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Radiocarbon (Δ 14 C) was measured for four years (2019-2022) in Zagreb (Croatia) and in Cvetković village near Jastrebarsko (Zagreb County, Croatia) to see whether there are differences between the city site and the rural one because of the fossil fuel combustion. The δ 13 C CO2 was measured as grab samples once in a month in period December 2020-November 2022. The bomb-produced 14 C has been globally distributed across the planet, but the combustion of fossil fuels that do not contain 14 C causes a local effect of lowering Δ 14 C. Zagreb is considered to be a location with heavy fossil fuel combustion as compared to the Cvetković (rural site). Monthly 14 C activity at Zagreb is constantly below the 14 C activity at Cvetković. Mean 14 C activity at Zagreb (Δ 14 C Zagreb  = -18.4 ± 2.6 ‰) is lower than that in Cvetković (Δ 14 C Cve  = -2.9 ± 2.1 ‰) due to fossil fuel combustion in the city of Zagreb. This is especially pronounced during winter when the mean value in Zagreb is Δ 14 C Zagreb  = -26.0 ± 4.3 ‰ and in Cvetković Δ 14 C Cve  = -5.9 ± 3.4 ‰. Natural gas consumption was used as the proxy for fossil fuel combustion, and it shows better correlation with Δ 14 C in Zagreb than in Cvetković. The Δ 14 C difference, Δ 14 C Cve ‒ Δ 14 C Zagreb , becomes statistically negligible when natural gas consumption is small. No difference is observed on δ 13 C CO2 ; in Zagreb mean δ 13 C CO2 is -11.0 ± 1.3 ‰, and in Cvetković -11.4 ± 1.4 ‰. Lower δ 13 C CO2 values are observed in winter (Zagreb -11.9 ± 1.1 ‰, -12.2 ± 1.5 ‰ Cvetković) than in summer (-10.1 ± 0.8 ‰ vs. -10.4 ± 1.0 ‰) at both locations. Together with higher Δ 14 C in Cvetković, it indicates that at the area of Cvetković biogenic samples of modern origin (biomass, wood) as energy source for heating is more pronounced., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Heatwaves, expected to become more frequent, pose a significant threat to plant biomass production. This experiment was designed to estimate heatwave influence on Brassica juncea phytoremediation when superimposed on different CO 2 levels. A 7-day heatwave was generated during the species flowering stage. Heatwaves decreased all B. juncea dry weights. The lowest species dry weight was recorded when the heatwave was accompanied by 250 ppm CO 2 , in which the biomass significantly decreased by 40.0% relative to that of no heatwave under the same atmospheric CO 2 conditions. Heatwave superposition with 250 ppm CO 2 reduced the Cd content in B. juncea aerial parts by 28.1% relative to that of identical environmental conditions without heatwave, whereas the opposite result was observed under 550 ppm CO 2 conditions. The heatwave caused oxidative damage to B. juncea under all CO 2 conditions, as manifested by increased malondialdehyde levels in the plant shoots. With heatwave superposition, antioxidant enzyme activity was enhanced by exposure to 400 and 550 ppm CO 2 . Considering biomass yield generation and Cd uptake capacity, heatwave superposition decreased the B. juncea phytoremediation effects, and high atmospheric CO 2 conditions could alleviate detrimental effects to a certain extent. This study uniquely examines the combined effects of heatwaves and varying CO 2 levels on phytoremediation, providing microscopic insights into oxidative damage and enzyme activity, highlighting the potential for CO 2 enrichment to mitigate heatwave impacts, and offering comprehensive analysis for future agricultural practices and environmental management., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The Indo-Pacific warm pool (IPWP) is crucial for regional and global climates. However, the development of the IPWP and its effect on the regional climate during the Cenozoic remain unclear. Here, using a compilation of sea surface temperature (SST) records (mainly since the middle Miocene) and multimodel paleoclimate simulations, our results indicated that the extent, intensity and warmest temperature position of the IPWP changed markedly during the Cenozoic. Specifically, its extent decreased, its intensity weakened, and its warmest temperature position shifted from the Indian to western Pacific Ocean over time. The atmospheric CO 2 dominated its extent and intensity, while paleogeography, by restricting the distribution of the Indian Ocean and the width of the tropical seaways, controlled the shift in its warmest temperature position. In particular, the eastward shift to the western Pacific Ocean from the middle to late Miocene inferred from compiled SST records likely resulted from the constriction of tropical seaways. Furthermore, by changing the atmospheric thermal structure and atmospheric circulation, the reduced extent and intensity of the IPWP decreased the annual precipitation in the western Indian Ocean, eastern Asia and Australia, while the shift in the warmest temperature position from the Indian to western Pacific Ocean promoted aridification in Australia. Qualitative model-data agreements are obtained for both the IPWP SST and regional climate. From the perspective of past warm climates with high concentrations of atmospheric CO 2 , the expansion and strengthening of the IPWP will occur in a warmer future and favor excessive precipitation in eastern Asia and Australia., (Copyright © 2024 Science China Press. Published by Elsevier B.V. All rights reserved.)

