New assessment finds increased plant growth will absorb more carbon through end of the century
With temperatures in the Arctic warming far faster than the global average, scientists have been trying to quantify how climate change will affect the carbon cycle.
A new study led by U.S. Geological Survey and University of Alaska at Fairbanks scientists took a close look at the question in Alaska — an effort to get some baseline data on the carbon cycle against which to measure future changes.
Alaska makes up about 18 percent of the total U.S. land area but accounts for about 35 percent of the total carbon stock. The future of that carbon has big implications for global climate. If it’s released quickly, it could drive up global temperatures more than expected. And the carbon stored in high latitude ecosystems is considered to be vulnerable to climate change because of global warming.
“This new assessment specifically reveals how soil carbon losses in Alaska are amplified by wildfires, which have increased in size and frequency with the warming Arctic climate,” said Virginia Burkett, USGS Associate Director for Climate and Land Use Change.
The USGS inventory estimates the ability of different ecosystems to store carbon in vegetation, soils and sediment.
“The cold temperatures of Alaska have led over time to the storage of vast quantities of soil and biomass carbon,” said A. David McGuire, USGS scientist and professor of land ecology at the University of Alaska Fairbanks. “A major concern for this region is how interactions among warming temperatures, permafrost thaw, more frequent wildfires, and changes in stream flow will affect carbon storage and greenhouse gas exchange.”
For now, Alaska is to be considered an overall carbon sink, absorbing about 3.7 million metric tons per year from the atmosphere. And according to the new USGS research, the state could sequester even more carbon through 2100 because of increased vegetation growth
The increased vegetation growth more than counteracts increased carbon emissions from wildfires, a finding that may appear somewhat surprising. The assessment also found regional nuances. Boreal forests and Arctic wetlands will store less carbon, but Alaska’s southeast forest region will take up more.
Most of the total Alaska carbon stock — over 91 percent (estimated to range between 37 and 76.9 billion metric tons) — resides in soils and permafrost. From one-third to two-thirds of the state is underlain by near-surface permafrost.
Wildfire activity is projected to increase during the rest of the century, especially acorss the boreal forest region. A separate study conducted as part of the assessment shows that the permafrost extent could shrink by up to 25 percent by 2100, which could potentially lead to consequences such as altering landscapes, hydrology, biomes, and fire resiliency.
The assessment estimated methane emissions for wetlands in the boreal and arctic regions, indicating that the state’s wetlands are a significant source for greenhouse gas forcing potential in both the near and long-term future.
On the other hand, southeast Alaska is a productive forest region that serves as a carbon sink. The assessment estimates that the productivity of this region would increase under a scenario of climate change and forest management by 8 to 27 percent.
The study also found that birch and aspens will invade existing spruce forests, shifting habitat for wildlife and migratory birds.
“We continue to refine our knowledge of land carbon dynamics,” Burkett said. “It is absolutely vital that we pursue a field-based understanding of the carbon cycle of the Earth in various settings so we can better understand both the natural and the human-influenced mechanisms of climate change. This assessment was based on the best available data from field surveys, remote sensing, authoritative maps, and model simulations.”