Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Positive framing does not solve the tragedy of the commons
Isaksen, Elisabeth Thuestad ; Brekke, Kjell Arne ; Richter, Andries - \ 2019
Journal of Environmental Economics and Management 95 (2019). - ISSN 0095-0696 - p. 45 - 56.
Common pool experiment - Externality - Framing - Public goods experiment - Rivalry - Strategic complements - Strategic substitutes

We investigate whether positive framing increases cooperation in three social dilemmas with slightly different properties: a linear public goods (PG) game, a non-linear PG game, and a common pool resource (CPR) game. Results from our laboratory experiments show that contributions to a linear PG are higher if the externality is framed positively, rather than negatively, corroborating earlier findings by Andreoni (1995). By contrast, we find no such framing effects in the non-linear PG game or the CPR game. In these games, the best response in the material payoffs is to contribute less if others contribute more, counteracting effects of pro-social preferences. Positive framing therefore does not help to solve the tragedy of the commons.

Atmospheric composition change: Ecosystems-Atmosphere interactions
Fowler, D. ; Pilegaard, K. ; Sutton, M.A. ; Ambus, P. ; Raivonen, M. ; Duyzer, J. ; Simpson, D. ; Fagerli, H. ; Fuzzi, S. ; Schjoerring, J.K. ; Granier, C. ; Neftel, A. ; Isaksen, I.S.A. ; Laj, P. ; Maione, M. ; Monks, P.S. ; Burkhardt, J. ; Daemmgen, U. ; Neirynck, J. ; Personne, E. ; Wichink Kruit, R.J. ; Butterbach-Bahl, K. ; Flechard, C. ; Tuovinen, J.P. ; Coyle, M. ; Gerosa, G. ; Loubet, B. ; Altimir, N. ; Gruenhage, L. ; Ammann, C. ; Cieslik, S. ; Paoletti, E. ; Mikkelsen, T.N. ; Ro-Poulsen, H. ; Cellier, P. ; Cape, J.N. ; Horvath, L. ; Loreto, F. ; Niinemets, U. ; Palmer, P.I. ; Rinne, J. ; Misztal, P. ; Nemitz, E. ; Nilsson, D. ; Pryor, S. ; Gallagher, M.W. ; Vesala, T. ; Skiba, U. ; Brueggemann, N. ; Zechmeister-Boltenstern, S. ; Williams, J. ; O'Dowd, C. ; Facchini, M.C. ; Leeuw, G. de; Flossman, A. ; Chaumerliac, N. ; Erisman, J.W. - \ 2009
Atmospheric Environment 43 (2009)33. - ISSN 1352-2310 - p. 5193 - 5267.
volatile organic-compounds - relaxed eddy accumulation - dry deposition velocity - reaction mass-spectrometry - cloud condensation nuclei - gas-particle interactions - surface-exchange fluxes - nitric-oxide emissions - beech fagus-sylvatica - ozone risk-assessment
Ecosystems and the atmosphere: This review describes the state of understanding the processes involved in the exchange of trace gases and aerosols between the earth's surface and the atmosphere. The gases covered include NO, NO2, HONO, HNO3, NH3, SO2, DMS, Biogenic VOC, O-3, CH4, N2O and particles in the size range 1 nm-10 mu m including organic and inorganic chemical species. The main focus of the review is on the exchange between terrestrial ecosystems, both managed and natural and the atmosphere, although some new developments in ocean-atmosphere exchange are included. The material presented is biased towards the last decade, but includes earlier work, where more recent developments are limited or absent. New methodologies and instrumentation have enabled, if not driven technical advances in measurement. These developments have advanced the process understanding and upscaling of fluxes, especially for particles, VOC and NH3. Examples of these applications include mass spectrometric methods, such as Aerosol Mass Spectrometry (AMS) adapted for field measurement of atmosphere-surface fluxes using micrometeorological methods for chemically resolved aerosols. Also briefly described are some advances in theory and techniques in micrometeorology. For some of the compounds there have been paradigm shifts in approach and application of both techniques and assessment. These include flux measurements over marine surfaces and urban areas using micrometeorological methods and the up-scaling of flux measurements using aircraft and satellite remote sensing. The application of a flux-based approach in assessment of O-3 effects on vegetation at regional scales is an important policy linked development secured through improved quantification of fluxes. The coupling of monitoring, modelling and intensive flux measurement at a continental scale within the NitroEurope network represents a quantum development in the application of research teams to address the underpinning science of reactive nitrogen in the cycling between ecosystems and the atmosphere in Europe. Some important developments of the science have been applied to assist in addressing policy questions, which have been the main driver of the research agenda, while other developments in understanding have not been applied to their wider field especially in chemistry-transport models through deficiencies in obtaining appropriate data to enable application or inertia within the modelling community. The paper identifies applications, gaps and research questions that have remained intractable at least since 2000 within the specialized sections of the paper, and where possible these have been focussed on research questions for the coming decade. (C) 2009 Published by Elsevier Ltd.
