Description: Irreversible ocean thermal expansion under carbon dioxide removal Dana Ehlert and Kirsten Zickfeld Earth Syst. Dynam., 9, 197-210, https://doi.org/10.5194/esd-9-197-2018, 2018 This study uses a global climate model to explore the extent to which sea level rise due to thermal expansion of the ocean is reversible if the atmospheric concentration of carbon dioxide (CO 2 ) declines. It is found that sea level continues to rise for several decades after atmospheric CO 2 starts to decline and does not return to the pre-industrial level for over thousand years after atmospheric CO 2 is restored to the pre-industrial concentration.

Description: Changes in tropical cyclones under stabilized 1.5 and 2.0 °C global warming scenarios as simulated by the Community Atmospheric Model under the HAPPI protocols Michael F. Wehner, Kevin A. Reed, Burlen Loring, Dáithí Stone, and Harinarayan Krishnan Earth Syst. Dynam., 9, 187-195, https://doi.org/10.5194/esd-9-187-2018, 2018 The United Nations Framework Convention on Climate Change invited the scientific community to explore the impacts of a world in which anthropogenic global warming is stabilized at only 1.5 °C above preindustrial average temperatures. We present a projection of future tropical cyclone statistics for both 1.5 and 2.0 °C stabilized warming scenarios using a high-resolution global climate model. We find more frequent and intense tropical cyclones, but a reduction in weaker storms.

Description: Projected changes in crop yield mean and variability over West Africa in a world 1.5 K warmer than the pre-industrial era Ben Parkes, Dimitri Defrance, Benjamin Sultan, Philippe Ciais, and Xuhui Wang Earth Syst. Dynam., 9, 119-134, https://doi.org/10.5194/esd-9-119-2018, 2018 We present an analysis of three crops in West Africa and their response to short-term climate change in a world where temperatures are 1.5 °C above the preindustrial levels. We show that the number of crop failures for all crops is due to increase in the future climate. We further show the difference in yield change across several West African countries and show that the yields are not expected to increase fast enough to prevent food shortages.

Description: Tagging moisture sources with Lagrangian and inertial tracers: Application to intense atmospheric river events Vicente Pérez-Muñuzuri, Jorge Eiras-Barca, and Daniel Garaboa-Paz Earth Syst. Dynam. Discuss., https//doi.org/10.5194/esd-2018-8,2018 Manuscript under review for ESD (discussion: open, 1 comment) Two Lagrangian tracers tools are evaluated for studies on atmospheric moisture sources and pathways. Usual Lagrangian methods consider the initial moisture volume to remain constant and the particle follows flow path lines exactly. In a different approach, the initial volume can be considered to depend on time as it is advected by the flow, due to thermodynamic processes. Drag and buoyancy forces must be considered then.

Description: Assessing the Impact of a Future Volcanic Eruption on Decadal Predictions Sebastian Illing, Christopher Kadow, Holger Pohlmann, and Claudia Timmreck Earth Syst. Dynam. Discuss., https//doi.org/10.5194/esd-2018-5,2018 Manuscript under review for ESD (discussion: open, 0 comments) The likelihood of a large volcanic eruption in the future provides the largest uncertainty concerning the evolution of the climate system on the time scale of a few years; but also an excellent opportunity to learn about the behavior of the climate system, and our models thereof. So the question emerges how predictable is the response of the climate system to future eruptions? By this we mean, to what extent will the volcanic perturbation affect decadal climate predictions and how does the pre-eruption climate state influence the impact of the volcanic signal on the predictions? To address these questions, we performed decadal forecasts with the MiKlip prediction system in the low-resolution configuration for the initialization years 2012 and 2014, which differ in the Pacific Decadal Oscillation (PDO) phase among other things. Each forecast contains an artificial Pinatubo-like eruption starting in June of the first prediction year. For the construction of the aerosol radiative forcing, we used the global aerosol model ECHAM5-HAM in a version adapted for volcanic eruptions. We investigate the response of different climate variables, including near-surface air temperature, precipitation, frost days, and sea ice area fraction. Our results show that the average global cooling response over four years of about 0.2 K and the precipitation decrease of about 0.025 mm/day, is relatively robust throughout the different experiments and seemingly independent of the initialization state. However, on a regional scale, we find substantial differences between the initializations. The cooling effect in the North Atlantic and Europe lasts longer and the Arctic sea ice increase is stronger than in the simulations initialized in 2014. In contrast, the forecast initialized with a negative PDO shows a prolonged cooling in the North Pacific basin.

