Rascally rodents

Research released this week has shed new light on the role some rodent species play in contributing to climate change. And it's greater than imagined.

The way in which beavers and the Arctic ground squirrel (pictured above) interact with landscapes releases significant amounts of greenhouse gases, the studies show.

Research by Susan Natali and Nigel Golden on Arctic ground squirrels and climate change in Siberia was presented at the annual American Geophysical Union meeting, held December 15 through 19 in San Francisco.

On Wednesday, December 17, researcher Colin Whitfield released a study cataloguing methane emissions caused by beavers.

These two species are now understood to be significant sources of greenhouse gas emissions - comparable to previously known sources such as cud-chewing animals.

Squirrels thawing permafrost

Biogeochemist Susan Natali, who works at the Woods Hole Research Center in Massachusetts, partnered with wildlife biologist Nigel Golden on the Arctic ground squirrel project.

Arctic permafrost can be found on more than a quarter of the land area in the northern hemisphere. Arctic ground squirrels live in the thawed layer of soil above the permafrost layer.

A team surveyed how Arctic ground squirrels change permafrost in Siberia and followed up with laboratory experiments on soils. Natali told DW they came up with two major findings.

"The squirrels' burrowing activity removes organic material, which is a very good insulator," Natali explained. This increases the ground temperature, leading to more permafrost thaw.

The ground squirrels' urine and feces also adds nutrients like nitrogen to the soil. Combined with aeration from churning up the soil, this creates a friendly environment for microbes, which "consume the organic carbon in the soil, then respire the greenhouse gas carbon dioxide," Natali said.

"In the areas we looked at, there is less carbon in the soil, and the temperatures are higher," Natali said.

The preliminary finding is significant considering that 1,500 billion tons of carbon are locked up in Arctic permafrost ice crystals.

This also presents a potential feedback loop with current warming: as global temperatures increase, more permafrost thaws, providing more potential habitat for the Arctic ground squirrels. But if squirrels colonize more permafrost zones, they could accelerate permafrost thaw and thus carbon release, contributing to the global greenhouse effect.

Beaver dams

Colin Whitfield, also a biogeochemist, examined how beavers contribute to climate change.

Furry, cheeky beavers are known for their dam-building, which creates ponds for habitat. "This slows the rate of water flow, and organic plant material rich in carbon - like leaves and branches - ends up being trapped in the bottom of the ponds," Whitfield told DW.

The lack of oxygen at the pond floors "leads to anaerobic decomposition, which generates methane," explained Whitfield, who is based at the University of Saskatchewan Centre for Hydrology in Canada.

The majority of the global beaver population is in North America - yet early settlers considered the toothy rodent to be a pest, and by around 1900 it was nearly wiped out due to hunting and trapping, also for its pelt.

Conservation efforts in the 1940s helped the species bounce back in North America. Even though this has increased emissions of the potent greenhouse gas methane, Whitfield pointed out numerous benefits of beaver ponds, which support biodiversity and help the land hold water.

Whitfield described such ponds as "important hotspots for methane generation." Greenhouse gas emissions caused by beavers, his study concluded, "matters because it is large - the same order of magnitude as that from wild ruminants."

Big beasts

Wild cud-chewing animals, or ruminants - like moose, deer, and antelope - emit about 6 million tons of carbon dioxide equivalent per year, according to Alexander Hristov, a professor in the Department of Animal Science at Pennsylvania State University. Ruminants have a complex stomach and graze on fibrous food, he says. One of these stomachs - the rumen - acts as a fermentation chamber.

Hristov called the symbiotic relationship between microbes and ruminants a "wonder of nature."

"The animal provides constant temperature, an inflow of nutrients, and an anaerobic environment," Hristov told DW. In exchange, microbial fermentation gives the animal nutrients in the form of volatile fatty acids.

The fermentation produces byproduct gases, Hristov continued, adding that "Almost nothing comes from the backside - they are belching methane." This, too, is a significant source of greenhouse gases.

In North America, before European settlement, up to 75 million bison produced 154 million tons of carbon dioxide equivalent per year.

That's more than the approximately 134 million tons of carbon dioxide equivalent currently generated annually by domesticated, farmed ruminants in the US.

"We've replaced the bison with cattle," Hristov says.

Important for carbon inventory

All the scientists emphasized that wild animal greenhouse gas emissions are fractional compared to anthropogenic (human) sources.

Presently, wild ruminants contribute 4.3 percent of all ruminant greenhouse gas emissions in the US, Hristov said. The rest comes from cattle.

Beaver dams do even less damage than their wild ruminant neighbors, resulting in just one-sixth the emissions. Beaver-generated methane, Whitfield says, is still "less than 1 percent of anthropogenic fossil fuel combustion."

And Natali adds that, compared to fossil fuels, carbon release due to Arctic ground squirrel activity "won't be a significant source" of greenhouse gas emissions. She said the climate concern there is more over permafrost thaw.

Yet all of these data will help in creating a better picture of how wildlife interacts with the landscape and contributes to climate change.

"We really need an accurate inventory of these sources of greenhouse gases in order to accurately predict how climate might change," Whitfield says.

So don't blame the rodents, or the cud-chewers. Human beings, after all, are still the number one animal driving climate change.