Search

East Asia (China, Japan, Koreas, and Mongolia) has been the world's economic engine over at least the past two decades, exhibiting a rapid increase in fossil fuel emissions of greenhouse gases (GHGs) and has expressed the recent ambition to achieve climate neutrality by mid‐century. However, the GHG balance of its terrestrial ecosystems remains poorly constrained. Here, we present a synthesis of the three most important long‐lived greenhouse gases (CO2, CH4, and N2O) budgets over East Asia during the decades of 2000s and 2010s, following a dual constraint approach. We estimate that terrestrial ecosystems in East Asia is close to neutrality of GHGs, with a magnitude of between −46.3 ± 505.9 Tg CO2eq yr−1 (the top‐down approach) and −36.1 ± 207.1 Tg CO2eq yr−1 (the bottom‐up approach) during 2000–2019. This net GHG sink includes a large land CO2 sink (−1229.3 ± 430.9 Tg CO2 yr−1 based on the top‐down approach and −1353.8 ± 158.5 Tg CO2 yr−1 based on the bottom‐up approach) being offset by biogenic CH4 and N2O emissions, predominantly coming from the agricultural sectors. Emerging data sources and modeling capacities have helped achieve agreement between the top‐down and bottom‐up approaches, but sizable uncertainties remain in several flux terms. For example, the reported CO2 flux from land use and land cover change varies from a net source of more than 300 Tg CO2 yr−1 to a net sink of ∼−700 Tg CO2 yr−1. Although terrestrial ecosystems over East Asia is close to GHG neutral currently, curbing agricultural GHG emissions and additional afforestation and forest managements have the potential to transform the terrestrial ecosystems into a net GHG sink, which would help in realizing East Asian countries' ambitions to achieve climate neutrality. Plain Language Summary: East Asia (China, Japan, Koreas and Mongolia) is not only the hotspot of anthropogenic greenhouse gas (GHG, including CO2, CH4 and N2O) emissions, but also a region with large CO2 sink. However, the greenhouse gas balance of greenhouse gases over the region is poorly understood. In this study, we performed a synthesis for over 40 flux terms to provide the first‐of‐its‐kind GHG budget assessment over the decades of 2000s and 2010s. We find terrestrial ecosystems in East Asia is close to neutrality of GHGs. The bottom‐up approach summing up component fluxes estimated a net balance of −36.1 ± 207.1 Tg CO2eq yr−1, while the top‐down approach based on atmospheric inversions estimated a net balance of −46.3 ± 505.9 Tg CO2eq yr−1. This results from compensation of the large CO2 sink by CH4 and N2O emissions, and from compensation of net GHG sink over natural ecosystems by net GHG source over agricultural ecosystems. Thus, curbing agricultural GHG emissions has the potential to realizing the ambitious goal of achieving climate neutrality over East Asia. Key Points: A comprehensive greenhouse gas (CO2, CH4 and N2O) accounting including about 40 flux terms over East Asia is reportedTerrestrial ecosystems in East Asia are close to greenhouse gas neutralNatural ecosystems is a net greenhouse gas sink, compensated by a net source from agricultural ecosystems [ABSTRACT FROM AUTHOR]

Seasonal change of atmospheric potential oxygen (APO ∼ O2 + CO2) is a tracer for air‐sea O2 flux with little sensitivity to the terrestrial exchange of O2 and CO2. In this study, we present the tropospheric distribution and inventory of APO in each hemisphere with seasonal resolution, using O2 and CO2 measurements from discrete airborne campaigns between 2009 and 2018. The airborne data are represented on a mass‐weighted isentropic coordinate (Mθe) as an alternative to latitude, which reduces the noise from synoptic variability in the APO cycles. We find a larger seasonal amplitude of APO inventory in the Southern Hemisphere relative to the Northern Hemisphere, and a larger amplitude in high latitudes (low Mθe) relative to low latitudes (high Mθe) within each hemisphere. With a box model, we invert the seasonal changes in APO inventory to yield estimates of air‐sea flux cycles at the hemispheric scale. We found a larger seasonal net outgassing of APO in the Southern Hemisphere (518 ± 52.6 Tmol) than in the Northern Hemisphere (342 ± 52.1 Tmol). Differences in APO phasing and amplitude between the hemispheres suggest distinct physical and biogeochemical mechanisms driving the air‐sea O2 fluxes, such as fall outgassing of photosynthetic O2 in the Northern Hemisphere, possibly associated with the formation of the seasonal subsurface shallow oxygen maximum. We compare our estimates with four model‐ and observation‐based products, identifying key limitations in these products or in the tools used to create them. Plain Language Summary: A better understanding of the air‐sea O2 fluxes facilitates the study of marine productivity, global carbon cycle and ocean heat transport. Seasonal air‐sea exchange of O2 has been estimated by combining precise measurements of atmospheric O2 and CO2 into atmospheric potential oxygen (APO ∼ O2 + CO2). Using APO observations from nine global airborne campaigns between 2009 and 2018, we resolved the seasonal cycle of atmospheric APO concentration in multiple pressure and latitude bands, yielding estimates of the tropospheric APO inventory, and area‐integrated air‐sea APO flux of each hemisphere. To a first approximation, the ocean is a source of APO in the spring and summer but a sink in the fall and winter, tracking the seasonal warming and cooling of the ocean as well as different ocean biogeochemistry and ventilation regimes. In addition, these cycles show clear asymmetry between hemispheres and display a progressive shift in the seasonal phase and amplitude across latitudes. It is therefore important to understand the physical and biogeochemical processes that lead to these differences. Key Points: From airborne atmospheric potential oxygen (APO) data, we resolve seasonal cycles of APO and hemisphere‐integrated air‐sea APO fluxesWe resolved clear hemispheric differences in the seasonal amplitude and shape of the APO flux cyclesThis study identifies limitations in the Garcia and Keeling O2 flux climatology, pointing to the need for an improved climatology [ABSTRACT FROM AUTHOR]

