Some Arctic shrubs could be making climate change worse

As the Arctic gets warmer and greener, some northern plants appear to be contributing carbon dioxide to the atmosphere rather than removing it.

Researchers say that’s because in Arctic ecosystems, most carbon is found in the soil and permafrost. Some plant species in the region get nutrients by decomposing carbon stored in the soil, then releasing it into the atmosphere as carbon dioxide. 

The scientists involved say this needs to be better represented in global models – which, they argue, currently underestimate how the phenomenon affects climate change.

“You might lose enough carbon from the soil to mean that actually makes things worse, rather than better,” explained lead author Dr Lorna Street, from the University of Edinburgh’s School of GeoSciences. 

Researchers compared the impact of birch and alder shrubs on soil carbon. Photo: Lorna Street

The study, published in the journal Global Change Biology, examined birch and alder shrubs in the Trail Valley Creek area, about 60 km north of Inuvik.

Researchers found that while alder shrubs increased the amount of carbon collected in the soil, birch shrubs were releasing carbon that had been stored in the soil for more than 50 years.

Street believes that’s because alder shrubs don’t rely on the decomposition of soil carbon to get nutrients, while birch shrubs do. 

“If the abundance of alder increases lots in the tundra then that’s probably a good thing, because it’s probably going to increase the amount of carbon that’s stored in the soil,” she said. “But if the abundance of birch in the tundra increases substantially, then that’s possibly not the case.”

Street noted if more carbon is released from the soil, that could accelerate climate change on a global level. More locally, she said, if the tundra changes to more shrubby vegetation then soil characteristics could change, affecting the ecosystem and rate of thaw.

The biggest lesson from the study, Street said, is that researchers might be underestimating the impact of soil carbon decomposition on climate change. She said this process needs to be accounted for in climate models to better understand what could happen in the future.

“That is really important when it comes to knowing how much work we have to do to reduce human carbon emissions,” she said, highlighting targets in the Paris Agreement.

Street said similar studies will be required to verify the results, adding research groups plan to examine the same topic in different countries.