Global Dimming Research Articles

Attribution analyses of evapotranspiration and gross primary productivity changes in Ziya-Daqing basins, China during 2001–2015

Evapotranspiration (ETa) and gross primary productivity (GPP) are two of the key flux indices in a basin system. This study investigated the evolutions of ETa and GPP and the contributions of climate variables and vegetation index over multiple land cover types, simulated by the VIP model (Vegetation Interfaces Processes, RS version) with Terra-Modis 250 m Normalized Difference Vegetation Index (NDVI) dataset in the Ziya-Daqing basins (ZDB), China, during 2001–2015. The nonparametric Mann-Kendall test was used to analyze the changes in ETa and GPP. Contributions to the variations of ETa and GPP were explored using a differential equation method. The analyses revealed that ETa and GPP were high in the eastern plain, and spatial distributions were mainly associated with distributions of the major land-cover types. ETa and GPP showed positive trends in the western Taihang Mountains and negative trends in the eastern plain region. The annual ETa and GPP increased from 2001 to 2015 in most land-use types except cropland and urban. The decreases in ETa and GPP were primarily attributed to solar dimming in cropland and urban. The increases in ETa and GPP mainly occurred in the natural land-cover types (e.g., mixed forest and grassland) as a tradeoff between the positive effect of greening and the negative effect of declined radiation. In ZDB, the contributions of net radiation, air temperature, wind speed, and leaf area index to the change in ETa were − 0.681%, − 0.379%, − 0.032%, and 1.442%, respectively. The contributions of net short-wave radiation, air temperature, relative humidity, and fraction of photosynthetically active radiation to the change in GPP were − 2.411%, 0.085%, − 0.020%, and 10.224%, respectively. Thus, the “greening” was the major reason for ETa and GPP increases in natural vegetations, whereas solar dimming was the major reason for ETa and GPP decreases in cropland.

Impacts of global warming on photovoltaic power generation over West Africa

Many West African countries are plagued with poor electricity. The abundance of solar irradiance over the region makes solar energy an attractive solution to the problem, but there is a dearth of information on how the ongoing solar dimming and global warming may alter the solar energy over the region in the future at various global warming levels. This study investigates the impact of climate change on photovoltaic power generation potential (PVP) over West Africa under four global warming levels (1.5 °C; 2.0 °C; 2.5 °C and 3.0 °C) and under the representative concentration pathway 8.5 (RCP 8.5) climate change scenario. Fourteen regional climate model simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX) were analysed for the study. The capability of the simulations to reproduce the PVP and climate variables over West Africa is quantified. The results show that the CORDEX simulation ensemble captures the spatial distribution and the annual cycle of climate variables and PVP over West Africa, though with few biases. The simulation and observation indicate that PVP over West Africa ranges from 8% to 25% and the annual cycle is influenced by the seasonal variation of the monsoon system. The simulation ensemble projects a decrease of PVP over West Africa in the future and indicates that the magnitude of the decrease grows with warming levels. The maximum decrease in PVP projected over any country or zone in the region is less than 3.8% even for a warming level of 3.0 °C. Hence, the study suggests that ongoing global warming may have an influence on PVP over West Africa.

The fertilization effect of global dimming on crop yields is not attributed to an improved light interception.

Global dimming, a decadal decrease in incident global radiation, is often accompanied with an increase in the diffuse radiation fraction, and, therefore, the impact of global dimming on crop production is hard to predict. A popular approach to quantify this impact is the statistical analysis of historical climate and crop data, or use of dynamic crop simulation modelling approach. Here, we show that statistical analysis of historical data did not provide plausible values for the effect of diffuse radiation versus direct radiation on rice or wheat yield. In contrast, our field experimental study of 3years demonstrated a fertilization effect of increased diffuse radiation fraction, which partly offset yield losses caused by decreased global radiation, in both crops. The fertilization effect was not attributed to any improved canopy light interception but mainly to the increased radiation use efficiency (RUE). The increased RUE was explained not only by the saturating shape of photosynthetic light response curves but also by plant acclimation to dimming that gradually increased leaf nitrogen concentration. Crop harvest index slightly decreased under dimming, thereby discounting the fertilization effect on crop yields. These results challenge existing modelling paradigms, which assume that the fertilization effect on crop yields is mainly attributed to an improved light interception. Further studies on the physiological mechanism of plant acclimation are required to better quantify the global dimming impact on agroecosystem productivity under future climate change.