Multimodel ensemble simulations of present-day and near-future tropospheric ozone
Stevenson, D.S. ; Dentener, F.J. ; Schultz, M.G. ; Ellingsen, K. ; Noije, T.P.C. van; Wild, O. ; Zeng, G. ; Amann, M. ; Atherton, C.S. ; Bell, N. ; Bergmann, D.J. ; Bey, I. ; Butler, T. ; Cofala, J. ; Collins, W.J. ; Derwent, R.G. ; Doherty, R.M. ; Drevet, J. ; Eskes, H.J. ; Fiore, A.M. ; Gauss, M. ; Hauglustaine, D.A. ; Horowitz, L.W. ; Isaksen, I.S.A. ; Krol, M.C. ; Lamarque, J.F. ; Lawrence, M.G. ; Montanaro, V. ; Muller, J.F. ; Pitari, G. ; Prather, M.J. ; Pyle, J.A. ; Rast, S. ; Rodriguez, J.M. ; Sanderson, M.G. ; Savage, N.H. ; Shindell, D.T. ; Strahan, S.E. ; Sudo, K. ; Szopa, S. - \ 2006
Journal of Geophysical Research: Atmospheres 111 (2006). - ISSN 2169-897X - p. D08301 - D08301.
chemistry transport models - general-circulation model - biogenic nox emissions - global chemical-model - aircraft mozaic data - climate-change - nonmethane hydrocarbons - methane emissions - surface ozone - atmospheric chemistry
Global tropospheric ozone distributions, budgets, and radiative forcings from an ensemble of 26 state-of-the-art atmospheric chemistry models have been intercompared and synthesized as part of a wider study into both the air quality and climate roles of ozone. Results from three 2030 emissions scenarios, broadly representing “optimistic,” “likely,” and “pessimistic” options, are compared to a base year 2000 simulation. This base case realistically represents the current global distribution of tropospheric ozone. A further set of simulations considers the influence of climate change over the same time period by forcing the central emissions scenario with a surface warming of around 0.7K. The use of a large multimodel ensemble allows us to identify key areas of uncertainty and improves the robustness of the results. Ensemble mean changes in tropospheric ozone burden between 2000 and 2030 for the 3 scenarios range from a 5% decrease, through a 6% increase, to a 15% increase. The intermodel uncertainty (±1 standard deviation) associated with these values is about ±25%. Model outliers have no significant influence on the ensemble mean results. Combining ozone and methane changes, the three scenarios produce radiative forcings of -50, 180, and 300 mW m-2, compared to a CO2 forcing over the same time period of 800–1100 mW m-2. These values indicate the importance of air pollution emissions in short- to medium-term climate forcing and the potential for stringent/lax control measures to improve/worsen future climate forcing. The model sensitivity of ozone to imposed climate change varies between models but modulates zonal mean mixing ratios by ±5 ppbv via a variety of feedback mechanisms, in particular those involving water vapor and stratosphere-troposphere exchange. This level of climate change also reduces the methane lifetime by around 4%. The ensemble mean year 2000 tropospheric ozone budget indicates chemical production, chemical destruction, dry deposition and stratospheric input fluxes of 5100, 4650, 1000, and 550 Tg(O3) yr-1, respectively. These values are significantly different to the mean budget documented by the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR). The mean ozone burden (340 Tg(O3)) is 10% larger than the IPCC TAR estimate, while the mean ozone lifetime (22 days) is 10% shorter. Results from individual models show a correlation between ozone burden and lifetime, and each model's ozone burden and lifetime respond in similar ways across the emissions scenarios. The response to climate change is much less consistent. Models show more variability in the tropics compared to midlatitudes. Some of the most uncertain areas of the models include treatments of deep tropical convection, including lightning NO x production; isoprene emissions from vegetation and isoprene's degradation chemistry; stratosphere-troposphere exchange; biomass burning; and water vapor concentrations.
