The warming climate shifts the dynamics of tundra environments and makes them release trapped carbon, these changes could transform tundra areas from carbon sinks into a carbon source, worsening the effects of climate change.
Researchers from the University of Nottingham were part of a team of over 70 scientists who 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 study has been published today in Nature.
Tundra ecosystems are treeless regions found in the artic and on the tops of mountains. The climate is usually cold and windy with little rainfall. Tundra areas are home to hardy flora and fauna which are responding to warming conditions, particularly in the summer months.
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 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.
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.
Sofie Sjogersten, Professor in Environmental Science at the University of Nottingham's School of Biosciences is an author on the study, she led research that established OTC's in northern Sweden, these are now some of the oldest warming experiments used in the study.
The strong increase in carbon losses from tundra ecosystems that we have shown in our study shows that tundra systems are highly responsive to changes in temperature. Since the Arctic is already warming at a greater rate than other areas we expect the findings from these experiments to reflect ongoing changes in the carbon dynamics of Arctic landscapes.
'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 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.
