Arctic Peatlands Are Expanding Outward at More Than a Metre a Year in Some Locations

Arctic peatlands cover roughly 3% of Earth's surface but hold an estimated 600 billion tons of carbon - more than the combined biomass of all the world's forests. These waterlogged ecosystems accumulate dead plant material faster than it decomposes, locking carbon in layers of peat that can extend meters deep and span thousands of years of accumulation. What happens to that carbon as the Arctic warms is one of the more consequential open questions in climate science.

The Arctic is warming faster than any other region on the planet. Average temperatures across the Arctic have risen approximately 4 degrees Celsius over the past four decades - roughly four times the global average warming rate over the same period. The ecological consequences are substantial and accelerating: sea ice loss, permafrost thaw, shifts in vegetation communities, and changes in the distribution and dynamics of peatlands.

What the Peat Cores Revealed

A study led by the University of Exeter, published in Global Change Biology under the title "Pan-Arctic peatlands have expanded during recent warming," used a direct physical record to assess whether Arctic peatlands have been growing. Rather than relying solely on satellite data - which provides area measurements but limited temporal depth - the researchers analyzed 91 peat core samples from 12 sites spanning the European and Canadian Arctic.

Peat cores are tube-shaped samples extracted vertically from peat deposits. By dating the material at the edges and base of cores, researchers can determine when peat first began accumulating at each location and how far outward the peatland has extended over time. The results showed consistent post-1950 expansion at all 12 sampled sites, with peatland edges now at their greatest areal extent in at least 200 to 300 years - and potentially longer, though the cores' temporal resolution does not extend confidently beyond that window at most sites.

At some locations, peatland edges are advancing outward at more than a metre per year - a rate that, sustained over decades, represents substantial lateral growth of these carbon-storing ecosystems.

"We used peatland cores to assess whether Arctic peatlands are expanding outwards, and if so, how quickly this has happened, and whether it varies regionally," said lead author Dr. Josie Handley, now at the University of Cambridge. "Our results indicate that the peatlands in our study now cover a greater area than at any point during the past 200-300 years - and potentially earlier - and are actively accumulating new peat."

The Carbon Balance Question

Expanding peatlands accumulate additional carbon, which is a negative feedback on warming: more carbon stored in peat means less carbon dioxide in the atmosphere. If Arctic peatlands are growing in area and accumulating peat more rapidly due to increased plant growth in a warmer climate, that could partially offset carbon emissions from other sources.

But the same warming that is driving peatland expansion also increases the risk of peatland degradation through different mechanisms - permafrost thaw, which can drain waterlogged peat and expose organic material to aerobic decomposition; and drought, which can dry peat surfaces and make them vulnerable to fire. A peatland that expands under moderate warming may contract or collapse under more extreme warming, releasing centuries of stored carbon in a relatively short period.

Professor Angela Gallego-Sala, from the University of Exeter, framed the tension directly: "Peatland expansion across the Arctic will profoundly change the fate of carbon in the region, and in the atmosphere. More carbon storage will help to slow climate change, but extreme future warming could cause loss of peatlands and the release of that carbon."

Implications for Arctic Land Use Policy

The study notes that the Arctic is under increasing industrial pressure from shipping, mining, and energy extraction - activities whose expansion is itself partly enabled by Arctic warming and sea ice loss. Peatlands' growing extent and their increasingly recognized importance as carbon stores have direct relevance for decisions about land use and protection in Arctic regions.

"Our study confirms that Arctic peatlands are expanding, highlighting the growing importance of these fragile ecosystems, and the urgent need for them to be protected and valued," said Dr. Katherine Crichton, also from the University of Exeter.

The study did not assess total peatland area across the Arctic - it characterized expansion at the edges of 12 studied sites. Extrapolating edge expansion rates to total area estimates requires additional work, including landscape-level surveys and integration with remote sensing data to understand how representative the 12 sampled sites are of broader Arctic peatland dynamics.

The research is part of the Increased Accumulation in Arctic Peatlands (ICAAP) project, funded by the Natural Environment Research Council, involving international collaborators including Queens University Belfast, Universite du Quebec at Montreal and at Trois-Rivieres, University of Helsinki, and University of Hawaii at Mauna Loa.