A flagship UN report on livestock emissions is facing calls for retraction from two key experts it cited who say that the paper “seriously distorted” their work.

The UN Food and Agriculture Organization (FAO) misused their research to underestimate the potential of reduced meat intake to cut agricultural emissions, according to a letter sent to the FAO by the two academics, which the Guardian has seen.

Paul Behrens, an associate professor at Leiden University and Matthew Hayek, an assistant professor at New York University, both accuse the FAO study of systematic errors, poor framing, and highly inappropriate use of source data.

Hayek told the Guardian: “The FAO’s errors were multiple, egregious, conceptual and all had the consequence of reducing the emissions mitigation possibilities from dietary change far below what they should be. None of the mistakes had the opposite effect.”

Agriculture accounts for 23% of global greenhouse gas emissions, most of which are attributable to livestock in the form of methane from burps and manure, and deforestation for grazing and feed crops. As global meat production leapt by 39% in the first two decades of this century, agricultural emissions also rose by 14%.

At the Cop28 climate summit in December, the FAO published the third in a series of studies of the livestock emissions problem. As well as reducing the FAO’s estimate of livestock’s contribution to overall global heating for a third consecutive time, it used a paper written by Behrens and others in 2017 to argue that shifts away from meat eating could only reduce global agri-food emissions by between 2 and 5%.

Behrens’s paper from 2017 assessed the environmental impacts of government-backed nationally recommended diets (NRDs) of the time, which have since become outdated. Many countries, such as China and Denmark, have drastically reduced their recommended meat intake since then, while Germany now proposes a 75% plant-based diet in its NRD.

Behrens says “voluminous evidence” from larger environmental reports which recommended reductions in meat content, such as the Eat-Lancet Planetary Health Diet, were ignored, according to the letter.

“The scientific consensus at the moment is that dietary shifts are the biggest leverage we have to reduce emissions and other damage caused by our food system,” Behrens told the Guardian. “But the FAO chose the roughest and most inappropriate approach to their estimates and framed it in a way that was very useful for interest groups seeking to show that plant-based diets have a small mitigation potential compared to alternatives.”

Of more than 200 climate scientists surveyed by Behrens and Hayek for a recent paper, 78% said it was important for livestock herd sizes to peak by 2025 if the world was to stand a chance of preventing dangerous global heating.

As well as using obsolete NRDs, the scientists say the FAO report “systematically underestimates” the emissions-cutting potential of dietary shifts through what the letter calls a “series of methodological errors”.

The authors say these include: double-counting meat emissions until 2050, mixing different baseline years in analyses, and channelling data inputs that inappropriately favour diets allowing increased global meat consumption. The FAO paper also skips over the opportunity cost of carbon sequestration on non-farmed land.

Hayek said the FAO inappropriately cited a report he co-authored that measured all agri-food emissions, and applied it to livestock emissions alone. “It wasn’t just like comparing apples to oranges,” he said. “It was like comparing really small apples to really big oranges.”

Correspondingly, the mitigation potential from farming less livestock was underestimated by a factor of between 6 and 40, he said.

The FAO is the world’s primary source for agricultural data, and its reports are routinely used by authoritative bodies such as the UN’s Intergovernmental Panel on Climate Change (IPCC). But the FAO is also mandated to increase livestock productivity so as to bolster nutrition and food security, arguably creating a conflict of interests.

Former officials have accused the FAO of censoring and sabotaging their work when it challenged livestock industry positions. A recent FAO roadmap to making the sector sustainable also omitted the option of reducing meat intake from a list of 120 policy interventions.

That paper received praise from meat industry lobbyists, one of whom called it “music to our ears” when it was released at Cop28.

An FAO spokesperson said: “As a knowledge-based organisation, FAO is fully committed to ensuring accuracy and integrity in scientific publications, especially given the significant implications for policymaking and public understanding.

“We would like to assure you that the report in question has undergone a rigorous review process with both an internal and external double-blind peer review to ensure that the research meets the highest standards of quality and accuracy, and that potential biases are minimised. FAO will look into the issues raised by the academics and undertake a technical exchange of views with them.”

The sound of an earthworm is a distinctive rasping and scrunching. Ants sound like the soothing patter of rain. A passing, tunnelling vole makes a noise like a squeaky dog’s toy repeatedly being chewed.

On a spring day at Rothamsted Research, an agricultural research institution in Hertfordshire, singing skylarks and the M1 motorway are competing for the airways. But the attention here is on the soundscapes underfoot: a rich ecosystem with its own alien sounds. More than half of the planet’s species live in the soil, and we are just starting to tune into what they are up to. Beetle larvae, millipedes, centipedes and woodlice have other sound signatures, and scientists are trying to decipher which sounds come from which creatures.

In a field divided up into test strips, Carlos Abrahams pushes a sensor the length of a knitting needle into the soil. With a pair of headphones on, he listens to the “poor man’s rainforest”: a dark landscape of miniature caves, tunnels and decomposing matter stewing away under our feet.

“A few ticks and clicks going on,” says Abrahams, an ecoacoustics specialist from Baker Consultants, as he listens in.

Abrahams and scientists from the University of Warwick are building up libraries of subterranean sounds. The soil makes different noises depending on the season and whether it’s night or day. Even in the afternoon when the soil has warmed up, sounds get richer, research suggests.

“The soil is such a mystery,” says Dr Jacqueline Stroud, from the University of Warwick’s Crop Centre. “This is like opening the door and seeing what is going on below ground. It’s a different way of exploring the world.”

Until recently, soil had been a relative blank spot for monitoring species abundance. Farmers and gardeners hoping to find out how healthy their soils were had to dig up spadefuls and carry out laborious tests.

