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The Younger Dryas-Holocene transition represents a period of significant thermal change, comparable in magnitude to modern warming, yet in a colder context and without the effect of anthropogenic disturbance. This is useful as a reference to tackle how biodiversity is affected by temperature in natural conditions. Here, we addressed the thermal change during this period in a southern Baltic coastal lake (Konarzewo Lake, Poland), as inferred by chironomid remains. We evaluated changes in chironomid communities and used Hill numbers to explore how commonness and rarity underlie biodiversity changes attributable to warming. We found evidence of warming at Konarzewo Lake during the Younger Dryas-Holocene transition, with inferred temperatures in the Younger Dryas period supporting the NW–SE gradient in Younger Dryas summer temperatures across Europe. Chironomid communities drastically changed during the thermal transition. However, Hill numbers showed no response to temperature when rare morphotypes were emphasized (order q = 0) or a weak response when they were balanced with common morphotypes (order q = 1). Hill number of order q = 2, emphasizing the most common morphotypes, consistently increased with temperature across different sample sizes or coverages. This illustrates how common morphotypes, rather than the rare ones, may boost biodiversity facing warming. [ABSTRACT FROM AUTHOR]

Extreme thermal conditions have been known for a long time as is evidenced by the oldest preserved historical accounts referring to weather. However, direct data, that is, air temperature measurements, which began in Europe in the 17th century, are the only reliable source of information. They provide insight into how climate evolved over the characteristic period of the climate timeline known as the Little Ice Age. This study focuses on extreme climatic phenomena, referred to here as exceptionally cold (EC) and exceptionally warm (EW) months and seasons that occurred in the early instrumental period (until 1830). The research is based on average monthly air temperature values (of different lengths) from five meteorological stations in Europe. The Central England Temperature series (CET) offers the longest series that spans 172 years whereas Padua has the shortest, 57 years. Consequently, the year 1659, which is the start date of the Central England Temperature series, marks the beginning of the study period for the research presented in this article. Thermally anomalous periods are identified based on the standard deviation of the average temperature from the corresponding long‐term average (1831–2020). The highlights of the study include the identification of the pronounced prevalence at all five stations of EC months and seasons when compared to EW months and seasons, especially in Western Europe (CET) during the Maunder Minimum. The study also finds a lack of synchronicity in the timing of the anomalous periods under investigation in the different parts of Europe. [ABSTRACT FROM AUTHOR]

The relationship between body size, colour and hairiness of Procladius of the Diptera family Chironomidae and climate measured as annual mean air temperature was analysed. The study was based on 453 males representing 31 species from 253 localities in 27 countries in Europe and six elsewhere. Wing length as well as three other characters reflecting body size showed significant decrease with warmer climate conditions. The results are in line with several other studies of insects concluding that adult insects are smaller in warmer climate, also considering the implications of global warming. Likewise, all five characters representing colour lightness showed significantly lighter coloured Procladius specimens with warmer climate. The relationship between hairiness and annual mean air temperature was weaker than that of size or colour and temperature, but all five characters studied showed a statistically significant decrease in hairiness with warmer climate. The biological relevance of smaller size, lighter colour and less hairiness in warmer climate can be related to several factors regulating flight and swarming, including less need of protection against cold weather, overheating avoidance, mating success agility and predator escape. [ABSTRACT FROM AUTHOR]

The onset of periods with very high or low air temperatures has aroused general interest for a long time, which is understandable since it has many dangerous effects directly affecting humans. Such perilous climatic phenomena include exceptionally cold and exceptionally warm months, which this study investigates for all Europe and for its five physico‐geographic regions over the 190‐year period of 1831–2020. Therefore, the research in this paper includes two periods characteristic of the history of climate – the late Little Ice Age (LIA) and present‐day warming. The studies are based on average monthly air temperature values from 40 weather stations in Europe. In this paper, exceptionally cold months (ECMs) or exceptionally warm months (EWMs) are considered to have occurred when the average air temperature at a station differed from the respective long‐term average by at least two standard deviations. The highlights of the study include the identification of a drop in the number of ECMs by 20 over the entire 190‐year period, and a highly statistically significant increase in EWMs by 44 between 1980 and 2020. These changes proceeded with different intensities from one physico‐geographic region of Europe to another. [ABSTRACT FROM AUTHOR]

