The return of the Eastern European carbon sink

Abstract:

Five years ago, Reuter and co-workers claimed the existence of a large carbon sink in Eastern geographic Europe, undetected by current in-situ observation networks which only cover the western side of the continent. This claim was based on notoriously uncertain infra-red satellite column CO2 soundings and X-band vegetation optical depth. Here we revisit the possibility of a large carbon sink in Eastern Europe. This part of the continent has the largest forest area and experienced a major transition of land use in the 1990s, with the abandonment of marginal croplands and the intensification of remaining ones. In the same time, increased gross forest loss occurred in the early 2000s, followed by reduced timber harvesting in the late 2000s. Here we used new results from 1) CO2 inversions based on surface networks and on OCO-2 and GOSAT data, the latter having the advantage to cover the Eastern part of Europe as well as the Western part and 2) above ground biomass changes derived from L-land vegetation optical depth data from the SMOS passive microwave space-borne sensor. Our results tend to confirm the early claim of Reuter, with the existence of an average sink larger in the East, both on an area basis and considering regional budgets. This sink seems to have decreased after 2014, possibly due to more intense timber harvesting. Combining the new HILDA+ land use change dataset at 1 km over Europe with the BLUE bookkeeping model, we conclude that only a small fraction of the current Eastern European sink can be explained by land use change. Forest stands thickening in established forests in response to management and climate trends and possibly soil carbon increase may explain the sink deduced from recent EO data.