Last year, a study found soil was the single most species-rich habitat on Earth, with more than half of all species living in it. But only a fraction have been identified, and most are too small to see. Soundscapes are becoming an increasingly popular way of monitoring wildlife abundance, above ground, beneath the earth and underwater.

Noisy soil is generally healthier because it contains a greater range of bugs and worms busying around. Soil organisms alter and improve the structure of soil by passing nutrients between one another and creating an environment that is well ventilated and diverse. These webs provide food, fibre and clean water for people – topsoil is where 95% of the planet’s food is grown.

Soils that have little biodiversity are more fragile: they have lost the structure and connections that keep particles together. This means they are more likely to be washed away by floods or blown away by strong winds. An estimated 24bn tonnes of fertile soil is lost every year through intensive farming, according to a UN-backed study, the Global Land Outlook.

Farmers have repeatedly asked for more efficient ways of measuring the abundance of earthworms, which are a good indicator of the heath of soils, according to researchers.

Baker Consultants and the University of Warwick have funding for a two-year research project developing a recording unit prototype. The aim is to record soil sounds at “big data” scales.

On the land Abrahams is testing, scientists are trialling more ecological ways of farming, including crop rotations with legumes and higher proportions of oats. In total there are 70 scientists working on this bit of land, marked out in 66 plots of 24m by 24m, finding out new things about soil structure, viruses, microbes and fungi – making it among the most studied soil in the world. “It’s a unique outdoor laboratory,” says Kim Hammond-Kosack from Rothamsted Research, who set up the experiments.

Abrahams and Stroud’s teams started their sampling at Rothamsted in October last year. Each month they take two recordings on each of the plots, measuring how activity above the ground affects what is happening in the soil.

Dr Simon Butler from the University of East Anglia has been listening to the soil before and after the application of zebra dung in Eswatini (previously known as Swaziland). The soil fizzed with activity post-application. “I’ve never really considered the sound of soils, so it was fascinating to hear how the acoustic properties change in response to the presence of fresh dung,” he says.

The sounds being produced are within the lower range of human hearing, so it’s possible there are sounds in the soil we haven’t heard yet. Early research from Switzerland shows soils were producing the most complex sounds in spring and summer, which declined in autumn and winter. Abrahams’ previous research has shown that soils in restored forests in the UK seem to have a greater diversity of sounds than soil from deforested plots. He says: “As a general rule, the more diverse it is above ground, the more that is going on in the soil.”

In January, researchers published what they believe is the first paper listening to tropical forest soils, which are among the most biodiverse habitats in the world. Like others, they documented multiple mysterious sounds. The next task is to create a library of soil sounds so they can work out what they’re actually listening to.

Find more age of extinction coverage here, and follow biodiversity reporters Phoebe Weston and Patrick Greenfield on X for all the latest news and features

Good news for lazy gardeners: one labour-saving tweak could almost double the number of butterflies in your garden, according to a new scientific study – let the grass grow long.

In recent years nature lovers have been extolling the benefits of relaxed lawn maintenance with the growing popularity of the #NoMowMay campaign. Now an analysis of six years of butterfly sightings across 600 British gardens has provided the first scientific evidence that wilder lawns boost butterfly numbers.

The benefits of leaving areas of grass long were most pronounced in gardens within intensively farmed landscapes, with up to 93% more butterflies found and a greater range of species. Gardens with long grass in urban areas showed an 18% boost to butterfly abundance.

“We wanted to be able to give tried and tested gardening advice that will benefit butterflies, as we know lots of people want to help,” said Dr Richard Fox, the head of science at Butterfly Conservation and a co-author of the study, published in the journal Science of the Total Environment. “This study proves, for the first time, that allowing a patch of grass to grow long will attract more butterflies into your garden.”

The study found that another butterfly bonus for gardens was flowering ivy, which can flourish on walls in urban backyards. This increased the numbers of the holly blue – the caterpillars feed on ivy and holly – and the red admiral and comma, which benefit from its flowers as a crucial nectar source in autumn.

According to the study, long grass in gardens attracts more butterfly species whose caterpillars feed on grasses. These include meadow browns, gatekeepers, speckled woods, ringlets and small skippers. Fox said this suggested the boost in population was not simply because long grass provided more nectar from wildflowers within it, such as dandelions or knapweed, but because butterflies were seeking or actually breeding in rewilded lawns.

“It’s a really positive sign,” said Fox. “What people are doing with long grass in gardens is creating potential or actual breeding habitat. In order to make an impact on the biodiversity crisis we need to be creating places where butterflies and other wildlife can breed. This is simple, doesn’t cost anything and saves you time and effort.

“If you have a patch of long grass you may have grasshoppers, beetles and ant hills as well – there will be all these spinoffs.”

Private outdoor space makes up 7,280 sq km of land across Britain – an area larger than the counties of Derbyshire, Leicestershire and Nottinghamshire combined – and an estimated 62% of this is vegetated gardens, and so potentially vital wildlife habitat.

According to Butterfly Conservation, the benefits of long grass to butterflies and other invertebrates is likely to be found in other grassy public spaces too, such as parks, school grounds, allotments and road verges. Through its Wild Spaces programme, the charity aims to transform 100,000 areas across the UK to help support butterfly populations.

Fox said the principle of managing long grass for butterflies was the same as wildlife-friendly meadow management: don’t do everything all at once.

To provide good habitat for butterfly caterpillars, long grass has to be left until late September or October before being cut lightly, and some species such as small skippers require long grass all year round.

“If you take part in #NoMowMay our message is, don’t just mow your grass in June,” said Fox.