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- ItemQuantifying uncertainties in soil carbon responses to changes in global mean temperature and precipitation(München : European Geopyhsical Union, 2014) Nishina, K.; Ito, A.; Beerling, D.J.; Cadule, P.; Ciais, P.; Clark, D.B.; Friend, A.D.; Kahana, R.; Kato, E.; Keribin, R.; Lucht, W.; Lomas, M.; Rademacher, T.T.; Pavlick, R.; Schaphoff, S.; Vuichard, N.; Warszawaski, L.; Yokohata, T.Soil organic carbon (SOC) is the largest carbon pool in terrestrial ecosystems and may play a key role in biospheric feedbacks with elevated atmospheric carbon dioxide (CO2) in a warmer future world. We examined the simulation results of seven terrestrial biome models when forced with climate projections from four representative-concentration-pathways (RCPs)-based atmospheric concentration scenarios. The goal was to specify calculated uncertainty in global SOC stock projections from global and regional perspectives and give insight to the improvement of SOC-relevant processes in biome models. SOC stocks among the biome models varied from 1090 to 2650 Pg C even in historical periods (ca. 2000). In a higher forcing scenario (i.e., RCP8.5), inconsistent estimates of impact on the total SOC (2099–2000) were obtained from different biome model simulations, ranging from a net sink of 347 Pg C to a net source of 122 Pg C. In all models, the increasing atmospheric CO2 concentration in the RCP8.5 scenario considerably contributed to carbon accumulation in SOC. However, magnitudes varied from 93 to 264 Pg C by the end of the 21st century across biome models. Using the time-series data of total global SOC simulated by each biome model, we analyzed the sensitivity of the global SOC stock to global mean temperature and global precipitation anomalies (ΔT and ΔP respectively) in each biome model using a state-space model. This analysis suggests that ΔT explained global SOC stock changes in most models with a resolution of 1–2 °C, and the magnitude of global SOC decomposition from a 2 °C rise ranged from almost 0 to 3.53 Pg C yr−1 among the biome models. However, ΔP had a negligible impact on change in the global SOC changes. Spatial heterogeneity was evident and inconsistent among the biome models, especially in boreal to arctic regions. Our study reveals considerable climate uncertainty in SOC decomposition responses to climate and CO2 change among biome models. Further research is required to improve our ability to estimate biospheric feedbacks through both SOC-relevant and vegetation-relevant processes.
- ItemThe role of the North Atlantic overturning and deep ocean for multi-decadal global-mean-temperature variability(München : European Geopyhsical Union, 2014) Schleussner, C.F.; Runge, J.; Lehmann, J.; Levermann, A.Earth's climate exhibits internal modes of variability on various timescales. Here we investigate multi-decadal variability of the Atlantic meridional overturning circulation (AMOC), Northern Hemisphere sea-ice extent and global mean temperature (GMT) in an ensemble of CMIP5 models under control conditions. We report an inter-annual GMT variability of about ±0.1° C originating solely from natural variability in the model ensemble. By decomposing the GMT variance into contributions of the AMOC and Northern Hemisphere sea-ice extent using a graph-theoretical statistical approach, we find the AMOC to contribute 8% to GMT variability in the ensemble mean. Our results highlight the importance of AMOC sea-ice feedbacks that explain 5% of the GMT variance, while the contribution solely related to the AMOC is found to be about 3%. As a consequence of multi-decadal AMOC variability, we report substantial variations in North Atlantic deep-ocean heat content with trends of up to 0.7 × 1022 J decade−1 that are of the order of observed changes over the last decade and consistent with the reduced GMT warming trend over this period. Although these temperature anomalies are largely density-compensated by salinity changes, we find a robust negative correlation between the AMOC and North Atlantic deep-ocean density with density lagging the AMOC by 5 to 11 yr in most models. While this would in principle allow for a self-sustained oscillatory behavior of the coupled AMOC–deep-ocean system, our results are inconclusive about the role of this feedback in the model ensemble.
- ItemExtreme summer heat in Phoenix, Arizona (USA) under global climate change (2041-2070)(Berlin : Gesellschaft für Erdkunde, 2014) Grossman-Clarke, Susanne; Schubert, Sebastian; Clarke, Thomas R.; Harlan, Sharon L.Summer extreme heat events in the arid Phoenix, Arizona (USA) metropolitan region for the period 2041-2070 are projected based on the ensemble of ten climate models from the North American Regional Climate Change Assessment Program for the SRES A2 greenhouse gas emissions scenario by the Intergovernmental Panel on Climate Change. Extreme heat events are identified by measures related to two thresholds of the maximum daily air temperature distribution for the historical reference period 1971-2000. Comparing this reference period to the model ensemble-mean, the frequency of extreme heat events is projected to increase by a factor of six to 1.9 events per summer and the average number of event days per year is projected to increase by a factor of 14. The inter-model range for the average number of EHE days per summer is larger for the projected climate, 10.6 to 42.2 days, than for simulations of the past climate simulations (1.5 to 2.4 days).
