How much longer can we rely on plants and soils to reduce some of the harm we cause ourselves by eliminating carbon pollution from the atmosphere as the world warms up as a result of climate change?
Using a daring new method for estimating the temperature sensitivity of ecosystem respiration, which represents one side of the equation balancing carbon dioxide uptake and output in terrestrial environments, new research led by Carnegie’s Wu Sun and Anna Michalak addresses this important question. Their findings are published in Nature Ecology & Evolution.
“Right now, plants in the terrestrial biosphere perform a ‘free service’ to us, by taking between a quarter and a third of humanity’s carbon emissions out of the atmosphere,” Michalak explained. “As the world warms, will they be able to keep up this rate of carbon dioxide removal? Answering this is critical for understanding the future of our climate and devising sound climate mitigation and adaptation strategies.”
To produce sugars for food, photosynthesis, a process used by plants, algae, and some bacteria, needs atmospheric carbon dioxide to be taken up. This takes place in the daytime. But just like us, these identical organisms also engage in respiration during the day and night, ‘breathing’ carbon dioxide out.
It will help scientists’ models for climate change scenarios to be able to more accurately assess the balance of these two processes across all elements of land-based ecosystems, from soil bacteria to trees and everything in between.
In recent years, researchers including Carnegie’s Joe Berry have developed groundbreaking approaches for measuring the amount of carbon dioxide taken up by plants through photosynthesis, such as using satellites to monitor global photosynthetic activity and measuring the concentration of the atmospheric trace gas carbonyl sulfide.
We set out to develop a new way to infer how respiration is affected by changes in temperature over various ecosystems in North America. This is absolutely crucial for refining our climate change projections and for informing mitigation strategies.
Carnegie’s Wu Sun
To track respiration at the scale of entire biomes or continents, however, such techniques have not yet been able to be developed. As a result, respiration is frequently calculated indirectly as the difference between photosynthesis and total carbon dioxide intake.
“We set out to develop a new way to infer how respiration is affected by changes in temperature over various ecosystems in North America,” said Sun. “This is absolutely crucial for refining our climate change projections and for informing mitigation strategies.”
Michalak, Sun, and their colleagues developed a new way to infer at large scales how much respiration increases when temperatures warm using measurements of atmospheric carbon dioxide concentrations. A network of dozens of monitoring stations across North America took these measurements.
It was discovered by the team that atmospheric observations point to lower temperature sensitivities of respiration than are often depicted in cutting-edge models. They also discovered that croplands and woodlands exhibit different levels of sensitivity.
Since earlier research concentrated on sensitivities for much smaller plots of land, temperature sensitivities of respiration have not yet been restricted using observational data at this scale.
“The beauty of our approach is that measurements of atmospheric carbon dioxide concentrations from a few dozen well-placed stations can inform carbon fluxes at the scale of entire biomes over North America,” Sun explained.
“This enables a more comprehensive understanding of respiration at the continental scale, which will help us assess how future warming affects the biosphere’s ability to retain carbon,” Sun emphasized.
At the biome or continental size, the researchers unexpectedly discovered that respiration is less responsive to warming than previously believed. But they caution that this temperature sensitivity is just one piece of a complex puzzle.
“Although our work indicates that North American ecosystems may be more resilient to warming than plot-scale studies had implied, hitting the brakes on climate change ultimately depends on us ceasing to inject more and more carbon into the atmosphere as quickly as possible. We cannot rely on the natural components of the global carbon cycle to do the heavy lifting for us,” Michalak cautioned. “It is up to us to stop the runaway train.”
Other members of the research team include: Xiangzhong Luo, Yao Zhang, and Trevor Keenan of the University of California Berkeley and Lawrence Berkeley National Laboratory; Yuanyuan Fang of the Bay Area Air Quality Management District; Yoichi P. Shiga of the Universities Space Research Association; and Joshua Fisher of Chapman University.
