As Charles Darwin knew, earthworms enrich the soil. But they also increase greenhouse gas emissions. That's according to a meta-analysis in the journal Nature Climate Change. [Ingrid M. Lubbers et al, Greenhouse-gas emissions from soils increased by earthworms]

Soil scientists and biologists reviewed 57 studies to see how earthworms affected the soil from a climate change perspective. The issue is substantive: nearly a fifth of global carbon dioxide emissions come from soil. And earthworms are on the move, spreading anew through North America for the first time in tens of thousands of years after being brought over by European colonists.

All that soil digestion in the guts of worms means more CO2 and more nitrous oxide emanating from the dirt. The presence of earthworms increased N2O emissions by more than 40 percent. And laughing gas is also a potent greenhouse gas.

Worms also upped soil CO2 emissions, though it remains unclear whether this is a short-term effect likely to be balanced out by all the carbon that earthworms bury over the longer term. But that doesn't mean that earthworms don't play an important part in the history of the world, just as Darwin suggested, especially as the climate changes.

—David Biello

[The above text is a transcript of this podcast.]

[Scientific American is part of Nature Publishing Group.]