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Earth system and environmental impact studies need high quality and up-to-date estimates of atmospheric deposition. This study demonstrates the methodological benefits of multimodel ensemble and measurement-model fusion mapping approaches for atmospheric deposition focusing on 2010, a year for which several studies were conducted. Global model-only deposition assessment can be further improved by integrating new model-measurement techniques, including expanded capabilities of satellite observations of atmospheric composition. We identify research and implementation priorities for timely estimates of deposition globally as implemented by the World Meteorological Organization.

Achieving the long-term temperature goal of the Paris Agreement requires forest-based mitigation. Collective progress towards this goal will be assessed by the Paris Agreement’s Global stocktake. At present, there is a discrepancy of about 4 GtCO2yr−1in global anthropogenic net land-use emissions between global models (reflected in IPCC assessment reports) and aggregated national GHG inventories (under the UNFCCC). We show that a substantial part of this discrepancy (about 3.2 GtCO2yr−1) can be explained by conceptual differences in anthropogenic forest sink estimation, related to the representation of environmental change impacts and the areas considered as managed. For a more credible tracking of collective progress under the Global stocktake, these conceptual differences between models and inventories need to be reconciled. We implement a new method of disaggregation of global land model results that allows greater comparability with GHG inventories. This provides a deeper understanding of model–inventory differences, allowing more transparent analysis of forest-based mitigation and facilitating a more accurate Global stocktake.

Forest-based climate mitigation may occur through conserving and enhancing the carbon sink and through reducing greenhouse gas emissions from deforestation. Yet the inclusion of forests in international climate agreements has been complex, often considered a secondary mitigation option. In the context of the Paris Climate Agreement, countries submitted their (Intended) Nationally Determined Contributions ((I)NDCs), including climate mitigation targets. Assuming full implementation of (I)NDCs, we show that land use, and forests in particular, emerge as a key component of the Paris Agreement: turning globally from a net anthropogenic source during 1990–2010 (1.3 ± 1.1 GtCO2e yr−1) to a net sink of carbon by 2030 (up to −1.1 ± 0.5 GtCO2e yr−1), and providing a quarter of emission reductions planned by countries. Realizing and tracking this mitigation potential requires more transparency in countries’ pledges and enhanced science-policy cooperation to increase confidence in numbers, including reconciling the ≍3 GtCO2e yr−1difference in estimates between country reports and scientific studies.

Quantification of the disease burden caused by different risks informs prevention by providing an account of health loss different to that provided by a disease-by-disease analysis. No complete revision of global disease burden caused by risk factors has been done since a comparative risk assessment in 2000, and no previous analysis has assessed changes in burden attributable to risk factors over time.

Nitrous oxide (N2O) is an important anthropogenic greenhouse gas and agriculture represents its largest source. It is at the heart of debates over the efficacy of biofuels, the climate-forcing impact of population growth, and the extent to which mitigation of non-CO2emissions can help avoid dangerous climate change. Here we examine some of the major debates surrounding estimation of agricultural N2O sources, and the challenges of projecting and mitigating emissions in coming decades. We find that current flux estimates — using either top-down or bottom-up methods — are reasonably consistent at the global scale, but that a dearth of direct measurements in some areas makes national and sub-national estimates highly uncertain. We also highlight key uncertainties in projected emissions and demonstrate the potential for dietary choice and supply-chain mitigation.

A global assessment of the impact of the anthropogenic perturbation of the nitrogen and sulfur cycles on forest ecosystems is carried out for both the present-day [1980–1990] and for a projection into the future [2040–2050] under a scenario of economic development which represents a medium path of development according to expert guess [IPCC IS92a]. Results show that forest soils will receive considerably increasing loads of nitrogen and acid deposition and that deposition patterns are likely to change. The regions which are most prone to depletion of soils buffering capacity and supercritical nitrogen deposition are identified in the subtropical and tropical regions of South America and Southeast Asia apart from the well known ‘hotspots’ North-Eastern America and Central Europe. The forest areas likely to meet these two risks are still a minor fraction of the global forest ecosystems, though. But the bias between eutrophication and acidification will become greater and an enhanced growth triggered by the fertilizing effects of increasing nitrogen input cannot be balanced by the forest soils nutrient pools.