The study specifies the circulation conditions, the frequency of occurrence, long‐term changes, and thermal characteristics of air masses over east‐central Europe in the years 1951–2020. The division of air masses utilized by The Polish Institute of Meteorology and Water Management was used, where, based on the geographical location of the source areas, Arctic (A), Polar maritime fresh (mPf), Polar maritime old (transformed) (mPo), Polar maritime warm (mPw), Polar continental (cP), and Tropical (T) air masses are distinguished. It has been shown that western circulation dominates in this area (60% of days on average), during which the advection of maritime air masses occurs. The share of Arctic air mass flowing from the north (about 12% of days a year) and Tropical air mass from the southern sector (4% of days) is clearly smaller. The results of the research have shown that the frequency of the majority of the analysed air masses was subject to short‐term changes in the studied period. On the other hand, long‐term changes in this frequency concerned two air masses flowing from lower latitudes (mPw and T). In the case of mPw, in the period 1951–2020 there was a significant increase in frequency, not only on a yearly basis, but also in all seasons. In the last two decades, the frequency of Tropical air mass has also increased significantly, while the increase took place only in the summer period. Therefore, the increase in air temperature recorded in east‐central Europe since the 1990s, mainly in the warm half of the year, should to a large extent be attributed to both the greater frequency of the inflow of air masses from lower latitudes (mPw and T) and the increase in temperature in virtually all separated air masses, which in turn is a result of progressing global warming. [ABSTRACT FROM AUTHOR]

Aim: Distribution ranges of temperate tree species are shifting poleward and upslope into cooler environments due to global warming. Successful regeneration is crucial for population persistence and range expansion. Thus, we aimed to identify environmental variables that affect germination and seedling establishment of Europe's dominant forest tree, to compare the importance of plasticity and genetic variation for regeneration, and to evaluate the regeneration potential at and beyond the southern and northern distribution margins. Location: Europe. Time period: 2016–2018. Major taxa studied: European beech (Fagus sylvatica (L.)). Methods: We investigated how germination, establishment and juvenile survival change across a reciprocal transplantation experiment using over 9,000 seeds of beech from 7 populations from its southern to its northern distribution range margins. Results: Germination and establishment at the seedling stage were highly plastic in response to environmental conditions. Germination success increased with warmer and declined with colder air temperature, whereas establishment and survival were hampered under warmer and drier conditions. Germination differed among populations and was positively influenced by seed weight. However, there was no evidence of local adaptation in any trait. Main conclusions: The high plasticity in the early life‐history traits found irrespective of seed origin may allow for short‐term acclimatization. However, our results also indicate that this plasticity might not be sufficient to ensure the regeneration of beech in the future due to the low survival found under dry and hot conditions. The future climatic conditions in parts of the distribution centre and at the rear edge might thus become limiting for natural regeneration, as the likelihood of extreme heat and drought events will increase. By contrast, at the cold distribution margin, the high plasticity in the early life‐history traits may allow for increasing germination success with increasing temperatures and may thus facilitate natural regeneration in the future. [ABSTRACT FROM AUTHOR]

The article analyzes continentality changes in Europe in the period between 1938 and 2018. We use the raw data of monthly air temperature averages, obtained from the website: European Climate Assessment & Dataset, collected by 443 climate stations. The data is processed with the program MATLAB and the results are plotted with Excel and ArcGIS. The results show that there are differences between the Supan, Gorczynski and Conrad Continentality Indices. We also found that in the period from 1938 to 2018, the trends of continentality indices have changed. Our results have shown that the climate in some parts of Europe is becoming more maritime, especially in the Northern and Eastern regions, while in other territories it is becoming more continental, especially in the Mediterranean coastal regions. [ABSTRACT FROM AUTHOR]

