2016

1. [Casanueva et al. 2016] Abstract Both statistical and dynamical downscaling methods are well established techniques to bridge the gap between the coarse information produced by global cir- culation models and the regional-to-local scales required by the climate change Im- pacts, Adaptation, and Vulnerability (IAV) communities. A number of studies have analyzed the relative merits of each technique by inter-comparing their performance in reproducing the observed climate, as given by a number of climatic indices (e.g. mean values, percentiles, spells). However, in this paper we stress that fair compar- isons should be based on indices that are not affected by the calibration towards the observed climate used for some of the methods. We focus on precipitation (over continental Spain) and consider the output of eight Regional Climate Models (RCMs) from the EURO-CORDEX initiative at 0.44◦ resolution and five Statistical Downscaling Methods (SDMs) —analog resampling, weather typing and generalized linear models— trained using the Spain044 obser- vational gridded dataset on exactly the same RCM grid. The performance of these models is inter-compared in terms of several standard indices —mean precipitation, 90th percentile on wet days, maximum precipitation amount and maximum number of consecutive dry days— taking into account the parameters involved in the SDM training phase. It is shown, that not only the directly affected indices should be care- fully analyzed, but also those indirectly influenced (e.g. percentile-based indices for precipitation) which are more difficult to identify.
   cordex

2. [Cuesta-Valero et al. 2016] ABSTRACT: Although much of the energy gained by the climate system over the last century has been stored in the oceans, continental energy storage remains important to estimate the Earth's energy imbalance and also because crucial positive climate feedback processes such as soil carbon and permafrost stability depend on continental energy storage. Here for the first time, 32 general circulation model simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) are examined to assess their ability to characterize the continental energy storage. Results display a consistently lower magnitude of continental energy storage in CMIP5 simulations than the estimates from geothermal data. A large range in heat storage is present across the model ensemble, which is largely explained by the substantial differences in the bottom boundary depths used in each land surface component.
   CMIP5, heat storage

3. [Eyring et al. 2016] CMIP6
   cmip6

4. [Gagen et al. 2016] Certain large, sustained anomalies in European temperatures in the past millennium are probably the result of internal variation. Such internal variations can modulate regional temperatures away from the expected response to greenhouse gas forcing. Here we assess the causes of European summer temperature variability over the past millennium using temperature observations, simulations and reconstructions. We find multidecadal-mean summer temperatures have varied within a span of 1 K, largely controlled by external forcing. By contrast, we find subcontinental variations, described by the temperature contrast between northern and southern Europe (the meridional temperature gradient), vary with a span of 2 K, and are controlled by internal processes. These variations are the result of redistributions of precipitation and cloud cover linked to oscillations in the position of the summer storm track. In contrast to recent twentieth-century winter-time trends, variations of the summer storm track over the past millennium show a weak response to external forcing, and instead are dominated by stochastic internal variability. We argue that the response of European summer temperatures to anthropogenic greenhouse forcing is likely to be spatially modulated by the same stochastic internal processes that have caused periods of cool, wet summers in northern Europe over the last millennium.
   Storm tracks, Europe, Last Millennium

   [Gonzalez-Hidalgo et al. 2016] ABSTRACT: The most recent debate on global warming focuses on the hiatus in global temperature, for which several explanations have been proposed. On the other hand, spatial variability and nonlinearity in temperature evolution has been recognized as a key point in global change analyses. In this study, we analyse the evolution of the warming rate in the Spanish mainland using the MOTEDAS data set for the last 60 years (1951–2010). Our special emphasis is on the last decades to detect and identify a possible hiatus, and to determine the effects of daytime (Tmax) and night-time (Tmin) records at annual and seasonal scale on the hiatus. Moving windows running trend analyses were applied to calculate temperature trend and significance for any temporal window from the beginning to the end of the series, ranging from 20 years to the whole series length (60 years) The results suggest that the warming rate in the Spanish mainland reached a maximum between 1970 and 1990, followed by a decrease in intensity in both Tmax and Tmin until the present. Furthermore, the decrease in the warming rate in Tmax has been higher than in Tmin for the last three decades; therefore, recent annual warming rates appears to depend more on Tmin than on Tmax. Significant trends disappear from the middle of the 1980s at any temporal window length in both Tmax and Tmin at annual and seasonal scales except in spring Tmin. Some differences among seasons are evident and, during the last few decades, the highest rates of warming are found in spring and summer, with Tmax and Tmin behaving in different ways. This study highlights how the warming rate is highly dependent on the length of the period analysed.
   Climate change, temperature trends Spain

