Max-Planck-Institute for Meteorology: CO2 emission reductions only distinctly attributable in the atmosphere after a decade

In a new study Aaron Spring, Dr. Tatiana Ilyina and Prof. Jochem Marotzke, scientists at the Max Planck Institute for Meteorology (MPI-M), show that atmospheric CO2 concentrations fluctuate so much that a slowdown in CO2 increase would only be distinctly attributable to CO2 emission reductions after a decade.

The amount of anthropogenic CO₂ emissions remaining in the atmosphere varies each year because land and ocean efficiency to take up parts of those emissions depends on the current state of the climate. For example, in warm and wet years, trees grow stronger and take up more carbon from the atmosphere. Therefore, the remaining atmospheric increase is less strong than in cold or dry years. Currently, under strong and increasing CO₂ emissions, this variability due to the carbon sinks is not obvious to pick up from the Keeling curve, a daily record of atmospheric carbon dioxide concentration.

Figure 1: Frequency of the trend change in atmospheric CO2. — Figure 1: Frequency of the trend change in atmospheric CO2, over the period 2021-2025 compared to 2016-2020, in 100 simulations that all assume the same reduction in CO2 emissions. Adapted from Spring, 2021, Abb. 2c.

Spring and his co-authors used 100 numeric simulations based on the Max Planck Institute Earth system model (MPI-ESM), started with slightly perturbed initial conditions (https://mpimet.mpg.de/en/science/projects/integrated-activities/grand-ensemble). They investigated after how many years CO₂ emission reductions would cause a reduction in the present increasing trend.

They found that the atmospheric CO₂ growth in the five years after CO₂ emission reductions started decreases in 70 simulations and the average of all simulations compared to the five years before [see Figure 1]. That implies that in 30 simulations atmospheric CO₂ increases stronger than before despite CO₂ emission reductions on the basis of internal variability. Only when considering 10-year trends, a slowdown in atmospheric CO₂ increase is caused by CO₂ emission reductions distinctly.

These results show that policy-makers, when assessing mitigation efforts every five years, should not pay too much attention to previous multi-year trends in atmospheric CO₂ observations, because these are prone to internal variability.

Original publication:

Spring, A., Ilyina, T., & Marotzke, J. (2020). Inherent Uncertainty Disguises Attribution of Reduced Atmospheric CO₂ Growth to CO₂ Emission Reductions for up to a Decade. Environmental Research Letters. doi: 10.1088/1748-9326/abc443

Reference paper:

Marotzke, J. (2019). Quantifying the irreducible uncertainty in near-term climate projections. Wiley Interdisciplinary Reviews - Climate Change, 10: e563. doi:10.1002/wcc.563

Contact:

Aaron Spring
Max Planck Institute for Meteorology
Email: aaron.spring@we dont want spammpimet.mpg.de

Dr. Tatiana Ilyina
Max Planck Institute for Meteorology
Email: tatiana.ilyina@we dont want spammpimet.mpg.de

Prof. Dr. Jochem Marotzke
Max Planck Institute for Meteorology
Phone: +49 (0)40 41173 311 (Assistant Kornelia Müller)
Email: jochem.marotzke@we dont want spammpimet.mpg.de

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