New method makes it possible to assess the direct effects of human land use on the carbon cycle

Vegetation and soil are the most important carbon sinks on land, as they currently absorb nearly a third of human-caused carbon dioxide emissions, helping to significantly slow global warming. In addition to energy production and industry, land use contributes substantially to the global anthropogenic CO2 emissions.

However, forests and woodlands do not sequester carbon as reliably as previously believed: their function as a carbon sink is subject to large annual fluctuations and they are susceptible to various environmental influences, even without direct human activity. This was revealed by the results of a new modeling approach developed by a team under LMU geographer Prof. Julia Pongratz.

According to these results, it is not only direct human activities such as deforestation or reforestation/afforestation that determine the effectiveness of the forest as a carbon sink. Natural environmental factors such as forest fires and extreme weather events, and indirect anthropogenic influences such as increasing atmospheric CO2 concentration also affects the amount of carbon that can be captured by trees and other woody vegetation.

To better understand these dynamics, Selma Bultan, a member of Pongratz’s team and lead author of the study, has developed a methodology that allows scientists to discern the direct effects of human land use on global CO2.2 fluxes from those of natural environmental factors based on satellite and other Earth observation data.

“We are integrating Earth observation data into a model that simulates CO2 fluxes through land use. NASA colleagues have provided us with new global vegetation data from the past twenty years,” explains Selma Bultan. The development of this new modeling approach was made possible by the extensive spatial and temporal coverage of the data.

Human and environmental influences on the carbon cycle can be distinguished

“Our study addresses the challenge of separating direct human influences through land use from indirect side effects and natural processes,” explains Pongratz.

“This differentiation is important, because isolating the direct anthropogenic effects shows the real progress of climate protection measures. In contrast, the environmental effects indicate how reliably the terrestrial biosphere absorbs and stores CO.2 from the atmosphere. If we constantly give the model used in this study new data, it could help scientists monitor the success of climate protection measures, especially the implementation of international agreements to reduce CO2 emissions.2 emissions from land use change, such as deforestation. This allows an objective assessment of the extent to which countries are meeting their climate targets.”

The study also examines how climate change affects vegetation’s ability to store carbon. “Our results show that the CO2 sinking in forests and woodlands is subject to stronger annual fluctuations and responds more sensitively to extreme events such as droughts than previously believed,” says Bultan.

“Thanks to these findings, we can better estimate the potential contribution of land use to climate protection, for example through the use of technologies to actively remove CO2 from the atmosphere.”

Both LMU scientists also contribute to the Global Carbon Project (GCP), an international collaborative effort of researchers, exploring the dynamics of global CO2 fluxes, summarized in an annual report. According to the latest report, land use currently accounts for about nine percent of all anthropogenic CO2 emissions. How people interact with terrestrial ecosystems is therefore also crucial for achieving the climate goals of the Paris Agreement.

Researchers can now draw on an extensive database of remote sensing images from satellites for integration into process-based models to increase our understanding of the global carbon cycle and to monitor how climate change is evolving and how successful climate protection measures are in mitigating it. “Time is on our side: The satellite age now spans a long enough period to monitor the impact of political developments on deforestation or observe the influence of increasing drought on vegetation,” said Raphael Ganzenmüller, another LMU geographer involved. used to be. in the study.

“The more data we have – for example on grassland vegetation and on soil organic carbon – the more accurately we can estimate natural and anthropogenic CO2 fluxes, furthering our understanding of the entire terrestrial carbon cycle,” says Selma Bultan.

Increased temporal resolution of the data could also allow scientists to analyze the impact of short-term extreme events, such as individual droughts within a year. “Our study reveals the potential of integrating observational data into models for more robust estimates of global CO2 fluxes – this demonstrates the ever-expanding possibilities offered by satellite-based Earth observation.”

The research was published in nature communication.