The CO 2 and 14 CO 2 levels in air samples from the northern foot of the Qinling Mountains (Xi'an, China) were determined. In 2021, a hexacopter unmanned aerial vehicle sampled air at different heights, from near-ground to 2000 m. The objectives of this study were to determine vertical characteristics of CO 2 and 14 CO 2 , the sources of different-height CO 2 , and the influence of air mass transport. The CO 2 concentrations mainly exhibited a slight decreasing trend with increasing height during summer observations, which was in contrast to the increasing trend that was followed by a subsequent gradual decreasing trend during early winter observations, with peak CO 2 levels (443.4 ± 0.4-475.7 ± 0.5 ppm) at 100-500 m. The variation in vertical concentrations from 20 to 1000 m in early winter observations (21.6 ± 19.3 ppm) was greater than that in summer observations (14.6 ± 14.3 ppm), and the maximum vertical variation from 20 to ∼2000 m reached 61.1 ppm. Combining Δ 14 C and δ 13 C vertical measurements, the results showed that fossil fuel CO 2 (CO 2ff , 56.1 ± 15.2 %), which mainly come from coal combustion (81.2 ± 3.4 %), was the main contributor to CO 2 levels in excess of the background level (CO 2ex ) during early winter observations. In contrast, biological CO 2 (CO 2bio ) dominated CO 2ex in summer observations. The vertical distributions of CO 2ff in early winter observations and CO 2bio in summer observations were consistent with those of CO 2 during early winter and summer observations, respectively. The strong correlation between winter CO 2bio and ΔCO (r = 0.81, p < 0.01) indicated that biomass burning was the main contributor to CO 2bio during early winter observations. Approximately half of the air masses originated from the Guanzhong Basin during observations. The results provide insights into the vertical distribution of different-sources of atmospheric CO 2 in scientific support of formulating carbon emission-reduction strategies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The present study investigated the effects of land use/land cover (LU/LC) changes on atmospheric carbon dioxide (CO 2 ) and methane (CH 4 ) concentrations over the sub-urban region of India (Shadnagar) using continuous decadal CO 2 and CH 4 in-situ data measured by the greenhouse gas analyser (GGA). Data was collected from 2013 to 2022 at a 1 Hz frequency. Analysis of the current study indicates that during pre-monsoon, the seasonal maximum of CO 2 was 409.91 ± 9.26 ppm (μ ± 1σ), while the minimum during monsoon was about 401.64 ± 7.13 ppm. Post-monsoon has a high seasonal mean CH 4 concentration of 2.08 ± 0.06 ppm, while monsoon has a low seasonal mean CH 4 concentration of 1.88 ± 0.03 ppm. The primary classes, such as forest, crop, and built-up, were considered to estimate the effect of LU/LC changes on atmospheric CO 2 and CH 4 concentrations. Between 2005 and 2021, the study's results show that the built-up area at radii of 10 km, 20 km, and 50 km increased by 0.17 %, 0.10 %, and 0.4 %, respectively. While other LU/LC categories declined by 30 %, agriculture areas increased by 30 % on average. As a result, the CO 2 and CH 4 concentrations at the study site are increased by 6 % (26 ppm) and 6.5 % (140 ppb), respectively. The present study utilised the fire-based carbon emissions data from the Global Fire Emissions Database (GFED) to understand the impact on atmospheric CO 2 and CH 4 . Analysis of the present work investigated the influence of transported airmass on CO 2 and CH 4 during the pre-monsoon and post-monsoon seasons using the HYSPLIT trajectories and found emissions were from the northwest, southeast, and northeast of the study site. Further, in-situ CO 2 and CH 4 records are compared against the MIROC4-ACTM simulation, and strong agreement was found with bias of 1.80 ppm and 0.98 ppb for CO 2 and CH 4 , respectively., Competing Interests: Declaration of competing interest The authors declare they have no conflict of Interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Understanding the primary factors influencing atmospheric carbon dioxide (CO 2 ) dynamics is essential for addressing global climate change. However, these factors' spatial and temporal impact is seldom considered in the extant literature. This study employs a geographically and temporally weighted regression (GTWR) to examine the magnitude and direction of the effects that human activities, ecological conditions, and meteorological parameters exert on atmospheric CO 2 variations. This examination encompasses 356 Chinese cities, utilizing satellite-derived column-averaged dry air mole fraction of carbon dioxide (XCO 2 ) data from 2010 to 2019. Our findings reveal that