A comprehensive methane (CH4) budget, including spatial and temporal patterns of sources and sinks, is pivotal for effective climatic mitigation and prediction. This study used a bottom‐up approach to evaluate the CH4 budget of Asia during 1970–2021. Natural sources and sinks were evaluated using a process‐based biogeochemical model and with ground and satellite observations. Anthropogenic sources were evaluated using emission inventories produced by socioeconomic studies. During the 1970s and 2010s, anthropogenic emissions accounted for 78% and 84% of the emitted total CH4 budget of 140.2 and 207.6 Tg CH4 yr−1, respectively. Anthropogenic sources were responsible for a 49% increase in total emissions. During 2001–2021, Central, East, South, Southeast, and West Asia accounted for 3.3%, 35.1%, 25.6%, 23.1%, and 13.0%, respectively, of Asian emissions. Sectoral compositions and temporal variations differed among subregions. Emissions from paddy field soils in Asia were smaller in 2021 (33.6 Tg CH4 yr−1) than in 1970 (39.2 Tg CH4 yr−1) because of changes in agricultural production. Among natural sources, wetlands accounted for 63% of total emissions in East Asia, but geological emissions predominated in Central and West Asia. Interannual variability of the net CH4 budget was mainly due to wetland and biomass burning emissions, whereas decadal variability was due to anthropogenic sectors. δ13C‐CH4 and isoflux analysis of sector‐specific fluxes and isotopic ratios indicated the effects of the regional budget on atmospheric trends. Bottom‐up evaluations of regional budgets can provide information critical to the Global Stocktake of the Paris Agreement, the Global Methane Pledge, and other related actions. Key Points: We used a bottom‐up approach to estimate methane emissions from Asia and their spatial distribution during 1970–2021Asia was estimated to be a net source of methane of 207.6 Tg CH4 yr−1 in the 2010s, 84% of which came from anthropogenic sourcesThe estimated net emissions and their δ13C signature suggested that Asia made a large contribution to atmospheric methane trends [ABSTRACT FROM AUTHOR]

Understanding terrestrial ecosystems and their response to anthropogenic climate change requires quantification of land‐atmosphere carbon exchange. However, top‐down and bottom‐up estimates of large‐scale land‐atmosphere fluxes, including the northern extratropical growing season net flux (GSNF), show significant discrepancies. We developed a data‐driven metric for the GSNF using atmospheric carbon dioxide concentration observations collected during the High‐Performance Instrumented Airborne Platform for Environmental Research Pole‐to‐Pole Observations and Atmospheric Tomography Mission flight campaigns. This aircraft‐derived metric is bias‐corrected using three independent atmospheric inversion systems. We estimate the northern extratropical GSNF to be 5.7 ± 0.3 Pg C and use it to evaluate net biosphere productivity from the Coupled Model Intercomparison Project phase 5 and 6 (CMIP5 and CMIP6) models. While the model‐to‐model spread in the GSNF has decreased in the CMIP6 models relative to that of the CMIP5 models, there is still disagreement on the magnitude and timing of seasonal carbon uptake with most models underestimating the GSNF and overestimating the length of the growing season relative to the observations. We also use an emergent constraint approach to estimate annual northern extratropical gross primary productivity to be 56 ± 17 Pg C, heterotrophic respiration to be 25 ± 13 Pg C, and net primary productivity to be 28 ± 12 Pg C. The flux inferred from these aircraft observations provides an additional constraint on large‐scale gross fluxes in prognostic Earth system models that may ultimately improve our ability to accurately predict carbon‐climate feedbacks. Plain Language Summary: The exchange of carbon between the land and atmosphere is an important part of the Earth's climate, and this exchange might change due to human‐caused climate change. However, estimates of land‐atmosphere carbon fluxes made using different techniques do not agree with each other. We use atmospheric carbon dioxide observations collected during two flight campaigns to show that 5.7 Pg C is exchanged between the atmosphere and the land in the northern hemisphere during the summer growing season. This estimate is used to evaluate the performance of two generations of climate prediction models. The newer generation of models show less spread than the older generation, but there is still significant disagreement on the magnitude and timing of land‐atmosphere carbon exchange among models. Most models underestimate the growing season net flux and overestimate the length of the growing season. We also use our observational estimate to reduce the spread on component fluxes of carbon exchange, namely uptake by photosynthesis and release by respiration. Key Points: Aircraft observations of atmospheric carbon dioxide concentrations are used to infer the net flux of the northern extratropical growing season net fluxThe observations suggest a larger net flux and shorter growing season than those simulated in Earth system modelsAn emergent constraint approach is used to estimate productivity and respiration fluxes [ABSTRACT FROM AUTHOR]