Brighten the dark skies

An unwelcome effect of rapid industrialization in China over the past 60 years has been the rise in air pollution. Researchers now estimate how the solar dimming caused by pollution reduced the potential for solar energy generation in China. However, reduction of pollution to 1960s levels can increase this potential significantly.

Modeling of the Effects of Wintertime Aerosols on Boundary Layer Properties Over the Indo Gangetic Plain

AbstractWintertime fog and severe aerosol loading in the boundary layer over South Asia, especially Indo Gangetic Plain (IGP), causes disruptions in the day‐to‐day life of millions of people living in the region, and these heavy pollution episodes result in relentless effects on human health. Weather Research Forecasting model coupled with aerosol chemistry is used to investigate the radiative effects and feedbacks of aerosols on the evolution and structure of the planetary boundary layer over the region. In general, aerosols lead to cooling at the surface, which decreases the nonradiative fluxes (latent and sensible heat fluxes), weakens the turbulent diffusion, and inhibits/delays the growth of convective boundary layer. The impact was maximum over IGP where aerosol‐induced solar dimming (60–80 W/m2) led to a cooling of −0.6 to −2 ° C at the surface, which decreases the noontime boundary layer height by ∼200 m. This effect overwhelms the diabatic heating due to absorbing aerosols in the atmosphere. The significant decrease in sensible (∼11–23 W/m2) and latent heat flux (5–14 W/m2) was observed over IGP and western India. Aerosol boundary layer interaction increases the aerosol loading near the surface (PM2.5) by 3 to 30 μg/m3, which further deteriorate the air quality and visibility over the region. The aerosol forcing increases the relative humidity in the lower boundary layer and amplifies the aerosol forcing. The fog events over the Indian regions identified using INSAT‐3D observations coincide with the regions where aerosol‐boundary layer interactions are very significant. The aerosol‐boundary layer interaction has significance in forecasting fog events and planning mitigation strategies for improving the air quality over the region.

Global surface solar radiation and photovoltaic power from Coupled Model Intercomparison Project Phase 5 climate models

In this study, historical surface solar radiation (1850–2005) and future photovoltaic power output (2006–2100) are analyzed to investigate the spatial distribution and long-term variation in global solar energy based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) models and the Global Energy Balance Archive (GEBA) database. The results show that global mean surface solar radiation significantly decreased by 0.014 W m−2 year−1 in 1850–2005. According to the Model for Interdisciplinary Research on Climate (MIROC5), surface solar radiation significantly decreased by 3.42 W m−2 year−1 in 1951–1992 and increased by 4.75 W m−2 year−1 in 1993–2005. Global dimming and brightening were observed before and after the 1990s, respectively. The transition of surface solar radiation from dimming to brightening in Europe and the southeastern United States was detected in the 1980s. Stations in Northeast China, Japan, Southeast Africa, the Middle East, and the west coast of India all showed renewed decreasing trends after the 1990s. The direct and indirect effects of anthropogenic aerosols and cloudiness in different periods and regions were the main causes of the changes. To better understand the utilization of global solar energy, global potential photovoltaic power outputs were estimated in future scenarios with an empirical model. Significant increases in potential photovoltaic power are expected in East Asia, Europe, Central Africa and Central America in 2006–2100. The largest increase is expected in central China, where increases are occurring at 3 kWh m−2 year−1. Significantly decreasing potential photovoltaic power is observed in North Africa, the Middle East, Central Asia and Australia. The greatest decrease is observed in the Tibetan Plateau area (approximately −3.0 kWh m−2 year−1 in 2006–2100). With respect to the global distribution of potential photovoltaic power output, large quantities of photovoltaic power are distributed in the northern and southern parts of Africa, the Middle East, the Tibetan Plateau area, the west coasts of North and South America and most of Australia. The yearly mean sum photovoltaic power in these regions is larger than 2000 kW h m−2. Due to the long-term decreasing photovoltaic power (0.67 kWh m−2 year−1) expected worldwide in 2006–2100, effective and rational utilization of solar energy is of great importance.

