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    The Scenario Model Intercomparison Project (ScenarioMIP) for CMIP6
    (München : European Geopyhsical Union, 2016) O'Neill, Brian C.; Tebaldi, Claudia; van Vuuren, Detlef P.; Eyring, Veronika; Friedlingstein, Pierre; Hurtt, George; Knutti, Reto; Kriegler, Elmar; Lamarque, Jean-Francois; Lowe, Jason; Meehl, Gerald A.; Moss, Richard; Riahi, Keywan; Sanderson, Benjamin M.
    Projections of future climate change play a fundamental role in improving understanding of the climate system as well as characterizing societal risks and response options. The Scenario Model Intercomparison Project (ScenarioMIP) is the primary activity within Phase 6 of the Coupled Model Intercomparison Project (CMIP6) that will provide multi-model climate projections based on alternative scenarios of future emissions and land use changes produced with integrated assessment models. In this paper, we describe ScenarioMIP's objectives, experimental design, and its relation to other activities within CMIP6. The ScenarioMIP design is one component of a larger scenario process that aims to facilitate a wide range of integrated studies across the climate science, integrated assessment modeling, and impacts, adaptation, and vulnerability communities, and will form an important part of the evidence base in the forthcoming Intergovernmental Panel on Climate Change (IPCC) assessments. At the same time, it will provide the basis for investigating a number of targeted science and policy questions that are especially relevant to scenario-based analysis, including the role of specific forcings such as land use and aerosols, the effect of a peak and decline in forcing, the consequences of scenarios that limit warming to below 2°C, the relative contributions to uncertainty from scenarios, climate models, and internal variability, and long-term climate system outcomes beyond the 21st century. To serve this wide range of scientific communities and address these questions, a design has been identified consisting of eight alternative 21st century scenarios plus one large initial condition ensemble and a set of long-term extensions, divided into two tiers defined by relative priority. Some of these scenarios will also provide a basis for variants planned to be run in other CMIP6-Endorsed MIPs to investigate questions related to specific forcings. Harmonized, spatially explicit emissions and land use scenarios generated with integrated assessment models will be provided to participating climate modeling groups by late 2016, with the climate model simulations run within the 2017–2018 time frame, and output from the climate model projections made available and analyses performed over the 2018–2020 period.
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    Global consequences of afforestation and bioenergy cultivation on ecosystem service indicators
    (München : European Geopyhsical Union, 2017) Krause, Andreas; Pugh, Thomas A.M.; Bayer, Anita D.; Doelman, Jonathan C.; Humpenöder, Florian; Anthoni, Peter; Olin, Stefan; Bodirsky, Benjamin L.; Popp, Alexander; Stehfest, Elke; Arneth, Almut
    Land management for carbon storage is discussed as being indispensable for climate change mitigation because of its large potential to remove carbon dioxide from the atmosphere, and to avoid further emissions from deforestation. However, the acceptance and feasibility of land-based mitigation projects depends on potential side effects on other important ecosystem functions and their services. Here, we use projections of future land use and land cover for different land-based mitigation options from two land-use models (IMAGE and MAgPIE) and evaluate their effects with a global dynamic vegetation model (LPJ-GUESS). In the land-use models, carbon removal was achieved either via growth of bioenergy crops combined with carbon capture and storage, via avoided deforestation and afforestation, or via a combination of both. We compare these scenarios to a reference scenario without land-based mitigation and analyse the LPJ-GUESS simulations with the aim of assessing synergies and trade-offs across a range of ecosystem service indicators: carbon storage, surface albedo, evapotranspiration, water runoff, crop production, nitrogen loss, and emissions of biogenic volatile organic compounds. In our mitigation simulations cumulative carbon storage by year 2099 ranged between 55 and 89 GtC. Other ecosystem service indicators were influenced heterogeneously both positively and negatively, with large variability across regions and land-use scenarios. Avoided deforestation and afforestation led to an increase in evapotranspiration and enhanced emissions of biogenic volatile organic compounds, and to a decrease in albedo, runoff, and nitrogen loss. Crop production could also decrease in the afforestation scenarios as a result of reduced crop area, especially for MAgPIE land-use patterns, if assumed increases in crop yields cannot be realized. Bioenergy-based climate change mitigation was projected to affect less area globally than in the forest expansion scenarios, and resulted in less pronounced changes in most ecosystem service indicators than forest-based mitigation, but included a possible decrease in nitrogen loss, crop production, and biogenic volatile organic compounds emissions.