Multi-model ensemble simulations of troposheric NO2 compared with GOME retrievals for the year 2000
Noije, T.P.C. van; Eskes, H.J. ; Dentener, F.J. ; Stevenson, D.S. ; Ellingsen, K. ; Schultz, M.G. ; Wild, O. ; Amann, M. ; Atherton, C.S. ; Bergmann, D. ; Bey, I. ; Boersma, K.F. ; Butler, T. ; Cofala, J. ; Drevet, J. ; Fiore, A.M. ; Gauss, M. ; Hauglustaine, D.A. ; Horowitz, L.W. ; Isaksen, I.S.A. ; Krol, M.C. ; Lamarque, J.F. ; Lawrence, M.G. ; Martin, R.V. ; Montanaro, V. ; Muller, J.F. ; Pitari, G. ; Prather, M.J. ; Pyle, J.A. ; Richter, A. ; Rodriguez, J.M. ; Savage, N.H. ; Strahan, S.E. ; Sudo, K. ; Szopa, S. ; Roozendael, M. van - \ 2006
Atmospheric Chemistry and Physics 6 (2006)10. - ISSN 1680-7316 - p. 2943 - 2979.
chemical-transport model - ozone monitoring experiment - radiative-transfer model - aircraft mozaic data - satellite-observations - nitrogen-dioxide - nonmethane hydrocarbons - surface reflectivity - global distributions - 3-dimensional model
We present a systematic comparison of tropospheric NO2 from 17 global atmospheric chemistry models with three state-of-the-art retrievals from the Global Ozone Monitoring Experiment (GOME) for the year 2000. The models used constant anthropogenic emissions from IIASA/EDGAR3.2 and monthly emissions from biomass burning based on the 1997¿2002 average carbon emissions from the Global Fire Emissions Database (GFED). Model output is analyzed at 10:30 local time, close to the overpass time of the ERS-2 satellite, and collocated with the measurements to account for sampling biases due to incomplete spatiotemporal coverage of the instrument. We assessed the importance of different contributions to the sampling bias: correlations on seasonal time scale give rise to a positive bias of 30¿50% in the retrieved annual means over regions dominated by emissions from biomass burning. Over the industrial regions of the eastern United States, Europe and eastern China the retrieved annual means have a negative bias with significant contributions (between ¿25% and +10% of the NO2 column) resulting from correlations on time scales from a day to a month. We present global maps of modeled and retrieved annual mean NO2 column densities, together with the corresponding ensemble means and standard deviations for models and retrievals. The spatial correlation between the individual models and retrievals are high, typically in the range 0.81¿0.93 after smoothing the data to a common resolution. On average the models underestimate the retrievals in industrial regions, especially over eastern China and over the Highveld region of South Africa, and overestimate the retrievals in regions dominated by biomass burning during the dry season. The discrepancy over South America south of the Amazon disappears when we use the GFED emissions specific to the year 2000. The seasonal cycle is analyzed in detail for eight different continental regions. Over regions dominated by biomass burning, the timing of the seasonal cycle is generally well reproduced by the models. However, over Central Africa south of the Equator the models peak one to two months earlier than the retrievals. We further evaluate a recent proposal to reduce the NOx emission factors for savanna fires by 40% and find that this leads to an improvement of the amplitude of the seasonal cycle over the biomass burning regions of Northern and Central Africa. In these regions the models tend to underestimate the retrievals during the wet season, suggesting that the soil emissions are higher than assumed in the models. In general, the discrepancies between models and retrievals cannot be explained by a priori profile assumptions made in the retrievals, neither by diurnal variations in anthropogenic emissions, which lead to a marginal reduction of the NO2 abundance at 10:30 local time (by 2.5¿4.1% over Europe). Overall, there are significant differences among the various models and, in particular, among the three retrievals. The discrepancies among the retrievals (10¿50% in the annual mean over polluted regions) indicate that the previously estimated retrieval uncertainties have a large systematic component. Our findings imply that top-down estimations of NOx emissions from satellite retrievals of tropospheric NO2 are strongly dependent on the choice of model and retrieval.