5. [Hagemann et al. 2016] Abstract. Permafrost or perennially frozen ground is an important part of the terrestrial cryosphere; roughly one quarter of Earth's land surface is underlain by permafrost. The currently observed global warming is most pronounced in the Arctic region and is projected to persist during the coming decades due to anthropogenic CO2 input. This warming will certainly have effects on the ecosystems of the vast permafrost areas of the high northern latitudes. The quantification of such effects, however, is still an open question. This is partly due to the complexity of the system, including several feedback mechanisms between land and atmosphere. In this study we contribute to increasing our understanding of such land–atmosphere interactions using an Earth system model (ESM) which includes a representation of cold-region physical soil processes, especially the effects of freezing and thawing of soil water on thermal and hydrological states and processes. The coupled atmosphere–land models of the ESM of the Max Planck Institute for Meteorology, MPI-ESM, have been driven by prescribed observed SST and sea ice in an AMIP2-type setup with and without newly implemented cold-region soil processes. Results show a large improvement in the simulated discharge. On the one hand this is related to an improved snowmelt peak of runoff due to frozen soil in spring. On the other hand a subsequent reduction in soil moisture enables a positive feedback to precipitation over the high latitudes, which reduces the model's wet biases in precipitation and evapotranspiration during the summer. This is noteworthy as soil-moisture–atmosphere feedbacks have previously not been the focus of research on the high latitudes. These results point out the importance of high-latitude physical processes at the land surface for regional climate.
   Permafrost, jsbach

6. [Huang 2016] Abstract Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is one of the most damaging insect pests in the world. However, little is known about the effects of snow cover and soil temperature on the overwintering pupae of H. armigera. A field experiment was conducted from Novem- ber 2, 2012 to April 24, 2013 at the agrometeorological ex- perimental station in Wulanwusu, China. Overwintering pu- pae were embedded into the soil at depths of 5, 10, and 15 cm in the following four treatments: without snow cover, snow cover, and increased temperatures from 600 and 1200 W in- frared lights. The results showed that snow cover and rising temperatures could all markedly increase soil temperatures, which was helpful in improving the survival of the overwintering pupae of H. armigera. The mortality of overwintering pupae (MOP) at a depth of 15 cm was the highest, and the MOP at a depth of 5 cm followed. The lower accumulated temperature (≤0 C) (AT ≤ C) led to the higher MOP, and the lower diurnal soil temperature range (DSTR) likely led to the lower MOP. After snowmelt, the MOPs at the depths of 5 and 10 cm increased as the soil temperature in- creased, especially in April. The AT of the soil (≤0 °C) was the factor with the strongest effect on MOP. The soil moisture content was not a major factor affecting the MOP in this semi- arid region because precipitation was 45 mm over the entire experimental period. With climate warming, the MOP will likely decrease, and the overwintering boundary air tempera- tures of H. armigera should be expanded due to higher soil temperatures and increased snow cover.
   soil temperature and snow cover on ecosystem

7. [Lawrence et al. 2016] Abstract. Human land-use activities have resulted in large changes to the Earth’s surface, with resulting implications for climate. In the future, land-use activities are likely to expand and intensify further to meet growing demands for food, fiber, and energy. The Land Use Model Intercompari- son Project (LUMIP) aims to further advance understanding of the impacts of land-use and land-cover change (LULCC) on climate, specifically addressing the following questions. (1) What are the effects of LULCC on climate and biogeo- chemical cycling (past–future)? (2) What are the impacts of land management on surface fluxes of carbon, water, and en- ergy, and are there regional land-management strategies with the promise to help mitigate climate change? In addressing these questions, LUMIP will also address a range of more detailed science questions to get at process-level attribution, uncertainty, data requirements, and other related issues in more depth and sophistication than possible in a multi-model context to date. There will be particular focus on the separa- tion and quantification of the effects on climate from LULCC relative to all forcings, separation of biogeochemical from biogeophysical effects of land use, the unique impacts of land-cover change vs. land-management change, modulation of land-use impact on climate by land–atmosphere coupling strength, and the extent to which impacts of enhanced CO2 concentrations on plant photosynthesis are modulated by past and future land use. LUMIP involves three major sets of science activities: (1) development of an updated and expanded historical and future land-use data set, (2) an experimental protocol for spe- cific LUMIP experiments for CMIP6, and (3) definition of metrics and diagnostic protocols that quantify model per- formance, and related sensitivities, with respect to LULCC. In this paper, we describe LUMIP activity (2), i.e., the LU- MIP simulations that will formally be part of CMIP6. These experiments are explicitly designed to be complementary to simulations requested in the CMIP6 DECK and histori- cal simulations and other CMIP6 MIPs including Scenari- oMIP, C4MIP, LS3MIP, and DAMIP. LUMIP includes a two- phase experimental design. Phase one features idealized cou- pled and land-only model simulations designed to advance process-level understanding of LULCC impacts on climate, as well as to quantify model sensitivity to potential land- cover and land-use change. Phase two experiments focus on quantification of the historic impact of land use and the po- tential for future land management decisions to aid in miti- gation of climate change. This paper documents these sim- ulations in detail, explains their rationale, outlines plans for analysis, and describes a new subgrid land-use tile data re- quest for selected variables (reporting model output data sep- arately for primary and secondary land, crops, pasture, and urban land-use types). It is essential that modeling groups participating in LUMIP adhere to the experimental design as closely as possible and clearly report how the model experi- ments were executed.
   IPCC communication, flesh reading scores