- ItemClimate impacts on human livelihoods: Where uncertainty matters in projections of water availability(München : European Geopyhsical Union, 2014) Lissner, T.K.; Reusser, D.E.; Schewe, J.; Lakes, T.; Kropp, J.P.Climate change will have adverse impacts on many different sectors of society, with manifold consequences for human livelihoods and well-being. However, a systematic method to quantify human well-being and livelihoods across sectors is so far unavailable, making it difficult to determine the extent of such impacts. Climate impact analyses are often limited to individual sectors (e.g. food or water) and employ sector-specific target measures, while systematic linkages to general livelihood conditions remain unexplored. Further, recent multi-model assessments have shown that uncertainties in projections of climate impacts deriving from climate and impact models, as well as greenhouse gas scenarios, are substantial, posing an additional challenge in linking climate impacts with livelihood conditions. This article first presents a methodology to consistently measure what is referred to here as AHEAD (Adequate Human livelihood conditions for wEll-being And Development). Based on a trans-disciplinary sample of concepts addressing human well-being and livelihoods, the approach measures the adequacy of conditions of 16 elements. We implement the method at global scale, using results from the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP) to show how changes in water availability affect the fulfilment of AHEAD at national resolution. In addition, AHEAD allows for the uncertainty of climate and impact model projections to be identified and differentiated. We show how the approach can help to put the substantial inter-model spread into the context of country-specific livelihood conditions by differentiating where the uncertainty about water scarcity is relevant with regard to livelihood conditions – and where it is not. The results indicate that livelihood conditions are compromised by water scarcity in 34 countries. However, more often, AHEAD fulfilment is limited through other elements. The analysis shows that the water-specific uncertainty ranges of the model output are outside relevant thresholds for AHEAD for 65 out of 111 countries, and therefore do not contribute to the overall uncertainty about climate change impacts on livelihoods. In 46 of the countries in the analysis, water-specific uncertainty is relevant to AHEAD. The AHEAD method presented here, together with first results, forms an important step towards making scientific results more applicable for policy decisions.
- ItemMechanism for potential strengthening of Atlantic overturning prior to collapse(München : European Geopyhsical Union, 2014) Ehlert, D.; Levermann, A.The Atlantic meridional overturning circulation (AMOC) carries large amounts of heat into the North Atlantic influencing climate regionally as well as globally. Palaeo-records and simulations with comprehensive climate models suggest that the positive salt-advection feedback may yield a threshold behaviour of the system. That is to say that beyond a certain amount of freshwater flux into the North Atlantic, no meridional overturning circulation can be sustained. Concepts of monitoring the AMOC and identifying its vicinity to the threshold rely on the fact that the volume flux defining the AMOC will be reduced when approaching the threshold. Here we advance conceptual models that have been used in a paradigmatic way to understand the AMOC, by introducing a density-dependent parameterization for the Southern Ocean eddies. This additional degree of freedom uncovers a mechanism by which the AMOC can increase with additional freshwater flux into the North Atlantic, before it reaches the threshold and collapses: an AMOC that is mainly wind-driven will have a constant upwelling as long as the Southern Ocean winds do not change significantly. The downward transport of tracers occurs either in the northern sinking regions or through Southern Ocean eddies. If freshwater is transported, either atmospherically or via horizontal gyres, from the low to high latitudes, this would reduce the eddy transport and by continuity increase the northern sinking which defines the AMOC until a threshold is reached at which the AMOC cannot be sustained. If dominant in the real ocean this mechanism would have significant consequences for monitoring the AMOC.
- ItemProjecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models(München : European Geopyhsical Union, 2014) Levermann, A.; Winkelmann, R.; Nowicki, S.; Fastook, J.L.; Frieler, K.; Greve, R.; Hellmer, H.H.; Martin, M.A.; Meinshausen, M.; Mengel, M.; Payne, A.J.; Pollard, D.; Sato, T.; Timmermann, R.; Wang, W.L.; Bindschadler, R.A.The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02–0.14 m; 90% range: 0.0–0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04–0.21 m; 90% range: 0.01–0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these values increase to 0.09 m (66% range: 0.04–0.17 m; 90% range: 0.02–0.25 m) for RCP-2.6 and 0.15 m (66% range: 0.07–0.28 m; 90% range: 0.04–0.43 m) for RCP-8.5. All probability distributions are highly skewed towards high values. The applied ice-sheet models are coarse resolution with limitations in the representation of grounding-line motion. Within the constraints of the applied methods, the uncertainty induced from different ice-sheet models is smaller than that induced by the external forcing to the ice sheets.