cities in eastern China predominantly exhibit higher atmospheric CO 2 concentrations, with most average values exceeding 399.34 ppm. Conversely, western regions generally maintain levels below 398.98 ppm. Trend analyses show a consistent increase over the decade, with a rate of 2.25-2.54 ppm/yr, coupled with pronounced seasonal variations. Anthropogenic emissions are found to amplify atmospheric CO 2 concentrations during springs (overall-averaged GTWR coefficient of 0.72 ppm), autumns (0.51 ppm), and winters (0.87 ppm), especially in western cities. Vegetative activities can effectively reduce atmospheric CO 2 during summers nationwide (temporally-averaged GTWR coefficients of -5.67 ~ -0.41 ppm) and autumn in southern cities (-1.32-0.00 ppm). From a meteorological perspective, increased summer relative humidity (overall-averaged coefficient of 2.41 ppm) and precipitation (1.57 ppm) can intensify atmospheric CO 2 in most Chinese Cities. At the same time, warmer winter temperatures (-0.63 ppm) can mitigate it. Wind speed generally reduces atmospheric CO 2 levels during spring (-1.02 ppm), autumn (-1.55 ppm), and winter (-1.76 ppm). Yet, it can heighten atmospheric CO 2 concentrations during summers, particularly in eastern cities (0.07 ppm). The relationships between atmospheric CO 2 concentrations and their influencing factors present significant spatial and seasonal variations. These findings offer comprehensive guidance for regions in developing targeted carbon emission control policies and enable a more practical approach to sustainable development., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

In southern China, Chinese fir Cunninghamia lanceolata is one of the most important native conifer trees, widely used in afforestation programs. This area has the largest forestland atmospheric carbon sink, and a relatively young stand age characterizes these forests. However, how C. lanceolata forests evolved regarding their ability to sequester carbon remains unclear. Here we present data on carbon storage and sequestration capacity of C. lanceolata at six stand ages (5-, 10-, 15-, 20-, 30- and 60 - year-old stands). Results show that the carbon stock in trees, understory, vegetation, litter, soil, and ecosystem significantly increased with forest age. The total ecosystem carbon stock increased from 129.11 to 348.43 Mg ha -1 in the 5- and 60 - year-old stands. The carbon sequestration rate of C. lanceolata shows an overall increase in the first two stand intervals (5-10 and 10-15), peaks in the 15-20 stand intervals, and then decreases in the 20-30 and 30-60 stand intervals. Our result revealed that carbon sequestration rate is a matter of tree age, with the highest sequestration rates occurring in the middle age forest (15-20 - year-old). Therefore, this information may be useful for national climate change mitigation actions and afforestation programs, since forests are primarily planted for this purpose., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The temporal variation of greenhouse gas concentrations in China during the COVID-19 lockdown in China is analyzed in this work using high resolution measurements of near surface △CO 2 , △CH 4 and △CO concentrations above the background conditions at Lin'an station (LAN), a regional background station in the Yangtze River Delta region. During the pre-lockdown observational period (IOP-1), both △CO 2 and △CH 4 exhibited a significant increasing trend relative to the 2011-2019 climatological mean. The reduction of △CO 2 , △CH 4 and △CO during the lockdown observational period (IOP-2) (which also coincided with the Chinese New Year Holiday) reached up to 15.0 ppm, 14.2 ppb and 146.8 ppb, respectively, and a reduction of △CO 2 /△CO probably due to a dramatic reduction from industrial emissions. △CO 2 , △CH 4 and △CO were observed to keep declining during the post-lockdown easing phase (IOP-3), which is the synthetic result of lower than normal CO 2 emissions from rural regions around LAN coupled with strong uptake of the terrestrial ecosystem. Interestingly, the trend reversed to gradual increase for all species during the later easing phase (IOP-4), with △CO 2 /△CO constantly increasing from IOP-2 to IOP-3 and finally IOP-4, consistent with recovery in industrial emissions associated with the staged resumption of economic activity. On average, △CO 2 declined sharply throughout the days during IOP-2 but increased gradually throughout the days during IOP-4. The findings showcase the significant role of emission reduction in accounting for the dramatic changes in measured atmospheric △CO 2 and △CH 4 associated with the COVID-19 lockdown and recovery., (Copyright © 2021. Published by Elsevier B.V.)