8. [Otto-Bliesner et al. 2016] Natural variability can explain fluctuations in surface temperatures but can it account for the current slowdown in warming?Abstract The climate of the past millennium provides a baseline for understanding the background of natural climate variability upon which current anthropogenic changes are superimposed. As this period also contains high data density from proxy sources (e.g. ice cores, stalagmites, corals, tree rings, and sediments), it provides a unique opportunity for understanding both global and regional-scale climate responses to natural forcing. Towards that end, an ensemble of simulations with the Community Earth System Model (CESM) for the period 850-2005 (the CESM Last Millennium Ensemble, or CESM-LME) is now available to the community. This ensemble includes simulations forced with the transient evolution of solar intensity, volcanic emissions, greenhouse gases, aerosols, land use conditions, and orbital parameters, both together and individually. The CESM-LME thus allows for evaluation of the relative contributions of external forcing and internal variability to changes evident in the paleoclimate data record, as well as providing a longer-term perspective for understanding events in the modern instrumental period. It also constitutes a dynamically consistent framework within which to diagnose mechanisms of regional variability. Results demonstrate an important influence of internal variability on regional responses of the climate system during the past millennium. All the forcings, particularly large volcanic eruptions, are found to be regionally influential during the preindustrial period, while anthropogenic greenhouse gas and aerosol changes dominate the forced variability of the mid to late 20th century.
   Last millennium, ncar simulations

9. [Rauert and Harner 2016] The suitability of Red Pine trees (Pinus Resinosa) to act as passive samplers for persistent organic pollutants (POPs) in outdoor air and to provide historic information on air concentration trends was demonstrated in this preliminary investigation. Red Pine tree cores from Toronto, Canada, were tested for polycyclic aromatic hydrocarbon (PAHs), alkylated-PAHs, nitro and oxy-PAHs, polybrominated diphenyl ethers (PBDEs) and novel brominated flame retardants (novel BFRs). The PBDEs and novel BFRs demonstrated a similar relative contribution in cores representing 30 years of tree growth, to that re- ported in contemporary air samples. Analysis of tree ring segments of 5e15 years resulted in detectable concentrations of some PAHs and alk-PAHs and demonstrated a transition from petrogenic sources to pyrogenic sources over the period 1960e2015. A simple uptake model was developed that treats the tree rings as linear-phase passive air samplers. The bark infiltration factor, IFBARK, is a key parameter of the model that reflects the permeability of the bark to allow chemicals to be transferred from ambient air to the outer tree layer (cambium). An IFBARK of about 2% was derived for the Red Pine trees based on tree core and air monitoring data.
   Tree rings and PAH

