Worms are moving, and people are nervous.

That’s because they’re taking over territory in the Far North that’s been worm-free since the last ice age. Scientists say the expansion will inevitably change northern ecosystems, with implications for the entire planet, in ways we don’t fully understand and probably can’t undo.

“We should be careful about an organism that comes in and is going to be really hard to get rid of,” said Jonatan Klaminder, a professor of ecology at Umea University in Sweden who studies earthworms. “We should really, really study carefully what the effects of this organism will be.”

In much of the temperate world, shoveling a patch of soil full of common earthworms is a sign of healthy soil full of flora, fungi and good bacteria. Earthworms actively contribute to soil health by eating decaying organic matter and excreting nutrient-rich manure.

But this means that worms also have the potential to upset the natural balance of ecosystems in Arctic and sub-Arctic zones. For example, by encouraging the growth of certain plants at the expense of others, changing entire food webs and squeezing out rare, native flora that is already threatened by climate change.

“Earthworms, at least locally, are more powerful in changing vegetation than temperature,” said Dr. Klaminder.

They can also trigger microbial activity that can help unlock powerful greenhouse gases like carbon dioxidemethane and nitrogen that are stored in the soil.

Worms did not reach the Far North on their own. Research shows that people bring them, intentionally and unintentionally, to remote locations above the Arctic Circle and to sub-Arctic areas since at least the mid-1800s by importing soil for lawns and gardens and for use as fishing bait. recent there is an increase in travel to these areas may also contribute to the invasion. Worms go where people go.

Now, as human-caused climate change raises temperatures and melts the permafrost, the worms take hold. Only without feet. Once established in the soil, they don’t even need to find a partner of the opposite sex to reproduce. Earthworms are hermaphrodites, which means they have both male and female reproductive organs. So, anyone will do.

Due to changes in the chemistry and physics of the soil, grasses and shrubby plants tend to thrive, taking over from tundra mosses and lichens. That’s good news for the lemmings and voles that favor such plants, according to Hanna Jonsson, an ecology researcher at Umea University. But probably not good for other herbivores, who may not easily adapt to a change in available food.

Most importantly, these changes can reduce the amount of snow cover that reflects solar heat back into space from the top of the world. That means the earth can absorb exponentially even more heat.

Something similar happens in temperate and boreal forests in North America, from Indiana to Alberta, where worms helps weeds and grasses take territory from pines, spruces and larches, according to Dylan Craven, a plant ecologist at Universidad Mayor in Santiago, Chile.

That makes for a complicated global picture, and scientists aren’t yet sure exactly how these earthworm invasions might affect the planet’s ecosystems and overall greenhouse gas levels.

“You get into a situation where there are so many different impacts that it’s hard to predict the outcome,” said Lee Frelich, director of the Center for Forest Ecology at the University of Minnesota. “The effects can really vary enormously and it sounds contradictory, but they can literally do opposite things depending on the context.”

Initial research by Dr. Klaminder and Ms. Jonsson suggests that, depending on vegetation, the total impact on the planet’s carbon balance could amount to zero or even a net reduction. That’s because any release of carbon dioxide from the decomposition of organic matter caused by worms could be offset by growing plants that can suck up some carbon from the air.

Other experts, including Dr. Frelich and Dr. Craven, say that any such virtuous effect on the carbon balance could be canceled out by the decline in tree growth in North America’s forests. And any kind of carbon dioxide sequestration that earthworms could do in the long term would be too little, too late.

“The world has a problem with too much CO2 in the atmosphere right now,” Dr. Frelich said.

What scientists agree on is that the worm changes are definitely significant. They are happening very quickly in a region that is warming much faster than the rest of the planet and hosts some of the world’s last intact ecosystems and some of its most vulnerable species of flora and fauna.

The changes are probably irreversible, as earthworms are very difficult to eradicate. And, we are very likely to see settlements expand as the Far North becomes warmer and more hospitable.

“The first step of the Arctic perspective is actually getting a good estimate of the scale of the problem,” said Dr. Klaminder. “Because, as I see it now, the Arctic is one of the last untouched areas where human settlements haven’t really spread across the entire landscape.”

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