- ItemClimate impact research: Beyond patchwork(München : European Geopyhsical Union, 2014) Huber, V.; Schellnhuber, H.J.; Arnell, N.W.; Frieler, K.; Gerten, D.; Haddeland, I.; Kabat, P.; Lotze-Campen, H.; Lucht, W.; Parry, M.; Piontek, F.; Rosenzweig, C.; Schewe, J.; Warszawski, L.Despite significant progress in climate impact research, the narratives that science can presently piece together of a 2, 3, 4, or 5 °C warmer world remain fragmentary. Here we briefly review past undertakings to characterise comprehensively and quantify climate impacts based on multi-model approaches. We then report on the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP), a community-driven effort to compare impact models across sectors and scales systematically, and to quantify the uncertainties along the chain from greenhouse gas emissions and climate input data to the modelling of climate impacts themselves. We show how ISI-MIP and similar efforts can substantially advance the science relevant to impacts, adaptation and vulnerability, and we outline the steps that need to be taken in order to make the most of the available modelling tools. We discuss pertinent limitations of these methods and how they could be tackled. We argue that it is time to consolidate the current patchwork of impact knowledge through integrated cross-sectoral assessments, and that the climate impact community is now in a favourable position to do so.
- ItemWeibull-distributed dyke thickness reflects probabilistic character of host-rock strength([London] : Nature Publishing Group UK, 2014) Krumbholz, Michael; Hieronymus, Christoph F.; Burchardt, Steffi; Troll, Valentin R.; Tanner, David C.; Friese, NadineMagmatic sheet intrusions (dykes) constitute the main form of magma transport in the Earth’s crust. The size distribution of dykes is a crucial parameter that controls volcanic surface deformation and eruption rates and is required to realistically model volcano deformation for eruption forecasting. Here we present statistical analyses of 3,676 dyke thickness measurements from different tectonic settings and show that dyke thickness consistently follows the Weibull distribution. Known from materials science, power law-distributed flaws in brittle materials lead to Weibull-distributed failure stress. We therefore propose a dynamic model in which dyke thickness is determined by variable magma pressure that exploits differently sized host-rock weaknesses. The observed dyke thickness distributions are thus site-specific because rock strength, rather than magma viscosity and composition, exerts the dominant control on dyke emplacement. Fundamentally, the strength of geomaterials is scale-dependent and should be approximated by a probability distribution.
- ItemGuidance of mesenchymal stem cells on fibronectin structured hydrogel films(San Francisco, California, US : PLOS, 2014) Kasten, Annika; Naser, Tamara; Brüllhoff, Kristina; Fiedler, Jörg; Müller, Petra; Möller, Martin; Rychly, Joachim; Groll, Jürgen; Brenner, Rolf E.; Engler, Adam J.Designing of implant surfaces using a suitable ligand for cell adhesion to stimulate specific biological responses of stem cells will boost the application of regenerative implants. For example, materials that facilitate rapid and guided migration of stem cells would promote tissue regeneration. When seeded on fibronectin (FN) that was homogeneously immmobilized to NCO-sP(EO-stat-PO), which otherwise prevents protein binding and cell adhesion, human mesenchymal stem cells (MSC) revealed a faster migration, increased spreading and a more rapid organization of different cellular components for cell adhesion on fibronectin than on a glass surface. To further explore, how a structural organization of FN controls the behavior of MSC, adhesive lines of FN with varying width between 10 µm and 80 µm and spacings between 5 µm and 20 µm that did not allow cell adhesion were generated. In dependance on both line width and gaps, cells formed adjacent cell contacts, were individually organized in lines, or bridged the lines. With decreasing sizes of FN lines, speed and directionality of cell migration increased, which correlated with organization of the actin cytoskeleton, size and shape of the nuclei as well as of focal adhesions. Together, defined FN lines and gaps enabled a fine tuning of the structural organization of cellular components and migration. Microstructured adhesive substrates can mimic the extracellular matrix in vivo and stimulate cellular mechanisms which play a role in tissue regeneration.
- ItemWill the world run out of land? A Kaya-type decomposition to study past trends of cropland expansion(Bristol : IOP Publishing, 2014) Huber, Veronika; Neher, Ina; Bodirsky, Benjamin L.; Höfner, Kathrin; Schellnhuber, Hans JoachimGlobally, the further expansion of cropland is limited by the availability of adequate land and by the necessity to spare land for nature conservation and carbon sequestration. Analyzing the causes of past land-use changes can help to better understand the potential drivers of land scarcities of the future. Using the FAOSTAT database, we quantify the contribution of four major factors, namely human population growth, rising per-capita caloric consumption (including food intake and household waste), processing losses (including conversion of vegetal into animal products and non-food use of crops), and yield gains, to cropland expansion rates of the past (1961–2007). We employ a Kaya-type decomposition method that we have adapted to be applicable to drivers of cropland expansion at global and national level. Our results indicate that, all else equal, without the yield gains observed globally since 1961, additional land of the size of Australia would have been put under the plough by 2007. Under this scenario the planetary boundary on global cropland use would have already been transgressed today. By contrast, without rising per-capita caloric consumption and population growth since 1961, an area as large as nearly half and all of Australia could have been spared, respectively. Yield gains, with strongest contributions from maize, wheat and rice, have approximately offset the increasing demand of a growing world population. Analyses at the national scale reveal different modes of land-use transitions dependent on development stage, dietary standards, and international trade intensity of the countries. Despite some well-acknowledged caveats regarding the non-independence of decomposition factors, these results contribute to the empirical ranking of different drivers needed to set research priorities and prepare well-informed projections of land-use change until 2050 and beyond.