Effects of large-scale atmospheric flow and sunshine duration on the evolution of minimum and maximum temperature in Switzerland

The evolution of mean annual minimum (TMIN) and maximum temperature (TMAX) on the Swiss Plateau shows distinct differences over the last 150 years. TMIN increased relatively steadily by about 3 °C. TMAX increased by only 1.5 °C with substantial decadal variability and hardly any increase until about 1940. However, in the most recent decades, TMAX trends are somewhat larger than TMIN trends. While most aspects of the TMIN evolution can be well explained by the global forcing and the modifying effects of the large-scale atmospheric flow alone, local sunshine duration (SD) information is crucial to explain major features of the TMAX series and the differences between TMIN and TMAX since about 1950. SD shows no clear trend until 1950, a decline from 1950 to 1980 and an increase since 1980 resembling the global dimming and brightening signal. TMAX is strongly influenced by SD and the TMAX evolution can be well reconstructed with local TMIN and SD. Strong TMAX declines are found from 1950 to the 1970s. TMIN shows no trend in this period. Between 1980 and about 2005, both TMIN and TMAX show strong increases caused by the greenhouse gas forcing, decreasing aerosols and probably also decreasing cloud cover. Since about 2005, the increases are weaker. The brightening has weakened and the warming effect of the continuously growing greenhouse gas forcing has additionally been reduced by cooling effects caused by large-scale atmospheric flow anomalies. The reasons for the considerable differences in the TMIN and TMAX evolution prior to 1950 remain unknown and further investigations are needed to shed more light on this disparity.

Color breakup suppression based on global dimming for field sequential color displays using edge information in images.

Considering the high complexity of local dimming backlight that is necessary to effectively suppress color breakups for field sequential color liquid crystal displays (FSC-LCDs), a global dimming-based solution is proposed. This solution involves considering that the color breakups mainly occur at object edges of an image. By introducing an algorithm to present the edge information in a single field, evaluating color breakup performances, and experimentally verifying based on a 240-Hz LCD, lighter color breakups are revealed compared with mainstream local dimming-based solutions. Therefore, the proposed solution can achieve FSC-LCDs with better performance and practicality for advanced display applications.

Implication of data uncertainty in the detection of surface radiation trends and observational evidence of renewed solar dimming over India

Analysis of the daily surface solar radiation (SSR) data over the 12 stations spread across India revealed that the data have many missing values and significant variability, which induce large uncertainties in the seasonal and annual means. Since the number of missing values and data variability change over time, ignoring them in the trend analysis, as done in most previous studies, may lead to erroneous results. We propose a method to incorporate the data uncertainty in the trend analysis and compare it with the traditional method, that ignores uncertainty, using the synthetic data with a known trend and having a different percentage of missing values. The proposed method is able to capture the trends in more than 85% of the cases, whereas the traditional method does it for less than 70% of the cases. Analysis of the SSR data by the proposed method revealed a renewed stronger solar dimming of about − 45 W/m2 per decade over the last decade (2006–2015) at all the 12 stations. Analysis of an independent satellite-derived SSR data from the Breathing Earth System Simulator (generated using the MODIS satellite data) also showed the significantly decreasing trends of about − 20 W/m2 per decade in the annual SSR over the entire India. The SSR proxies (sunshine duration and diurnal temperature range) and the wind speed also exhibited the trends consistent with the renewed dimming and suggest that it can be attributed to the increasing aerosol concentration over India in the recent decade.

