Global Worming

It seems that us humans aren’t the only culprits in contributing to the problem of climate change. The humble earthworm could be having an impact too, according to findings reported in a new study.

Although earthworms contribute little directly, they have a big effect on the soil surrounding them. Soil plays a major role in greenhouse gas emissions; approximately 20% of global carbon dioxide, a third of methane, and two-thirds of nitrous oxide emissions originate from soils.

It is thought that earthworms have a number of effects on their underground habitat. Not only do they stimulate natural biological processes involving plant roots and microorganisms, but their burrowing also has big consequences for the physical structure of the soil. These activities can increase greenhouse gas emissions, but they can also act to help the soil store carbon more efficiently. Thus, the net effect of the presence of earthworms in the soil has been unclear.

A team of scientists working in the Netherlands, the US, and Colombia recently sought to determine the overall effect. They looked at the results of 237 separate experiments from other published studies to explore the role that earthworms play in global greenhouse gas emissions.

The researchers discovered that the presence of earthworms in soil increased carbon dioxide emissions by 33% and nitrous oxide emissions by 42%. However, these statistics are complicated by the fact that earthworms can increase emissions of one greenhouse gas while reducing emissions of the other. To work out the overall impact, scientists need to scrutinise experiments that look at both gases at the same time. When the research team did this, they discovered that earthworms increased the global warming potential of soil by 16% overall.

However, before we form vigilante groups to seek out and destroy the earthworm population, it’s important to remember that humans, not earthworms, remain the major cause of global warming. In fact, we are directly affecting the soil, which in turn alters the behaviour of its vermian inhabitants. Ingrid Lubbers, a soil scientist and lead author of the report in question, said, “our study shows earthworms are an important actor through which humans can cause nitrous oxide emissions”. She continued, “it also suggests that, due to the increasing habitat for earthworms over the coming decades, earthworm-induced emissions may increase. But these emissions are largely conditional on humans adding fertiliser to agricultural systems”.

As modern farming adapts and expands to deal with the increasing demand for food that a growing population requires, the human-induced effects of earthworms will surely only increase. However, the debate is still open as to the overall effect of these creatures. Prof. Keith Goulding, Scientific Director of the Department of Sustainable Soils and Grassland Systems based at the Rothamsted Research Institute in Hertfordshire, is wary of these findings. He said of the study, “yes, soil with earthworms might release more nitrous oxide and carbon dioxide but the worms improve soil structure, reducing compaction and waterlogging, and thus denitrification, and are vital for the incorporation of organic material”. He concluded, “while just measuring carbon dioxide and nitrous oxide might show greater emission when worms are present, the bigger picture shows them to be beneficial”.

So, while the earthworm population is set to increase over the coming decades it seems that the overall effect of this on global warming is still a hot topic for debate. A veritable can of worms has been opened…