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Anthropogenic activities have substantially enhanced the loadings of reactive nitrogen (Nr) in the Earth system since pre-industrial times1,2, contributing to widespread eutrophication and air pollution3-6. Increased Nr can also influence global climate through a variety of effects on atmospheric and land processes but the cumulative net climate effect is yet to be unravelled. Here we show that anthropogenic Nr causes a net negative direct radiative forcing of -0.34 [-0.20, -0.50] W m-2 in the year 2019 relative to the year 1850. This net cooling effect is the result of increased aerosol loading, reduced methane lifetime and increased terrestrial carbon sequestration associated with increases in anthropogenic Nr, which are not offset by the warming effects of enhanced atmospheric nitrous oxide and ozone. Future predictions using three representative scenarios show that this cooling effect may be weakened primarily as a result of reduced aerosol loading and increased lifetime of methane, whereas in particular N2O-induced warming will probably continue to increase under all scenarios. Our results indicate that future reductions in anthropogenic Nr to achieve environmental protection goals need to be accompanied by enhanced efforts to reduce anthropogenic greenhouse gas emissions to achieve climate change mitigation in line with the Paris Agreement.

Process-based land surface models are important tools for estimating global wetland methane (CH4) emissions and projecting their behavior across space and time. So far there are no performance assessments of model responses to drivers at multiple time scales. In this study, we apply wavelet analysis to identify the dominant time scales contributing to model uncertainty in the frequency domain. We evaluate seven wetland models at 23 eddy covariance tower sites. Our study first characterizes site-level patterns of freshwater wetland CH4 fluxes (FCH4) at different time scales. A Monte Carlo approach was developed to incorporate flux observation error to avoid misidentification of the time scales that dominate model error. Our results suggest that (a) significant model-observation disagreements are mainly at multi-day time scales (32 days) for the boreal and Arctic tundra wetland sites but have significant bias in variability at seasonal time scales for temperate and tropical/subtropical sites; (c) model errors exhibit increasing power spectrum as time scale increases, indicating that biases at time scales

Climate change scenarios established by the Intergovernmental Panel on Climate Change have developed a significant tool for analyzing, modeling, and predicting future climate change impacts in different research fields after more than 30 years of development and refinement. In the wake of future climate change, the changes in forest structure and functions have become a frontier and focal area of global change research. This study mainly reviews and synthesizes climate change scenarios and their applications in forest ecosystem research over the past decade. These applications include changes in (1) forest structure and spatial vegetation distribution, (2) ecosystem structure, (3) ecosystem services, and (4) ecosystem stability. Although climate change scenarios are useful for predicting future climate change impacts on forest ecosystems, the accuracy of model simulations needs to be further improved. Based on existing studies, climate change scenarios are used in future simulation applications to construct a biomonitoring network platform integrating observations and predictions for better conservation of species diversity. Key words: global change, carbon stocks, forest vulnerability, CMIP6, land surface models, 1. Introduction Based on the Sixth Assessment Report from the Intergovernmental Panel on Climate Change (IPCC), the recent worldwide average surface temperature for 2011-2020 was 1.09 [degrees]C warmer than that [...]

Urban ecosystems are complex systems with anthropogenic features that generate considerable C[O.sub.2] emissions, which contributes to global climate change. Quantitative estimates of the carbon footprint of urban ecosystems are crucial for developing low-carbon development policies to mitigate climate change. Herein, we reviewed more than 195 urban carbon footprint and carbon footprint related studies, collated the recent progress in carbon footprint calculation methods and research applications of the urban ecosystem carbon footprint, analyzed the research applications of the carbon footprint of different cities, and focused on the need to study the urban ecosystem carbon footprint from a holistic perspective. Specifically, we aimed to: (i) compare the strengths and weaknesses of five existing carbon footprint calculation methods [life cycle assessment, input-output analysis, hybrid life cycle assessment, carbon footprint calculator, and Intergovernmental Panel on Climate Change (IPCC)]; (ii) analyze the status of current research on the carbon footprint of different urban subregions based on different features; and (iii) highlight new methods and areas of research on the carbon footprint of future urban ecosystems. Not all carbon footprint accounting methods are applicable to the carbon footprint determination of urban ecosystems; although the IPCC method is more widely used than the others, the hybrid life cycle assessment method is more accurate. With the emergence of new science and technology, quantitative methods to calculate the carbon footprint of urban ecosystems have evolved, becoming more accurate. Further development of new technologies, such as big data and artificial intelligence, to assess the carbon footprint of urban ecosystems is anticipated to help address the emerging challenges in urban ecosystem research effectively to achieve carbon neutrality and urban sustainability under global change. Key words: accounting systems, climate change, carbon sequestration, C[O.sub.2] emissions assessment, hybrid life cycle assessment. Les ecosystemes urbains sont des systemes complexes presentant des caracteristiques anthropiques qui generent des emissions considerables de C[O.sub.2] contribuant aux changements climatiques mondiaux. Les estimations quantitatives de l'empreinte carbone des ecosystemes urbains sont cruciales pour l'elaboration de politiques de developpement a faible emission de carbone visant a attenuer les changements climatiques. Dans cet article, les auteurs ont passe en revue plus de 195 etudes sur l'empreinte carbone urbaine et reliees a l'empreinte carbone urbaine, collige les progres recents en matiere de methodes de calcul de l'empreinte carbone et les applications de la recherche sur l'empreinte carbone des ecosystemes urbains, analyse les applications de recherche de l'empreinte carbone de differentes villes et mis l'accent sur la necessite d'etudier l'empreinte carbone des ecosystemes urbains d'un point de vue holistique. Plus precisement, ils ont cherche a: (i) comparer les forces et les faiblesses de cinq methodes existantes de calcul de l'empreinte carbone [evaluation du cycle de vie, analyse entree-sortie, evaluation hybride du cycle de vie, calculateur de l'empreinte carbone et celle du Groupe d'experts intergouvernemental sur revolution du climat (GIEC)]; (ii)analyser l'etat de la recherche actuelle sur l'empreinte carbone de differentes sous-regions urbaines en fonction de differentes caracteristiques; et (iii) mettre en lumiere de nou-velles methodes et de nouveaux domaines de recherche sur l'empreinte carbone des futurs ecosystemes urbains. Toutes les methodes de comptabilisation de l'empreinte carbone ne sont pas applicables a la determination de l'empreinte carbone des ecosystemes urbains; bien que la methode du GIEC soit plus largement utilisee que les autres, la methode hybride d'evaluation du cycle de vie est plus precise. Avec les avancees de la science et l'emergence de nouvelles technologies, les methodes quantitatives de calcul de l'empreinte carbone des ecosystemes urbains ont evolue et sont devenues plus precises. Le developpement ulterieur de nouvelles technologies, telles que celles qui utilisent les donnees massives et l'intelligence artificielle, pour evaluer l'empreinte carbone des ecosystemes urbains devrait aider a relever efficacement les nouveaux defisde la recherche sur les ecosystemes urbains afind'atteindre la neutralite carbone et la durabilite urbaine dans le contexte des changements climatiques mondiaux. [Traduit par la Redaction] Mots-cles: systemes de comptabilite, changements climatiques, sequestration du carbone, evaluation des emissions de CO2, analysehybrideducycledevie., Introduction Approximately half of the Earth's terrestrial surface is currently affected by human activities that are accelerating C[O.sub.2] emissions and increasingly becoming detrimental for several ecosystems (Lambin et al. 2003). [...]