The present study evaluates the performance of 19 climate models that participated in the coupled model intercomparison project phase 5 (CMIP5) in reproducing climatology, the standard deviation, and the dominant mode of spring surface air temperature (SAT) variations over the mid-high latitudes of Eurasia based on historical runs. Future change of the Eurasian spring SAT under the anthropogenic global warming is also examined by comparing the historical and RCP4.5 run. All the 19 CMIP5 models capture well the observed spatial structure of climatological spring SAT, with the pattern correlation coefficients all larger than 0.94. However, most of the models tend to underestimate the SAT over north Europe and north Siberia and overestimate the SAT south of 50°N. There exists large inter-model spreads in the standard deviation of the spring SAT. Most of the models capture realistically the observed dominant mode of interannual variations of spring SAT. Analyses show that the ability of a CMIP5 model in capturing the dominant mode of Eurasian spring SAT variations is connected with the model's performance in representing the observed atmospheric circulation anomalies related to the Arctic Oscillation and the dominant mode of the atmospheric variations over Eurasia. Six best models are selected based on the ability in simulating the dominant mode of the spring SAT variations in the historical runs. These six models project an increase in the SAT climatology but a decrease in the standard deviation over most of Eurasia. These six models project a decrease in the explained variance as well as in the amplitude of the spring SAT and atmospheric anomalies related to the dominant mode. [ABSTRACT FROM AUTHOR]

Europe and in particular its southern part are expected to undergo serious climate changes during summer in response to anthropogenic forcing, with large surface warming and decrease in precipitation. Yet, serious uncertainties remain, especially over central and western Europe. Several mechanisms have been suggested to be important in that context but their relative importance and possible interplays are still not well understood. In this paper, the role of soil-atmosphere interactions, cloud-temperature interactions and land-sea warming contrast in summer European climate change and how they interact are analyzed. Models for which evapotranspiration is strongly limited by soil moisture in the present climate are found to tend to simulate larger future decrease in evapotranspiration. Models characterized by stronger present-day anti-correlation between cloud cover and temperature over land tend to simulate larger future decrease in cloud cover. Large model-to-model differences regarding land-sea warming contrast and its impacts are also found. Warming over land is expected to be larger than warming over sea, leading to a decrease in continental relative humidity and precipitation because of the discrepancy between the change in atmospheric moisture capacity over land and the change in specific humidity. Yet, it is not true for all the models over our domain of interest. Models in which evapotranspiration is not limited by soil moisture and with a weak present-day anti-correlation between cloud cover and temperature tend to simulate smaller land surface warming. In these models, change in specific humidity over land is therefore able to match the continental increase in moisture capacity, which leads to virtually no change in continental relative humidity and smaller precipitation change. Because of the physical links that exist between the response to anthropogenic forcing of important impact-related climate variables and the way some mechanisms are simulated in the context of present-day variability, this study suggests some potentially useful metrics to reduce summer European climate change uncertainties. [ABSTRACT FROM AUTHOR]

The paper focuses on exceptionally hot summers (EHS) as a manifestation of contemporary climate warming. The study identifies EHS occurrences in Central and Eastern Europe and describes the characteristic features of the region's thermal conditions. Average air temperatures in June, July and August were considered, as well as the number of days with maximum temperatures exceeding 25, 30 and 35 °C, and with a minimum temperature greater than >20 °C, as recorded at 59 weather stations in 1951-2010. Extremely hot summers are defined as having an average temperature equal to or greater than the long-term average plus 2 SD. A calendar of EHSs was compiled and their spatial extent identified. The region experienced 12 EHSs, which occurred in a given year at 5 % or more stations (1972, 1981, 1988, 1992, 1997, 1998, 1999, 2002, 2003, 2006, 2007 and 2010). The EHS frequency of occurrence was found to be clearly on an increase. Indeed, only one EHS occurred during the first 30 years, but these occurred five times during the last 10 years of the study period. Their geographical extent varied both in terms of location and size. EHSs were observed at 57 out of the total of 59 weather stations in the study (the exceptions were Pecora and Cluj). The average air temperature of EHSs tended to exceed the relevant long-term average by 2-4 °C. The summer of 2010 was among the hottest (temperature anomaly 5.5-6 °C) and spatially largest. [ABSTRACT FROM AUTHOR]

