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Carbon emissions elimination in the rapid urbanization areas contributes to regional sustainable development and global climate change mitigation. With the target of carbon neutrality, the global top-class Beijing-Tianjin-Hebei Urban Agglomeration which confronts with the dual pressure of excess carbon emissions and shrink ecological space has increased its carbon reduction coordination cooperation, among which energy consumption carbon emission control and natural resource sink maintenance have been recognized as the key strategy. However, the study on carbon balance prediction is lack and the amount of energy consumption carbon emissions in the future can be offset by the ecological carbon sink is still unknown. To estimate the gap to carbon neutrality, this study proposes a framework for carbon offset analysis and prediction which takes various carbon emission scenarios and the potential of natural resource on carbon reduction into consideration. After the framework conduction in the agglomeration, it is revealed that the regional least carbon emissions of 29.51 Mt mainly derive from the population and economic growth brought by urbanization process, while the carbon sink predicted to be 2552.31 Kt is still far to cover the emissions. With the regional carbon offset rate decline from 0.68% to 0.63%, the ecological carbon sink in Beijing will offset 1.21% of its carbon emission, while the least ecological space keep city Tianjin is predicted to suffer the lowest offset rate of 0.09%. The research results contribute to recognize the key factors on carbon emission control and key areas for carbon maintenance in following years, as well as narrowing the gap to neutrality with both consideration of carbon emission reduction and sink maintenance. [Display omitted] • Framework on energy consumption carbon offset analysis was established. • Regional carbon emissions, sinks and offset rate were predicted. • Drop from 0.68% in 2020 to 0.63% in 2030, the declining offset rate indicates the gap to neutrality is still large. • Implications for each area's carbon emission offset rate improvement were discussed. [ABSTRACT FROM AUTHOR]

The renewal of old bridges is sometimes restricted to avoid the high carbon emissions caused by materials and construction, which however might not be conductive to climate change mitigation due to their insufficient functions. In order to facilitate the optimization of renewal timing and strategy from the perspective of reducing the comprehensive global warming impacts, we put forward the low-carbon bridge renewal decision method referring to the ideas of consequential life cycle assessment (LCA) and dynamic LCA. In the proposed method, a comparative system boundary matching the bridge renewal characteristics is constructed, where the carbon emission reduction owing to the traffic efficiency improvement by functional updating is incorporated as the low-carbon benefits of renewal, and three types of time-dependent factors, i.e., time-dependent characterization factor, trend factors and changes of traffic demands, are introduced to characterize the influence of renewal timing. The proposed method provided guidance for the renewal of Maogang Bridge, the first long-span cable-stayed bridge in Shanghai. Results illustrate that the global warming impacts of renewal construction activities and the low-carbon benefits from functional updating decrease with the renewal timing. For Maogang Bridge, the rapidly increasing traffic demands inevitably advocated renewal in advance, and the reduction of global warming impacts from emission reduction or carbon uptake could be manifested for renewal in advance. Adopting material recycling in the disposal of old bridge helped reconstructing a new bridge while deconstructing the old one in 2019 becoming the finally selected low-carbon renewal strategy, which is expected to reduce 15.04 kt CO 2 e-2019 compared to the essential renewal in 2050 with the landfill disposal method. The robustness of the strategy choice has been justified, given the variations of analytical time horizon, expected emission trends and repair emissions. In this way, the low-carbon renewal decision method could build a quantitative basis for judging the urgency of functional updating and verifying the low-carbon benefits of immediate concrete recycling in up-coming urban renewals. • Low-carbon bridge renewal decision optimizes renewal timing and strategy. • System boundary is expanded for quantifying benefits from functional updating. • Emission trends and time-dependent characterization factors are explored. [ABSTRACT FROM AUTHOR]