How does Eocene warming affected elevation-dependent warming?

To explore the driving mechanisms of elevation-dependent warming (EDW) over the Tibetan Plateau (TP), the output from a suite of numerical experiments with different cumulus parameterization schemes (CPs) under the Coordinated Regional Climate Downscaling Experiments-East Asia (CORDEX-EA-II) project is examined. Results show that all experiments can broadly capture the observed temperature distributions over the TP with consistent cold biases, and the spread in temperature simulations commonly increases with elevation with the maximum located around 4000–5000 m. Such disagreements among the temperature simulations could to a large extent be explained by their spreads in the surface albedo feedback (SAF). All the experiments reproduce the observed EDW below 5000 m in winter but fail to capture the observed EDW above 4500 m in spring. Further analysis suggests that the simulated EDW during winter is mainly caused by the SAF, and the clear-sky downward longwave radiation (LWclr) plays a secondary role in shaping EDW. The models’ inability in simulating EDW during spring is closely related to the SAF and the surface cloud radiative forcing (CRFs). Furthermore, the magnitude and structure of the simulated EDW are sensitive to the choice of CPs. Different CPs generate diverse snow cover fractions, which can modulate the simulated SAF and its effect on EDW. Also, the CPs show great influence on the LWclr via altering the low-level air temperature. Additionally, the mechanism for different temperature changes among the experiments varies with altitudes during summer and autumn, as the diverse temperature changes appear to be caused by the LWclr for the low altitudes while by the SAF for the middle-high altitudes.

Under the Coordinated Regional Climate Downscaling Experiments‐East Asia (CORDEX‐EA‐II), the outputs from two regional climate models (RCMs) driven by four global climate models (GCMs) are used to investigate the characteristics and possible mechanisms of the projected elevation‐dependent warming (EDW) over the Tibetan Plateau (TP) under the Representative Concentration Pathway emission scenario 8.5 (RCP8.5). Results show that widespread warming over the TP is projected with considerable disagreements in warming intensity and the maximum warming center among RCMs. The largest spread in the surface air temperature (Tas) projections is found above 5,000 m, indicating that a large uncertainty exists over the higher elevations. A marked EDW signal over the TP is simulated under the RCP 8.5 by the multi‐RCM ensemble mean for all seasons, particularly in autumn. Based on the analysis of the surface energy budget, it is found that the surface albedo feedback (SAF) is the primary contributor to EDW and acts as the main source of uncertainty in EDW projections among RCMs. The downward longwave radiation (DLW) is found to be the dominant factor in regulating Tas change over the TP, and its contribution to EDW is model‐dependent. Furthermore, the structure and magnitude of projected EDW are sensitive to the RCM physics and driving GCM, as they can alter the projections of snow cover and albedo, which modulate the simulated SAF and its effect on EDW. Additionally, RegCM4 shows a higher sensitivity to the anthropogenic greenhouse forcing than WRF, evidenced by the larger temperature projections and stronger EDW signal in RegCM4.

The enhancement of warming rates with elevation, so-called elevation-dependent warming (EDW), is one of the regional, still not completely understood, expressions of global warming. Sentinels of climate and environmental changes, mountains have experienced more rapid and intense warming trends in the recent decades, leading to serious impacts on mountain ecosystems and downstream. In this paper we use a state-of-the-art Global Climate Model (EC-Earth) to investigate the impact of model spatial resolution on the representation of this phenomenon and to highlight possible differences in EDW and its causes in different mountain regions of the Northern Hemisphere. To this end we use EC-Earth climate simulations at five different spatial resolutions, from sim 125 to sim 16 km, to explore the existence and the driving mechanisms of EDW in the Colorado Rocky Mountains, the Greater Alpine Region and the Tibetan Plateau–Himalayas. Our results show that the more frequent EDW drivers in all regions and seasons are the changes in albedo and in downward thermal radiation and this is reflected in both daytime and nighttime warming. In the Tibetan Plateau-Himalayas and in the Greater Alpine Region, an additional driver is the change in specific humidity. We also find that, while generally the model shows no clear resolution dependence in its ability to simulate the existence of EDW in the different regions, specific EDW characteristics such as its intensity and the relative role of different driving mechanisms may be different in simulations performed at different spatial resolutions. Moreover, we find that the role of internal climate variability can be significant in modulating the EDW signal, as suggested by the spread found in the multi-member ensemble of the EC-Earth experiments which we use.

