Annual Growth Rates of Column-Averaged CO2 on Global Scale Inferred from Long-Term TCCON Observations

To adhere to the Paris Agreement and restrict the rise in global temperatures to 1.5 degrees, it is imperative to significantly decrease anthropogenic greenhouse gas emissions, ultimately achieving net-zero emissions by the year 2050. To evaluate the reductions in CO2 emissions, it is essential to assess the related changes in CO2 mixing ratios in the atmosphere. An appropriate quantity to be used for this assessment in the years to come is the global annual growth rate of atmospheric CO2. As a data basis for this, in-situ measurement station networks can be used, and annual growth rates are being inferred, e.g., from the Mauna Loa station. On the other hand, TCCON, operating 30 stations worldwide, is committed to measuring greenhouse gas total column mixing ratios through the use of ground-based solar viewing FTIR instruments. The advantage of TCCON column observations is that they are less sensitive to local emissions close to the measurement site and are more representative of regional and global scale emissions and trends in greenhouse gas mixing ratios. TCCON data, therefore, represent a potent alternative data source. A recent algorithmic approach to infer annual growth rates from TCCON data by Sussmann and Rettinger (2020) considers the temporal sampling of TCCON, accounting for data gaps due to sun-viewing geometry, and has been successfully demonstrated for selected TCCON sites. The goal of our ongoing work, presented here, is to extend the retrieval of annual growth rates to more TCCON stations and compare our TCCON results with results from the in-situ networks. Reference: Sussmann, R., and Rettinger, M.: Can We Measure a COVID-19-Related Slowdown in Atmospheric CO2 Growth? Sensitivity of Total Carbon Column Observations, Remote Sens., 12, 2387, https://doi.org/10.3390/rs12152387, 2020.