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    Towards a comprehensive climate impacts assessment of solar geoengineering
    (Hoboken, NJ : Wiley, 2016) Irvine, Peter J.; Kravitz, Ben; Lawrence, Mark G.; Gerten, Dieter; Caminade, Cyril; Gosling, Simon N.; Hendy, Erica J.; Kassie, Belay T.; Kissling, W. Daniel; Muri, Helene; Oschlies, Andreas; Smith, Steven J.
    Despite a growing literature on the climate response to solar geoengineering—proposals to cool the planet by increasing the planetary albedo—there has been little published on the impacts of solar geoengineering on natural and human systems such as agriculture, health, water resources, and ecosystems. An understanding of the impacts of different scenarios of solar geoengineering deployment will be crucial for informing decisions on whether and how to deploy it. Here we review the current state of knowledge about impacts of a solar‐geoengineered climate and identify the major research gaps. We suggest that a thorough assessment of the climate impacts of a range of scenarios of solar geoengineering deployment is needed and can be built upon existing frameworks. However, solar geoengineering poses a novel challenge for climate impacts research as the manner of deployment could be tailored to pursue different objectives making possible a wide range of climate outcomes. We present a number of ideas for approaches to extend the survey of climate impacts beyond standard scenarios of solar geoengineering deployment to address this challenge. Reducing the impacts of climate change is the fundamental motivator for emissions reductions and for considering whether and how to deploy solar geoengineering. This means that the active engagement of the climate impacts research community will be important for improving the overall understanding of the opportunities, challenges, and risks presented by solar geoengineering.
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    The world’s biggest gamble
    (Hoboken, NJ : Wiley, 2016) Rockström, Johan; Schellnhuber, Hans Joachim; Hoskins, Brian; Ramanathan, Veerabhadran; Schlosser, Peter; Brasseur, Guy Pierre; Gaffney, Owen; Nobre, Carlos; Meinshausen, Malte; Rogelj, Joeri; Lucht, Wolfgang
    The scale of the decarbonisation challenge to meet the Paris Agreement is underplayed in the public arena. It will require precipitous emissions reductions within 40 years and a new carbon sink on the scale of the ocean sink. Even then, the world is extremely likely to overshoot. A catastrophic failure of policy, for example, waiting another decade for transformative policy and full commitments to fossil‐free economies, will have irreversible and deleterious repercussions for humanity's remaining time on Earth. Only a global zero carbon roadmap will put the world on a course to phase‐out greenhouse gas emissions and create the essential carbon sinks for Earth‐system stability, without which, world prosperity is not possible.
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    Management scenarios of the Grand Ethiopian Renaissance Dam and their impacts under recent and future climates
    (Basel : MDPI, 2017) Liersch, Stefan; Koch, Hagen; Hattermann, Fred Fokko
    Close to the border with Sudan, Ethiopia is currently building the largest hydroelectric power plant in Africa with a storage volume corresponding to approximately 1.5 years of the mean discharges of the Blue Nile. This endeavor is controversially debated in the public and the scientific literature. Contributing to this discussion, by shading some light on climate change issues, an eco-hydrological model, equipped with a reservoir module, was applied to investigate downstream hydrological impacts during filling and regular operation, the latter considering climate change projected by an ensemble of 10 global and regional climate models. Our results show that at the earliest after 20 months, the dam could produce hydroelectric power. Full supply level may be reached after four years or not at all, depending on filling policies and assumptions of seepage rates. Under recent hydro-climatic conditions, the dam may produce 13 TWh −a , which is below the envisaged target of 15.7 TWh −a . The ensemble mean suggests slightly increasing hydropower production in the future. Almost independently of the operation rules, the highly variable discharge regime will be significantly altered to a regime with almost equal flows each month. Achieving a win-win situation for all riparian countries requires a high level of cooperation in managing the Eastern Nile water resources.
