Nearly two years ago, we all had a hearty laugh about 30 to 50 feral hogs. Turns out that all those pigs aren’t just a horribly invasive species, but they could be wreaking real havoc when it comes to climate change. According to a new study published Monday in Global Change Biology, wild pigs around the world are releasing the equivalent of 1.1 million cars’ worth of carbon dioxide each year — just from digging around in the dirt.
“Given that wild pigs are known to damage soil, we realised that no other study had looked at the total area at risk at a global scale,” Christopher O’Bryan, the study’s lead author and a research fellow at the University of Queensland, said over email. “Knowing how important soil is at storing carbon, we wanted to assess the risk of wild pig soil damage on carbon emissions.”
Piggies can be really cute, sure, but they’re pretty bad news. Feral hogs put endangered native species at risk of extinction. They also tear up crops, causing between $US1.5 ($2) and $US2.5 ($3) billion worth of damage in the U.S. (A group of feral hogs even killed a woman in Texas in 2019.)
“Wild pigs are essentially farm animals gone rogue,” O’Bryan said.
All that crop destruction isn’t just bad for business — it’s bad for the planet. Soil is packed with carbon dioxide, and it’s been well documented that human agricultural activity that disturbs the soil — like the very common practice of tilling — brings up carbon stored underground and encourages its release into the air. But there’s been surprisingly little research on how invasive species can also stir stuff up when they disturb the soil. It would stand to reason that hogs, which are basically little tractors, would have a similar effect: Their whole deal is rummaging around in the dirt for food, meaning that they can really root up a bunch of dirt.
O’Bryan said that while other research has looked at the carbon dioxide footprint of hogs locally in Switzerland, China, and the Americas, this is the first study to “connect the dots at a global scale.” In order to fully calculate the impact of wild hogs all over the world, O’Bryan and his team created three models: one that predicts wild pig densities, one that converts pig density into soil area disturbed, and one that estimates carbon emissions. They then ran 10,000 simulations to account for the potential uncertainties in each model.
According to the models O’Bryan and his colleagues developed, wild pigs are uprooting anywhere between almost 36,214 square kilometres to 123,517 square kilometres in their non-native habitats. And all this digging has serious consequences for the carbon dioxide stored in soil. Around 5.37 million tons of carbon dioxide each year are released due to wild pig activities.
Even though we may all enjoy a hog joke every once in a while, this research shows that the problems wild pigs pose are becoming more urgent to address.
Scientists have called wild pigs, or Sus scrofa, “one of the most prolific invasive mammals on Earth.” In the U.S. alone, hog populations have gone from being present in 27 states in 2000 to now being found in 48 states; their population ranges between 6 to 7 million in the U.S., and experts say managing this big group of pigs might mean a mass killing of between 60% to 80% of them. (Ironically, part of the reason they’re spreading in the U.S. so fast, experts think, is that people love to hunt them — Succession, anyone? — so some are driving hogs to new areas and then allowing the population to expand.)
The new findings show their impact on the climate is one more reason to end feral hogs’ reign of terror.
“Invasive species are a human-caused problem, so we need to acknowledge and take responsibility for their environmental and ecological implications,” Nicholas Patton, a University of Canterbury PhD candidate and coauthor of the study, said in a release.
“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. … 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.”