A majority of studies suggest that elevation dependent warming (EDW) has been verified in mountainous areas. However, there is some controversy about the EDW of high mountain Asia (HMA). Based on the analysis of the data from 128 meteorological stations in the entire region for 1961–2017, we found that there was no EDW in HMA on the time scale of 1961–2017 and the spatial scale of the altitude of 3500–5000 m. The EDW in HMA is the most obvious during the period of 1998–2012. In general, after 1980, there was EDW in the altitude of 2500–5000 m. The Southeastern Tibetan Plateau always has EDW phenomenon for most of the time scales while other areas only have EDW at certain periods. Therefore, we consider that the rate of warming is higher only in specific mountain areas and time scales.

Rapid elevation-dependent warming (EDW) in high mountain environments can accelerate the rate of change in permafrost and further induce the degradation of alpine tundra systems. However, how changes in area of alpine tundra response to EDW is difficult to be directly quantified at regional scales. Here, we project future changes in areal extent of the Koppen “alpine tundra” climate type in the Tibetan Plateau (TP), which is a potential indicator describing the climate conditions for the development of alpine tundra system, based on a suite of latest Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models under two emission scenarios (representative concentration pathways: RCP 4.5 and RCP 8.5). The results indicated that the Koppen “alpine tundra” climate type would gradually decrease in the TP for three future periods: 2011–2040, 2041–2070, and 2071–2100, especially under the RCP8.5 scenario. The decline in area of Koppen “alpine tundra” climate type mainly occurs above 2500 m above sea level (ASL) due to the EDW (> 10 °C) in the warmest months. The projected changes in area of “alpine tundra” climate type are overall consistent among different climate models, emission scenarios, and post-processing approaches (bias correction or not) used. The results obtained would thus deepen our understanding of future elevation-dependent warming and its potential influences on alpine tundra ecosystems in the Tibetan Plateau.

A scenario-based approach was used to test air and ground response to warming with and without changes to inverted surface lapse rates in four Yukon valleys. Generally, climate warming coupled with weakening of temperature inversions resulted in the greatest increase in air temperature at low elevations. However, ground temperatures at high elevations showed the greatest response to warming and variability between scenarios due to increased connectivity between air and ground. Low elevations showed less of a response to warming and permafrost was largely preserved in these locations. Local models also predicted higher permafrost occurrence compared to a regional permafrost probability model, due to the inclusion of differential surface and thermal offsets. Results show that the spatial warming patterns in these mountains may not follow those predicted in other mountain environments following elevation-dependent warming (EDW). As a result, the concept of EDW should be expanded to become more inclusive of a wider range of possible spatial warming distributions. The purpose of this paper is not to provide exact estimations of warming, but rather to provide hypothetical spatial warming patterns, based on logical predictions of changes to temperature inversion strength, which may not directly follow the distribution projected through EDW.

Spatiotemporal distribution variation of extreme temperatures under elevation-dependent warming and its response characteristics to regional warming in Qinling-Daba Mountains, China.

Rethinking spatiotemporal variations in air temperature over the Qilian Mountains, Western China, from 1979 to 2018