Abstract: This report presents a study of the variability in a recently published April to September gridded reconstruction temperatures in Europe and an analysis of their extremes. This reconstruction was based on tree rings, historical documents, pollen assemblages and ice cores. The methodology used, an original spectral analog method, preserves long-term variations and the variability of temperature series, which guarantees the pertinence of the analysis of the extremes over a period as long as the last millennium. The analysis of the extremes was performed with the peak-over-threshold (POT) method over two warm periods (A.D. 1000–1350 and 1880–2007) and a cold period (A.D. 1350–1950). We found that (1) according to the long-term variations shown in this reconstruction, the growing season temperature during the last decade has exceeded all of those observed during the Medieval period; (2) the return period of the maximum event of the Medieval period has been reduced by at least a factor of 5; and (3) all decades before A.D. 1350 were warm on average but relatively heterogeneous, while the last decade was homogeneously warmer. A new result of this study concerning Europe is that this anthropogenic change is characterized by spatial homogeneity, with similar changes in both average temperatures and in the distribution of extreme events, while natural climate forcings induce warm periods with heterogeneous spatial patterns and less frequent extreme events. [Copyright &y& Elsevier]

We investigate the relationship between a thousand-year history of violent conflict in Europe and various reconstructions of temperature and precipitation. We find that conflict was more intense during colder period, just like Zhang et al. (Clim Change 76:459–477, ) found for China. This relationship weakens in the industrialized era, and is not robust to the details of the climate reconstruction or to the sample period. As the correlation is negative and weakening, it appears that global warming would not lead to an increase in violent conflict in temperature climates. [ABSTRACT FROM AUTHOR]

Anomalies of mean air temperature of 12 consecutive months were detected recently at a number of spatial scales: from local via national and continental, to hemispheric. At all these spatial scales, pre-2007 records were exceeded by considerable margins. The recent rise in the mean temperature of 12 consecutive months at several scales has remained largely unnoticed, because the 12-month means are seldom analyzed. Broad attention is typically focused on monthly, seasonal and annual temperatures. Analysis of shifted 12-month periods helps spot peculiar 12-month episodes with remarkable temperature anomalies that do not coincide with a calendar year. Introducing 12-month running mean temperatures into the global warming debate can prove useful. [ABSTRACT FROM AUTHOR]

Simulations of the present-day temperature climate in Europe obtained with the dynamic regional climate model HadRM3P from the Hadley Centre are evaluated. Observed daily temperature maxima (Tx) and minima (Tn) for the 1961-1990 period at 185 stations are compared with their nearest corresponding HadRM3P grid-box data. The model generally performs well over the UK and elsewhere between latitudes 50 and 55°N, with biases mostly within ±0.5 K. In other areas coherent regions with seasonal biases up to more than ±5 K exist. In some areas, biases in climatological averages are associated with even larger errors (up to more than ±15 K) in the upper/lower extreme temperature range. Both areas with systematically overestimated and underestimated intra-seasonal daily temperature variances exist, but overestimation dominates. Too hot summerTx south of about 45°N are associated with drying soils in the model. This problem may occur further north in “future” integrations with a greenhouse-gas induced warming. Given the existence of errors in the simulations of the present-day climate, we recommend that results from future scenario integrations are treated with care. [ABSTRACT FROM AUTHOR]

The current climate warming phenomenon manifests itself with the occurrence of, among other characteristics, extremely hot months and seasons. Examples include the heat waves of April and May 2018 and of June 2019, which swept through large areas of Europe with considerable damage to nature and the economy. The study looks at thermal anomalies of this kind using average monthly air temperature records from 210 weather stations collected over the period 1951–2018. For the purpose of the study an anomaly was defined as a deviation of the average monthly temperature from the long-term average by at least two standard deviations. An anomaly was considered large-area if it occurred simultaneously at 20 or more stations, which corresponded to about one-tenth of the continent. The study found that positive large-area anomalies were increasingly frequent, some being recorded at 80 stations, and that no cool large-area anomalies were recorded after 2010. Large-area thermal anomalies of both types were the most frequent overall in Central Europe. Unlabelled Image • Large-area thermal anomalies (LATA, both negative and types) were the most frequent overall in Central Europe. • The bulk of LATA− occurred up to 1995, while the bulk of LATA+ were recorded after 1995. • The frequency of LATA+ is increasing faster than the frequency of LATA− is decreasing. [ABSTRACT FROM AUTHOR]

