Future levels of climate change depend not only on carbon emissions but also on carbon uptake by the land and the ocean. Here we are using the Earth System Model version of the Australian Community Climate and Earth System Simulator (ACCESS) to explore the potential and impact of removing CO₂ from the atmosphere through the climate and carbon cycle reversibility experiment. This experiment is part of the Carbon Dioxide Removal Model Intercomparison Project (CDRMIP), which is an endorsed MIP of CMIP6. First, atmospheric CO₂ concentrations are raised from pre-industrial levels (~280ppm) by 1% per annum over a 140 year period to 4xCO₂. Subsequently, CO₂ concentrations are reduced at the same rate which brings the CO₂ back to pre-industrial levels. We then continue to run the model with constant CO₂ for another 500 years.

Our analysis focuses on the response of the land carbon cycle at the global, latitudinal and regional scale. We find that carbon stores are largely reversible at the global scale over the time scale of changing CO₂. However, carbon stores continue to decrease after CO₂ returns to its initial value, and the land loses more carbon with the largest change in the tropics (overshoot). It takes about 300 years beyond the period of changing CO₂ for the carbon stores to recover. Interestingly, we saw strong regional variations in the strength of the land response to changing CO₂. Understanding the processes underlying the response and the sensitivity of these processes within our model will benefit future multi-model analyses of this reversibility experiment.