Microbes in the Arctic may be emitting higher levels of climate-warming gases

The Earth’s tundra is warming about four times faster than the rest of the planet. The increase in heat in this Arctic ecosystem is being driven by carbon dioxide (CO₂). A new study suggests that underground microbes may be causing global warming, which could create a feedback loop that leads to even more warming.

Tundra is typically covered with shrubs, grasses, and lichens. The soils in these frigid lands tend to be rich in organic carbon. Normally, the tundra is a “sleeping biome,” says Sibryn Maas, an environmental scientist at Umeå University in Sweden. But Global warming will awaken a sleeping giant. This could lead soil microbes to release more CO₂, a powerful greenhouse gas.

So far, this trend has been hard to see in practice, so Maes and his team decided to try and see if it was possible.

In total, about 70 scientists took measurements in 28 tundra locations around the world. During the summer growing season, they set up open, clear plastic containers on the ground. Each was about one meter (39 inches) in diameter, and allowed light and rainwater through but kept out wind. Summer temperatures inside the containers were on average 1.4 degrees Fahrenheit (2.5 degrees Celsius) warmer than nearby, uncovered sites.

The researchers also measured soil microbial respiration, i.e. CO₂. The researchers filmed the plumes of smoke rising from the soil and shooting into the air. They then compared these data with data from nearby, uncovered soil. Some of the data lasted for a year, but in other locations, the team collected data for much longer, up to 25 growing seasons.

The 1.4 degree rise in temperature significantly increased breathing. Increased by almost a third across all sites. Overall, the effects appear to be fairly consistent over time, the researchers concluded.

They released their findings in May. Nature.

Some sites were more sensitive

The new data showed that there was a lot of variation from place to place. For example, the increases in CO2 were most pronounced in places where the soil had the least nitrogen. Why? As the soil warms, plants become more active. Plants need a nutrient called nitrogen to grow. Soil microbes tend to harvest the nitrogen on behalf of the plants. And in places where these microbes were really active, trying to find and extract nitrogen, they exhaled more CO₂ in the air.

These new findings provide the best evidence yet that warming increases microbial activity and CO₂. Nicholas Bauskill is an environmental microbiologist at the Lawrence Berkeley National Laboratory in California. Previous studies on this have been much smaller, and have produced some conflicting results. Including a 2020 study by Bousquille’s team).

The long-term problem, Bouskill said, is that “these areas [CO₂] will continue to primarily store carbon?”

NASA has discovered that the Arctic permafrost stores 1.7 trillion tonnes of carbon. Recent studies suggest that by 2100, thawing the Tundra could release between 22 billion and 524 billion tonnes of stored carbon – how much is lost depends on how quickly the climate warms.

Given the expected increase in CO₂ from the release of carbon dioxide by microorganisms and the potential for that to further warm the Earth’s climate, “this is a catastrophic scenario,” Mars said.

But she added that the findings don’t mean that tundra carbon emissions will skyrocket. Eventually, other processes might counter this. For example, plants might speed up photosynthesis. In the process, they’ll absorb and store more CO₂. And these studies don’t look at what happens outside the Arctic summer.

Including data on all events in the Arctic could improve predictions of how the tundra is responding to global warming, and the data could also help gauge how Arctic influences affect the climate in other parts of the world.