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A comprehensive assessment of twenty-first century climate change in the European Alps is presented. The analysis is based on the EURO-CORDEX regional climate model ensemble available at two grid spacings (12.5 and 50 km) and for three different greenhouse gas emission scenarios (RCPs 2.6, 4.5 and 8.5). The core simulation ensemble has been subject to a dedicated evaluation exercise carried out in the frame of the CH2018 Climate Scenarios for Switzerland. Results reveal that the entire Alpine region will face a warmer climate in the course of the twenty-first century for all emission scenarios considered. Strongest warming is projected for the summer season, for regions south of the main Alpine ridge and for the high-end RCP 8.5 scenario. Depending on the season, medium to high elevations might experience an amplified warming. Model uncertainty can be considerable, but the major warming patterns are consistent across the ensemble. For precipitation, a seasonal shift of precipitation amounts from summer to winter over most parts of the domain is projected. However, model uncertainty is high and individual simulations can show change signals of opposite sign. Daily precipitation intensity is projected to increase in all seasons and all sub-domains, while the wet-day frequency will decrease in the summer season. The projected temperature change in summer is negatively correlated with the precipitation change, i.e. simulations and/or regions with a strong seasonal mean warming typically show a stronger precipitation decrease. By contrast, a positive correlation between temperature change and precipitation change is found for winter. Among other indicators, snow cover will be strongly affected by the projected climatic changes and will be subject to a widespread decrease except for very high elevation settings. In general and for all indicators, the magnitude of the change signals increases with the assumed greenhouse gas forcing, i.e., is smallest for RCP 2.6 and largest for RCP 8.5 with RCP 4.5 being located in between. These results largely agree with previous works based on older generations of RCM ensembles but, due to the comparatively large ensemble size and the high spatial resolution, allow for a more decent assessment of inherent projection uncertainties and of spatial details of future Alpine climate change.

Enhanced shrub growth and expansion are widespread responses to climate warming in many arctic and alpine ecosystems. Warmer temperatures and shrub expansion could cause major changes in plant community structure, affecting both species composition and diversity. To improve our understanding of the ongoing changes in plant communities in alpine tundra, we studied interrelations among climate, shrub growth, shrub cover and plant diversity, using an elevation gradient as a proxy for climate conditions. Specifically, we analyzed growth of bilberry (Vaccinium myrtillus L.) and its associated plant communities along an elevation gradient of ca. 600 vertical meters in the eastern European Alps. We assessed the ramet age, ring width and shoot length of V. myrtillus, and the shrub cover and plant diversity of the community. At higher elevation, ramets of V. myrtillus were younger, with shorter shoots and narrower growth rings. Shoot length was positively related to shrub cover, but shrub cover did not show a direct relationship with elevation. A greater shrub cover had a negative effect on species richness, also affecting species composition (beta-diversity), but these variables were not influenced by elevation. Our findings suggest that changes in plant diversity are driven directly by shrub cover and only indirectly by climate, here represented by changes in elevation.

The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature–trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming. Analyses of the relationships between temperature, moisture and seven key plant functional traits across the tundra and over time show that community height increased with warming across all sites, whereas other traits lagged behind predicted rates of change.

Alpine landscapes are projected to be degraded under climate change, which would threaten their benefits to society. Previous studies, however, have been limited to aesthetic change, and it remains unclear how much the aesthetic change would affect human welfare. To address this issue and gain insights into climate change adaptation policies, we conducted a choice experiment survey using digitally manipulated images based on climate change scenarios and natural scientific knowledge in a mountainous national park in Japan. We uncovered that park visitors appreciate the alpine landscapes that include snow patches on mountains and some types of alpine flowers by analyzing the data from 445 respondents. Conversely, both the invasion of alpine vegetation by dwarf bamboo and the disappearance of snow patches due to climate change substantially deteriorated the perceived aesthetic benefits from alpine landscapes. The economic loss caused by climate-induced landscape degradation was estimated at more than 100 USD per visitor, at maximum; the disappearance of snow patches and invasion by dwarf bamboo reduced the benefits by approximately 13 USD and 101 USD, respectively. Our findings suggest that sustaining the aesthetic value of alpine landscapes in national parks via climate change adaptation has potentially significant economic benefits. By supposing that the mountain national park attracts 70,000 visitors in summer, climate change would cause as a minimum of eight million USD economic loss at the park without appropriate measures annually. Our findings highlight the importance of climate change measures by considering climate change impacts on social benefits associated with alpine landscapes.

