Effects of land use and anthropogenic aerosol emissions in the Roman Empire Climate of the Past DOI 10.5194/cp-15-1885-2019 8 November 2019 Using the global aerosol–climate model ECHAM-HAM-SALSA, the effect of humans on European climate in the Roman Empire was quantified. Both land use and novel estimates of anthropogenic aerosol emissions were considered. We conducted simulations with fixed sea-surface temperatures to gain a first impression about the anthropogenic impact. While land use effects induced a regional warming for one of the reconstructions, aerosol emissions led to a cooling associated with aerosol–cloud interactions. Read more
Electron pairing in mirror modes: surpassing the quasi-linear limit Annales Geophysicae DOI 10.5194/angeo-37-971-2019 8 November 2019 The mirror mode starts as a zero-frequency ion fluid instability and saturates quasi-linearly at very low magnetic level, while forming extended magnetic bubbles. These trap the adiabatically bouncing electron component which forms pairs near the mirror points. The large pair anisotropy causes further growth beyond quasilinear level. Including pressure equilibrium gives and estimate of the required pair density. Read more
Microbial community composition and abundance after millennia of submarine permafrost warming Biogeosciences DOI 10.5194/bg-16-3941-2019 8 November 2019 Permafrost temperatures increased substantially at a global scale, potentially altering microbial assemblages involved in carbon mobilization before permafrost thaws. We used Arctic Shelf submarine permafrost as a natural laboratory to investigate the microbial response to long-term permafrost warming. Our work shows that millennia after permafrost warming by > 10 °C, microbial community composition and population size reflect the paleoenvironment rather than a direct effect through warming. Read more
The biophysics, ecology, and biogeochemistry of functionally diverse, vertically and horizontally heterogeneous ecosystems: the Ecosystem Demography model, version 2.2 – Part 1: Model description Geoscientific Model Development DOI 10.5194/gmd-12-4309-2019 8 November 2019 Our paper describes the Ecosystem Demography model. This computer program calculates how plants and ground exchange heat, water, and carbon with the air, and how plants grow, reproduce and die in different climates. Most models simplify forests to an average big tree. We consider that tall, deep-rooted trees get more light and water than small plants, and that some plants can with shade and drought. This diversity helps us to better explain how plants live and interact with the atmosphere. Read more
The biophysics, ecology, and biogeochemistry of functionally diverse, vertically and horizontally heterogeneous ecosystems: the Ecosystem Demography model, version 2.2 – Part 2: Model evaluation for tropical South America Geoscientific Model Development DOI 10.5194/gmd-12-4347-2019 29 October 2019 The Ecosystem Demography model calculates the fluxes of heat, water, and carbon between plants and ground and the air, and the life cycle of plants in different climates. To test if our calculations were reasonable, we compared our results with field and satellite measurements. Our model predicts well the extent of the Amazon forest, how much light forests absorb, and how much water forests release to the air. However, it must improve the tree growth rates and how fast dead plants decompose. Read more
Modeling forest plantations for carbon uptake with the LPJmL dynamic global vegetation model Earth System Dynamics DOI 10.5194/esd-10-617-2019 29 October 2019 We developed a computer model that simulates forests plantations at global scale and how fast such forests can take up CO2from the atmosphere. Using this new model, we performed simulations for a scenario in which a large fraction (14 %) of global croplands and pastures are either converted to planted forests or natural forests. We find that planted forests take up CO2substantially faster than natural forests and are therefore a viable strategy for reducing climate change. Read more
Contrasting thinning patterns between lake- and land-terminating glaciers in the Bhutanese Himalaya The Cryosphere DOI 10.5194/tc-13-2733-2019 29 October 2019 We investigate thickness change of Bhutanese glaciers during 2004–2011 using repeat GPS surveys and satellite-based observations. The thinning rate of Lugge Glacier (LG) is > 3 times that of Thorthormi Glacier (TG). Numerical simulations of ice dynamics and surface mass balance (SMB) demonstrate that the rapid thinning of LG is driven by both negative SMB and dynamic thinning, while the thinning of TG is minimised by a longitudinally compressive flow regime. Read more
Ensemble models from machine learning: an example of wave runup and coastal dune erosion Natural Hazards and Earth System Sciences DOI 10.5194/nhess-19-2295-2019 29 October 2019 Wave runup is important for characterizing coastal vulnerability to wave action; however, it is complex and uncertain to predict. We use machine learning with a high-resolution dataset of wave runup to develop an accurate runup predictor that includes prediction uncertainty. We show how uncertainty in wave runup predictions can be used practically in a model of dune erosion to make ensemble predictions that provide more information and greater predictive skill than a single deterministic model. Read more
Geologic and geomorphic controls on rockfall hazard: how well do past rockfalls predict future distributions? Natural Hazards and Earth System Sciences DOI 10.5194/nhess-19-2249-2019 11 October 2019 Here we evaluate geologic, geomorphic, and anthropogenic controls on rockfall hazard and highlight the complexity of interpreting future rockfall hazard based on former boulder distributions. To evaluate how past rockfall deposits relate to contemporary rockfall hazard, we mapped then compared the locations, physical characteristics, and lithologies of rockfall boulders deposited during the 2010–2011 Canterbury earthquake sequence (n= 185) with their prehistoric counterparts (n= 1093). Read more
Relative impact of aerosol, soil moisture, and orography perturbations on deep convection Atmospheric Chemistry and Physics DOI 10.5194/acp-19-12343-2019 7 October 2019 This study addresses the relative impact of orography, soil moisture, and aerosols on precipitation over Germany in different weather regimes. We find that the impact of these perturbations is higher for weak than for strong large-scale forcing. Furthermore, aerosols and soil moisture are both of similar importance for precipitation forecasting, which indicates that their inclusion in operational ensemble forecasting should be assessed in the future. Read more