Description: Contribution of atmospheric circulation to recent off-shore sea-level variations in the Baltic Sea and the North Sea Sitar Karabil, Eduardo Zorita, and Birgit Hünicke Earth Syst. Dynam., 9, 69-90, https://doi.org/10.5194/esd-9-69-2018, 2018 We analysed the contribution of atmospheric factors to interannual off-shore sea-level variability in the Baltic Sea region. We identified a different atmospheric circulation pattern that is more closely linked to sea-level variability than the NAO. The inverse barometer effect contributes to that link in the winter and summer seasons. Freshwater flux is connected to the link in summer and net heat flux in winter.The new atmospheric-pattern-related wind forcing plays an important role in summer.

Description: How Robust is Your System Resilience? Mehran Homayounfar, Rachata Muneepeerakul, and John M. Anderies Earth Syst. Dynam. Discuss., https//doi.org/10.5194/esd-2017-124,2018 Manuscript under review for ESD (discussion: open, 1 comment) For many complex social-ecological systems, robustness and resilience are difficult to quantify and the connections and trade-offs between them difficult to study. In this study, we present an analytical framework to address the linkage between robustness and resilience more systematically. The results reveal the tradeoffs between robustness and resilience. They also show how the nature of such tradeoffs varies with the choices of certain policies internal stresses and external disturbances.

Description: Process-level improvements in CMIP5 models and their impact on tropical variability, the Southern Ocean, and monsoons Axel Lauer, Colin Jones, Veronika Eyring, Martin Evaldsson, Stefan Hagemann, Jarmo Mäkelä, Gill Martin, Romain Roehrig, and Shiyu Wang Earth Syst. Dynam., 9, 33-67, https://doi.org/10.5194/esd-9-33-2018, 2018 The performance of updated versions of the four earth system models (ESMs) CNRM, EC-Earth, HadGEM, and MPI-ESM is assessed in comparison to their predecessor versions used in Phase 5 of the Coupled Model Intercomparison Project. The Earth System Model Evaluation Tool (ESMValTool) is applied to evaluate selected climate phenomena in the models against observations. This is the first systematic application of the ESMValTool to assess and document the progress made during an extensive model development and improvement project. This study focuses on the South Asian monsoon (SAM) and the West African monsoon (WAM), the coupled equatorial climate, and Southern Ocean clouds and radiation, which are known to exhibit systematic biases in present-day ESMs. The analysis shows that the tropical precipitation in three out of four models is clearly improved. Two of three updated coupled models show an improved representation of tropical sea surface temperatures with one coupled model not exhibiting a double Intertropical Convergence Zone (ITCZ). Simulated cloud amounts and cloud–radiation interactions are improved over the Southern Ocean. Improvements are also seen in the simulation of the SAM and WAM, although systematic biases remain in regional details and the timing of monsoon rainfall. Analysis of simulations with EC-Earth at different horizontal resolutions from T159 up to T1279 shows that the synoptic-scale variability in precipitation over the SAM and WAM regions improves with higher model resolution. The results suggest that the reasonably good agreement of modeled and observed mean WAM and SAM rainfall in lower-resolution models may be a result of unrealistic intensity distributions.

Description: Selecting a climate model subset to optimise key ensemble properties Nadja Herger, Gab Abramowitz, Reto Knutti, Oliver Angélil, Karsten Lehmann, and Benjamin M. Sanderson Earth Syst. Dynam., 9, 135-151, https://doi.org/10.5194/esd-9-135-2018, 2018 Users presented with large multi-model ensembles commonly use the equally weighted model mean as a best estimate, ignoring the issue of near replication of some climate models. We present an efficient and flexible tool that finds a subset of models with improved mean performance compared to the multi-model mean while at the same time maintaining the spread and addressing the problem of model interdependence. Out-of-sample skill and reliability are demonstrated using model-as-truth experiments.

Description: Reliability ensemble averaging of 21st century projections of terrestrial net primary productivity reduces global and regional uncertainties Jean-François Exbrayat, A. Anthony Bloom, Pete Falloon, Akihiko Ito, T. Luke Smallman, and Mathew Williams Earth Syst. Dynam., 9, 153-165, https://doi.org/10.5194/esd-9-153-2018, 2018 We use global observations of current terrestrial net primary productivity (NPP) to constrain the uncertainty in large ensemble 21st century projections of NPP under a "business as usual" scenario using a skill-based multi-model averaging technique. Our results show that this procedure helps greatly reduce the uncertainty in global projections of NPP. We also identify regions where uncertainties in models and observations remain too large to confidently conclude a sign of the change of NPP.