Water in a warmer world – is atmospheric evaporative demand changing in viticultural areas?

The predicted developments in climate are region-specific and adaptation can only be successful considering the regional characteristics with its diverse technical, environmental, economic and social implications. One of the key concerns for many regions is the availability of water through precipitation, the distribution of precipitation throughout the year, and possible changes in evaporative demand of the atmosphere and thus water use. From rising temperatures it is mostly assumed that water holding capacity of the atmosphere will increase in the future as a function of the Clausius-Clapeyron law, which predicts an increase in the saturation vapour pressure of the atmosphere of 6–7% per degree Celsius. As a consequence, a simultaneous increase in potential evapotranspiration (ETp, the amount of water that could potentially be evaporated from soils and transpired by plants due to changes in climatic factors such as temperature, vapour pressure deficit, radiation and wind speed) is assumed in many cases, which would alter soil and plant water relations. However, the same underlying principles also predict an increase in precipitation by 1–2% per degree warming. Additionally, model predictions for many regions forecast altered precipitation patterns and thus in combination with the possibility of increased ETp, farmers around the world fear an increase in the likelyhood of water deficit and a reduction in the availability of water for irrigation. Contrary to expectations, there have been reports on a reduction in evaporative demand worldwide despite increasing temperatures. In many cases this has been related to a decrease in solar radiation observed for many areas on earth including wine growing regions in Europe until the beginning of the 80th (global dimming) of the last century. However, since then, solar radiation has increased again, but ETp did not always follow and a worldwide decrease in wind speed and pan evaporation has been observed. In order to evaluate different grape growing regions with respect to observed changes on precipitation patterns and ETp, the data of seven wine-growing areas in five countries in the Northern and Southern hemisphere across a large climatic trans-sect were analyzed (Rheingau, Germany, Burgundy, Rhone Valley, France, Napa Valley, USA, Adelaide Hills, Tasmania, Australia, Marlborough, New Zealand) were analyzed. Precipitation patterns differed vastly between locations and showed very different trends over observation periods ranging from 23 to 60 years. The ETp has increased continuously in only two of the seven wine growing areas (Rheingau and Marlborough). In most other areas, ETp has been stable during winter and summer for at least 22 years (Rhone Valley, Napa Valley, Tasmania), sometimes much longer (45 years Adelaide Hills), and has been declining in Burgundy after a period of strong increase for the last 13 years. The potential underlying factors are discussed in relation to observed shifts in precipitation patterns.

Assessment of the Effects of Climate Change on Evapotranspiration with an Improved Elasticity Method in a Nonhumid Area

Climatic elasticity is a crucial metric to assess the hydrological influence of climate change. Based on the Budyko equation, this study performed an analytical derivation of the climatic elasticity of evapotranspiration (ET). With this derived elasticity, it is possible to quantitatively separate the impacts of precipitation, air temperature, net radiation, relative humidity, and wind speed on ET in a watershed. This method was applied in the Wuding River Watershed (WRW), located in the center of the Yellow River Watershed of China. The estimated rate of change in ET caused by climatic variables is −10.69 mm/decade, which is close to the rate of change in ET (−8.06 mm/decade) derived from observable data. The accurate estimation with the elasticity method demonstrates its reliability. Our analysis shows that ET in the WRW had a significant downward trend, but the ET ratio in the WRW has increased continually over the past 52 years. Decreasing precipitation is the first-order cause for the reduction of ET, and decreasing net radiation is the secondary cause. Weakening wind speed also contributed to this reduction. In contrast, regional warming led to an increase in ET that partly offset the negative contributions from other climatic variables. Moreover, reforestation can affect the energy budget of a watershed by decreasing albedo, compensating for the negative influence of global dimming. The integrated effect from precipitation and temperature can affect the energy budget of a watershed by causing a large fluctuation in winter albedo.

