Arctic tundra, a frozen treeless biome which has stored carbon for thousands of years, has now become a source of heat-trapping greenhouse gases (GHGs) which are the primary drivers of global warming, according to a new report by the National Oceanic and Atmospheric Administration’s (NOAA). Increased wildfires and unusually high temperatures are the main reasons behind the dramatic transformation of this Arctic ecosystem.
The analysis, ‘Arctic Report Card’, is a yearly report on the polar region and was published last week.
Arctic tundra emitting more carbon than storing it would have global consequences as this would exacerbate climate change, whose adverse impacts are already unfolding across the world.
How does the Arctic tundra store carbon?
In a typical ecosystem, plants absorb carbon dioxide (CO2) from the atmosphere through photosynthesis. These plants grow, die, or are eaten by animals which also grow and die. When they die, the carbon in their corpse feeds microorganisms such as bacteria or fungi which break down larger molecules and return CO2 to the atmosphere, thereby completing the carbon cycle.
However, in the case of Arctic tundra, the decomposition of organic matter is dramatically slowed down due to the cold climate. Plant and animal remains can stay trapped for thousands of years in a layer of permafrost — any ground that stays frozen for at least two years straight — thwarting CO2 from getting released back into the atmosphere. Scientists estimate that Arctic soils store more than 1.6 trillion metric tonnes of carbon across the region. That is about double the amount of carbon in the atmosphere, according to a report by Vox.
Why is the Arctic tundra emitting more carbon than absorbing it?
In recent years, however, the Arctic tundra’s ability to emit less and absorb more carbon has taken a hit. The new analysis, which incorporated more data and better methods of examination, confirmed that the ecosystem has now become a source of CO2 and methane (CH4) — a more potent GHG — emissions.
That has happened for two main reasons. One is rising temperatures. The report said the Arctic is warming four times the global rate, and that annual surface air temperatures in the Arctic in 2024 were the second-warmest on record since 1900.
As a result, the Arctic’s permafrost is thawing, meaning microbes in the soil are becoming active and breaking the organic matter down, releasing CO2 and CH4 into the atmosphere.
Speaking to NPR, Twila Moon, lead editor of the Arctic Report Card and a scientist at the National Snow and Ice Data Center, said permafrost is like chicken in the freezer — as long as it stays frozen, microbes stay away.
“Once you have that chicken out of your freezer, it is thawing and all those microbes are getting to work, breaking down the chicken, making it rot,” she said. “The permafrost is really doing the same thing.”
Another reason is that, in recent years, the Arctic has witnessed an increase in the frequency and intensity of wildfires. Last year was the worst wildfire season in the Arctic on record, and 2024 was the second-biggest year for wildfire emissions, according to the Vox report. Wildfire smoke adds GHG emissions to the atmosphere while also speeding up the thawing of permafrost.
Wildfires and rising temperatures together, between 2001 and 2020, caused the Arctic tundra to release more carbon than its plants removed from the air, probably for the first time in many millennia, the report said.
What happens next?
The analysis said it is still possible to flip the Arctic tundra in the other direction, making it absorb more carbon than emitting it. The only way to do so is to reduce global GHG emissions.
Brendan Rogers, a scientist at the Woodwell Climate Research Center who contributed to the Arctic Report Card, told NPR, “With lower levels of climate change, you get lower levels of emissions from permafrost… That should motivate us all to work towards more aggressive emissions reductions.”
However, this is unlikely to happen as the world continues to emit GHGs into the atmosphere at unprecedented levels. A new research by the Global Carbon Project science team published in November found that emissions from burning fossil fuels are likely to increase slightly in 2024 compared to last year.
“With projected emissions from land-use change (such as deforestation) of 4.2 billion tonnes, total CO2 emissions are projected to be 41.6 billion tonnes in 2024, up from 40.6 billion tonnes last year,” the study said.
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