An increase in the region's CO2 emissions could accelerate climate change even further.

The Earth's tundra is heating up approximately four times faster than the rest of the planet. According to a new study, this rapid warming in the Arctic ecosystem is stimulating the production of carbon dioxide (CO2) by underground microbes. If this trend holds true, it could establish a feedback loop that exacerbates global warming.

Typically, the tundra is blanketed with small shrubs, grasses, and lichen. Its soils are also rich in organic carbon. "The tundra is normally a sleepy biome," says Sybryn Maes, an environmental scientist at Umeå University in Sweden. However, increasing temperatures are likely to awaken this dormant giant, prompting soil microbes to emit more CO2, a potent greenhouse gas.

Confirming this trend in the wild has been challenging so far. To address this, Maes and her team undertook a study to see if they could verify it. A team of around 70 scientists conducted measurements at 28 tundra sites worldwide. During the summer growing season, they placed clear, open-topped plastic chambers, about a metre (39 inches) in diameter, over patches of ground. These chambers allowed light and precipitation to enter but blocked the wind. The temperatures inside the chambers were, on average, 1.4 degrees Celsius (2.5 degrees Fahrenheit) warmer than at nearby uncovered sites.

The researchers also measured the soil microbes' respiration — the amount of CO2 they emitted into the air. They compared these data to those from nearby uncovered soil patches. Some data were collected over a single year, while other data spanned up to 25 growing seasons. The 1.4 degree Celsius increase significantly boosted respiration, with emissions rising by nearly one-third across the covered sites. The researchers found these effects to be fairly consistent over time.

Their findings were published in May in the journal Nature.

The new data revealed significant variability between sites. Notably, the increase in CO2 emissions was highest in areas where soils had the least nitrogen. Why? As soils warm, plants become more active and require nitrogen, an essential nutrient, for growth. Soil microbes assist by harvesting this nitrogen for the plants. In areas where microbes were highly active in extracting nitrogen, they also released more CO2 into the atmosphere.

These findings provide the strongest evidence yet that warming enhances microbial activity and CO2 emissions, according to Nicholas Bouskill, an environmental microbiologist at Lawrence Berkeley National Laboratory in California. Previous studies on this topic were much smaller and often had conflicting results, including a 2020 study by Bouskill's team.

The long-term question, Bouskill notes, is whether these areas will become net sources of CO2 or if they will continue to store carbon.

NASA estimates that Arctic permafrost stores around 1,700 billion metric tonnes of carbon. Recent studies suggest that by 2100, thawing tundra could release between 22 billion and 524 billion metric tonnes of this stored carbon, depending on the rate of warming.

Given the anticipated increase in CO2 emissions from microbes and their potential to further warm Earth’s climate, "you could say this is a doom scenario," says Sybryn Maes, an environmental scientist at Umeå University in Sweden.

However, Maes notes that the study’s results do not necessarily mean a dramatic spike in the tundra’s overall carbon release. Other processes might offset this effect. For instance, plants could increase their photosynthesis, thereby absorbing and storing more CO2. Additionally, these studies have primarily focused on the Arctic summer, leaving out data from other seasons.

Incorporating data from all seasons and processes in the Arctic could enhance predictions of how the tundra is responding to global warming. This comprehensive understanding could also help gauge the broader impacts of Arctic changes on Earth's climate.

You can read more about studies of gas emissions in the Arctic in our other material.

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