Global heating

High emissions will subject over 1 billion cows to lethal heat stress

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Expanded cattle farming is creating deadly conditions for the animals

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More than 1 billion cows around the world will experience heat stress by the end of the century if carbon emissions are high and environmental protection is low, according to new research published in Environmental Research Letters

This would mean cattle farming would face potentially lethal heat stress in much of the world, including Central America, tropical South America, Equatorial Africa, and South and Southeast Asia. The research also found that rapidly reducing greenhouse gas emissions, as well as keeping cattle production close to current levels, would reduce these impacts by at least 50% in Asia, 63% in South America, and 84% in Africa.

Extreme heat harms cattle in many different ways, especially when combined with high humidity. It reduces fertility, impairs the growth of calves, and can result in increased deaths. In dairy cows, it also reduces milk production. All of these impact the viability of livestock farming, reducing animal welfare and farm income.

The researchers project that if future carbon emissions are very high, nine in ten cows around the world will experience 30 or more days of heat stress per year, and more than three in ten will experience it all year-round by the end of the century. While the most affected countries will be in tropical regions, many other parts of the world will also face multiple months of heat stress conditions every year, including parts of Europe and North America. Some areas of Japan, Australia and Mexico, among others, will experience 180 heat stress days or more per year.

Rising temperatures and humidity will force farmers to adapt to these new conditions, for example, by providing ventilation or even air conditioning for the animals or switching to heat-adapted cattle breeds. But these measures will become increasingly expensive with future warming and will not be possible in all places, meaning cattle farming could no longer be viable in places where it is currently a major occupation, for example in India, Brazil, Paraguay, Uruguay and north-eastern Argentina, and across the Sahelian and east African countries.

Cutting carbon emissions rapidly and maintaining livestock production within current levels would greatly reduce the number of cattle exposed to heat stress, particularly in some of the most affected regions, including Asia, South America and Africa. Reducing emissions will also protect cattle in temperate regions from experiencing heat stress for more than half the year.

The researchers stress that today’s decisions will be critical for the coming decades. For example, cutting down tropical forests to farm livestock in places like the Amazon and central Africa will not only increase the number of cattle in areas that are already experiencing the most heat stress, but will also worsen climate change, making cattle ranching extremely difficult in these regions and elsewhere.

Reducing the amount of beef in diets, and eating more plant-based products, would reduce consumer demand for cattle products. This would put fewer animals at risk from heat stress, while also providing opportunities for forest protection and the restoration of degraded lands that could help limit temperature rise.

Dr. Michelle North, veterinarian and researcher at the University of KwaZulu-Natal, said:

“Our study clearly shows that cattle are increasingly exposed to temperatures that impact their welfare, reducing growth and production and potentially leading to increasing deaths, in many parts of the world that are currently seen as prime cattle-farming territory. It is also important to remember that we are only looking at heat stress here, and do not consider changes to water availability. What this means, is that cattle farming will become less and less viable in many parts of the world.”

Dr. Christopher Trisos, ecologist and climate change researcher at University of Cape Town, said:

“We’ve seen the deadly impacts for humans of climate change intensifying heatwaves, but the animals that feed us are also at severe risk from heat. We need to act now to limit the risk. Expanding cattle production by cutting down or burning tropical forests is unsustainable, it worsens climate change and will undermine the welfare of hundreds of millions more cattle that will be exposed to severe, year-round heat stress.”

(Adapted from materials provided by IOP Publishing.)

Environmental Research Letters, August 24, 2023

Global risk of heat stress to cattle from climate change
by Michelle A. North, James A, Franke, Birgitt Ouwenee, and Christopher H. TrisosCattle farming is a major source of global food production and livelihoods that is being impacted by climate change. However, despite numerous studies reporting local-scale heat impacts, quantifying the global risk of heat stress to cattle from climate change remains challenging.We conducted a global synthesis of documented heat stress for cattle using 164 records to identify temperature-humidity conditions associated with decreased production and increased mortality, then projected how future greenhouse gas emissions and land-use decisions will limit or exacerbate heat stress, and mapped this globally.The median threshold for the onset of negative impacts on cattle was a temperature-humidity index of 68.8 (95% C.I.: 67.3–70.7). Currently, almost 80% of cattle globally are exposed to conditions exceeding this threshold for at least 30 days a year.For global warming above 4°C, heat stress of over 180 days per year emerges in temperate regions, and year-round heat stress expands across all tropical regions by 2100. Limiting global warming to 2°C, limits expansion of 180 days of heat stress to sub-tropical regions. In all scenarios, severity of heat stress increases most in tropical regions, reducing global milk yields.Future land-use decisions are an important driver of risk. Under a low environmental protection scenario (SSP3-RCP7.0), the greatest expansion of cattle farming is projected for tropical regions (especially Amazon, Congo Basin, and India), where heat stress is projected to increase the most. This would expose over 500 million more cattle in these regions to severe heat risk by 2090 compared to 2010.

A less resource-intensive and higher environmental protection scenario (SSP1-RCP2.6) reduces heat risk for cattle by at least 50% in Asia, 63% in South America, and 84% in Africa.

These results highlight how societal choices that expand cattle production in tropical forest regions are unsustainable, both worsening climate change and exposing hundreds of millions more cattle to large increases in severe, year-round heat stress.