Will Climate Warming Trigger Carbon Release from Tundra? Massive Study Provides Long-Awaited Answers

Media contact: Diana Kenney dkenney@mbl.edu; 508-685-3525

The cold, treeless tundra landscape that encircles the Earth just below the Arctic ice caps - including much of Alaska and Canada - is known to contain huge stores of carbon in its frozen soils. But a big unknown in global change biology has been whether a warming climate will cause this carbon to be released as carbon dioxide, a greenhouse gas, creating a positive feedback loop into climate change.

Today, a massive synthesis study published in Nature confirms that climate warming shifts the dynamics of tundra environments and makes them release stores of trapped carbon. These changes could transform tundras from carbon sinks into a carbon source, exacerbating the effects of climate change.

A team of over 70 scientists, including the late Jianwu (Jim) Tang, senior scientist in the MBL Ecosystems Center, used open-top chambers (OTCs) to experimentally simulate the effects of warming on 28 tundra sites around the world. OTCs basically serve as mini-greenhouses, blocking wind and trapping heat to create local warming.

The warming experiments led to 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. These changes boosted ecosystem respiration (carbon dioxide production) by 30% during the growing season, causing more carbon to be released because of increased metabolic activity in soil and plants. 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.

A plaque memorializing the late MBL scientist Jim Tang in the MBL Quad. Credit: Diana Kenney

The increase in ecosystem respiration also varied with local soil conditions – 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.

For their contribution to the study, Jim Tang and co-author Thomas Parker, then a postdoctoral scientist with Tang, measured the impact of warming on ecosystem respiration at Toolik Field Station in arctic Alaska in 2015 and 2016.

"We are a small part of a big study, but it is interesting to see that our study sites fit comfortably within the overall patterns around the Arctic," Parker says.

‘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 analyzing how the experimental sites change over time and expand the experiment’s scope to include new sites.

Citation:

Maes, S. L. et al. (2024). Environmental drivers of increased ecosystem respiration in a warming tundra. Nature, DOI: 10.1038/s41586-024-07274-7

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