New directions : watching over tropospheric hydroxyl (OH)
Lelieveld, J. ; Brenninkmeijer, C.A.M. ; Joeckel, P. ; Isaksen, I.S.A. ; Krol, M.C. ; Mak, J.E. ; Dlugokencky, E. ; Montzka, S.A. ; Novelli, P.C. ; Peters, W. ; Tans, P.P. - \ 2006
Atmospheric Environment 40 (2006)29. - ISSN 1352-2310 - p. 5741 - 5743.
The global atmospheric environment for the next generation
Dentener, F. ; Stevenson, D. ; Ellingsen, K. ; Noije, T. van; Schultz, M. ; Amann, M. ; Atherton, C. ; Bell, N. ; Bergmann, D. ; Bey, I. ; Bouwman, L. ; Butler, T. ; Cofala, J. ; Collins, B. ; Drevet, J. ; Doherty, R. ; Eickhout, B. ; Eskes, H. ; Fiore, A. ; Gauss, M. ; Hauglustaine, D. ; Horowitz, L. ; Isaksen, I.S.A. ; Josse, B. ; Lawrence, M. ; Krol, M.C. ; Lamarque, J.F. ; Montanaro, V. ; Müller, J.F. ; Peuch, V.H. ; Pitari, G. ; Pyle, J. ; Rast, S. ; Rodriguez, J. ; Sanderson, M. ; Savage, N.H. ; Shindell, D. ; Strahan, S. ; Szopa, S. ; Sudo, K. ; Dingenen, R. van; Wild, O. ; Zeng, G. - \ 2006
Environmental Science and Technology 40 (2006)11. - ISSN 0013-936X - p. 3586 - 3594.
nitrogen deposition - tropospheric ozone - surface ozone - impact - africa
Air quality, ecosystem exposure to nitrogen deposition, and climate change are intimately coupled problems: we assess changes in the global atmospheric environment between 2000 and 2030 using 26 state-of-the-art global atmospheric chemistry models and three different emissions scenarios. The first (CLE) scenario reflects implementation of current air quality legislation around the world, while the second (MFR) represents a more optimistic case in which all currently feasible technologies are applied to achieve maximum emission reductions. We contrast these scenarios with the more pessimistic IPCC SRES A2 scenario. Ensemble simulations for the year 2000 are consistent among models and show a reasonable agreement with surface ozone, wet deposition, and NO2 satellite observations. Large parts of the world are currently exposed to high ozone concentrations and high deposition of nitrogen to ecosystems. By 2030, global surface ozone is calculated to increase globally by 1.5 +/- 1.2 ppb (CLE) and 4.3 +/- 2.2 ppb (A2), using the ensemble mean model results and associated +/- 1 sigma standard deviations. Only the progressive MFR scenario will reduce ozone, by -2.3 +/- 1.1 ppb. Climate change is expected to modify surface ozone by -0.8 +/- 0.6 ppb, with larger decreases over sea than over land. Radiative forcing by ozone increases by 63 +/- 15 and 155 +/- 37 mW m(-2) for CLE and A2, respectively, and decreases by -45 +/- 15 mW m(-2) for MFR. We compute that at present 10.1% of the global natural terrestrial ecosystems are exposed to nitrogen deposition above a critical load of 1 g N m(-2) yr(-1). These percentages increase by 2030 to 15.8% (CLE), 10.5% (MFR), and 25% (A2). This study shows the importance of enforcing current worldwide air quality legislation and the major benefits of going further. Nonattainment of these air quality policy objectives, such as expressed by the SRES-A2 scenario, would further degrade the global atmospheric environment.
Multimodel simulations of carbon monoxide: Comparison with observations and projected near-future changes
Shindell, D.T. ; Faluvegi, G. ; Stevenson, D.S. ; Krol, M.C. ; Emmons, L.K. ; Lamarque, J.F. ; Petron, G. ; Dentener, F.J. ; Ellingsen, K. ; Schultz, M.G. ; Wild, O. ; Amann, M. ; Atherton, C.S. ; Bergmann, D.J. ; Bey, I. ; Butler, T. ; Cofala, J. ; Collins, W.J. ; Derwent, R.G. ; Doherty, R.M. ; Drevet, J. ; Eskes, H.J. ; Fiore, A.M. ; Gauss, M. ; Hauglustaine, D.A. ; Horowitz, L.W. ; Isaksen, I.S.A. ; Lawrence, M.G. ; Montanaro, V. ; Muller, J.F. ; Pitari, G. ; Prather, M.J. ; Pyle, J.A. ; Rast, S. ; Rodriguez, J.M. ; Sanderson, M.G. ; Savage, N.H. ; Strahan, S.E. ; Sudo, K. ; Szopa, S. ; Unger, N. ; Noije, T.P.C. van; Zeng, G. - \ 2006
Journal of Geophysical Research: Atmospheres 111 (2006). - ISSN 2169-897X - 24 p.