El Niño Southern Oscillation (ENSO) influence on carbon dioxide (CO2) growth rates are not spatially uniform or simultaneous around the globe. Using atmospheric CO2 observations and atmospheric chemistry‐transport model (ACTM), we show that anomalies in CO2 fluxes and growth rate originate in the tropics, as an effect of ENSO. The CO2 anomalies are then propagated from the equator toward the poles with asymmetric delays. A maximum delay of about 8 and 4 months are found at the northern hemisphere (NH) and southern hemisphere (SH) high latitudes, respectively. This asymmetric time delay is because of the CO2 flux anomaly mainly originate in the tropical SH land and transport of SH air into the NH is slower than that for NH air into the SH. The poleward increase of time delay is more homogeneous in the upper troposphere, as per the ACTM simulations, but observational evidence suffers from gaps in long‐term measurements. Plain Language Summary: El Niño Southern Oscillation (ENSO) is a dominant tropical climate mode that has uneven impact on carbon dioxide (CO2) growth rates in different parts of the globe. In this study, we show an asymmetric meridional evolution of ENSO signal imprinted on CO2 growth rate using observations and chemistry‐transport model simulations. A time delay of 8 and 4 months between ENSO and CO2 growth rate are found near northern and southern high latitudes. This propagation asymmetry near the surface is linked to asymmetry in poleward transport of airmass and dominance of southern tropical flux variability to ENSO. The propagation is more homogenous in the upper atmosphere, where the flux signals are mixed. The terrestrial biosphere flux and fire emissions are reiterated as the underlying biophysical process in CO2 anomaly influenced by ENSO. Key Points: El Niño Southern Oscillation (ENSO) events strongly influence tropical land carbon dioxide (CO2) flux variability, and global CO2 variability both at surface and upper atmosphereAsymmetrical meridional propagation of the ENSO‐CO2 flux signal is imprinted on CO2 growth rate near the surfaceThe terrestrial biosphere fluxes and fire induced emissions from the tropical southern hemisphere show dominant CO2 flux variability [ABSTRACT FROM AUTHOR]

Interhemispheric transport (IHT) of airmass is an important parameter for understanding the transport of air pollutants in the troposphere. Although the IHT time of surface emissions is about 1.39 years, the mechanisms and location for transport through the tropics and the role of monsoonal circulations are poorly understood due to lacking observational evidence. This study clarifies the transport pathways that connect the Northern and Southern Hemispheres by analyzing global three‐dimensional distributions of methane (CH4), observed by the thermal infrared (TIR) sensor onboard the Greenhouse gases Observation SATellite (GOSAT), and simulations of an atmospheric chemistry‐transport model (ACTM). CH4 has a chemical lifetime of about 1 year in the tropical troposphere and increased quickly to about 100 years in heights of the tropopause and above, which makes CH4 an ideal species for studying IHT. We found that the most active IHT occurs in the altitude region of the upper troposphere, in a layer of 200 hPa below the tropopause. The IHT over tropical South America and Africa is active almost all year long, while in the Asia region there is significant seasonality caused by the South Asian summer monsoon (ASM). We confirm and clarify the influence of zonally asymmetric heating on IHT in the ASM. We highlight an important role of the monsoon‐induced eddy circulation in the cross‐Equator transport of long‐lived trace gases in the extended zone between tropical Africa and Southeast Asia. The zones of the most active IHT are clearly marked and quantified over the Asian, African, and American continents. Plain Language Summary: Materials transport occurs in the Earth's atmosphere by prevailing winds, and the distance traveled by different species depends on their lifetimes and wind speed. Methane is an important greenhouse gas, with a chemical lifetime ranging from about 1 year in the tropical troposphere to more than 100 years at the tropopause and in the stratosphere. Because of the chemical lifetime comparable to the interhemispheric transport (IHT) time scales of about 1.4 years and emissions mostly in the tropical and Northern Hemisphere lands, methane offers a unique opportunity to study the transport pathways between the two hemispheres. The global satellite (GOSAT‐TIR) measurements of methane vertical profiles fulfill the requirements at reasonable measurement accuracy throughout the free troposphere. We also use an atmospheric chemistry‐transport model (ACTM) to test the hypothesis of IHT through tropical Asian, African, and American continents at the upper‐tropospheric altitudes. Key Points: Interhemispheric transport (IHT) ducts are located over the tropical South America, tropical Africa, and Southeast AsiaMost efficient IHT pathways are located at the upper troposphere, in a layer of 200 hPa below the tropopauseThe South Asian summer monsoon has a dual effect on IHT: blocking over the Indian Ocean and enhancement over tropical Africa [ABSTRACT FROM AUTHOR]

