Frozen carbon in northern permafrost is in motion – we calculated how much

Among the most rapidly changing parts of our planet are the coldest landscapes at the top of the globe, south of the Arctic. The region is warming two to four times faster than the global average.

The frozen ground beneath these “boreal” forests and treeless plains or “tundras” is rapidly thawing. This is a problem because permafrost contains enormous amounts of vulnerable carbon, more than twice as much carbon as is already present in the atmosphere. Some of this carbon is now in motion.

We wanted to find out how much carbon and nitrogen are being released from the northern permafrost region. The environment can be a source of greenhouse gases or a “sink”—effectively absorbing carbon and removing it from the atmosphere. Therefore, we had to determine and balance the budget.

Within Global Carbon Projectwe have now published The first comprehensive greenhouse gas budget, calculating sources and sinks of greenhouse gases for the northern permafrost region. It contains a mixed bag of good and not-so-good climate news.

What is permafrost and why should we worry?

Permafrost it is the ground that remains frozen. It may contain soil, peat, rocks and ice. Often the remains of ancient plants and animals, such as those now extinct Woolly Mammoth can also be seen.

In such cold conditions, plants primarily grow in the summer. New leaf litter and dead plants are then quickly frozen and stored for thousands of years. This has led to the accumulation of phenomenal carbon reserves: more than a trillion tons. By comparison, all tropical forests and soils store less than half this amount.

While the top “active” layer of soil may thaw naturally during warmer months, the lower layers usually remain frozen. But now, as human-caused climate change makes soils warmer, the thawing season is getting longer, and permanently frozen carbon is melting, too.

Once the soil has thawed, microbes go to work breaking down dead plants and other decaying organic matter. When this process occurs in the presence of oxygen, carbon dioxide (CO₂) is released. In the absence of oxygen (for example, in lakes and water-saturated soils), methane (CH₄) is released.

Methane is a more potent greenhouse gas than CO₂ because it traps more heat in the atmosphere, so it is of particular concern. Unfortunately, melting ice in the permafrost leaves much of the earth wet and low in oxygen, so it releases more methane.

Decaying soil organic matter also contains nitrogen, which causes emissions of nitrous oxide, another powerful greenhouse gas.

The process of warming leading to more greenhouse gas emissions, which in turn leads to more warming and more greenhouse gas emissions, is known as a “positive” carbon-climate feedback loop. To limit global warming, it is important to avoid these positive or self-reinforcing processes.

Another type of feedback loop is “negative” carbon climate feedback, although this is actually a good thing. It is negative because it reduces the total amount of emissions remaining in the atmosphere.

In this study, we found evidence of a negative feedback between carbon emissions and climate, which reduces the total amount of emissions remaining in the atmosphere. Longer growing seasons (due to global warming), increased available nitrogen in soils, and higher concentrations of CO₂ in the atmosphere all help plants grow longer and store more carbon.

What have we done?

A team of scientists from 35 research institutions collected and assessed all available observations and modeling of greenhouse gas emissions on land, in fresh water and in the atmosphere. Using this information, we developed a combined greenhouse gas budget for CO₂, methane and nitrous oxide for the period 2000–2020.

This attempt was part global assessment of all regions and oceans.

Carbon on the move

We found that permafrost is a small to medium-sized CO₂ sink, storing between 29 and 500 million tons of carbon per year.

Boreal forests in Canada and Russia, as well as other smaller regions, were largely responsible for sequestering CO₂ during the study period from 2000 to 2020, which saw increased plant growth and longer growing seasons. But at the same time, lakes, rivers and forest fires were sources of CO₂.

The region was also a source of methane and nitrous oxide, the world’s second and third most important greenhouse gases after CO₂.

Although methane emissions were already occurring before anthropogenic warming, the number of sources has increased over time. We found that wetlands are the largest source of methane, and as the frozen ground melts, much of the landscape becomes saturated with water.

The largest sources of nitrous oxide emissions, although relatively small per unit area, come from dry tundra and boreal forests.

Based on calculations over 100 years, the combined contribution of all three greenhouse gases to global warming is close to neutral. This means that the CO₂ sink results in cooling that offsets the warming from methane and nitrous oxide emissions. The Intergovernmental Panel on Climate Change (IPCC) uses a 100-year time period to compare all greenhouse gases in the 21st century.

But within 20 years, current greenhouse gas emissions will become a net source of warming. The strong warming potential of methane emissions is what influences temperatures in the short term.

What does the future hold for us?

It is not yet clear how greenhouse gas emissions in the permafrost region will change in the future. But we know that methane emissions are already rising in many regions, and this trend is likely to continue.

Earth system models used by the IPCC suggest that it is possible maintain CO₂ absorber in the 21st century under different emission scenarios. But these models largely ignore local destruction of permafrost (as opposed to slow thawing) and extreme wildfires, which can lead to rapid increases in greenhouse gas emissions.

Forest fires in permafrost regions are a growing concern. Our last budget year was 2020, so we missed unprecedented bushfires 2021 in Siberia And 2023 in Canada. Wildfire emissions from each of these two events amounted to about half a billion tons of carbon, enough to neutralize and even switch the CO₂ sink to a clean source.

The only way to keep permafrost carbon in the ground is to quickly reduce and ultimately eliminate greenhouse gas emissions from human activities. If this is not done, global warming is likely to help, as warming causes permafrost to melt and release more carbon and nitrogen from ancient reserves, creating a continuous feedback loop.