EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Variability of atmospheric CO2 in Earth System model large-ensemble simulations with an interactive carbon cycle

Kelli Johnson1,2, Hongmei Li2, and Tatiana Ilyina2
Kelli Johnson et al.
  • 1Universität Hamburg, Institute of Oceanography, Hamburg, Germany
  • 2Max Planck Institut für Meteorologie, The Ocean in the Earth System, Hamburg, Germany

Atmospheric CO2 concentrations have increased from around 280 parts per million (ppm) in 1800 to over 416 ppm in 2020. This is a direct result of increasing anthropogenic emissions of CO2 since the industrial era. Nearly half of the emitted anthropogenic CO2 is taken up by the ocean and terrestrial ecosystems, while the remaining half remains in the atmosphere, where it is a heat-trapping greenhouse gas. The growth of atmospheric CO2 varies from year to year with inhomogeneous spatial distribution depending on the CO2 uptake by the ocean and land. The CO2 uptake by the natural sinks and atmospheric growth are affected by the climate variations and the long-term changes; in turn, the variations of the carbon cycle also modulate global climate change. The state-of-the-art large ensemble simulations based on Earth System Models (ESMs) prescribe the concentration of atmospheric CO2, but the missing interactive response of atmospheric CO2 changes to the CO2 fluxes into the ocean and the land hinders the investigation of the variability in atmospheric CO2. Furthermore, such simulations will be insufficient to represent the changes in the efficiency of the land and ocean carbon sinks once emissions start to decline. Based on the low-resolution version of the Max Planck Earth System Model v1.2 (MPI-ESM-1.2-LR), we have done a novel set of 30-member ensemble simulations driven by anthropogenic CO2 emissions. In such simulations, atmospheric CO2 concentrations are computed prognostically, modulated by the strength of CO2 fluxes to the land and the ocean. While general trends in atmospheric CO2 concentrations for different Shared Socioeconomic Pathways (SSP) are well known, trends in its global dispersion and variations within the seasons of each year have not been investigated in ESMs with an interactive carbon cycle. In this project, we use MPI-ESM-1.2-LR large ensemble simulations under four SSP scenarios, i.e., SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5, together with historical runs to analyze changes of atmospheric CO2 concentrations. We focus on seasonal variability and spatial distribution of atmospheric CO2 changes in the presence of internal climate variability. We address two questions: first, what is the temporal evolution of atmospheric CO2 in regard to its seasonal variability by the end of the century following different emission pathways; and second, how does atmospheric CO2 evolve spatially (horizontally across the globe and vertically into the stratosphere) in the historical period and future projections until 2100? This study aims to refine our understanding of the spatial and temporal variations of CO2 in support of activities to monitor and verify decarbonization measures.

How to cite: Johnson, K., Li, H., and Ilyina, T.: Variability of atmospheric CO2 in Earth System model large-ensemble simulations with an interactive carbon cycle, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7740,, 2023.

Supplementary materials

Supplementary material file