Long‐term measurements at the Mauna Loa Observatory (MLO) show that the CO2 seasonal cycle amplitude (SCA) increased from 1959 to 2019 at an overall rate of 0.22 ± $\pm $ 0.034 ppm decade−1 while also varying on interannual to decadal time scales. These SCA changes are a signature of changes in land ecological CO2 fluxes as well as shifting winds. Simulations with the TM3 tracer transport model and CO2 fluxes from the Jena CarboScope CO2 Inversion suggest that shifting winds alone have contributed to a decrease in SCA of −0.10 ± $\pm $ 0.022 ppm decade−1 from 1959 to 2019, partly offsetting the observed long‐term SCA increase associated with enhanced ecosystem net primary production. According to these simulations and MIROC‐ACTM simulations, the shorter‐term variability of MLO SCA is nearly equally driven by varying ecological CO2 fluxes (49%) and varying winds (51%). We also show that the MLO SCA is strongly correlated with the Pacific Decadal Oscillation (PDO) due to varying winds, as well as with a closely related wind index (U‐PDO). Since 1980, 44% of the wind‐driven SCA decrease has been tied to a secular trend in the U‐PDO, which is associated with a progressive weakening of westerly winds at 700 mbar over the central Pacific from 20°N to 40°N. Similar impacts of varying winds on the SCA are seen in simulations at other low‐latitude Pacific stations, illustrating the difficulty of constraining trend and variability of land CO2 fluxes using observations from low latitudes due to the complexity of circulation changes. Plain Language Summary: The CO2 seasonal amplitude is an indicator of the growing‐season productivity of land ecosystems. CO2 observation at Mauna Loa Observatory (MLO) showed an increasing amplitude from 1959 to 2019, probably due to significantly enhanced productivity over the Eurasia temperate and boreal forest. In this study, we show that about a third of this observed amplitude increase at MLO was offset by long‐term circulation changes, which isolated the air at low latitudes from the influence of northern high‐latitude ecosystems. This wind‐driven impact is also important at other low‐latitude Pacific stations. The CO2 seasonal amplitude at MLO also has considerable short‐term variability (on the scale of multiple years to decades), roughly half of which is regulated by the changing winds, while the remaining half is driven by the variability of ecological CO2 fluxes. We show that the wind influence is closely associated with a climate index known as the Pacific Decadal Oscillation. Our study indicates that the attribution of amplitude changes at low‐latitudes stations to ecosystem changes is complicated by wind shifts. Key Points: The increasing CO2 seasonal amplitude observed at the Mauna Loa Observatory since 1959 has been significantly offset by circulation changesVariability of CO2 seasonal cycles at Mauna Loa is partly regulated by circulation changes associated with the Pacific Decadal OscillationCirculation changes complicate using low‐latitudes CO2 observation to constrain changing land carbon cycle [ABSTRACT FROM AUTHOR]

