Search

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]

During the period 2018–2020, Europe experienced a series of hot and dry weather conditions with significant socioeconomic and environmental consequences. Yet, the extremity of these multi‐year dry conditions is not recognized. Here, we provide a comprehensive spatio‐temporal assessment of the drought hazard over Europe by benchmarking past exceptional events during the period from 1766 to 2020. We identified the 2018–2020 drought event as a new benchmark having an unprecedented intensity that persisted for more than 2 years, exhibiting a mean areal coverage of 35.6% and an average duration of 12.2 months. What makes this event truly exceptional compared with past events is its near‐surface air temperature anomaly reaching +2.8 K, which constitutes a further evidence that the ongoing global warming is exacerbating present drought events. Furthermore, future events based on climate model simulations Coupled Model Intercomparison Project v5 suggest that Europe should be prepared for events of comparable intensity as the 2018–2020 event but with durations longer than any of those experienced in the last 250 years. Our study thus emphasizes the urgent need for adaption and mitigation strategies to cope with such multi‐year drought events across Europe. Plain Language Summary: This manuscript demonstrates that the 2018–2020 multi‐year drought event constitutes a new benchmark in Europe, with an unprecedented level of intensity over the past 250 years. What makes this event truly exceptional compared with past events is its temperature anomaly reaching +2.8 K. This finding provides new evidence that the ongoing global warming exacerbates current drought events. The key message of this study is that the projected future events across the European continent will have a comparable intensity as the 2018–2020 drought but exhibit considerably longer durations than any of those observed during the last 250 years. Our analysis also shows that these exceptional temperature‐enhanced droughts significantly negatively impact commodity crops across Europe. Key Points: The 2018–2020 multi‐year drought shows unprecedented level of intensity during the past 250 yearsThe 2018–2020 event reached record‐breaking +2.8 K temperature anomaly and negatively impacted major cropsFuture drought events reach comparable intensity of 2018–2020 but with considerably longer durations [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 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]

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]

The article outlines the study conducted by Nicoletta Cannone and colleagues on evaluating the impact of climatic changes in the European Alps. Researchers found that the stronger ice mass loss affects Sforzellina Glacier during 1996 to 2006 was attributed to the local summer warming combined with reduced precipitation and shortening of snow season. Such changes in climatic temperature results in changes in vegetation of glacier forefield due to the increase of colonization rates. The found that their is a strong link between the abiotic and biotic components of high altitude ecosystems, the impacts of climate change undergone dramatic acceleration during the last 35 years.

The temperatures in large parts of Europe have been record high during the meteorological autumn of 2006. Compared to 1961-1990, the 2 m temperature was more than three degrees Celsius above normal from the North side of the Alps to southern Norway. This made it by far the warmest autumn on record in the United Kingdom, Belgium, the Netherlands, Denmark, Germany and Switzerland, with the records in Central England going back to 1659, in the Netherlands to 1706 and in Denmark to 1768. The deviations were so large that under the obviously false assumption that the climate does not change, the observed temperatures for 2006 would occur with a probability of less than once every 10 000 years in a large part of Europe, given the distribution defined by the temperatures in the autumn 1901-2005. A better description of the temperature distribution is to assume that the mean changes proportional to the global mean temperature, but the shape of the distribution remains the same. This includes to first order the effects of global warming. Even under this assumption the autumn temperatures were very unusual, with estimates of the return time of 200 to 2000 years in this region. The lower bound of the 95% confidence interval is more than 100 to 300 years. Apart from global warming, linear effects of a southerly circulation are found to give the largest contributions, explaining about half of the anomalies. SST anomalies in the North Sea were also important along the coast. Climate models that simulate the current atmospheric circulation well underestimate the observed mean rise in autumn temperatures. They do not simulate a change in the shape of the distribution that would increase the probability of warm events under global warming. This implies that the warm autumn 2006 either was a very rare coincidence, or the local temperature rise is much stronger than modelled, or non-linear physics that is missing from these models increases the probability of warm extremes. [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]