Up until the 19th century, the fur trade decimated beaver populations worldwide. Conservationists stepped in to save these furry animals from extinction, which is good for the beaver, but may not be so great for the environment. According to new research, as the number of damming beavers increases, so does the amount of methane produced, with beaver ponds alone released 200 times more of this greenhouse gas than over a century ago.

"The dynamic nature of beaver-mediated methane emissions in recent years may portend the potential for future changes in this component of the global methane budget," Colin J. Whitfield of the University of Saskatchewan in Canada, who led the study, said in a statement.

So how exactly are damming beavers boosting methane production? Well, as their population has proliferated over the past 100 years, so has the number of ponds built by these aquatic rodents, who depend on them for vital habitat. In doing so, however, they have created conditions in which methane gas can be produced from this standing water and subsequently released into the atmosphere, contributing further to climate change.

And with beaver ranges expanding further thanks to conservation efforts, global methane emissions from this source are only expected to grow.

Beavers in North America, Europe and Asia were once entirely wiped out by the early 1900s, but today their numbers have dramatically grown to a staggering 10 million. Researchers behind the new study predict that the Eurasian population will grow by an additional four million as population recovery efforts continue.

And during this time, these dam-builders have created standing ponds and neighboring wetlands. Carbon builds up in the oxygen-poor bottoms of these shallow ponds - usually no more than 1.5 meters (5 feet) high - and generates methane gas.

Since 1900, the growing beaver population has dammed up in excess of 42,000 square kilometers of aquatic pond areas. Consequently, the end of the 20th century saw up to 800 million kilograms of methane released into the atmosphere each year - that's about 15 percent of what wild cud-chewing animals, such as deer or antelope, contributed.

"This, in combination with anticipated increases in surface water temperatures, and likely effects on rates of methanogenesis, suggests that the contribution of beaver activity to global methane emissions may continue to grow," Whitfield said.

The findings were published in the journal AMBIO.

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