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    Modeling of two different water uptake approaches for mono-and mixed-species forest stands
    (Basel : MDPI, 2015) Gutsch, Martin; Lasch-Born, Petra; Suckow, Felicitas; Reyer, Christopher P.O.
    To assess how the effects of drought could be better captured in process-based models, this study simulated and contrasted two water uptake approaches in Scots pine and Scots pine-Sessile oak stands. The first approach consisted of an empirical function for root water uptake (WU1). The second approach was based on differences of soil water potential along a soil-plant-atmosphere continuum (WU2) with total root resistance varying at low, medium and high total root resistance levels. Three data sets on different time scales relevant for tree growth were used for model evaluation: Two short-term datasets on daily transpiration and soil water content as well as a long-term dataset on annual tree ring increments. Except WU2 with high total root resistance, all transpiration outputs exceeded observed values. The strongest correlation between simulated and observed annual tree ring width occurred with WU2 and high total root resistance. The findings highlighted the importance of severe drought as a main reason for small diameter increment. However, if all three data sets were taken into account, no approach was superior to the other. We conclude that accurate projections of future forest productivity depend largely on the realistic representation of root water uptake in forest model simulations.
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    On the importance of cascading moisture recycling in South America
    (München : European Geopyhsical Union, 2014) Zemp, D.C.; Schleussner, C.-F.; Barbosa, H.M.J.; van der Ent, R.J.; Donges, J.F.; Heinke, J.; Sampaio, G.; Rammig, A.
    Continental moisture recycling is a crucial process of the South American climate system. In particular, evapotranspiration from the Amazon basin contributes substantially to precipitation regionally as well as over other remote regions such as the La Plata basin. Here we present an in-depth analysis of South American moisture recycling mechanisms. In particular, we quantify the importance of cascading moisture recycling (CMR), which describes moisture transport between two locations on the continent that involves re-evaporation cycles along the way. Using an Eulerian atmospheric moisture tracking model forced by a combination of several historical climate data sets, we were able to construct a complex network of moisture recycling for South America. Our results show that CMR contributes about 9–10% to the total precipitation over South America and 17–18% over the La Plata basin. CMR increases the fraction of total precipitation over the La Plata basin that originates from the Amazon basin from 18–23 to 24–29% during the wet season. We also show that the south-western part of the Amazon basin is not only a direct source of rainfall over the La Plata basin, but also a key intermediary region that distributes moisture originating from the entire Amazon basin towards the La Plata basin during the wet season. Our results suggest that land use change in this region might have a stronger impact on downwind rainfall than previously thought. Using complex network analysis techniques, we find the eastern side of the sub-tropical Andes to be a key region where CMR pathways are channeled. This study offers a better understanding of the interactions between the vegetation and the atmosphere on the water cycle, which is needed in a context of land use and climate change in South America.
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    Record Balkan floods of 2014 linked to planetary wave resonance
    (Washington, DC : American Association for the Advancement of Science, 2016) Stadtherr, Lisa; Coumou, Dim; Petoukhov, Vladimir; Petri, Stefan; Rahmstorf, Stefan
    In May 2014, the Balkans were hit by a Vb-type cyclone that brought disastrous flooding and severe damage to Bosnia and Herzegovina, Serbia, and Croatia. Vb cyclones migrate from the Mediterranean, where they absorb warm and moist air, to the north, often causing flooding in central/eastern Europe. Extreme rainfall events are increasing on a global scale, and both thermodynamic and dynamical mechanisms play a role. Where thermodynamic aspects are generally well understood, there is large uncertainty associated with current and future changes in dynamics. We study the climatic and meteorological factors that influenced the catastrophic flooding in the Balkans, where we focus on large-scale circulation. We show that the Vb cyclone was unusually stationary, bringing extreme rainfall for several consecutive days, and that this situation was likely linked to a quasi-stationary circumglobal Rossby wave train. We provide evidence that this quasi-stationary wave was amplified by wave resonance. Statistical analysis of daily spring rainfall over the Balkan region reveals significant upward trends over 1950–2014, especially in the high quantiles relevant for flooding events. These changes cannot be explained by simple thermodynamic arguments, and we thus argue that dynamical processes likely played a role in increasing flood risks over the Balkans.
