Understanding climate warming impacts on tundra carbon

Climate warming is shifting the dynamics of the world’s vast tundra environments and making them release trapped carbon, according to a new study supported by the Hutton and published in the journal Nature.

These changes could transform tundras – treeless landscapes in polar regions that cover around 10% of the earth’s surface – from carbon sinks into a carbon source, exacerbating the effects of climate change.

The study, involving a team of over 70 scientists, brought together data from 56 experiment sites spread across 28 arctic tundra locations around the world. Each experiment site used open-top chambers to act like mini-greenhouses to experimentally simulate the effects of warming.

This created a 1.4°C increase in air temperature and a 0.4°C increase in soil temperature, along with a 1.6% drop in soil moisture, at the sites. The result was a 30% boost in ecosystem respiration – plant and soil activity that releases CO₂ – during the growing season.

At some of the older experiment sites, the changes persisted for at least 25 years after the start of the experimental warming – which earlier studies hadn’t revealed.

“We knew from earlier studies that we were likely to find an increase in respiration with warming, but we found a remarkable increase – nearly four times greater than previously estimated, though it varied with time and location,” says Sybryn Maes of Umeå University, the study’s lead author.

Dr Thomas Parker, an ecologist at the Hutton who conducted two of the warming experiments in Alaska as part of the project and is a co-author on the Nature publication, says, “We’ve shown that carbon emissions from these landscapes increase in response to warming, but that’s one half of the balance. The other half is how much is then taken up by plants as vegetation grows. Warming will make plants grow faster, but we don’t yet know if what they take up as they will match how much is released.”

The increase in ecosystem respiration also varied with local soil conditions, such as nitrogen and pH levels. This means that differences in soil conditions and other factors lead to geographic differences in the response – some regions will see more carbon release than others. Understanding the links between soil conditions and respiration in response to warming is important for creating better climate models.

“Our work represents the first assessment of ecosystem respiration response to experimental warming across such a broad environmental gradient in the tundra, incorporating a comprehensive set of environmental drivers,” says Associate Professor Ellen Dorrepaal of Umeå University.

The study also offers a broader perspective on Arctic and alpine regions by predicting increases in respiration across the whole tundra area together with more detailed information about variation in the sensitivity of the response.

“We see that some areas, particularly parts of Siberia and Canada, exhibit greater sensitivity to warming,’ says Professor Matti Kummu of Aalto University. “We anticipate an increase in respiration across the whole Arctic and alpine tundra, but more in situ data, particularly on the local soil conditions, is key to addressing the outstanding uncertainties and refining our predictions.”

Understanding how ecosystems shift in response to climate change and how these changes feed back into the climate is vital to get an accurate picture of how our world will change. These findings serve as an important baseline for improved climate models, but the researchers plan to refine them further by analysing how the experimental sites change over time and expand the experiment’s scope to include new sites.

Dr Parker’s work at the Hutton continues with projects including the MYCONET project, which is an investigation into whether warming and increasing root and fungal activity is leading to increased carbon release from arctic soils. This will focus on how warming is enabling trees to grow in areas that were too cold for them before and if their growth results in increased emissions from the arctic ecosystem.


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