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Understanding the Global Climate-Carbon Feedback

A multinational study team led by environmental physicist Prof. André Butz of Heidelberg University discovered that end-of-dry-season CO2 pulses reoccur each year in the atmosphere over the Australian continent.

Understanding the Global Climate-Carbon Feedback

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The researchers investigated atmospheric CO2 measurements to examine carbon fluxes over Australia. According to their findings, CO2 emissions increase when heavy rain falls on dried-out soil, activating microbes. The findings show that dry regions have a greater influence on global carbon cycle changes than originally thought.

Dry ecosystems and extremely varied precipitation patterns predominate the Australian continent. CO2 emissions over Australia typically increase substantially at the conclusion of the dry season, when the first rains begin to fall.

This effect is well-known at the local level, but it was never observed at the continental level.

Eva-Marie Metz, Institute of Environmental Physics, Heidelberg University

Eva-Marie Metz is a doctoral candidate in Prof. Butz’s working group.

The Greenhouse Gas Observing Satellite (GOSAT) data on atmospheric CO2 concentrations were examined. The researchers discovered that the seasonal pattern of CO2 concentrations over Australia was far more dynamic than initially imagined, using satellite data from 2009 to 2018.

To date, the complete lack of measurement data on the ground has delayed the discovery of the mechanisms causing these variations. The GOSAT satellite data was entered into an atmospheric inversion model, which is used to quantify CO2 flux at the ground level.

According to Dr. Sanam Vardag, whose group also conducts research at Heidelberg University’s Institute of Environmental Physics, it became evident that there must be an unexplored mechanism of CO2 release in Australian terrestrial ecosystems.

Further research revealed that when dry soils are rewetted by heavy rains, CO2 concentrations always rise. According to Dr Vardag, this generates the so-called “Birch Effect.” Soil microorganisms that are dormant when dry are reactivated and proliferate, causing the soil to “breathe” and release CO2.

Because plant photosynthesis does not commence until later in the dry season, carbon dioxide is not bound towards the end of the dry season, resulting in the seasonally high spike in CO2 that the multinational team of researchers saw on a continental level.

Their research has offered an explanation for the variability in carbon fluxes from land to atmosphere. According to Prof. Butz, these findings are important because they indicate that arid regions, such as those seen in Australia, have a higher influence on global carbon cycle changes than previously thought.

Our findings, the first on a continental scale, can be used for climate modeling and thus contribute to a better understanding of the global climate-carbon feedbacks,” details the Heidelberg researcher.

The study was funded by the German Research Foundation.

In addition to the environmental physicists from Heidelberg, scientists from the Max Planck Institute for Biogeochemistry in Jena and the Max Planck Institute for Meteorology in Hamburg and from Australia, Canada, China, France, Japan, the United Kingdom, and the USA took part in the study.

Journal Reference:

Metz, E.-M., et al. (2023). Soil respiration–driven CO2 pulses dominate Australia’s flux variability. Science.


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