A new perspective on solar dimming over the Tibetan Plateau

Solar radiation changes (dimming/brightening) have recently received growing attention within the research community, although there is currently no generally accepted explanation. This article aims to provide a new perspective for identifying the reasons behind solar dimming/brightening by using long‐term measurements of direct and diffuse solar radiation, unlike previous studies which have focused on global solar radiation. We postulate that extinction processes can be more readily revealed by direct and diffuse radiation measurements with the help of a modelling tool that treats the two components separately. An example is presented for Golmud and Lhasa in the northern and southern Tibetan Plateau (TP) respectively, over the period 1957–2013. The following is found: (a) ground‐based observed cloud cover alone hardly explains the observed solar dimming at the two sites; (b) both the cloud‐free direct radiation transmittivity (τ dir) and diffuse radiation proportion (p dif) declined; (c) variations in p dif are overwhelmingly dominated by variations in aerosols, while those in τ dir are related to variations in both aerosol and water vapour; (d) on top of the suggested reduced aerosol concentrations, decreased snow cover can partly explain declined diffuse radiation via lowered surface albedo; (e) the decline in τ dir can be partly attributed to the wetting atmosphere via strengthened absorption; and (f) the impact of volcanic eruptions was also identified from such radiative parameters, lasting into the following summer and especially strong in the southern TP.

Recent rebound in observational large-pan evaporation driven by heat wave and droughts by the Lower Yellow River

Pan evaporation, as a straightforward proxy of potential evapotranspiration, has consistently decreased during the last several decades in many regions across the globe mainly because of global dimming and/or decreases in wind speed. Based on a robust measurement dataset of 30-year large-pan evaporation, however, we found that recent increasing extreme climate events have reversed the decreasing trend in pan evaporation by the Lower Yellow River, with a significant increase of up to 25.2 mm/yr during 2008–2014. Further analyses show that the decrease in large-pan evaporation during 1985–2008 (−5.1 mm/yr) was mainly caused by the decreased vapor pressure deficit (VPD) and sunshine hours. While the sharp increase in large-pan evaporation after 2008 was mainly caused by more frequent heat wave and drought events in spring and summer, which resulted in concurrent increases in air temperature, VPD, and sunshine hours. Our finding of evaporation rebound due to heat wave and droughts calls for improved strategies of water and crop managements for mitigating the negative effects of increasing extreme climate events.

Spatiotemporal variations of aridity in China during 1961–2015: decomposition and attribution

Changes in global climate intensify the hydrological cycle, directly influence precipitation, evaporation, runoff, and cause the re-distribution of water resources in time and space. The aridity index (AI), defined as the ratio of annual precipitation to annual potential evapotranspiration, is a widely used numerical indicator to quantify the degree of dryness at a given location. This study examined the effects of climate change on AI in China during 1961–2015. The results showed that the nationally averaged AI experienced a notable interdecadal transition in 1993, characterized by increasing AI (wetter) between 1961 and 1993, and decreasing AI (drier) after 1993. Overall, the decreased solar radiation (solar dimming) was the main factor affected the nationally averaged AI during 1961–1993, while the relative humidity dominated the variations of nationally averaged AI during 1993–2015. However, the roles of individual factors on the changes in AI vary in different subregions. Precipitation is one of the important contributing factors for the changes of AI in almost all subregions, except the Mid-Lower Yangtze and Huaihe basins. Solar radiation has been significantly decreased during 1961–1993 in South China, Southwest China, Mid-Lower Yangtze and Huaihe basins, and the Tibetan Plateau. Therefore, it dominated the trends of AI in these subregions. The relative humidity mainly affected the Mid-Lower Yangtze and Huaihe basins, Southwest China, and the Tibetan Plateau during 1993–2015, hence dominated the trends of AI in these subregions. The changes of temperature and wind speed, however, played a relatively weak role in the variations of AI.