chemical-transport model - stratosphere-troposphere exchange - general-circulation model - aircraft mozaic data - nonmethane hydrocarbons - ozone simulations - methane emissions - western pacific - climate-change - 3-d models
We analyze present-day and future carbon monoxide (CO) simulations in 26 state-of-the-art atmospheric chemistry models run to study future air quality and climate change. In comparison with near-global satellite observations from the MOPITT instrument and local surface measurements, the models show large underestimates of Northern Hemisphere (NH) extratropical CO, while typically performing reasonably well elsewhere. The results suggest that year-round emissions, probably from fossil fuel burning in east Asia and seasonal biomass burning emissions in south-central Africa, are greatly underestimated in current inventories such as IIASA and EDGAR3.2. Variability among models is large, likely resulting primarily from intermodel differences in representations and emissions of nonmethane volatile organic compounds (NMVOCs) and in hydrologic cycles, which affect OH and soluble hydrocarbon intermediates. Global mean projections of the 2030 CO response to emissions changes are quite robust. Global mean midtropospheric (500 hPa) CO increases by 12.6 +/- 3.5 ppbv (16%) for the high-emissions (A2) scenario, by 1.7 +/- 1.8 ppbv (2%) for the midrange (CLE) scenario, and decreases by 8.1 +/- 2.3 ppbv (11%) for the low-emissions (MFR) scenario. Projected 2030 climate changes decrease global 500 hPa CO by 1.4 +/- 1.4 ppbv. Local changes can be much larger. In response to climate change, substantial effects are seen in the tropics, but intermodel variability is quite large. The regional CO responses to emissions changes are robust across models, however. These range from decreases of 10-20 ppbv over much of the industrialized NH for the CLE scenario to CO increases worldwide and year-round under A2, with the largest changes over central Africa (20-30 ppbv), southern Brazil (20-35 ppbv) and south and east Asia (30-70 ppbv). The trajectory of future emissions thus has the potential to profoundly affect air quality over most of the world's populated areas.
Analysis and quantification of the diversities of aerosol life cycles within AeroCom
Textor, C. ; Schulz, M. ; Guibert, S. ; Kinne, S. ; Balkanski, Y. ; Bauer, S. ; Berntsen, T. ; Berglen, T. ; Boucher, O. ; Chin, M. ; Dentener, F. ; Diehl, T. ; Easter, R. ; Feichter, H. ; Fillmore, D. ; Ghan, S. ; Ginoux, P. ; Gong, S. ; Grini, A. ; Hendricks, J. ; Horowitz, L. ; Huang, P. ; Isaksen, I. ; Iversen, T. ; Kloster, S. ; Koch, D. ; Kirkevåg, A. ; Kristjansson, J.E. ; Krol, M.C. ; Lauer, A. ; Lamarque, J.F. ; Liu, X. ; Montanaro, V. ; Myhre, G. ; Penner, J. ; Pitari, G. ; Reddy, S. ; Seland, O. ; Stier, P. ; Takemura, T. ; Tie, X. - \ 2006
Atmospheric Chemistry and Physics 6 (2006). - ISSN 1680-7316 - p. 1777 - 1813.
