On controlling regional greenhouse gas emission inventories with landscape scale flux observations

Effective greenhouse gas (GHG) emission policies rely on accurate and actual GHG emission data. Uncertainties in inventories arise from limited knowledge of actual activity data, the technology actually used and local ecosystem features that altogether need to be considered when estimating GHG emissions from a specific area. Independent monitoring and verification are expected to increase credibility of inventory reports and scenario estimations, ideally at the same spatial and temporal level of integration as the desired GHG inventory.

One key challenge to verify distributed anthropogenic GHG emissions with measured net GHG fluxes is that conventional GHG flux observation techniques are limited to process, facility or ecosystem scales and do rarely integrate over a representative fraction of the gross anthropogenic GHG fluxes in a region or country. We developed and built an observation system based on tall tower eddy covariance as one of the pillars of a future measurement based Danish national GHG observation system and explore its effectiveness to observe the integrated GHG exchange in a representative agricultural landscape.

We measured CO₂, CH₄, N₂O and CO exchanges from a telecommunication mas (Hove, in a Danish agricultural landscape, West of Copenhagen (N 55.716, E12.238) for 15 months. We placed substantial efforts on estimating the origin of the measured fluxes and used this information to improve comparability of observed GHG exchanges with regional IPCC GHG emission inventories comparable.

The presentation focusses on 1. necessary processing steps for estimation of annual net GHG exchange budgets (spectral correction, data quality filtering and gap filling). 2. a novel “flux-landscape approach” to define a common reference area with inventories, and 3. an overview over the results of the comparison between observed GHG exchange and local IPCC inventory.

From these results we conclude that such comparisons strongly depend on the distinction of gross fluxes that are relevant for GHG accounting and reporting from other, biotic fluxes that are currently not climate policy relevant. This is particularly challenging for CO₂, where we observe a strong net uptake, while the inventory is dominated by gross emissions.

We acknowledge funding by DFF (Independent Research Fund Denmark, ref. 1127-00308B) and sponsoring by CIBICOM A/S Ballerup Denmark.