The ongoing development of the Global Carbon Project (GCP) global methane (CH4) budget shows a continuation of increasing CH4 emissions and CH4 accumulation in the atmosphere during 2000–2017. Here, we decompose the global budget into 19 regions (18 land and 1 oceanic) and five key source sectors to spatially attribute the observed global trends. A comparison of top‐down (TD) (atmospheric and transport model‐based) and bottom‐up (BU) (inventory‐ and process model‐based) CH4 emission estimates demonstrates robust temporal trends with CH4 emissions increasing in 16 of the 19 regions. Five regions—China, Southeast Asia, USA, South Asia, and Brazil—account for >40% of the global total emissions (their anthropogenic and natural sources together totaling >270 Tg CH4 yr−1 in 2008–2017). Two of these regions, China and South Asia, emit predominantly anthropogenic emissions (>75%) and together emit more than 25% of global anthropogenic emissions. China and the Middle East show the largest increases in total emission rates over the 2000 to 2017 period with regional emissions increasing by >20%. In contrast, Europe and Korea and Japan show a steady decline in CH4 emission rates, with total emissions decreasing by ~10% between 2000 and 2017. Coal mining, waste (predominantly solid waste disposal) and livestock (especially enteric fermentation) are dominant drivers of observed emissions increases while declines appear driven by a combination of waste and fossil emission reductions. As such, together these sectors present the greatest risks of further increasing the atmospheric CH4 burden and the greatest opportunities for greenhouse gas abatement. [ABSTRACT FROM AUTHOR]

Southeast Asia is a region known for active land‐use changes (LUC) over the past 60 years; yet, how trends in net CO2 uptake and release resulting from LUC activities (net LUC flux) have changed through past decades remains uncertain. The level of uncertainty in net LUC flux from process‐based models is so high that it cannot be concluded that newer estimates are necessarily more reliable than older ones. Here, we examined net LUC flux estimates of Southeast Asia for the 1980s−2010s from older and newer sets of Dynamic Global Vegetation Model simulations (TRENDY v2 and v7, respectively), and forcing data used for running those simulations, along with two book‐keeping estimates (H&N and BLUE). These estimates yielded two contrasting historical LUC transitions, such that TRENDY v2 and H&N showed a transition from increased emissions from the 1980s to 1990s to declining emissions in the 2000s, while TRENDY v7 and BLUE showed the opposite transition. We found that these contrasting transitions originated in the update of LUC forcing data, which reduced the loss of forest area during the 1990s. Further evaluation of remote sensing studies, atmospheric inversions, and the history of forestry and environmental policies in Southeast Asia supported the occurrence of peak emissions in the 1990s and declining thereafter. However, whether LUC emissions continue to decline in Southeast Asia remains uncertain as key processes in recent years, such as conversion of peat forest to oil‐palm plantation, are yet to be represented in the forcing data, suggesting a need for further revision. Key Points: Uncertainty remains in historical trends of CO2 fluxes from land‐use changes (LUC) of Southeast AsiaExisting process‐based models and book‐keeping models yielded two contrasting historical LUC transitions of Southeast AsiaIndependent data evaluations are supportive of the occurrence of peak emissions in the 1990s and declining thereafter [ABSTRACT FROM AUTHOR]

Distributions of trace gases in the atmosphere provide key information on the transport and chemical properties of the Earth's environment. In this study, we examine the observed seasonal variability of SF6, CO2, CH4, and N2O from commercial aircraft‐based measurements in the upper troposphere and lower stratosphere (UT/LS) in combination with atmospheric chemistry‐transport model (ACTM) simulations. We used a dynamical tropopause defined based on maximum PV gradient that better allows for model‐observation comparisons in the UT and LS regions separately. The ACTM simulated the following observed features well: (1) smaller seasonality in SF6 in the UT than in the LS due to seasonal change in the transport processes, (2) large seasonality in CO2 in the UT, in phase with the source‐sink balance on the Earth's surface, (3) pronounced seasonality in CH4 in the UT with opposite phase in the subtropics and Eurasian high latitudes as contrasting phases of source and chemical loss seasonality develop, and (4) small N2O variability in the UT but stratospheric loss produces distinct seasonality in the LS. Vertical profile comparisons of all the species show that ACTM better simulated the photo‐chemically inert CO2 vertical gradients in all seasons, suggesting a realistic representation of the Brewer‐Dobson circulation in the model. The seasonal variabilities of the long‐lived species in the LS can be explained based on age of air derived from CO2 in the older air regime, except for the months of May‐July, when the model mixes UT and LS air more vigorously than suggested by the observations. Key Points: We have analyzed seasonal variations of SF6, CO2, CH4, and N2O in the upper troposphere and lower stratosphereRoles of surface sources, transport processes, and chemical losses in variabilities of each species in the upper troposphere are discussedThe age of air diagnostic is used to explain their seasonal cycle variability due to the Brewer‐Dobson circulation in the lower stratosphere [ABSTRACT FROM AUTHOR]

