Though they were hunted to extinction in the medieval period, wild boar have made a comeback in the UK after escaping from farms in the 1980s and 90s, and are now established in several parts of the country.
Meanwhile, US populations of boar have surged in recent decades, while boar introduced into countries including Uruguay and Brazil during the 20th century and Australia during the 18th century, are considered a problematic invasive species.
But new research by researchers from The University of Queensland in Australia and The University of Canterbury in New Zealand, suggests wild boar are releasing around 4.9 million tonnes of carbon dioxide (CO2) a year around the world.
This is roughly the equivalent emissions from 1.1 million cars, they said.
The research team used predictive population models alongside new mapping technology to estimate the carbon footprint of wild boar across five continents.
Dr Christopher O’Bryan said the planet’s ever expanding population of wild boar could represent a threat to the climate.
“Wild pigs are just like tractors ploughing through fields, turning over soil to find food," he said.
“When soils are disturbed from humans ploughing a field or, in this case, from wild animals uprooting, carbon is released into the atmosphere.
“Since soil contains nearly three times as much carbon than in the atmosphere, even a small fraction of carbon emitted from soil has the potential to accelerate climate change.
“Our models show a wide range of outcomes, but they indicate that wild pigs are most likely currently uprooting an area of around 36,000 to 124,000 square kilometres, in environments where they’re not native.
Dr O’Bryan added: “This is an enormous amount of land, and this not only affects soil health and carbon emissions, but it also threatens biodiversity and food security that are crucial for sustainable development.”
The research team used existing models providing wild boar numbers and locations, and the team then simulated 10,000 maps to suggest potential global wild boar density.
They then modelled the amount of soil area disturbed from a long-term study of wild pig damage across a range of climatic conditions, vegetation types and elevations, from lowland grasslands to sub-alpine woodlands.
The team simulated the global carbon emissions from wild boar soil damage based on previous research in the Americas, Europe, and China.
Nicholas Patton from the University of Canterbury said the results from the research suggested greater action was needed to tackle the spread of wild boar around the world.
“Invasive species are a human-caused problem, so we need to acknowledge and take responsibility for their environmental and ecological implications,” he said.
“If invasive pigs are allowed to expand into areas with abundant soil carbon, there may be an even greater risk of greenhouse gas emissions in the future.
“Because wild pigs are prolific and cause widespread damage, they’re both costly and challenging to manage.
“Wild pig control will definitely require cooperation and collaboration across multiple jurisdictions, and our work is but one piece of the puzzle, helping managers better understand their impacts.
“It’s clear that more work still needs to be done, but in the interim, we should continue to protect and monitor ecosystems and their soil which are susceptible to invasive species via loss of carbon.”
Previous research undertaken in the Forest of Dean – a wild boar stronghold in the UK – has suggested the boars’ rootling can boost biodiversity, knocking back plants like bracken and allowing wildflowers to grow and letting some species of butterfly benefit.
However, without any natural predators in the UK anymore due to the loss of the wolf, boar are culled to keep numbers down.
According to a 2020 estimate there are believed to be around 4,000 boar in the UK. Meanwhile in France there are around 700,000.
The research is published in the journal Global Change Biology.