The importance of accurate monitoring of carbon dioxide (CO2) emissions from cities is underlined by the substantial urban contribution to global fossil fuel combustion. Typically, cities quantify emissions of CO2 using inventories and also use these models to design appropriate local mitigation policies and measures. However, inventories of individual cities can be uncertain (lack of appropriate activity data and emission factors, uncertainties in spatial downscaling) and furthermore often do not include estimates for the sector Land Use, Land-use Change and Forestry (LULUCF). While the relative, total contribution of LULUCF to a city’s annual CO2 balance may be assumed small, such an assumption should be verified. Furthermore, biogenic fluxes of photosynthesis and respiration may indeed be significant at higher temporal resolutions and omitting these fluxes can limit the conclusions drawn from comparisons of city CO2 inventories with estimates based on atmospheric CO2 observations.The Vienna Urban Carbon Laboratory is currently investigating how monitoring of CO2 emissions in Austria’s capital city can be supported by a range of atmospheric measurement methods, including a tall-tower, urban application of eddy covariance. Despite the focus on atmospheric observations, the project is also investigating the contribution of biogenic fluxes to Vienna’s net CO2 budget. A LULUCF model of annual carbon stock changes has been developed following the IPCC guidelines using inter alia local forest inventory data and spatially-explicit data on land use and urban tree crown cover. Parrellel to this, work is underway to implement spatially- and temporally resolved simulations of vegetation CO2 fluxes using semi-empirical models of photosynthesis and respiration. Ultimately, integrating these results (together with bottom-up estimates of human respiration) will provide a more meaningful comparison between the local CO2 inventory with the fluxes derived from the eddy covariance measurements.

The importance of accurate monitoring of carbon dioxide (CO2) emissions from cities is underlined by the substantial urban contribution to global fossil fuel combustion. Typically, cities quantify emissions of CO2 using inventories and also use these models to design appropriate local mitigation policies and measures. However, inventories of individual cities can be uncertain (lack of appropriate activity data and emission factors, uncertainties in spatial downscaling) and furthermore often do not include estimates for the sector Land Use, Land-use Change and Forestry (LULUCF). While the relative, total contribution of LULUCF to a city’s annual CO2 balance may be assumed small, such an assumption should be verified. Furthermore, biogenic fluxes of photosynthesis and respiration may indeed be significant at higher temporal resolutions and omitting these fluxes can limit the conclusions drawn from comparisons of city CO2 inventories with estimates based on atmospheric CO2 observations. The Vienna Urban Carbon Laboratory is currently investigating how monitoring of CO2 emissions in Austria’s capital city can be supported by a range of atmospheric measurement methods, including a tall-tower, urban application of eddy covariance. Despite the focus on atmospheric observations, the project is also investigating the contribution of biogenic fluxes to Vienna’s net CO2 budget. A LULUCF model of annual carbon stock changes has been developed following the IPCC guidelines using inter alia local forest inventory data and spatially-explicit data on land use and urban tree crown cover. Parrellel to this, work is underway to implement spatially- and temporally resolved simulations of vegetation CO2 fluxes using semi-empirical models of photosynthesis and respiration. Ultimately, integrating these results (together with bottom-up estimates of human respiration) will provide a more meaningful comparison between the local CO2 inventory with the fluxes derived from the eddy covariance measurements.

Zusammenfassung Die Technische Zusammenfassung des APCC-Sonderberichts ″Landnutzung und Klimawandel in Österreich″ umfasst die Kernbotschaften der Kapitel 1–9. In ihr sind die Hauptaussagen zu den sozioökonomischen und klimatischen Treibern der Landnutzungsänderungen, zu den Auswirkungen von Landnutzung und -bewirtschaftung auf den Klimawandel, zu Minderungs- und Anpassungsoptionen im Kontext nachhaltiger Entwicklungsziele sowie zu Synergien, Zielkonflikten und Umsetzungsbarrieren von Klimamaßnahmen enthalten.

Zusammenfassung Aufgrund der Größe der betroffenen Landflächen, den bei ihrer Nutzung emittierten und sequestrierten Treibhausgasen (THG) und des teilweise ungünstigen Zustands von Böden in Hinblick auf ihren Gehalt an organisch gebundenem Kohlenstoff (C) kommt der Landnutzung a priori eine wichtige Rolle bei Mitigationsbemühungen zu. Zur Minderung des Klimawandels ist eine Verringerung der atmosphärischen CO2-Konzentration erforderlich, die durch eine Abnahme der THG-Emissionen und durch Aufnahme und langfristige Speicherung von atmosphärischem Kohlenstoff in Biomasse und Boden erreicht werden kann (Chenu et al., 2019; Mayer et al., 2018; Paustian et al., 2016; Vos et al., 2018). Der Erhaltung bzw. idealerweise Erhöhung der organischen Substanz des Bodens durch geeignete Bodenschutzmaßnahmen kommt entscheidende Bedeutung zu.

The current state of research shows that there is big potential for the use of wood, particularly harvested wood products (HWP) to mitigate climate change and increase carbon stocks. Despite of discussions on different accounting approaches, the forest-based sector can contribute with the production of long-lasting wood products to reach international climate goals. This leads to high demands on forests and on what they can deliver both at EU and the national levels. In Austria it has been bemoaned by the Environmental Agency in its recent –eleventh- control report, that a comprehensive concept for the use of wood is missing. The report asks for consideration of increasing future needs for raw wood and energy under considerations of sustainability and under inclusion of all actors involved. Apparently there are some disparities within the different policy instruments. In order to successfully concertise the national policy framework it is of paramount importance to gather the policy actors involved and examine their suggestions for solving the issue. The article is enquiring amongst a number of high level Austrian experts and stakeholders about their perspectives and solutions for enhancing the contribution of the forest based sector to combat climate change. We examine the nature of the suggested instruments and outline the perceived options for action within the capacities of the forest based sector. This is done by way of a triangulation of face-to-face qualitative interviews, moderated focus group discussions and one survey. For the increase in carbon efficiency, all the participants notably emphasise long lasting material use and increase in use. Yet the opinions are contradicting when it comes to energetic use. Our findings indicate that the expert views reflect diverging perspectives on the use of wood for energy consumption. Some opt for policies that support energy consumption of wooden biomass to replace fossil fuels, others want any energy use of wood to become restricted drastically. As a final result, the article derives 16 principle policy measures and instruments that were brought up and assessed by the stakeholders in several rounds of interaction. We conclude that small improvements to existing measures could have ample impacts.

Anthropogenic GHG emissions add a fast reinforcing feedback cycle to global carbon dynamics which continues to influence GHG concentrations in the Earth's atmosphere. When looking at forest carbon cycles there is potential in utilizing another feedback cycle, namely the carbon cycle involving harvested wood products. To assess the potential of the mitigation options arising from these carbon flows, the forest-based sector in Austria was modelled to assess causal links, dependencies and dynamics involved in GHG-relevant processes. Carbon dynamics were investigated in forests and forest soil carbon, the forest product chain and life-cycle analyses for substitution of conventional products with wood products in a cascade of different modelling approaches and paradigms, and the results synthesized. It was found that material use of products from domestic timber sources has the highest climate change mitigation efficiency when originating from sustainably managed forests regarding biomass stocks. The emissions saved through building up a carbon stock from harvested wood products and through emissions substitution can be as high as similar to 20 years of total annual Austrian emissions in 90 years. Additional conservation measures while sustaining sawnwood production and the related GHG benefits at a high level had the highest contribution to an overall carbon sink.