Extreme heat is "pushing agri-food systems to the brink worldwide", according to a new report.

The report by the Food and Agriculture Organization of the United Nations (FAO) and the World Meteorological Organization (WMO) assesses risks and identifies adaptation options as rising temperatures pose hazards to people, crops, livestock, and fish.

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, the research has found.

Agricultural workers and agri-food systems are on the frontlines, absorbing the greatest impacts from extreme heat, the report said.

The frequency, intensity and duration of extreme heat events have risen sharply over the past half century, with worrying impacts on agri-food systems and landscapes.

Extreme heat

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.FAO director-general Qu Dongyu said this report "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".

Agri-food systems

WMO secretary-general Celeste Saulo said extreme heat is "increasingly defining the conditions under which agri-food systems operate".

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.

The report explains how 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°C of global warming, and quadruples at 3°, relative to a 1.5° increase in average global temperatures, according to the report.

Livestock

For the most common livestock species, stress begins at above 25°C, and a bit lower for chickens and pigs, which are unable to cool themselves by sweating, the report said.

"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," the report said.

"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."

Crops

For most major agricultural crops, yield declines begin to occur above 30°C - 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," the researchers said.

"Evidence points to a strong correlation between heat waves and wildfires, with longer and more intense fire seasons."

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 also highlights that critically, extreme heat "also takes a toll on humans, especially agricultural labourers, 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.

Recommendations

The report points to the need for "innovation and the implementation of adaptative measures".

These include 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.

"Access to financial services – cash transfers, insurance and payment schemes, shock-responsive social protection schemes and other forms – underpins all categories of adaptation options," according to the report.

"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."

The report adds that protecting the future of agriculture, agri-food 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".