Extreme temperature and precipitation response to solar dimming and stratospheric aerosol geoengineering

Abstract. We examine extreme temperature and precipitation under two potential geoengineering methods forming part of the Geoengineering Model Intercomparison Project (GeoMIP). The solar dimming experiment G1 is designed to completely offset the global mean radiative forcing due to a CO2-quadrupling experiment (abrupt4 × CO2), while in GeoMIP experiment G4, the radiative forcing due to the representative concentration pathway 4.5 (RCP4.5) scenario is partly offset by a simulated layer of aerosols in the stratosphere. Both G1 and G4 geoengineering simulations lead to lower minimum temperatures (TNn) at higher latitudes and on land, primarily through feedback effects involving high-latitude processes such as snow cover, sea ice and soil moisture. There is larger cooling of TNn and maximum temperatures (TXx) over land compared with oceans, and the land–sea cooling contrast is larger for TXx than TNn. Maximum 5-day precipitation (Rx5day) increases over subtropical oceans, whereas warm spells (WSDI) decrease markedly in the tropics, and the number of consecutive dry days (CDDs) decreases in most deserts. The precipitation during the tropical cyclone (hurricane) seasons becomes less intense, whilst the remainder of the year becomes wetter. Stratospheric aerosol injection is more effective than solar dimming in moderating extreme precipitation (and flooding). Despite the magnitude of the radiative forcing applied in G1 being ∼ 7.7 times larger than in G4 and despite differences in the aerosol chemistry and transport schemes amongst the models, the two types of geoengineering show similar spatial patterns in normalized differences in extreme temperatures changes. Large differences mainly occur at northern high latitudes, where stratospheric aerosol injection more effectively reduces TNn and TXx. While the pattern of normalized differences in extreme precipitation is more complex than that of extreme temperatures, generally stratospheric aerosol injection is more effective in reducing tropical Rx5day, while solar dimming is more effective over extra-tropical regions.

A baseline regional evapotranspiration (ET) and change hotspots over Indian sub-tropics using satellite remote sensing data

The annual water loss through evapotranspiration (ET) is an uncertain but significant component of India’s water budget. The present study generated independent estimates of baseline annual ET, calibrated with in situ micrometeorological data over Indian sub-continent, using surface energy balance framework and satellite-based long-term thermal remote sensing, visible and near-infrared observations as the primary data sources. Thirty years’ (1981–2010) of satellite-based ET estimates at 0.08° grid resolution were used to assess trend in regional ET, to find out change hot-spots and probable causes. Long-term collateral data, influencing ET, such as gridded (0.5° × 0.5°) annual rainfall (RF), annual mean surface soil moisture (SSM) at 25 km resolution from ESA scatterometers and annual mean incoming shortwave radiation from MERRA-2D reanalysis were also analyzed. Mean annual ET loss was found to be the highest for Indian cropland (890 Cubic Km) than forest (575 Cubic Km). Annual water consumption pattern over vegetation systems showed declining ET trend at the rate of -16 Cubic Km yr−1 upto 1995 during 30 years which might be due to declining rainfall and solar dimming. This was followed by increasing ET trend (34 Cubic Km yr−1). During 2001–2010, irrigated cropland showed a steep increase in water consumption pattern with an average rate of 4 Cubic Km yr−1 while grassland and forest showed declining consumption patterns since 2003 and 2007, respectively thus showing crossover points of their consumption patterns with irrigated cropland. Four agriculturally important Indian eastern, central, western and southern states showed significantly increasing ET trend with S-score of 15–25 and Z-score of 1.09–2.9 during this period. Increasing ET in western and southern states was found to be coupled with increase in annual rainfall and SSM. But in eastern and central states, no significant trend in rainfall was observed though significant increase in ET was noticed. Region-specific correlation of annual ET with natural forcing variables was higher for incoming shortwave radiation as compared to rainfall. The increase in ET over irrigated croplands as well as over some of the Indian states could be due to increase in anthropogenic factors which need more detailed investigations in future.