Robust estimates of CO2 budget, CO2 exchanged between the atmosphere and terrestrial biosphere, are necessary to better understand the role of the terrestrial biosphere in mitigating anthropogenic CO2 emissions. Over the past decade, this field of research has advanced through understanding of the differences and similarities of two fundamentally different approaches: "top‐down" atmospheric inversions and "bottom‐up" biosphere models. Since the first studies were undertaken, these approaches have shown an increasing level of agreement, but disagreements in some regions still persist, in part because they do not estimate the same quantity of atmosphere–biosphere CO2 exchange. Here, we conducted a thorough comparison of CO2 budgets at multiple scales and from multiple methods to assess the current state of the science in estimating CO2 budgets. Our set of atmospheric inversions and biosphere models, which were adjusted for a consistent flux definition, showed a high level of agreement for global and hemispheric CO2 budgets in the 2000s. Regionally, improved agreement in CO2 budgets was notable for North America and Southeast Asia. However, large gaps between the two methods remained in East Asia and South America. In other regions, Europe, boreal Asia, Africa, South Asia, and Oceania, it was difficult to determine whether those regions act as a net sink or source because of the large spread in estimates from atmospheric inversions. These results highlight two research directions to improve the robustness of CO2 budgets: (a) to increase representation of processes in biosphere models that could contribute to fill the budget gaps, such as forest regrowth and forest degradation; and (b) to reduce sink–source compensation between regions (dipoles) in atmospheric inversion so that their estimates become more comparable. Advancements on both research areas will increase the level of agreement between the top‐down and bottom‐up approaches and yield more robust knowledge of regional CO2 budgets. [ABSTRACT FROM AUTHOR]

Two recent studies using sulfur hexafluoride (SF6) observations to evaluate interhemispheric transport in two different ensembles of atmospheric chemistry models reached different conclusions on model performance. We show here that the different conclusions are due to the use of different metrics and not differences in the performance of the models. For both model ensembles, the multimodel mean interhemispheric exchange time τex agrees well with observations, but in nearly all models the SF6 age in the southern hemisphere is older than observed. This occurs because transport from the northern extratropics into the tropics is too slow in most models, and the SF6 age is more sensitive to this bias than τex. Thus, simulating τex correctly does not necessarily mean that transport from northern midlatitudes into the southern hemisphere is correct. It also suggests that more attention needs to be paid to evaluating transport from northern midlatitudes into the tropics. Plain Language Summary: Transport of air between hemispheres is important as most air pollutants are emitted predominantly in northern midlatitudes, and the rate of this interhemispheric transport influences the global distribution of these gases. Two recent studies analyzed simulations from two different model intercomparison projects and reached different conclusions on the models' ability to simulate the time scale for interhemispheric transport. In this study, we show that the different conclusions are due to the use of different metrics for quantifying the cross‐equator transport time scales, rather than different performances between models. For both groups of models, the mean of the models agrees with observed interhemispheric exchange time τex but overestimates the SF6 age at the surface level. This occurs because τex is an estimate of the time scale of transport across the equator, whereas the SF6 age in the southern hemisphere quantifies transport from northern midlatitudes into the tropics as well as transport across the equator. Our results indicate that transport into the tropics is generally too slow in models, resulting in too old SF6 ages compared to observed values, with little influence on τex. Key Points: Different conclusions from previous studies evaluating model simulations of interhemispheric transport are reconciledThe simulated interhemispheric exchange time τex agrees well with observations, but the simulated SF6 age in the SH is older than observedTransport from the northern extratropics into the tropics is too slow in most models, which has a larger effect on SF6 age in the SH than τex [ABSTRACT FROM AUTHOR]

Abstract: The increasing strength of land CO2 uptake in the 2000s has been attributed to a stimulating effect of rising atmospheric CO2 on photosynthesis (CO2 fertilization). Using terrestrial biosphere models, we show that enhanced CO2 uptake is induced not only by CO2 fertilization but also an increasing uptake by plant regrowth (accounting for 0.33 ± 0.10 Pg C/year increase of CO2 uptake in the 2000s compared with the 1960s–1990s) with its effect most pronounced in eastern North America, southern‐eastern Europe, and southeastern temperate Eurasia. Our analysis indicates that ecosystems in North America and Europe have established the current productive state through regrowth since the 1960s, and those in temperate Eurasia are still in a stage from regrowth following active afforestation in the 1980s–1990s. As the strength of model representation of CO2 fertilization is still in debate, plant regrowth might have a greater potential to sequester carbon than indicated by this study. [ABSTRACT FROM AUTHOR]