In high alpine environments, glacial shrinkage and permafrost warming due to climate change have significant consequences on mountaineering routes. Few research projects have studied the relationship between climate change and mountaineering; this study attempts to characterize and explain the evolution over the past 40 years of the routes described in The Mont Blanc Massif: The 100 Finest Routes, Gaston Rébuffat's emblematic guidebook, published in 1973.The main elements studied were the geomorphic and cryospheric changes at work and their impacts on the itinerary's climbing parameters, determining the manner and possibility for an itinerary to be climbed. Thirty-one interviews, and comparison with other guidebooks, led to the identification of 25 geomorphic and cryospheric changes related to climate change that are affecting mountaineering itineraries. On average, an itinerary has been affected by nine changes. Among the 95 itineraries studied, 93 have been affected by the effects of climate change - 26 of them have been greatly affected; and three no longer exist. Moreover, periods during which these itineraries can be climbed in good conditions in summer have tended to become less predictable and periods of optimal conditions have shifted toward spring and fall, because the itineraries have become more dangerous and technically more challenging.

Historical biome changes on the Tibetan Plateau provide important information that improves our understanding of the alpine vegetation responses to climate changes. However, a comprehensively quantitative reconstruction of the historical Tibetan Plateau biomes is not possible due to the lack of quantitative methods that enable appropriate classification of alpine biomes based on proxy data such as fossil pollen records. In this study, a pollen-based biome classification model was developed by applying a random forest algorithm (a supervised machine learning method) based on modern pollen assemblages on and around the Tibetan Plateau, and its robustness was assessed by comparing its results with the predictions of the biomisation method. The results indicated that modern biome distributions reconstructed using the random forest model based on modern pollen data generally concurred with the observed zonal vegetation. The random forest model had a significantly higher accuracy than the biomisation method, indicating the former is a more suitable tool for reconstructing alpine biome changes on the Tibetan Plateau. The random forest model was then applied to reconstruct the Tibetan Plateau biome changes from 22 ka BP to the present based on 51 fossil pollen records. The reconstructed biome distribution changes on the Tibetan Plateau generally corresponded to global climate changes and Asian monsoon variations. In the Last Glacial Maximum, the Tibetan Plateau was mainly desert with subtropical forests distributed in the southeast. During the last deglaciation, the alpine steppe began expanding and gradually became zonal vegetation in the central and eastern regions. Alpine meadow occupied the eastern and southeastern areas of the Tibetan Plateau since the early Holocene, and the forest-meadow-steppe-desert pattern running southeast to northwest on the Tibetan Plateau was established afterwards. In the mid-Holocene, subtropical forests extended north, which reflected the “optimum” condition. During the late Holocene, alpine meadows and alpine steppes expanded south.

The distributions of many high-elevation tree species have shifted as a result of recent climate change; however, there is substantial variability in the movement of alpine treelines at local to regional scales. In this study, we derive records of tree growth and establishment from nine alpine treeline ecotones in the Canadian Rocky Mountains, characterise the influence of seasonal climate variables on four tree species (Abies lasiocarpa, Larix lyallii, Picea engelmannii, Pinus albicaulis) and estimate the degree to which treeline movement in the twentieth century has lagged or exceeded the rate predicted by recent temperature warming. The growth and establishment records revealed a widespread increase in radial growth, establishment frequency and stand density beginning in the mid-twentieth century. Coinciding with a period of warming summer temperatures and favourable moisture availability, these changes appear to have supported upslope treeline advance at all sites (range, 0.23–2.00 m/year; mean, 0.83 + 0.67 m/year). However, relationships with seasonal climate variables varied between species, and the rates of treeline movement lagged those of temperature warming in most cases. These results indicate that future climate change impacts on treelines in the region are likely to be moderated by species composition and to occur more slowly than anticipated based on temperature warming alone.