The short-lived radionuclide Rn222is emitted at a fairly constant rate from the continents and is a good surrogate for studying the transport of “air pollution” from polluted continental areas to clean, remote regions. The large concentration gradients of 2–3 orders of magnitude which exist between the continents and the remote atmosphere present a major challenge to the modelling of horizontal and vertical atmospheric transport. We use the global off-line tracer transport model TM3 at 3 different resolutions. Input to the model consists of meteorological data for the year 1993 obtained from the European Centre for Medium Range Weather Forecasts (ECMWF). The same meteorological data is used to constrain the climate model ECHAM4-T42-L19. Using these meteorological data, Rn222simulations are used to evaluate and document model performance and associated uncertainties. High time-resolution measurements made at 2 continental stations, 2 stations under continental influence and 4 remote sites, and aircraft measurements obtained during the NARE aircraft campaign are used for a detailed comparison.Although in specific regions there are inter-model differences of up to a factor of 2 in the calculated boundary layer concentrations, these differences are not translated into a better performance of either model for the stations used for comparison. We generally obtain high correlations of model results and measurements; these range from r= 0.6–0.8 for the continental and coastal stations and 0.5–0.6 for the remote sites. Calculated mean concentrations and corresponding standard deviations generally agree favourably with observations, lending credibility to the usefulness of our models for evaluating transport of air pollutants from continental sources to remote regions. The main cause of model deviations is probably related to uncertainties in the meteorological input data set provided by the ECMWF model and to a lesser extent by our knowledge of the spatial distribution of Rn222emissions and uncertainties involving sub-grid scale parameterization of vertical transport, e.g., diffusion and convection.

The short‐lived radionuclide Rn222is emitted at a fairly constant rate from the continents and is a good surrogate for studying the transport of “air pollution” from polluted continental areas to clean, remote regions. The large concentration gradients of 2–3 orders of magnitude which exist between the continents and the remote atmosphere present a major challenge to the modelling of horizontal and vertical atmospheric transport. We use the global off‐line tracer transport model TM3 at 3 different resolutions. Input to the model consists of meteorological data for the year 1993 obtained from the European Centre for Medium Range Weather Forecasts (ECMWF). The same meteorological data is used to constrain the climate model ECHAM4‐T42‐L19. Using these meteorological data, Rn222simulations are used to evaluate and document model performance and associated uncertainties. High time‐resolution measurements made at 2 continental stations, 2 stations under continental influence and 4 remote sites, and aircraft measurements obtained during the NARE aircraft campaign are used for a detailed comparison.

Previous studies on ice core analyses and recent in situ measurements have shown that CH4has increased from about 0.75–1.73 μmol/mol during the past 150 years. Here, we review sources and sink estimates and we present global 3D model calculations, showing that the main features of the global CH4distribution are well represented. The model has been used to derive the total CH4emission source, being about 600 Tg yr-1. Based on published results of isotope measurements the total contribution of fossil fuel related CH4emissions has been estimated to be about 110 Tg yr-1. However, the individual coal, natural gas and oil associated CH4emissions can not be accurately quantified. In particular natural gas and oil associated emissions remain speculative. Since the total anthropogenic CH4source is about 410 Tg yr-1(~70% of the total source) and the mean recent atmospheric CH4increase is ~20 Tg yr-1an anthropogenic source reduction of 5% could stabilize the atmospheric CH4level. We have calculated the indirect chemical effects of increasing CH4on climate forcing on the basis of global 3D chemistry-transport and radiative transfer calculations. These indicate an enhancement of the direct radiative effect by about 30%, in agreement with previous work. The contribution of CH4(direct and indirect effects) to climate forcing during the past 150 years is 0.57W m-2(direct 0.44W m-2, indirect 0.13 W m-2). This is about 35% of the climate forcing by CO2(1.6W m-2) and about 22% of the forcing by all long-lived greenhouse gases (2.6 W m-2). Scenario calculations (IPCC-IS92a) indicate that the CH4lifetime in the atmosphere increased by about 25–30%during the past 150 years to a current value of 7.9 years. Future lifetime changes are expected to be much smaller, about 6%, mostly due to the expected increase of tropospheric O3(→OH) in the tropics. The global mean concentration of CH4may increase to about 2.55 μmol/mol, its lifetime is expected to increase to 8.4 years in the year 2050. Further, we have calculated a CH4global warming potential (GWP) of 21 (kgCH4/kgCO2) over a time horizon of 100 years, in agreement with IPCC (1996). Scenario calculations indicate that the importance of the climate forcing by CH4(including indirect effects) relative to that of CO2will decrease in future; currently this is about 35%, while this is expected to decrease to about 15% in the year 2050.