general-circulation model - global 3-dimensional model - chemical-transport model - sea-salt aerosol - dry deposition parameterization - size-segregated simulation - tropospheric sulfur cycle - air-quality models - large-scale models - optical-properties
Simulation results of global aerosol models have been assembled in the framework of the AeroCom intercomparison exercise. In this paper, we analyze the life cycles of dust, sea salt, sulfate, black carbon and particulate organic matter as simulated by sixteen global aerosol models. The differences among the results (model diversities) for sources and sinks, burdens, particle sizes, water uptakes, and spatial dispersals have been established. These diversities have large consequences for the calculated radiative forcing and the aerosol concentrations at the surface. Processes and parameters are identified which deserve further research. The AeroCom all-models-average emissions are dominated by the mass of sea salt (SS), followed by dust (DU), sulfate (SO4), particulate organic matter (POM), and finally black carbon (BC). Interactive parameterizations of the emissions and contrasting particles sizes of SS and DU lead generally to higher diversities of these species, and for total aerosol. The lower diversity of the emissions of the fine aerosols, BC, POM, and SO4, is due to the use of similar emission inventories, and does therefore not necessarily indicate a better understanding of their sources. The diversity of SO4-sources is mainly caused by the disagreement on depositional loss of precursor gases and on chemical production. The diversities of the emissions are passed on to the burdens, but the latter are also strongly affected by the model-specific treatments of transport and aerosol processes. The burdens of dry masses decrease from largest to smallest: DU, SS, SO4, POM, and BC. The all-models-average residence time is shortest for SS with about half a day, followed by SO4 and DU with four days, and POM and BC with six and seven days, respectively. The wet deposition rate is controlled by the solubility and increases from DU, BC, POM to SO4 and SS. It is the dominant sink for SO4, BC, and POM, and contributes about one third to the total removal of SS and DU species. For SS and DU we find high diversities for the removal rate coefficients and deposition pathways. Models do neither agree on the split between wet and dry deposition, nor on that between sedimentation and other dry deposition processes. We diagnose an extremely high diversity for the uptake of ambient water vapor that influences the particle size and thus the sink rate coefficients. Furthermore, we find little agreement among the model results for the partitioning of wet removal into scavenging by convective and stratiform rain. Large differences exist for aerosol dispersal both in the vertical and in the horizontal direction. In some models, a minimum of total aerosol concentration is simulated at the surface. Aerosol dispersal is most pronounced for SO4 and BC and lowest for SS. Diversities are higher for meridional than for vertical dispersal, they are similar for the individual species and highest for SS and DU. For these two components we do not find a correlation between vertical and meridional aerosol dispersal. In addition the degree of dispersals of SS and DU is not related to their residence times. SO4, BC, and POM, however, show increased meridional dispersal in models with larger vertical dispersal, and dispersal is larger for longer simulated residence times
An AeroCom initial assessment – optical properties in aerosol component modules of global models
Kinne, S. ; Schulz, M. ; Textor, C. ; Guibert, S. ; Balkanski, Y. ; Bauer, S. ; Berntsen, E. ; Berglen, T.F. ; Boucher, O. ; Chin, M. ; Collins, W. ; Dentener, F. ; Diehl, T. ; Easter, R. ; Feichter, J. ; Fillmore, D. ; Ghan, S. ; Ginoux, P. ; Gong, S. ; Grini, A. ; Hendricks, J. ; Herzog, M. ; Horowitz, L. ; Isaksen, I. ; Iversen, T. ; Kirkevåg, A. ; Kloster, S. ; Koch, D. ; Kristjansson, J.E. ; Krol, M.C. ; Lauer, A. ; Lamarque, J.F. ; Lesins, G. ; Liu, X. ; Lohmann, U. ; Montanaro, V. ; Myhre, G. ; Penner, J. ; Pitari, G. ; Reddy, S. ; Seland, O. ; Stier, P. ; Takemura, T. ; Tie, X. - \ 2006
Atmospheric Chemistry and Physics 6 (2006). - ISSN 1680-7316 - p. 1815 - 1834.
ocean - aeronet - depth - retrievals - period - land
The AeroCom exercise diagnoses multi-component aerosol modules in global modeling. In an initial assessment simulated global distributions for mass and mid-visible aerosol optical thickness (aot) were compared among 20 different modules. Model diversity was also explored in the context of previous comparisons. For the component combined aot general agreement has improved for the annual global mean. At 0.11 to 0.14, simulated aot values are at the lower end of global averages suggested by remote sensing from ground (AERONET ca. 0.135) and space (satellite composite ca. 0.15). More detailed comparisons, however, reveal that larger differences in regional distribution and significant differences in compositional mixture remain. Of particular concern are large model diversities for contributions by dust and carbonaceous aerosol, because they lead to significant uncertainty in aerosol absorption (aab). Since aot and aab, both, influence the aerosol impact on the radiative energy-balance, the aerosol (direct) forcing uncertainty in modeling is larger than differences in aot might suggest. New diagnostic approaches are proposed to trace model differences in terms of aerosol processing and transport: These include the prescription of common input (e.g. amount, size and injection of aerosol component emissions) and the use of observational capabilities from ground (e.g. measurements networks) or space (e.g. correlations between aerosol and clouds)
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