Confounding factors like urbanization and land-use change could introduce uncertainty to the estimation of global temperature trends related to climate change. In this work, we introduce a new way to investigate the nexus between temporal trends of temperature and urbanization data at the global scale in the period from 1992 to 2013. We analyze air temperature data recorded from more than 5000 weather stations worldwide and nightlight satellite measurements as a proxy for urbanization. By means of a range of statistical methods, our results quantify and outline that the temporal evolution of urbanization affects temperature trends at multiple spatial scales with significant differences at regional and continental scales. A statistically significant agreement in temperature and nightlight trends is detected, especially in low and middle-income regions, where urbanization is rapidly growing. Conversely, in continents such as Europe and North America, increases in temperature trends are typically detected along with non-significant nightlight trends. [ABSTRACT FROM AUTHOR]

Groundwater is the primary source of water supply for sustaining the lives of billion ofpeople and surrounding ecosystems around the Globe. Climate change and variabilitythreaten the sustainable use of renewable groundwater resources in many regions across theWorld. Yet the assessment on the effects of global warming on projected estimates ofrenewable groundwater resources and uncertainties surrounding those estimates at alocally relevant scale is lacking. Here, we provide a comprehensive, continental-scaleassessment of past, present, and future changes in renewable groundwater resources(as a form of groundwater recharge after being suitably aggregated to longer timescales) across Europe at an unprecedented spatial resolution of (5 X 5) km2 andlocal groundwater bodies as per the European Water Framework Directive (WFD).Specifically our aim here is to understand the response of Europe-wide groundwaterresources to different global warming levels in accordance to 2015 IPCC Parisagreement. Our analyses are based on multi-model ensemble simulations from theEDgE1 and HOKLIM2 projects (funded by ECMWF and BMBF-Germany) whichcomprises of four hydrologic and land-surface models (HMs: mHM, Noah-MP,PCR-GLOBWB, and VIC) driven by a suitably downscaled, observation basedE-OBS forcing data for the historical records (1950-2015) and five bias correctedCMIP5 GCMs datasets for the near-past to future climate conditions (1970-2100)under three representative concentration pathways (RCPs: 2.6, 6.0, and 8.5). Atime-sampling approach is applied to identify 30-year periods with distinct warming levelscorresponding to global surface air temperature increase of 1.5, 2.0, and 3.0 K compared tothe pre-industrial levels. We contrast the changes in the multi-model ensemblerecharge between the periods of distinct warming levels and to the contemporaryconditions (1971-2000). Our analyses show a clear North-South gradient of changes inmean annual recharge across Europe with declining trends being observed in theMediterranean region, and increased availability of groundwater resources in theNorth Scandinavian region with increased warming (at end of the Century). Thecontinental part of the Europe shows relatively lower changes in the mean renewablegroundwater resources. A greater sensitivity/amplifications in changes are noticed in theMediterranean region to the response of increased warming levels. Though limited, but ourensemble simulations allow disentangling the different sources of uncertainties(HMs vs. GCMs) – which generally pointed out a larger chunk of uncertainty inmodeling results arises due to differences among GCMs (forcings); but there are clearlyareas where the uncertainty due to (different process representation of) HMs issubstantial, and can not be neglected. Overall, our study underscores the need formulti-model ensembles for the assessment of future changes in renewable groundwaterresources across Europe, and discuss about related impacts avoided in higher warmingworlds. 1. www.edge.climate.copernicus.eu 2. www.ufz.de/hoklim [ABSTRACT FROM AUTHOR]