Warmer climate increases tundra carbon emissions
The warming climate is changing the dynamics of tundra environments and causing them to release sequestered carbon, according to a new study with researchers from the University of Gothenburg published in Nature. These changes can transform the tundra from a carbon sink to a carbon source, which in turn exacerbates the effects of climate change.
A team of over 70 scientists from different countries used open-top chambers (OTC) to experimentally simulate the effects of warming on 28 tundra areas around the world. OTC chambers basically work like mini greenhouses, shutting out wind and trapping heat to create localised warming.
The experiments led to an increase in air temperature by 1.4 degrees and soil temperature by 0.4 degrees. The changes increased ecosystem respiration, by 30 per cent during the growing season, which in turn led to more carbon being released due to increased metabolic activity in the soil and plants.
Remarkable increase
The changes persisted for at least 25 years after the start of experimental warming - something not shown in previous studies.
"We knew from previous studies that we were likely to see an increase in respiration with warming, but the increase we saw was remarkable – almost four times greater than previously estimated, although it varied with time and location," says Sybryn Maes from Umeå University, the study's lead author.
The University of Gothenburg research programme in Latnjajaure field station has been central to the study, as OTC measurements have been going on continuously for over 30 years at the site.
"This is one of the longest measurement periods included in the study. Previously, it was thought that changes in respiration would level off over time, but we see no such trend," says Mats Björkman, Associate Professor at the University of Gothenburg and one of the project leaders of the study.
Variations with soil conditions
How much ecosystem respiration increased also varied with local soil conditions, such as nitrogen and pH levels. Differences in soil conditions and other factors lead to geographical differences in the response – some regions will see more carbon emissions than others. Understanding the links between soil conditions and respiration in response to warming is important for creating better climate models.
The study also provides a broader perspective in terms of Arctic and alpine regions by predicting how respiration will increase across the entire tundra area, along with more detailed information on how the sensitivity of the response varies.
"We see that some areas, especially parts of Siberia and Canada, are more sensitive to warming," says Professor Matti Kummu of Aalto University. "We expect increased respiration throughout the Arctic and the alpine tundra, but more in situ data, especially on the local soil conditions, is essential to address the uncertainties that remain and refine our projections."
Understanding how ecosystems are changing as a result of climate change and how these changes feed back into the climate is crucial to getting an accurate picture of how our world will change.
Scientific article in Nature: Environmental drivers of increased ecosystem respiration in a warming tundra.
Contact: Mats Björkman, Senior Lecturer at the Department of Biology and Environmental Sciences at the University of Gothenburg, telephone: 031-786 28 74, e-mail: mats.bjorkman@gu.se.
Professor Robert G. Björk of the Department of Earth Sciences at the University of Gothenburg is also involved in the study.