extreme heat reduces dairy yields as well as fat and protein content - which inter alia worsens the carbon footprint of animal-sourced foods. Fish can suffer cardiac failure as they struggle to maintain elevated respiration rates in waters where extreme heat events drive dissolved oxygen levels lower. In 2024, 91 percent of the global ocean experienced at least one marine heatwave.
For most major agricultural crops, yield declines begin to occur above 30 degrees Celsius -lower for some crops such as potatoes and barley - leading to weakened cell walls, sterile pollens and the production of toxic oxidative compounds. Under extreme temperatures rates of tree photosynthesis and respiration diverge, creating an energy imbalance, resulting in reduced growth and less carbon removal from the atmosphere. Evidence points to a strong correlation between heat waves and wildfires, with longer and more intense fire seasons.
Critically extreme heat also takes a toll on humans, especially agricultural laborers, for whom it can be fatal. The number of days each year when it is simply too hot to work may rise to 250 in much of South Asia, tropical Sub-Saharan Africa and parts of Central and South America, according to the report.
Compound effects
The full danger of extreme heat lies not only in its direct impacts, but also in its role as a risk multiplier, amplifying the effect of water stress, serving as a trigger of flash droughts and elevating the risk of wildfires, or fostering the spread of pests and diseases. The report offers a comprehensive look at such compound effects.
Flash droughts are often triggered by extreme heat events that deplete moisture from the topsoil and root zone. Notable cases occurred in the United States of America in 2012 and 2017, the Russian Federation in 2010, Australia in 2018 and 2019, China in 2022, and Brazil in late 2023 and 2024, which saw soybean yields fall by as much as 20 percent as temperatures averaged as much as 7 degrees higher for protracted periods. Data show they are starting earlier, lasting longer, and exposing more and more cropland, forested areas and human populations to their impacts. They can leave lasting effects such as hardened soils with reduced ability to absorb water and greater vulnerability to erosion.
Numerous case studies are presented in the report, including that of a monumental heatwave covering 3 million square kilometers in North America in 2021, when peak temperatures rose to four standard deviations above normal, leading to major yield drops in fruit orchards and Christmas tree plantations and a calamitous spike in forest fires. Remote sensing analysis and ground surveys revealed multiple feedback loops were activated, such as dry soil conditions exacerbating the heating effect of solar radiation.
Key recommendations
The report points to the need for innovation and the implementation of adaptative measures such as selective breeding and crop choices adjusted to the new climate reality, adjusting planting windows and altering management practices that can shelter crops and agricultural activities from the impacts of extreme heat. Early warning systems are a particularly important tool in aiding farmers in their efforts to respond to extreme heat.
Access to financial services - cash transfers, insurance and payment schemes, shock-responsive social protection schemes and other forms - underpins all categories of adaptation options. Technical solutions are necessary but by themselves will be insufficient without addressing pervasive socio-economic barriers in low- and middle-income countries, including limited access to information, education, awareness and training.
"Protecting the future of agriculture and ensuring global food security will require not only building on-farm resilience but also exercising international solidarity and collective political will for risk sharing, and a decisive transition away from a high-emissions future," the report says.