Profound Changes in the Physical Environment of Lake Taihu From 25 Years of Long‐Term Observations: Implications for Algal Bloom Outbreaks and Aquatic Macrophyte Loss

AbstractThe global environment has experienced rapid changes over the past three decades, including global warming, global dimming and brightening, and abnormal climate fluctuations. However, direct evidence of global change in the regional physical environment of a lake is rare especially in China because long‐term observations are lacking. Here we demonstrate the profound changes in the physical environment of Lake Taihu using 25 years of long‐term meteorological, hydrological, and limnological observations and elucidate the potential implications for algal bloom outbreaks and aquatic macrophyte loss. We document significant increasing rates of 0.36 and 0.37°C/decade for the yearly mean air and water temperatures, respectively. In addition, significant increases are observed for the yearly total sunshine duration and yearly mean water level with the rates of 165.0 hr/decade and 0.15 m/decade. In contrast, significant decreases are documented for the yearly mean wind speed and Secchi disk depth with the rates of 0.27 m/(s · decade) and 0.21 m/decade for the macrophyte‐dominated regions, respectively. Therefore, the significant increasing ratio of temperature to wind promoted algal bloom formation and outbreaks, while the decreasing ratio of Secchi disk depth to water level resulted in the loss of aquatic macrophytes, which accelerated the shift from a clear macrophyte‐dominated state to a turbid phytoplankton‐dominated state in Lake Taihu. Forecasts of increased climatic variability in the future pose serious ramifications for both the ecosystem diversity and service functions of large shallow lakes. Our findings highlight the importance of long‐term physical environment monitoring data for understanding ecosystem response to global climate change.

Solar dimming above temperate forests and its impact on local climate

Vegetation has a substantial impact on the local climate. Land cover changes through afforestation or deforestation can amplify or mitigate climate warming by changes in biophysical and biogeochemical mechanisms. In the montane to subalpine area of the Eastern Alps in Europe, where forests have constantly expanded in the last four decades, data of meteorological stations show a consistent reduction in incoming global radiation for the period 2000–2015. To assess the potential role of forests in contributing to such a reduction, three site pairs in Central Europe with neighbouring forest and non-forest sites were analysed. In all the pairs, a lower amount of incoming radiation was recorded at the forest site. When biophysical mechanisms such as albedo, surface roughness and Bowen ratio changes were modelled together with changes in global radiation, the total radiative forcing accounted for a rate of change in air temperature was equal to 0.032 °C ± 0.01 °C per Wm−2. These results suggest that local climate is influenced by land cover change through afforestation both via albedo and radiation feedbacks but also by means of indirect biophysical and species-dependent mechanisms. The data obtained for the site pairs in Central Europe are finally discussed to infer the occurrence of similar forest-driven effects in the Eastern Alps which may explain part of the solar dimming observed in high elevation weather stations.

A Revisit of Global Dimming and Brightening Based on the Sunshine Duration

AbstractObservations show that the surface incident solar radiation (Rs) decreased over land from the 1950s to the 1980s and increased thereafter, known as global dimming and brightening. This claim has been questioned due to the inhomogeneity and low spatial‐temporal coverage of Rs observations. Based on direct comparisons of ~200 observed and sunshine duration (SunDu) derived Rs station pairs, meeting data record lengths exceeding 60 months and spatial distances less than 110 km, we show that meteorological observations of SunDu can be used as a proxy for measured Rs. Our revised results from ~2,600 stations show global dimming from the 1950s to the 1980s over China (−1.90 W/m2 per decade), Europe (−1.36 W/m2 per decade), and the United States (−1.10 W/m2 per decade), brightening from 1980 to 2009 in Europe (1.66 W/m2 per decade) and a decline from 1994 to 2010 in China (−1.06 W/m2 per decade). Even if 1994–2010 is well known as a period of global brightening, the observed and SunDu‐derived Rs over China still exhibit declining trends. Trends in Rs from 1923 to 1950 are also found over Europe (1.91 W/m2 per decade) and the United States (−1.31 W/m2 per decade), but the results in Europe may not well represent the actual trend for the European continent due to poor spatial sampling.

基于S曲线全局动态调光的改进算法

基于S曲线全局动态调光的改进算法