High-altitude regions have been identified as hotspots of climate change. In particular, the dependence of warming rates on elevation, known as Elevation-Dependent Warming (EDW), has been extensively discussed in the literature. Recently, the focus has expanded to the broader concept of Elevation-Dependent Climate Change (EDCC), with attention to precipitation and its extremes, given their importance for mountain hydrological resources and their role in triggering geo-hydrological hazards. Recent studies have investigated the elevational stratification of precipitation in in-situ observations and reanalysis datasets, showing a lack of uniform patterns of EDCC across the world, which point to the need for common methodologies and insight in the driving mechanisms. In this study, we extend results we obtained with the ERA5 reanalysis to CMIP6 global climate models, and study EDCC in key mountain regions of the world: Tibetan Plateau, the US Rocky Mountains, the Greater Alpine Region, and the Andes. We focus on precipitation and its extremes, assessing the ability of the models to reproduce historical patterns of stratification by comparison with ERA5 reanalysis data and other observation-based gridded datasets. We also explore how the stratification in other key climate variables, such as cloud cover, humidity, besides temperature, influence the elevational patterns of precipitation and precipitation extremes and their trends. Our analysis aims to determine whether the observed elevation-dependent precipitation patterns are primarily driven by dynamical, thermodynamical, or microphysical processes, identifying seasonal variations and the specific precipitation type (i.e., stratiform vs convective) mostly affected. Particular attention is given to the role of the model spatial resolution, including regional climate models in a case study analysis over the Greater Alpine Region.

Tropical Andean ecosystems are critical for biodiversity conservation and water regulation. Climate change is affecting these ecosystems, but research at high altitudes is still scarce. We aim to understand the complex relationships between surface temperatures and seasons, El Niño Southern Oscillation phenomenon (ENSO), elevation, and slope direction, using novel in situ monitoring data in Northern South America (i.e., Cocuy National Park, Colombia). We analyzed hourly surface temperature data recorded from 2011 to 2019 at four summits between 4050 and 4400 m elevation, collected using self-logging thermometers as part of the Global Observation Research Initiative in Alpine Environments (GLORIA) Andes network. Furthermore, we assessed temperature trends and differences in relation to elevation, season, slope, and ENSO. Contrary to other regional results, surface warming in these summits did not increase with altitude i.e., no local evidence of elevation-dependent warming (EDW). Even more, minimum and maximum temperatures exhibited contrasting trends: minimum and maximum temperatures increased over time at the lowest elevation, while minima increased and maxima decreased at the highest elevation. Also, lower elevations warmed faster during the dry season. Surface temperatures were weakly correlated with the Oceanic Niño Index (ONI), and the other El Niño indices (1+2, 3 and 4). Given that the ONI index reflects both the effects of El Niño and La Niña, we observed that during La Niña there was a significant intensification of warming for minimum temperatures and cooling for maximum temperatures at the highest elevation. Slope orientation played an important role. Contrary to what other studies have found, minimum temperature trends on slopes exposed to predominant winds (i.e., northeasterlies) were significantly different (warmer) from the leeward slopes (cooler). These findings underscore the need for continued research and monitoring to better understand microclimate variability and heterogeneity in these complex topographic regions. Such efforts are essential for improving climate model accuracy and guiding effective natural resource management in the face of a changing climate.

In this comment we examine a recent study published in Environmental Research Letters that analysed fire history data from forests in Western Australia to suggest that changes in forest structure result in a long-term reduction of fire risk after 56 years since last fire. We examine the data underpinning this study and find that its strongly skewed sample size distribution creates a bias to the extent that the analytical approach would find a pattern of declining fire risk even when there was no decline. Moreover, the very small sample sizes of the longest unburned forests mean that fire mapping errors as small as 1–2 ha can reverse key findings. With documented mapping errors orders of magnitude larger, the dataset is not robust to analysis at this level of precision. An appropriate conclusion, taking into account these detection and sensitivity issues, would be that likelihood of subsequent wildfire is reduced in the first ∼6 years following fire, and remains fairly consistent at a higher level for at least the next 3 decades, with no evidence for a long-term reduction of fire risk. This is relevant given that many fire and forest management decisions are made based on scientific literature. Rather than wildfire risk reducing with increasing time since fire, our projections indicate that ceasing active fire management in the sampled forests could result in landscape wildfire extent 25%–65% above current levels. We recommend further steps that would help provide sound, evidence-based knowledge to inform science, management, and policy.

