Arctic shrubs may cause greenhouse emissions, report says

One of the largest ever studies of how climate change is remakingthe face of the Arctic has found that shrubs are gradually takingover the tundra.

And David Hik, co-author of the paper in Nature Climate Change,said the increasing dominance of shrubs over grasses is likely to bethe cause of its own climate feedback.

"The shrubs are a dark surface and they reflect less of thesun's radiation back into the atmosphere," he said.

Shrub roots, which penetrate deeper into the soil than grassroots, are also likely to break up permafrost and allow water totrickle down into it.

"All of the evidence is that that leads to the release of storedcarbon into the atmosphere," Hik said.

9 countries, 60 years

Hik and his colleagues completed a study that looked across nineArctic countries and used data collected over 60 years. Althoughscientists have known for some time that shrubs were graduallymoving north, the rate at which the "shrubline" is moving indifferent parts of the Arctic has been a mystery.

Hik's paper suggests the changes are happening faster in northernEurope and Russia than they are in North America.

They also foundthat soil moisture and depth are crucial factors in how fast shrubsexpand their range.

The slow shift from grassy to shrubby landscapes could haveprofound consequences for the people and animals that live there.

Caribou can't eat shrubs

Caribou, for example, require the lichens found in the opentundra and can't eat shrubs. Moose, on the other hand, love tobrowse on shrubs and their population has been growing in the North.

As well, Arctic permafrost is considered one of the globe's greatstorehouses of greenhouse gases such as methane, which is much morepotent in its climate-changing effects than carbon dioxide.

Studies such as this, which collect and digest data from vastareas of the globe, are the future of climate science, said Hik.

"We're now putting all of our data together and trying tounderstand what's happening at a larger scale.

Canadian scientist Isla Myers-Smith headed the research team.She examined rings of willow shrubs to compare annual growth.

She says this is one of the most significant examples of the effect of climate change on ecosystems.