By the end of this century, agricultural workers across much of South Asia, tropical sub-Saharan Africa, and parts of Central and South America could face up to 250 days a year of conditions so hot that their bodies cannot sustain meaningful physical labour.

As India and much of the world brace for another brutal summer — with forecasters warning of a super El Niño and record-breaking global temperatures — a new report by two United Nations agencies lays bare how much agriculture, and the billions who depend on it, are already losing to extreme heat, and how much worse it is set to become.

In one of the most comprehensive global assessments of how rising temperatures are reshaping the conditions under which food is grown, the Food and Agriculture Organization (FAO) and the World Meteorological Organization (WMO) warn that extreme heat has become one of the most serious hazards facing agriculture worldwide, threatening the food security and livelihoods of over a billion people.

The human cost is already mounting. Agricultural workers are 35 times more likely to die from occupational heat exposure than workers in any other sector, and extreme heat is already causing 470 billion working hours to be lost globally each year, according to the report, Extreme Heat and Agriculture.

What is ‘extreme heat’

The report defines extreme heat as the point at which temperature thresholds are exceeded in ways that cause moderate or greater physiological stress, or direct physical damage, to crops, livestock, fish and workers.

It describes extreme heat as a contextual, impact-based concept, noting that this creates methodological challenges — particularly for crops, where research has often focused on identifying temperature thresholds for yield loss rather than on heat events as a whole.

The report also brings up the concept of “thermal safety margin” — the gap between the highest temperatures a species normally encounters and the point at which those temperatures begin to cause damage. As average temperatures rise, this margin narrows. The closer temperatures move towards a species’ damage threshold, the less it takes to push it beyond its limits, like a shorter heatwave or even a slightly hotter afternoon.

“Thus, it becomes increasingly easy for extreme heat events (of decreasing magnitude) to breach the damage threshold,” the report notes.

Reports by the Intergovernmental Panel on Climate Change (IPCC) have already warned that, compared with 1.5 degrees Celsius (°C) of warming, the intensity of extreme heat is likely to increase by at least 100 per cent at 2°C and by 300 per cent at 3°C. This a trajectory that would push more species, landscapes and farming systems beyond the thresholds they can withstand.

Drawing on the latest climate observations and agrifood systems research, the report examines risks that have often been under-recognised in climate and development planning. It highlights not only the direct damage caused by extreme heat but also its role as what FAO Director-General Qu Dongyu described as “a major risk multiplier”, placing additional pressure on crops, livestock, fisheries, forests, and the communities and economies that depend on them.

When the fields become too hot to work

Around one billion people work in agriculture globally, accounting for approximately 28 per cent of the employed population, according to estimates by the International Labour Organization (ILO). Of these, about 450 million are waged workers, many dependent on plantation-based incomes.

The burden of extreme heat falls disproportionately on the poorest. In countries with the lowest human development scores, 87 per cent of all lost labour hours are concentrated in agriculture.

Women face an additional layer of risk. Female agricultural workers, often paid by output, frequently restrict their water intake and delay urination due to a lack of sanitation in the fields. This pattern was directly linked by the report to increased rates of chronic kidney disease.

These pressures are particularly acute in India. The Indo-Gangetic Plain (IGP) in India spans Punjab, Haryana, Uttar Pradesh, Bihar and West Bengal, and producing the bulk of the country’s wheat and rice, and lies at the epicentre of what the report identifies as one of the world’s most heat-affected and vulnerable agricultural regions.

Around 46 per cent of India’s workforce is engaged in agriculture, according to the Periodic Labour Force Survey (PLFS) for 2019-20 to 2022-23.

Rice and maize farmers in the region experienced heat exposure nearly twice as high between 2001 and 2019 compared with the period from 1979 to 2000.

Under a high-emissions scenario, the report warns that average growing-season work capacity across the IGP could fall below 40 per cent by the end of the century. Workers would be able to perform less than half their normal output during the months most critical to India’s food supply.

Under a 3°C warming scenario, the report projects a 25 per cent decline in the combined measure of labour supply and productivity across Asia, with consequences it describes as profound for long-term economic growth and inequality.

The risks to crops

The damage to crops is already measurable, the report warned. For most major agricultural crops, yield declines begin between 30°C and 35°C, as plants start to experience failures in photosynthesis and reproductive processes that can be irreversible.

At these temperatures, proteins and critical enzymes denature, cell walls weaken, and toxic oxidative compounds accumulate, triggering cell death, the report explained. More worryingly, high night-time temperatures compound the damage, leaving plants no opportunity to recover between episodes.

The four staple crops that together supply around 60 per cent of global caloric intake — maize, rice, soy and wheat — were all significantly affected. A meta-analysis cited in the report found that yields decline with each 1°C rise in temperature by 7.5 per cent for maize, 6.0 per cent for wheat, 6.8 per cent for soybean and 1.2 per cent for rice.

Projected future losses per additional degree of warming range from 4 per cent to 10 per cent for maize, 3.8 per cent to 10 per cent for wheat, and 2.9 per cent to 5.4 per cent for soy.

The report also highlights the growing threat of “flash drought” — a phenomenon in which rapid temperature spikes, rather than prolonged rainfall deficits, cause soils and crops to dry out with little warning.

Over the past 64 years, flash drought has replaced traditional drought in 74 per cent of at-risk regions globally, with severity increasing by between 6.7 per cent and 90.8 per cent. When extreme heat combines with such sudden moisture loss, crop damage intensifies sharply: heatwaves alone have led to yield losses of around 9 per cent in affected regions, but when combined with low rainfall, losses have reached nearly 25 per cent.

The report’s findings on adaptation are perhaps the most troubling. An analysis of grain production over the past 50 years found no statistically significant evidence of net adaptation to extreme heat at the global level, suggesting that crops remain almost as vulnerable today as they were half a century ago.

The broader impact on agricultural productivity is substantial. Since 1961, heat stress has led to an estimated 21 per cent loss in total factor productivity in agriculture. This is equivalent to erasing around seven years of global productivity gains. To compensate, an additional 88 million hectares of land were brought under cultivation across 110 countries between 1992 and 2020, resulting in an estimated 21.8 billion tonnes of additional greenhouse gas emissions.

The report describes this as a feedback loop: heat reduces productivity, prompting expansion of agricultural land, which in turn increases emissions and drives further warming.

Animals, fish and forests under stress

Animals, fish, and trees are also not spared. 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 noted that 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 2025, more than 90 per cent of the global ocean experienced at least one marine heatwave, according to WMO’s State of the Global Climate 2025 report.

An analysis of 37 years of data across 2,088 fisheries in 128 regions and 108 countries found that marine heatwaves had already impacted 15 per cent of fisheries, causing production losses of over 5.6 million tonnes and economic losses of $6.6 billion.

On land, forests were faring no better. The report warned that forests are approaching, and at times already exceeding, critical physiological tolerances. As temperatures rise, trees increase their rate of transpiration, drawing more water from soils even as heat makes that water harder to retain. The result is a system under compounding stress: forests that once acted as buffers against climate extremes are themselves becoming casualties of them, with consequences for the ecosystems, water cycles, and agricultural landscapes they support.

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