Are earthworms driving climate change?

Scientists have unearthed an unexpected contributor to global climate change, the earthworm. It releases tonnes of carbon and nitrous oxides but its discharges have remained hidden until now.

A collaboration involving scientists from Ireland, the Netherlands, the US and Colombia today spill the beans on the lowly worm, revealing that it throws up significant amounts of these greenhouse gases. They publish the nefarious details collected from 57 experiments conducted around the world in a research paper in the journal Nature Climate Change.

"Earthworms help us to produce more food through improving soil fertility, but by doing so they also contribute to global warming by increasing greenhouse gas emissions from soils," says lead author in the study Ingrid Lubbers of Wageningen University, Netherlands.

Soils are an important sink for carbon dioxide and nitrous oxide, but the team, including Dr Kees Jan van Groenigen, a Trinity College Dublin research fellow who co-authored the paper wanted to confirm suspicions that the beneficial work done by worms also freed these greenhouse gases.

They compared gas release in soils with and without earthworms and found there was a huge difference. Worm activity increased CO2 discharges by 33 per cent and N2O discharges rose by 42 per cent when the worms were present, said Dr van Groenigen.

"It is rather unfortunate that the presence of earthworms, which we try to stimulate in sustainable agriculture due to their positive effect on soil fertility, at the same time has an unwanted effect on greenhouse gas emissions," he said.

He pointed out however that the experiments were done on soils alone, not soils that also supported growing plants. "This is important, because earthworms tend to stimulate plant growth, and in that way also stimulate CO2 uptake from the atmosphere," he said. The experiments did not test releases of greenhouse gas emissions from an ecosystem as a whole.

The researchers also concluded that the worms did not dislodge the large amounts of carbon that are naturally locked up in soils, the "soil organic carbon", he added. There was more carbon in soils than in the atmosphere and agricultural soils were the single largest source of nitrous oxide emissions, said Dr Jan Willem van Groenigen of Wageningen University. "Small changes in soil greenhouse gas dynamics can therefore have important repercussions for global warming," he said.

"We need more experiments that include growing plants, as well as more long-term studies and more field studies before we can decide to what extent global worming leads to global warming," Ms Lubbers concluded.