Global climate changes are predicted for the 21st century. Alterations in soil contaminants' availability and soil invertebrates' behavior are expected, which may interfere with the avoidance capacity that invertebrates may have towards contaminated soils and, therefore, compromise their role in soil functioning. This study aimed to assess the individual effects of air temperature, ultraviolet (UV) radiation and atmospheric CO 2 concentration on the avoidance behavior of the arthropod Folsomia candida and the soft-bodied oligochaete Enchytraeus crypticus towards metal(loid)-contaminated soils. Avoidance behavior was evaluated under distinct climate treatments (simulating increases in air temperature, UV radiation exposure or atmospheric CO 2 concentration) and compared to the response obtained at the standard conditions recommended by ISO guidelines. Both soil invertebrate species behave differently under standard conditions, with F. candida not avoiding the contaminated soils while E. crypticus did. Increases in air temperature and exposure to UV radiation did not change F. candida behavior towards contaminated soils. However, high atmospheric CO 2 concentration modified this pattern and induced avoidance towards contaminated soils. As for E. crypticus, contaminated soils were also avoided under the different climate treatments simulated. Thus, our study shows that, depending on the species and the climate factor, changes in climate conditions may alter soil invertebrates' behavioral pattern towards meta(loid)-contaminated soils., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Elevated atmospheric CO 2 concentration (eCO 2 ) exerts significant influence on nutrient requirement in plant. The investigation of C:N:P ratios in major cropping soils is important for managing nutrient balance and maximizing their use efficiency in future farming systems. This study aimed to examine the effect of eCO 2 on the C:N:P ratios in different plant parts among soybean cultivars. Twenty-four soybean cultivars were planted in open top chambers at two CO 2 concentrations (390 and 550 ppm) and sampled at the initial pod filling stage (R5) and the full maturity stage (R8). The C, N and P concentrations in root, stem, leaf and seed were determined. Elevated CO 2 decreased the N concentrations in stem (-5.1%) and leaf (-3.2%) at R5, and in root (-24%), stem (-25%) and seed (-6.2%) at R8, resulting in a significant decrease of C:N ratio in the corresponding parts. The P concentration was significantly increased in root (6.0%), stem (7.9%) and leaf (16%) at R5, and in root (2.6%), stem (29%) and seed (16%) at R8 across 24 cultivars, leading to a decrease in the C:P ratio. Elevated CO 2 significantly decreased the N:P ratio in root (-4.5%), stem (-12%) and leaf (-17%) at R5, and in root (-26%), stem (-57%) and seed (-22%) at R8. Furthermore, the response of C:N:P ratios to eCO 2 varied greatly among soybean cultivars leading to significant CO 2  × cultivar interactions. Nitrogen, but not P was the limiting factor for the soybean plants grown in Mollisols under eCO 2 . The considerable variation in the C:N:P ratios among cultivars in response to eCO 2 indicates a potential improvement in soybean adaptability to climate change via selection new cultivars. Cultivars SN22 and ZH4 that did not considerably altered the C:N and C:P ratios in response to eCO 2 are likely the optimal genomes in soybean breeding programs for eCO 2 adaption., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Photoautotrophs are capable of consuming high quantities of CO 2 , yet scant research exists examining the influence of different CO 2 concentrations on the growth of freshwater diazotrophic or non-diazotrophic cyanobacteria. In this study, we cultured two cyanobacteria taxa (Dolichospermum circinale and Microcystis aeruginosa) within controlled atmospheric CO 2 chambers at pre-industrial, and post-industrial concentrations. Biovolume and chlorophyll a (Chl-a) differed as a consequence of the adjusted CO 2 gradients. Significantly higher biovolume measurements were observed in the elevated CO 2 treatment for the diazotrophic species in the initial experiment. However, a follow-up experiment, with a corrected culture replenishment regime showed Chl-a measurements were greater for the diazotrophic and non-diazotrophic species in the elevated CO 2 treatment. Increasing CO 2 presents a risk to already compromised eutrophic and hyper-eutrophic ecosystems, and we reason increasing CO 2 concentrations could affect photosynthetic performance and CO 2 assimilation of surface dwelling cyanobacteria. Further experimental work is required to establish ecological thresholds for freshwater ecosystems, as pH levels showed a measurable reduction within the elevated CO 2 treatments. As cyanobacteria species may respond quite differently to future CO 2 concentrations similar comparative studies should be carried out that focus on CO 2 dynamics and pH. The findings of the study indicate diazotrophic cyanobacteria growth in particular may benefit from elevated atmospheric CO 2 concentrations., (Copyright © 2018. Published by Elsevier B.V.)