Crops with origins in tropics and subtropics undergo physiological injury when subjected to nonfreezing temperatures below 12°C. Application of heat and chemical shocks to tissue prior to chilling induces chilling tolerance. This study was undertaken to investigate the effects of low oxygen and high carbon dioxide atmospheres on subsequent chilling tolerance. Cucumber seedlings (Cucumis sativus L., cv. Poinsett 76) with radicles 8 to 12 mm long were subjected to 0% to 21% oxygen and/or 0% to 20% CO2 atmospheres for 0 to 72 hr at 2.5 or 15°C. After chilling, they were placed at 25°C for three additional days. Radicle growth was used to assess chilling injury. Modification of the individual germination plates was necessary to ensure seedling exposure to the desired atmospheres. Chilling injury was reduced by exposure to oxygen levels below 1% and to carbon dioxide levels above 5%. Effects of brief exposures were small in comparison to prolonged exposures during chilling. Seed to seed variability was high and obscured some results. The effects of the various atmospheres were greater with the less vigorous seedlings.

The Alpine area is one of the most vulnerable and sensitive regions to the continuous warming of climate and it is considered an important hotspot of climate change. In particular, climate change is expected to exert a strong influence on all components of the hydrological cycle, including river regimes, with consequent effects on the services offered by the freshwater ecosystem, as well as on water availability for users, thus affecting  several socio-economic sectors. Climate change assessment in the Alpine region relies on direct application of climate observations and, thus, their quality may strongly impact climate and hydrological studies results and predictions in terms of reliability, accuracy and precision. Here, we present an extended climatological-trend analysis focused on the Alpine region over the 1961-2020 period. The potential of a recently developed and unprecedented observational dataset, addressing the key issues in terms of spatial density, data quality, time resolution and completeness, was exploited. About 300 time series of air temperature and 1000 of precipitation, covering homogeneously the extent and the elevation gradient of this area, were selected depending on World Meteorological Organization (WMO) requirements. Climatological and trend analysis was carried out on different time scales considering both mean values and a selection of ETCCDI indices. The phenomena of elevation-dependent warming (EDW) and precipitation change (EDPC) were also assessed. A pca-based clustering approach was applied to identify climatic regions and evaluate the spatial-dependency of trends. A further analysis concerned the relationship between detrended time series and the main teleconnection patterns. The present study aims to provide a reliable analysis of the evolution of key climate variables in the Alpine region. Being a study based on the most comprehensive spatial coverage in this area to date, the related results significantly increase the amount of information available to involved stakeholders to prevent and quickly plan for disaster management, risk mitigation and formulating proper locally relevant adaptation strategies.

Here, we report research design, methodological framework and preliminary findings of a treeline research, based on several sites covering much of the Indian Himalayas. Apart from investigating tree populations, this study expands the treeline concept to community and ecosystem levels. A treeline ecotone consists not only of trees but also several species of herbs and other growth forms. The paper sheds light on methods to delineate treelines and timberlines and to characterize species distribution patterns. Treeline landscapes have complex mosaics of ecosystems, diverse in physiognomy, such as forests, juniper mats and rhododendron krummholz, isolated trees and trees in clusters and rows. Several ecosystem characters change rapidly as forests approach treelines, including a drastic drop in biomass accumulation, which leads to treeline formation. A compilation of treeline elevation studies at the regional level indicates that its elevation can vary widely, by 1800 m across the Himalayan Arc. A similar elevational range is indicated by mapping with the help of remote sensing. The common treeline genera are Betula, Abies, Picea and Juniperus, forming almost all treeline forms described in the literature. We found a relatively lower Temperature Lapse Rate (TLR) value, partly because of elevation-dependent warming (EDW) which needs to be analysed. The upward movement of treelines due to climatic warming could be restricted by pre-monsoon droughts as the studies based on tree ring width chronology suggest. During winters, trees have access to water for only a limited part of the day as the soil remains frozen most of the time. Response to early snowmelt seems to vary from species to species.

Continental Physiography, Climate, and the Global Distribution of Human Population