Plant functional traits are key to predict community responses to abiotic and biotic disturbances. Grazing is the dominant land‐use form in drylands and alpine environments, especially in Central Asian rangelands. Here, we address grazing effects and their relative importance against environmental controls on plant traits. We sampled 14 plant functional traits, which are potentially sensitive to grazing, from 127 taxa distributed across three grassland types in Tibetan grasslands exposed to increasing levels of precipitation: steppe, steppe‐meadow and meadow. We performed principal components analysis and fourth‐corner analysis to explore the impacts of grazing and environment on multiple community‐weighted mean (CWM) traits. We also used generaliszed linear mixed models to test the effects of grazing and environment on each CWM trait, and on three dimensions of functional trait diversity, i.e. functional richness (FRic), evenness (FEve) and divergence (FDiv). In addition, we undertook a mini‐review of former studies on grazing effects on plant traits in Chinese grasslands. We found that CWM traits were mainly affected by climate and elevation rather than by grazing intensity. Only plant tissue C content was negatively affected by intensified grazing across grassland types. Plant growth form and life form were mainly influenced by elevation, while heights of canopy and inflorescence were controlled by temperature. Specific leaf area was positively correlated with precipitation and soil total N content in steppes, while plant tissue N content was only correlated to livestock dung cover. Regarding functional trait diversity, FDiv in steppe‐meadows and meadows, and FEve in meadows were reduced by grazing. Synthesis. Our results confirmed that environmental controls override grazing impact on CWM traits across Tibetan alpine grasslands. Most plants and their respective traits are adaptive to alpine climates as well as to grazing, and are thus hardly affected by locally intensified grazing intensity. In steppes, functional diversity is insensitive to grazing due to the combined stress of drought and grazing. However, in steppe‐meadows and meadows, grazing may affect ecosystem functioning, as shown by the reduced values of FDiv and FEve under more intense grazing. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

We assessed if the relative importance of biotic and abiotic factors for plant community composition differs along environmental gradients and between functional groups, and asked which implications this may have in a warmer and wetter future. The study location is a unique grid of sites spanning regional-scale temperature and precipitation gradients in boreal and alpine grasslands in southern Norway. Within each site we sampled vegetation and associated biotic and abiotic factors, and combined broad- and fine-scale ordination analyses to assess the relative explanatory power of these factors for species composition. Although the community responses to biotic and abiotic factors did not consistently change as predicted along the bioclimatic gradients, abiotic variables tended to explain a larger proportion of the variation in species composition towards colder sites, whereas biotic variables explained more towards warmer sites, supporting the stress gradient hypothesis. Significant interactions with precipitation suggest that biotic variables explained more towards wetter climates in the sub alpine and boreal sites, but more towards drier climates in the colder alpine. Thus, we predict that biotic interactions may become more important in alpine and boreal grasslands in a warmer future, although more winter precipitation may counteract this trend in oceanic alpine climates. Our results show that both local and regional scales analyses are needed to disentangle the local vegetation-environment relationships and their regional- scale drivers, and biotic interactions and precipitation must be included when predicting future species assemblages.

Long-term effects of climate change on lakes globally will include a substantial modification in the thermal regime and the oxygen solubility of lakes, resulting in the alteration of ecosystem processes, habitats, and concentrations of critical substances. Recent efforts have led to the development of long-term model projections of climate change effects on lake thermal regimes and oxygen solubility. However, such projections are hardly ever confronted with observations extending over multiple decades. Furthermore, global-scale forcing parameters in lake models present several limitations, such as the need of significant downscaling. In this study, the effects of climate change on thermal regime and oxygen solubility were analyzed in the four largest French peri-alpine lakes over 1850–2100. We tested several one-dimensional (1D) lake models' robustness for long-term variations based on up to 63 years of limnological data collected by the French Observatory of LAkes (OLA). Here, we evaluate the possibility of forcing mechanistic models by following the long-term evolution of shortwave radiation and air temperature while providing realistic seasonal trends for the other variables for which local-scale downscaling often lacks accuracy. Based on this approach, MyLake, forced by air temperatures and shortwave radiations, predicted accurately the variations in the lake thermal regime over the last 4 to 6 decades, with RMSE < 1.95 ∘C. Over the previous 3 decades, water temperatures have increased by 0.46 ∘C per decade (±0.02 ∘C) in the epilimnion and 0.33 ∘C per decade (±0.06 ∘C) in the hypolimnion. Concomitantly and due to thermal change, O2 solubility has decreased by −0.104 mg L−1 per decade (±0.005 mg L−1) and −0.096 mg L−1 per decade (±0.011 mg L−1) in the epilimnion and hypolimnion, respectively. Based on the shared socio-economic pathway SSP370 of the Intergovernmental Panel on Climate Change (IPCC), peri-alpine lakes could face an increase of 3.80 ∘C (±0.20 ∘C) in the next 70 years, accompanied by a decline of 1.0 mg L−1 (±0.1 mg L−1) of O2 solubility. Together, these results highlight a critical alteration in lake thermal and oxygen conditions in the coming decades, and a need for a better integration of long-term lake observatories data and lake models to anticipate climate effects on lake thermal regimes and habitats.