Abstract: We have conducted simultaneous measurements of the mole fraction and carbon and hydrogen isotope ratios (δ13C and δD) of atmospheric methane (CH4) at Churchill (58°44′N, 93°49′W) in the northern part of the Hudson Bay Lowlands (HBL), Canada, since 2007. Compared with the measurements at an Arctic baseline monitoring station, Ny‐Ålesund, Svalbard (78°55′N, 11°56′E), CH4 mole fraction is generally higher and δ13C and δD are lower at Churchill due to regional biogenic CH4 emissions. Clear seasonal cycles in the CH4 mole fraction, δ13C, and δD are observable at Churchill, and their seasonal phases in summer are earlier by approximately 2 weeks than those at Ny‐Ålesund. Using the one‐box model analysis, the phase difference is ascribed to the different seasonal influence of CH4 emissions from boreal wetlands on the two sites. Short‐term CH4 variations are also observed at Churchill throughout the year. The analysis of the observed isotopic signatures of atmospheric CH4 confirmed that the short‐term CH4 variations are mainly produced by biogenic CH4 released from the HBL wetlands in summer and by fossil fuel CH4 transported over the Arctic in winter. Forward simulations of an atmospheric chemistry‐transport model, with wetland CH4 fluxes prescribed by a process‐based model, show unrealistically high CH4 mole fractions at Churchill in summer, suggesting that CH4 emissions assigned to the HBL wetlands are overestimated. Our best estimate of the HBL CH4 emissions is 2.7 ± 0.3 Tg CH4 yr−1 as an average of 2007–2013, consistent with recent estimations by inverse modeling studies. [ABSTRACT FROM AUTHOR]

ABSTRACT With their unique structure and physicochemical properties, single\-walled carbon nanotubes (SWCNTs) have many potential new applications in medicine and industry. However, there is lack of detailed information concerning their impact on human health and the environment. The aim of this study was to assess the effects, after intraperitoneal injection of functionalized SWCNTs (f-SWCNT) on the induction of reactive oxygen species (ROS), frequency of structural chromosomal aberrations (SCA), frequency of micronuclei induction, mitotic index, and DNA damage in Swiss-Webster mice. Three doses of f-SWCNTs (0.25, 0.5, and 0.75 mg/kg) and two controls (negative and positive) were administered to mice, once a day for 5 days. Bone marrow and peripheral blood samples were collected 24 h after the last treatment following standard protocols. F -SWCNT exposure significantly enhanced ROS, increased ( p < 0.05) the number of SCA and the frequency of micronucleated cells, increased DNA damage, and decreased the mitotic index in exposed groups compared to negative control. The scientific findings reported here suggest that purified f-SWCNT have the potential to induce oxidative stress mediated genotoxicity in Swiss-Webster mice at higher level of exposure. Further characterization of their systemic toxicity, genotoxicity, and carcinogenicity is also essential. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1091-1102, 2016. [ABSTRACT FROM AUTHOR]

In the pursuit of advanced polymer composites, nanoscale fillers have long been championed as promising candidates for structural reinforcement. Despite progress, questions remain as to how these diminutive fillers influence the distribution of stresses within the matrix and, in turn, influence bulk mechanical properties. The dynamic mechanical behavior of elastomer-impregnated forests of carbon nanotubes (CNTs) has revealed distinct orientation-dependent behavior that sheds light on these complicated interactions. When compressed along the axis of the fillers, the composite will mimic open-cell foams and exhibit strain softening for increasing amplitudes due to the collective Euler buckling of the slender nanotubes. In contrast, the same material will behave similarly to the neat polymer when compressed orthogonal to the alignment direction of the nanotubes. However, in this orientation the material is incapable of achieving the same ultimate compressive strain due to the role that the embedded nanotubes play in augmenting the effective cross-link density of the polymer network. Both of these responses are recoverable, robust, and show little dependency on the diameter and wall-number of the included CNTs. Such observations give insight into the mechanics of polymer/nanoparticle interactions in nanocomposite structures under strain, and the thoughtful control of such coordinated buckling behavior opens the possibility for the development of foam-like materials with large Poisson ratios. [ABSTRACT FROM AUTHOR]

Inverse-estimated net carbon exchange time series spanning two decades for six North American regions are analyzed to examine long-term trends and relationships to temperature and precipitation variations. Results reveal intensification of carbon uptake in eastern boreal North America (0.1 PgC/decade) and the Midwest United States (0.08 PgC/decade). Seasonal cross-correlation analysis shows a significant relationship between net carbon exchange and temperature/precipitation anomalies during the western United States growing season with warmer, dryer conditions leading reduced carbon uptake. This relationship is consistent with 'global change-type drought' dynamics which drive increased vegetation mortality, increases in dry woody material, and increased wildfire occurrence. This finding supports the contention that future climate change may increase carbon loss in this region. Similarly, higher temperatures and reduced precipitation are accompanied by decreased net carbon uptake in the Midwestern United States toward the end of the growing season. Additionally, intensified net carbon uptake during the eastern boreal North America growing season is led by increased precipitation anomalies in the previous year, suggesting the influence of 'climate memory' carried by regional snowmelt water. The two regions of boreal North America exhibit opposing seasonal carbon-temperature relationships with the eastern half experiencing a net carbon loss with near coincident increases in temperature and the western half showing increased net carbon uptake. The carbon response in the boreal west region lags the temperature anomalies by roughly 6 months. This opposing carbon-temperature relationship in boreal North America may be a combination of different dominant vegetation types, the amount and timing of snowfall, and temperature anomaly differences across boreal North America. [ABSTRACT FROM AUTHOR]

