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A new report, from the Food and Agriculture Organization of the United Nations (FAO) and the World Meteorological Organization (WMO), highlights the major risk posed by the rise of extreme heat events and their effects on agri-food systems worldwide.

According to the report, titled Extreme heat and agriculture, the frequency, intensity and duration of extreme heat events have risen sharply over the past half century.

These extreme heat events threaten the livelihood and health of over a billion people, causing half a trillion work hours to be lost annually – and the prospect of damage to livestock herds and crop yields is set to soar higher in future, the organisations emphasised.

Extreme heat refers to situations where daytime and nighttime temperatures rise above their typical ranges for a protracted period. This leads to physiological stress and direct damage to food crops, livestock, fish, trees and human beings, with agricultural workers and systems absorbing the greatest impact.

FAO and WMO’s report highlights how extreme heat ripples through these agricultural systems, and how it 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.

It gives the example of a spring 2025 event in Kyrgyzstan’s Fergana mountain range which saw temperatures stretch to 30.8°c, 10°c higher than usual. This caused a thermal shock to fruit and wheat crops, which contributed to a locust outbreak, heightened evaporation that reduced irrigation capacity, and eventually a 25% decline in cereal harvests.

Rising average global temperatures and more frequent, intense extreme heat events narrow the ‘thermal safety margin’ that species rely on for biological processes that support photosynthesis, cellular regeneration and reproduction, the FAO and WMO said.

Extreme heat intensity roughly doubles at 2°c of global warming, and quadruples at 3°c, relative to 1.5°c increase in average global temperatures, according to the report.

Impact on animals, crops and workers

For the most common livestock species, stress begins at above 25°c, and begins lower for chickens and pigs who cannot cool themselves by sweating. Above that threshold, animals begin to suffer. Initially they seek shade, drinking more water and moving less, but persistent exposure leads to digestive tract breakdowns, organ failure and cardiovascular shock.

Additionally, the FAO noted that even when not lethal, extreme heat reduces dairy yields as well as fat and protein content, worsening 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 reduce dissolved oxygen levels. In 2024, 91% of the global ocean experienced at least one marine heatwave.

For most major agricultural crops, yield declines start at above 30°c, lower for some crops like potatoes and barley. This leads to weakened cell walls, sterile pollens and the production of toxic oxidative compounds.

Meanwhile, rates of tree photosynthesis and respiration diverge under extreme temperatures, creating an energy imbalance that causes reduced growth and less carbon removal from the atmosphere. Evidence indicates a strong correlation between heatwaves and wildfires, with longer and more intense fire seasons.

For agricultural workers, critically extreme heat can be fatal. The report states that the number of days each year when it is too hot to safely work may rise to 250 in many parts of South Asia, tropical Sub-Saharan Africa and parts of Central and South America.

Extreme heat as a risk multiplier

Aside from extreme heat’s direct impacts, the report examines its multiplier effects. It exacerbates water stress, triggering flash droughts, and can also encourage the spread of pest and diseases.

The report points to notable cases in the US 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 drop by 20% as temperatures averaged as much as 7°C higher for protracted periods.

Data shows these events are beginning earlier, lasting longer and exposing more cropland, forested areas and human populations to their impacts. Lasting effects include hardened soils with reduced water absorption ability and greater erosion vulnerability.

Case studies presented in the report include a heatwave that covered 3 million square kilometres in North America in 2021. Peak temperatures rose to four standard deviations above normal, leading to major yield drops in fruit orchards and a spike in forest fires. Remote sensing analysis and ground surveys revealed multiple feedback loops were activated, such as dry soil conditions intensifying the heating effect of solar radiation.

Recommendations for the sector

Several key recommendations are made in the report, including the implementation of adaptative measures like selective breeding and crop choices adjusted to the new climate reality. It also recommends adjusting planting windows and altering management practices that can shelter systems from extreme heat’s impacts.

Early warning systems can also aid farmers critically in responding to such events, while access to financial services such as insurance schemes underpins all categories of adaptation options, FAO stressed.

While technical solutions are necessary, the report warns that they will be insufficient without addressing socio-economic barriers in low- and middle-income countries, including limited access to information, education 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 concludes.