Arctic greening will not slow local climate changes

Arctic greening will not occur quickly enough to sequester a substantial amount of atmospheric carbon dioxide, according to a new study from UC Irvine.

As the climate warms and more plants grow in the Arctic, there was hope that the vegetation would absorb large amounts of CO2 during photosynthesis. The new research suggests that the greening landscape will not be as powerful of a carbon sink as previously expected. 

The study was led by Jon Wang, an Earth system scientist at UCI, and Professor Mark Friedl of Boston University.

“What does greening really mean? Can we really trust it to save us from climate change?” said Wang. “A big question is: What’ll happen to the carbon that’s currently stored in these forests as above-ground biomass in the face of a changing climate?”

Unfortunately, the answer to this question is that much of the carbon is not staying stored in the plants. This is because wildfires and timber harvests are becoming more common in the Arctic – as climate change impacts high latitudes at an accelerated rate.

“What we found overall is across this whole domain over the past 31 years the carbon stocks have increased modestly,” said Wang. “What we estimate is that 430 million metric tons of biomass has accumulated over the last 31 years – but across this domain it would’ve been nearly double if it weren’t for these fires and harvests that are keeping it down.”

According to Wang, the assumption before was that Arctic greening was happening and it was going to help draw climate-warming carbon dioxide concentrations down – but no one knew the exact extent of that help.

To investigate, the researchers used observational satellite data to model the amount of carbon stored in biomass across a 2.8 million square kilometers in Canada and Alaska.

ICESat data provides measurements of the height of forest canopies, while Landsat data extends back 31 years to 1984 and provides information about plant biomass abundance. 

The study showed that plant biomass had increased, but not as much as previous computer models suggested it would. The difference is that previous models have struggled to account for increasing frequency and severity of wildfires in the Arctic. 

Wang hopes the results will help scientists construct more accurate models to inform the world of what to expect from climate change throughout the remainder of this century. 

Study co-author James Randerson believes the new data are important because they provide an independent means to test climate models, and because of the way they represent feedbacks between the carbon cycle and the climate system. 

“The rates of carbon accumulation in this region are lower that what previous studies have indicated, and will push the science community to look elsewhere for the main drivers of the terrestrial carbon sink,” said Randerson.

“The change is good news for climate – but it’s also much lower than we might’ve expected, because these fires have raged, and gotten more severe,” said Wang.

The study is published in the journal Nature Climate Change.

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By Chrissy Sexton, Earth.com Staff Writer