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    Impact of droughts on the carbon cycle in European vegetation: A probabilistic risk analysis using six vegetation models
    (München : European Geopyhsical Union, 2014) Van Oijen, M.; Balkovi, J.; Beer, C.; Cameron, D.R.; Ciais, P.; Cramer, W.; Kato, T.; Kuhnert, M.; Martin, R.; Myneni, R.; Rammig, A.; Rolinski, S.; Soussana, J.-F.; Thonicke, K.; Van der Velde, M.; Xu, L.
    We analyse how climate change may alter risks posed by droughts to carbon fluxes in European ecosystems. The approach follows a recently proposed framework for risk analysis based on probability theory. In this approach, risk is quantified as the product of hazard probability and ecosystem vulnerability. The probability of a drought hazard is calculated here from the Standardized Precipitation–Evapotranspiration Index (SPEI). Vulnerability is calculated from the response to drought simulated by process-based vegetation models. We use six different models: three for generic vegetation (JSBACH, LPJmL, ORCHIDEE) and three for specific ecosystems (Scots pine forests: BASFOR; winter wheat fields: EPIC; grasslands: PASIM). The periods 1971–2000 and 2071–2100 are compared. Climate data are based on gridded observations and on output from the regional climate model REMO using the SRES A1B scenario. The risk analysis is carried out for ~ 18 000 grid cells of 0.25 × 0.25° across Europe. For each grid cell, drought vulnerability and risk are quantified for five seasonal variables: net primary and ecosystem productivity (NPP, NEP), heterotrophic respiration (Rh), soil water content and evapotranspiration. In this analysis, climate change leads to increased drought risks for net primary productivity in the Mediterranean area: five of the models estimate that risk will exceed 15%. The risks increase mainly because of greater drought probability; ecosystem vulnerability will increase to a lesser extent. Because NPP will be affected more than Rh, future carbon sequestration (NEP) will also be at risk predominantly in southern Europe, with risks exceeding 0.25 g C m−2 d−1 according to most models, amounting to reductions in carbon sequestration of 20 to 80%.
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    An optical particle size spectrometer for aircraft-borne measurements in IAGOS-CARIBIC
    (München : European Geopyhsical Union, 2016) Hermann, Markus; Weigelt, Andreas; Assmann, Denise; Pfeifer, Sascha; Müller, Thomas; Conrath, Thomas; Voigtländer, Jens; Heintzenberg, Jost; Wiedensohler, Alfred; Martinsson, Bengt G.; Deshler, Terry; Brenninkmeijer, Carl A.M.; Zahn, Andreas
    The particle number size distribution is an important parameter to characterize the atmospheric aerosol and its influence on the Earth's climate. Here we describe a new optical particle size spectrometer (OPSS) for measurements of the accumulation mode particle number size distribution in the tropopause region on board a passenger aircraft (IAGOS-CARIBIC observatory: In-service Aircraft for a Global Observing System – Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container). A modified KS93 particle sensor from RION Co., Ltd., together with a new airflow system and a dedicated data acquisition system, is the key component of the CARIBIC OPSS. The instrument records individual particle pulse signal curves in the particle size range 130–1110 nm diameter (for a particle refractive index of 1.47-i0.006) together with a time stamp and thus allows the post-flight choice of the time resolution and the size distribution bin width. The CARIBIC OPSS has a 50 % particle detection diameter of 152 nm and a maximum asymptotic counting efficiency of 98 %. The instrument's measurement performance shows no pressure dependency and no particle coincidence for free tropospheric conditions. The size response function of the CARIBIC OPSS was obtained by a polystyrene latex calibration in combination with model calculations. Particle number size distributions measured with the new OPSS in the lowermost stratosphere agreed within a factor of 2 in concentration with balloon-borne measurements over western North America. Since June 2010 the CARIBIC OPSS is deployed once per month in the IAGOS-CARIBIC observatory.