Methane budget estimates in Finland from the CarbonTracker Europe-CH₄ data assimilation system

Abstract

We estimated the CH₄ budget in Finland for 2004–2014 using the CTE-CH₄ data assimilation system with an extended atmospheric CH₄ observation network of seven sites from Finland to surrounding regions (Hyytiälä, Kjølnes, Kumpula, Pallas, Puijo, Sodankylä, and Utö). The estimated average annual total emission for Finland is 0.6 ± 0.5 Tg CH₄ yr⁻¹. Sensitivity experiments show that the posterior biospheric emission estimates for Finland are between 0.3 and 0.9 Tg CH₄ yr⁻¹, which lies between the LPX-Bern-DYPTOP (0.2 Tg CH₄ yr⁻¹) and LPJG-WHyMe (2.2 Tg CH₄ yr⁻¹) process-based model estimates. For anthropogenic emissions, we found that the EDGAR v4.2 FT2010 inventory (0.4 Tg CH₄ yr⁻¹) is likely to overestimate emissions in southernmost Finland, but the extent of overestimation and possible relocation of emissions are difficult to derive from the current observation network. The posterior emission estimates were especially reliant on prior information in central Finland. However, based on analysis of posterior atmospheric CH₄, we found that the anthropogenic emission distribution based on a national inventory is more reliable than the one based on EDGAR v4.2 FT2010. The contribution of total emissions in Finland to global total emissions is only about 0.13%, and the derived total emissions in Finland showed no trend during 2004–2014. The model using optimized emissions was able to reproduce observed atmospheric CH₄ at the sites in Finland and surrounding regions fairly well (correlation $> 0.75$, bias $< \pm 7$ ppb), supporting adequacy of the observations to be used in atmospheric inversion studies. In addition to global budget estimates, we found that CTE-CH₄ is also applicable for regional budget estimates, where small scale (1${}^{°}\times$1${}^{°}$ in this case) optimization is possible with a dense observation network.

Keywords:

• CH₄ flux
• atmospheric CH₄
• Finland
• data assimilation
• flux estimation

Acknowledgements

We thank Dr. Akihiko Ito for providing prior emissions of termites, and Ari Karppinen (FMI), Riitta Pipatti (Statistics Finland), Sini Niinistö (Statistics Finland), and Timo Kareinen (Statistics Finland) for their assistance in creating FIN-EDGAR emissions. We are grateful for Agencia Estatal de Meteorología (AEMET), CSIRO Oceans and Atmosphere, Swiss Federal Laboratories for Materials Science and Technology (EMPA), Environment and Climate Change Canada (ECCC), Laboratoire des Sciences du Climat et de leimatesiresinl (LSCE), the National Institute of Water and Atmospheric Research Ltd. (NIWA), the Environment Division Global Environment and Marine Department Japan Meteorological Agency (JMA), National Institute for Environmental Studies (NIES), Umweltbundesamt Germany/Federal Environmental Agency (UBA), Umweltbundesamt Austria/Environment Agency Austria (EAA) as the data provider for Sonnblick, the Southern African Weather Service (SAWS), the Main Geophysical Observatory (MGO), Meteorology, Climatology, and Geophysics Agency Indonesia (BMKG), University of Bristol (UNIVBRIS), University of Groningen, University of Malta, University of Urbino, Centre for Environmental Monitoring (RIVM), Institute of Atmospheric Sciences and Climate, Ricerca sul Sistema Energetico (RSE SpA), and Chinese Academy of Meteorological Sciences (CMA) for performing high-quality CH₄ measurements at global sites and making them available through the GAW-WDCGG. The observations by J.M.A. are a part of the GAW program of the WMO. We also appreciate Statistics Finland for developing and publishing national inventory data available for scientific research.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed here https://doi.org/10.1080/16000889.2018.1565030.

Additional information

Funding

This work was supported financially by the NordFrosk Nordic Centre of Excellence under grant no. 57001 (eSTICC) and the Academy of Finland under grant no. 285630 (CARB-ARC) and grant no. 307331 (UPFORMET). This work was also supported by EU-FP7 under grant no. 284274 (InGOS) and Academy of Finland Centre of Excellence under grant no. 272041, Academy Professor projects (no. 1284701 and 1282842) and ICOS-Finland (project no. 281255). Sebastian Lienert and Fortunat Joos acknowledge support by the Swiss National Science Foundation. Paul Miller and Tuula Aalto acknowledges support from the Swedish strategic research area Modelling the Regional and Global Earth System (MERGE), the Lund University Centre for the study of Climate and Carbon Cycle (LUCCI), the Swedish Research Council (VR) grant no. 2013-5487, and the Horizon 2020 Framework Programme, under Grant Agreement number 641816, the ‘Coordinated Research in Earth Systems and Climate: Experiments, Knowledge, Dissemination and Outreach (CRESCENDO)’ project (11/2015-10/2020) and Grant Agreement number 776810, the ‘Observation based system for monitoring and verification of greenhouse gases (VERIFY)’ project.