The chemical mode of action as a flame retardant of calcium carbonate nanoparticles combined with ammonium polyphosphate in polypropylene was investigated. Reduction in burning rates for 0.5 mm thick samples were observed without appreciable char formation up to 30 wt % loading of additives. Thermogravimetric analysis (TGA) of the mixture of CaCO and ammonium polyphosphate (APP) showed that calcium carbonate nanoparticles react with ammonium polyphosphate before the degradation of the phosphate chains. TGA-FTIR studies of the polymer composite samples and powder mixtures of the additives confirmed the evolution of ammonia and carbon dioxide due to interaction between the additives. X-ray diffraction (XRD) analysis of chars, obtained after burning the films, showed definite diffraction peaks corresponding to that of calcium metaphosphate. The inert gasses produced by the interaction of the additives hindered the advancing flame and, thus, reduces the burning rates, at times even without char formation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

The article presents information on a study which investigated the flame-retardant properties of nylon 6/organically modified montmorillonite (OMMT) thin films, fibers, and fabrics to determine the efficacy of condensed-phase flame-retardant mechanism in relation to montmorillonite concentration, sample geometry, and flame test conditions. The experimental procedures of the study include preparation of nanocomposite, fiber spinning, analysis of cone calorimeter, and horizontal flame spread test. The findings of the study demonstrated the interdependence of fabric tightness factor, OMMT concentration, and source of heat flux in forming a protective char and affecting the flammability of fabrics.

The atmosphere-land-ocean fluxes of CO2 were derived for 64 partitioned areas of the globe (22 over the ocean and 42 over the land) using a time-dependent inverse (TDI) model for the period of January 1988 to December 2001. The model calculation partially follow the TransCom-3 protocol, and is constrained by atmospheric CO2 concentration data from 87 stations and fully time-dependent atmospheric transport model simulations. The air-to-land and air-to-sea fluxes averaged over the 1990s are estimated at 1.15 ± 0.74 and 1.88 ± 0.53 Pg-C yr-1, respectively. These estimates, however, remain uncertain owing to sampling biases arising from the sparse distribution of atmospheric CO2 data, are compared with other estimates by various methods. The sensitivity analysis indicates that the differences in fluxes and flux variability caused by the choices of initial conditions for the TDI model are smaller compared to those due to the selection of measurement networks. Our model results capture interannual variations in global and regional CO2 fluxes realistically. The estimated oceanic CO2 flux anomalies appear to be closely related to prominent climate modes such as El Niño-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the Pacific Decadal Oscillation (PDO). The results from the correlation analyses show that the oceanic CO2 flux in the tropics is strongly influenced by the ENSO dynamical cycle, and that in the sub-polar regions by upwelling of sub-surface waters in the winter and plankton blooms in the spring. [ABSTRACT FROM AUTHOR]

A Time-dependent inverse (TDI) model is used to estimate carbon dioxide (CO2) fluxes for 64 regions of the globe from atmospheric measurements in the period January 1994 to December 2001. The global land anomalies agree fairly well with earlier results. Large variability in CO2 fluxes are recorded from the land regions, which are typically controlled by the available water for photosynthesis, and air temperature and soil moisture dependent heterotrophic respiration. For example, the anomalous CO2 emissions during the 1997/1998 El Niño period are estimated to be about 1.27 ± 0.22, 2.06 ± 0.37, and 1.17 ± 0.20 Pg-C yr-1 from tropical regions in Asia, South America, and Africa, respectively. The CO2 flux anomalies for boreal Asia region are estimated to be 0.83 ± 0.19 and 0.45 ± 0.14 Pg-C yr-1 of CO2 during 1996 and 1998, respectively. Comparison of inversion results with biogeochemical model simulations provide strong evidence that biomass burning (natural and anthropogenic) constitutes the major component in land-atmosphere carbon flux anomalies. The net biosphere-atmosphere carbon exchanges based on the biogeochemical model used in this study are generally lower than those estimated from TDI model results, by about 1.0 Pg-C yr-1 for the periods and regions of intense fire. The correlation and principal component analyses suggest that changes in meteorology (i.e., rainfall and air temperature) associated with the El Niño Southern Oscillation are the most dominant controlling factors of CO2 flux anomaly in the tropics, followed by the Indian Ocean Dipole Oscillation. Our results indicate that the Arctic and North Atlantic Oscillations are closely linked with CO2 flux variability in the temperate and high-latitude regions. [ABSTRACT FROM AUTHOR]