Given that cities contributed most of China's CO 2 emissions, understanding the emission characteristics of urban atmospheric CO 2 is critical for regulating CO 2 emissions. Regular observations of atmospheric CO 2 concentration, △ 14 C and δ 13 C values were performed at four different sites in Xi'an, China in 2016 to illustrate the temporal and spatial variations of CO 2 emissions and recognize their sources and sinks in urban carbon cycles. We found seasonal variations in CO 2 concentration and δ 13 C values, the peak to peak amplitude of which was 80.8ppm for CO 2 concentration and 4.0‰ for its δ 13 C. With regard to the spatial variations, the urban CO 2 "dome" effect was the most pronounced during the winter season. The use of △ 14 C combines with δ 13 C measurements aid in understanding the emission patterns. The results show that in the winter season, emissions from fossil fuel derived CO 2 (CO 2ff ) contributed 61.8±10.6% and 57.4±9.7% of the excess CO 2 (CO 2ex ) in urban and suburban areas respectively. Combining with the result of estimated δ 13 C value of fossil fuel (δ 13 C ff =-24‰), which suggest coal burning was the dominant source of fossil fuel emissions. In contrast, the proportions of CO 2ff in CO 2ex varied more in the summer season than that in the winter season, ranging from 42.3% to >100% with the average contributions of 82.5±23.8% and 90.0±24.8%. Given the estimation of δ 13 C value of local sources (δ 13 C s ) was -21.9‰ indicates that the intensively biogenic activities, such as soil respiration and corn growth have significantly impacted urban carbon cycles, and occasionally played a role of carbon sink., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Radiocarbon measurements of tree-ring samples collected in Vysoká pri Morave were compared with tree-ring data of the Žlkovce monitoring station situated 5km south-east from the Jaslovské Bohunice Nuclear Power Plant (NPP). Radiocarbon concentrations in Vysoká pri Morave and in Žlkovce tree rings were decreasing exponentially with decay constants of 14.48±1.23 y and 17.96±1.97 y, respectively, in agreement with similar results obtained at other radiocarbon stations. The Suess effect, represented by a dilution in 14 C levels by fossil fuel CO 2 emissions, was observed in both tree-ring data sets. The Vysoká pri Morave 14 C data were during 1974-1995 systematically lower by about 50‰ than the Schauinsland (Germany) clean air reference values due to a regional fossil-fuel impact. However, after 1996 the Vysoká pri Morave 14 C data were closer to the Schauinsland data due to lower CO 2 emissions as a result of closing some of the heavy industry technologies in the region., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Due to human activities, the atmospheric concentration of Carbon Dioxide (CO2) has been rising extensively since the Industrial Revolution. Indian summer monsoon (ISM) has a dominant westerly component from ocean to land with a strong tendency to ascend and hence may have role in CO2 distribution in lower and middle troposphere over Indian sub-continent. A substantial component of ISM variability arises from the fluctuations on the intra-seasonal scale between active and break phases which correspond to strong and weak monsoon circulation. In view of the above, an attempt is made in this study to examine the AIRS/AQUA satellite retrieved CO2 distribution in response to atmospheric circulation with focus on active and break phase. Correlation analysis indicates the increase in AIRS CO2 linked with strong monsoon circulation. Study also reveals that anomalous circulation pattern during active and break phase show resemblance with high and low values of AIRS CO2. Homogeneous monsoon regions of India show substantial increase in CO2 levels during active phase. Hilly regions of India show strong contrast in CO2 and vertical velocity during active and break