Previous studies on ice core analyses and recent in situ measurements have shown that CH4has increased from about 0.75–1.73 μmol/mol during the past 150 years. Here, we review sources and sink estimates and we present global 3D model calculations, showing that the main features of the global CH4distribution are well represented. The model has been used to derive the total CH4emission source, being about 600 Tg yr‐1. Based on published results of isotope measurements the total contribution of fossil fuel related CH4emissions has been estimated to be about 110 Tg yr‐1. However, the individual coal, natural gas and oil associated CH4emissions can not be accurately quantified. In particular natural gas and oil associated emissions remain speculative. Since the total anthropogenic CH4source is about 410 Tg yr‐1(∼70% of the total source) and the mean recent atmospheric CH4increase is ∼20 Tg yr‐1an anthropogenic source reduction of 5% could stabilize the atmospheric CH4level. We have calculated the indirect chemical effects of increasing CH4on climate forcing on the basis of global 3D chemistry‐transport and radiative transfer calculations. These indicate an enhancement of the direct radiative effect by about 30%, in agreement with previous work. The contribution of CH4(direct and indirect effects) to climate forcing during the past 150 years is 0.57W m−2(direct 0.44W m−2, indirect 0.13 W m−2). This is about 35% of the climate forcing by CO2(1.6W m−2) and about 22% of the forcing by all long‐lived greenhouse gases (2.6 W m−2). Scenario calculations (IPCC‐IS92a) indicate that the CH4lifetime in the atmosphere increased by about 25–30%during the past 150 years to a current value of 7.9 years. Future lifetime changes are expected to be much smaller, about 6%, mostly due to the expected increase of tropospheric O3(→OH) in the tropics. The global mean concentration of CH4may increase to about 2.55 μmol/mol, its lifetime is expected to increase to 8.4 years in the year 2050. Further, we have calculated a CH4global warming potential (GWP) of 21 (kgCH4/kgCO2) over a time horizon of 100 years, in agreement with IPCC (1996). Scenario calculations indicate that the importance of the climate forcing by CH4(including indirect effects) relative to that of CO2will decrease in future; currently this is about 35%, while this is expected to decrease to about 15% in the year 2050.

The global tropospheric budget of gaseous and particulate non‐methane organic matter (OM) is re‐examined to provide a holistic view of the role that OM plays in transporting the essential nutrients nitrogen and phosphorus to the ocean. A global 3‐dimensional chemistry‐transport model was used to construct the first global picture of atmospheric transport and deposition of the organic nitrogen (ON) and organic phosphorus (OP) that are associated with OM, focusing on the soluble fractions of these nutrients. Model simulations agree with observations within an order of magnitude. Depending on location, the observed water soluble ON fraction ranges from ∼3% to 90% (median of ∼35%) of total soluble N in rainwater; soluble OP ranges from ∼20–83% (median of ∼35%) of total soluble phosphorus. The simulations suggest that the global ON cycle has a strong anthropogenic component with ∼45% of the overall atmospheric source (primary and secondary) associated with anthropogenic activities. In contrast, only 10% of atmospheric OP is emitted from human activities. The model‐derived present‐day soluble ON and OP deposition to the global ocean is estimated to be ∼16 Tg‐N/yr and ∼0.35 Tg‐P/yr respectively with an order of magnitude uncertainty. Of these amounts ∼40% and ∼6%, respectively, are associated with anthropogenic activities, and 33% and 90% are recycled oceanic materials. Therefore, anthropogenic emissions are having a greater impact on the ON cycle than the OP cycle; consequently increasing emissions may increase P‐limitation in the oligotrophic regions of the world's ocean that rely on atmospheric deposition as an important nutrient source. A significant fraction of N and P deposition occurs as ON and OP~45% of the atmospheric ON sources are associated with anthropogenic activities~10% of atmospheric OP is derived from human activities