| The terrestrial biosphere has absorbed 13% of the fossil fuel emissions of EU-25 over the last decade. This net carbon sink is mainly located in forests and grasslands, while croplands are relatively carbon neutral, and managed peatlands are a carbon source. This net carbon sink is almost compensated by N2O and CH4 emissions from agriculture. However, these results strongly rely on models which have not been validated against the wealth of observational data obtained in CarboEurope-IP, suffer from inconsistencies in the time horizons and types of uncertainties considered as well as from lack of integration between CO2 measurements and other greenhouse gases (GHGs) (first achieved for few sites in NitroEurope-IP). Improved quantification of the annual to decadal variability in the European terrestrial C and GHG budget requires 1) the full exploitation of all available data streams, 2) much stronger data-model integration, 3) consistent temporal and spatial domain coverage and 4) complete consideration of error propagation at all calculation steps. The land use sector can play an important role in mitigating climate change via bioenergy production, carbon sequestration in soils and to a minor extent by reducing N2O and CH4 emissions (IPCC AR4 WG3 2007, UNFCCC 2008). However, biological systems have their intrinsic dynamics, and interact with climate change in a complex way that is not completely understood. This makes climate change mitigation measures in agriculture, forestry and other land uses more complicated and uncertain than in any other human sector. Ultimately, the scientific challenge is to determine how, and to what degree, the carbon cycle and GHG emissions in terrestrial ecosystems can be managed. This requires a much improved understanding of the response of biogeochemical processes in ecosystems to changes in natural and anthropogenic drivers. Natural and anthropogenic drivers of C and GHG fluxes in ecosystems are intimately linked. IPCC (2003) concluded that the scientific community cannot currently provide a practicable methodology that would factor out direct human-induced effects from indirect human-induced and natural effects for any broad range of LULUCF activities and circumstances. Nevertheless, factoring out as introduced in the Kyoto Protocol remains one of the most controversial topics in the post-2012 negotiations under the UNFCCC. Many countries, including some EU member states, insist that natural C sources and sinks in ecosystems shall be distinguished from anthropogenic ones. Since the IPCC statement in 2003, scientific advances have been made to single out the effects of individual drivers: elevated CO2, N deposition, land use and management at site level via manipulation treatments (e.g. Kammann et al., 2005) and factorial experiments (e.g. Smith et al., 2002); climate variability via decadal time series from ecosystem observation networks (Reichstein et al. 2007a, 2007b); and elevated CO2, N deposition, climate variability, past management and age-class effects in forests (Nabuurs et al. 2004, Böttcher et al. 2008, Ciais et al. 2008) and partially land use at landscape to continental scale via model experiments and scenarios (Vetter et al. 2008). Considerable progress in the attribution of the variability in C and GHG fluxes to multiple interacting factors by GHG-Europe can be expected by 1) the collection and synthesis of the fast growing observational evidence of ecosystem response to individual drivers, 2) improved representation of climate variability AND land use and management in ecosystem models, and 3) a coherent approach to address the interactions between drivers from local to continental scales. GHG-Europe is fully dedicated to improve our understanding and capacity for predicting the impact of natural and anthropogenic drivers on European terrestrial carbon and GHG budgets. We propose that this can only be achieved via a systematic, comprehensive and integrative approach. A multitude of experimental data, long-term observations of GHG fluxes and C pools along with meteorological observations, land use and management information is analysed by a range of advanced data mining techniques and integrated with stateof-the-art process modelling approaches. Among current EU projects, NitroEurope-IP investigates contemporary N and N2O budgets, CARBO-Extreme investigates the impact of climate variability and extremes on ecosystem and soil carbon, and CC-TAME develops tools for integrated assessment of EU policy impacts on land use. To maximize synergy with these projects, GHG-Europe focuses on the full GHG budget of terrestrial ecosystems and on the impacts of anthropogenic drivers and their interactions with climate on C and GHG budgets as the most critical and least characterised processes to complete the vulnerability assessment. |