phases., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Surface atmospheric CO2 mixing ratio reflects both natural fluctuation of the carbon cycle and the effect of anthropogenic activities. Long-term observation of atmospheric CO2 forms the basis for model simulations of the carbon cycle both in the straightforward and the inversion ways. Atmospheric CO2 has been measured on Rishiri Island (45.1°N, 141.2°E) in the western North Pacific since May 2006. We report the first 7-year temporal CO2 variations from diurnal to inter-annual scales and the implications on the vegetation phenology. Diurnally, an obvious cycle appeared as a minimum in the afternoon and maximum at midnight in the summer months, caused by local vegetation. Seasonally, the maximum CO2 concentration appeared around the beginning of April, while the minimum appeared around the middle of August. This seasonal variation implied the natural cycle of terrestrial biological activities of the boreal forest, mostly in the east Eurasia. A mean growing season length of ~126 days was estimated. In the period from 2007 to 2012, the peak-to-peak amplitude increased until 2009 and decreased thereafter, with a mean value of 19.7 ppm. Inter-annually, atmospheric CO2 is increasing by a mean growth rate of 2.1 ppm year(-1). The study provides invaluable dataset and useful information to better understand the carbon cycle and its interaction with climate change., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Tropical grassy biomes (TGBs) are globally extensive, provide critical ecosystem services, and influence the earth-atmosphere system. Yet, globally applied biome definitions ignore vegetation characteristics that are critical to their functioning and evolutionary history. Hence, TGB identification is inconsistent and misinterprets the ecological processes governing vegetation structure, with cascading negative consequences for biodiversity. Here, we discuss threats linked to the definition of TGB, the Clean Development Mechanism (CDM) and Reducing Emissions from Deforestation and Forest Degradation schemes (REDD+), and enhanced atmospheric CO2, which may facilitate future state shifts. TGB degradation is insidious and less visible than in forested biomes. With human reliance on TGBs and their propensity for woody change, ecology and evolutionary history are fundamental to not only the identification of TGBs, but also their management for future persistence., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Analyses of global warming impacts from forest bioenergy systems are usually conducted either at a single stand level or at a landscape level, yielding findings that are sometimes interpreted as contrasting. In this paper, we investigate and reconcile the scales at which environmental impact analyses of forest bioenergy systems are undertaken. Focusing on the changes caused in atmospheric CO2 concentration of forest bioenergy systems characterized by different initial states of the forest, we show the features of the analyses at different scales and depict the connections between them. Impacts on atmospheric CO2 concentration at a single stand level are computed through impulse response functions (IRF). Results at a landscape level are elaborated through direct application of IRFs to the emission profile, so to account for the fluxes from all the stands across time and space. Impacts from fossil CO2 emissions are used as a benchmark. At a landscape level, forest bioenergy causes an increase in atmospheric CO2 concentration for the first decades that is similar to the impact from fossil CO2, but then the dynamics clearly diverge because while the impact from fossil CO2 continues to rise that from bioenergy stabilizes at a certain level. These results perfectly align with those obtained at a single stand for which characterization factors have been developed. In the hypothetical case of a sudden cessation of emissions, the change caused in atmospheric CO2 concentration from biogenic CO2 emissions reverses within a couple of decades, while that caused by fossil CO2 emissions remains considerably higher for centuries. When counterfactual aspects like the additional sequestration that would have occurred in the forest if not harvested and the theoretical displacement of fossil CO2 are included in the analysis, results can widely differ, as the CO2 debt at a landscape level ranges from a few years to several centuries (depending on the underlying assumptions considered)., (Copyright © 2013 Elsevier Ltd. All rights reserved.)