10. [Rojas et al. 2016] Abstract. In this paper we assess South American monsoon system (SAMS) variability in the last millennium as depicted by global coupled climate model simulations. High- resolution proxy records for the South American monsoon over this period show a coherent regional picture of a weak monsoon during the Medieval Climate Anomaly and a stronger monsoon during the Little Ice Age (LIA). Due to the small external forcing during the past 1000 years, model simulations do not show very strong temperature anomalies over these two specific periods, which in turn do not translate into clear precipitation anomalies, in contrast with the rainfall reconstructions in South America. Therefore, we used an ad hoc definition of these two periods for each model simulation in order to account for model-specific signals. Thereby, several coherent large-scale atmospheric circulation anomalies are identified. The models feature a stronger monsoon during the LIA associated with (i) an enhancement of the rising motion in the SAMS domain in austral summer; (ii) a stronger monsoon-related upper-tropospheric anticyclone; (iii) activa- tion of the South American dipole, which results in a poleward shift of the South Atlantic Convergence Zone; and (iv) a weaker upper-level subtropical jet over South America. The diagnosed changes provide important insights into the mechanisms of these climate anomalies over South America dur- ing the past millennium.
    Tree rings and PAH

11. [Schellnhuber et al. 2016] The Paris Agreement duly reflects the latest scientific understanding of systemic global warming risks. Limiting the anthropogenic temperature anomaly to 1.5–2 C is possible, yet requires transformational change across the board of modernity.
    1.5ºC, 2ºC guardrails and a bit of holocene perspective

12. [Smerdon and Pollack 2016] Abstract: The last quarter century spans the publication of the first assessment report of the Intergovernmental Panel on Climate Change in 1990 and the latest report published in 2013–2014. The five assessment reports appearing over that interval reveal a marked increase in the number of paleoclimate studies addressing the climate of the last 2000 years (the Common Era). An important focus of this work has been on reconstruction of hemispheric and global temperatures. Several early studies in this area generated considerable scientific and public interest, and were followed by high-profile and sometimes vitriolic debates about the magnitude of temperature changes over all or part of the Common Era and their comparison to 20th- and 21st-century global temperature increases due to increasing levels of atmospheric greenhouse gases. Behind the more public debates, however, several consistent themes of scientific inquiry have developed to better characterize climate variability and change over the Common Era. These include attempts to collect more climate proxy archives and understand the signals they contain, improve the statistical methods used to estimate past temperature variability from proxies and their associated uncertainties, and to compare reconstructed temperature variability and change with climate model simulations. All of these efforts are driving a new age of research on the climate of the Common Era that is developing more cohesive and collaborative investigations into the dynamics of climate on time scales of decades to centuries, and an understanding of the implications for modeled climate projections of the future.
    Last2k

13. [Standen et al. 2016] The Met Office has developed the Virtual Met MastTM (VMM) tool for assessing the feasibility of potential wind farm sites. It provides site-specific climatological wind information for both onshore and offshore locations. The VMM relies on existing data from past forecasts from regional-scale numerical weather prediction (NWP) models, to which corrections are applied to account for local site complexity. The techniques include corrections to account for the enhanced roughness lengths used in NWP models to represent drag due to sub-grid orography and downscaling methods that predict local wind acceleration over small-scale terrain. The corrected NWP data are extended to cover long periods (decades) using a technique in which the data are related to alternative long-term datasets. For locations in the UK, the VMM currently relies on operational mesoscale model forecast data at 4 km horizontal resolution. Predictions have been verified against observations made at typical wind turbine hub heights at over 80 sites across the UK. In general, the predictions compare well with the observations. The tech- niques provide an efficient method for screening potential wind resource sites. Examples of how the VMM techniques can be used to produce local wind maps are also presented.
    Virtual Met Mast for potential wind farm sites

14. [Stocker and Plattner 2016] Based on the study of Barkemeyer et al.1 some commentators2 and the IPCC leadership3 have concluded that the top-level documents of the IPCC are harder to understand than a paper by Albert Einstein. Although meant as a metaphor, we disagree with the general conclusion that these documents stand out in terms of low readability as important evidence was ignored and text analyses in general tend to be surprisingly trivial.
    IPCC communication, flesh reading scores

15. [Wilkinson et al. 2016] There is an urgent need to improve the infrastructure supporting the reuse of scholarly data. A diverse set of stakeholders—representing academia, industry, funding agencies, and scholarly publishers—have come together to design and jointly endorse a concise and measureable set of principles that we refer to as the FAIR Data Principles. The intent is that these may act as a guideline for those wishing to enhance the reusability of their data holdings. Distinct from peer initiatives that focus on the human scholar, the FAIR Principles put specific emphasis on enhancing the ability of machines to automatically find and use the data, in addition to supporting its reuse by individuals. This Comment is the first formal publication of the FAIR Principles, and includes the rationale behind them, and some exemplar implementations in the community.
    FAIR data principles