Global Dimming Research Articles

Spatial and temporal patterns as well as major influencing factors of global and diffuse Horizontal Irradiance over China: 1960–2014

Global Horizontal Irradiance (GHI) on Earth is a central element of climate systems. With changes in the climate and regional development, the patterns and influencing factors of GHI, in addition to presenting global consistency, are increasingly showing regional particularities. Based on data for GHI, Diffuse Horizontal Irradiance (DHI) and potential impact factors (geographical position, elevation, cloud cover, water vapor, and ground atmospheric transparency related variables) from 1960 to 2014 in China, we analyzed the pattern and major influencing factors of GHI and DHI. The results showed that the major influencing factors of the GHI spatial pattern were the total cloud cover (TCC) and relative humidity (RH) in China. Dividing all of China into two regions, the major factors were the water vapor pressure (WVP) in the northern region and TCC in the southern region. And we divided the GHI and DHI data into two periods (1960–1987 and 1988–2014) due to global dimming and brightening observed in China in the late 1980s. The temporal GHI showed that 31 of 58 decreased significantly with an average decreasing rate of 95 MJ 10 yr−1 during the periods of 1960–2014 and 49 of 76 stations decreased significantly with an rate of 342 MJ 10 yr−1 during 1960–1987, whereas 57 of 88 stations did not change and 24 stations increased significantly with an rate of 201 MJ 10 yr−1 during the period of 1988–2014. The temporal DHI showed that 40 of 61sites did not change significantly from 1960 to 1987. The major influencing factors for temporal changes of GHI in nine typical cities from 1960 to 2013 were as follows: air quality-related variables in super cities, sandstorms and wind in desert oasis cities, clouds in cities with good air quality, and a low cloud amount (LCA) and annual fog days (FD) in Chengdu. Overall, we identified characteristics of GHI and DHI based on global climate change and regional urban development and found that the spatial characteristics of GHI results for China are consistent with global trends, whereas the spatial characteristics of DHI and temporal characteristics of GHI and DHI have changed significantly and exhibit these measurable trends due to strong regional influences of changing cloud amounts, water vapor, and air quality.

Competing Atmospheric and Surface-Driven Impacts of Absorbing Aerosols on the East Asian Summertime Climate

East Asia has some of the largest concentrations of absorbing aerosols globally, and these, along with the region’s scattering aerosols, have both reduced the amount of solar radiation reaching Earth’s surface regionally (solar dimming) and increased shortwave absorption within the atmosphere, particularly during the peak months of the East Asian summer monsoon (EASM). This study analyzes how atmospheric absorption and surface solar dimming compete in driving the response of regional summertime climate to anthropogenic aerosols, which dominates, and why—issues of particular importance for predicting how East Asian climate will respond to projected changes in absorbing and scattering aerosol emissions in the future. These questions are probed in a state-of-the-art general circulation model using a combination of realistic and novel idealized aerosol perturbations that allow analysis of the relative influence of absorbing aerosols’ atmospheric and surface-driven impacts on regional circulation and climate. Results show that even purely absorption-driven dimming decreases EASM precipitation by cooling the land surface, counteracting climatological land–sea contrast and reducing ascending atmospheric motion and onshore winds, despite the associated positive top-of-the-atmosphere regional radiative forcing. Absorption-driven atmospheric heating does partially offset the precipitation and surface evaporation reduction from surface dimming, but the overall response to aerosol absorption more closely resembles the response to its surface dimming than to its atmospheric heating. These findings provide a novel decomposition of absorbing aerosol’s impacts on regional climate and demonstrate that the response cannot be expected to follow the sign of absorption’s top-of-the-atmosphere or even atmospheric radiative perturbation.

Impacts of stratospheric sulfate geoengineering on tropospheric ozone

Abstract. A range of solar radiation management (SRM) techniques has been proposed to counter anthropogenic climate change. Here, we examine the potential effects of stratospheric sulfate aerosols and solar insolation reduction on tropospheric ozone and ozone at Earth's surface. Ozone is a key air pollutant, which can produce respiratory diseases and crop damage. Using a version of the Community Earth System Model from the National Center for Atmospheric Research that includes comprehensive tropospheric and stratospheric chemistry, we model both stratospheric sulfur injection and solar irradiance reduction schemes, with the aim of achieving equal levels of surface cooling relative to the Representative Concentration Pathway 6.0 scenario. This allows us to compare the impacts of sulfate aerosols and solar dimming on atmospheric ozone concentrations. Despite nearly identical global mean surface temperatures for the two SRM approaches, solar insolation reduction increases global average surface ozone concentrations, while sulfate injection decreases it. A fundamental difference between the two geoengineering schemes is the importance of heterogeneous reactions in the photochemical ozone balance with larger stratospheric sulfate abundance, resulting in increased ozone depletion in mid- and high latitudes. This reduces the net transport of stratospheric ozone into the troposphere and thus is a key driver of the overall decrease in surface ozone. At the same time, the change in stratospheric ozone alters the tropospheric photochemical environment due to enhanced ultraviolet radiation. A shared factor among both SRM scenarios is decreased chemical ozone loss due to reduced tropospheric humidity. Under insolation reduction, this is the dominant factor giving rise to the global surface ozone increase. Regionally, both surface ozone increases and decreases are found for both scenarios; that is, SRM would affect regions of the world differently in terms of air pollution. In conclusion, surface ozone and tropospheric chemistry would likely be affected by SRM, but the overall effect is strongly dependent on the SRM scheme. Due to the health and economic impacts of surface ozone, all these impacts should be taken into account in evaluations of possible consequences of SRM.

Long-term variability of annual sums of total and absorbed solar radiation in the Аrctic

Variability of total (Q) and absorbed (Q – R) radiation after the year 2000 at some Russian Arctic stations in comparison with the long-term variability of these characteristics since the beginning of observations and until 1992 was investigated. As estimating parameters, the normalized by multiyear averages for 1961–1990 of anomalies of annual sums of total and absorbed radiation were chosen. We have analyzed the variability of total cloudiness and integral optical thickness characterizing transparency of the atmosphere as the factors producing the largest influence on total radiation incoming to the land surface. The integral optical thickness of the atmosphere in the Arctic after 2000 was most likely determined by specifics of air pollutants coming to the Arctic atmosphere and was significantly higher in the western Arctic area, than in the eastern one. After 2000 practically at all stations considered, the income of total radiation appeared to be below the multiyear average. Significant by the absolute value, but different by the sign, changes of absorbed radiation were recorded. The long-term periods of decrease and the subsequent increase of the incoming solar radiation observed at the European stations and called as “global dimming and global brightening” were not revealed at the Russian Arctic actinometric stations.

Cuticle surfaces of fossil plants as a potential proxy for volcanic SO2 emissions: observations from the Triassic\u2013Jurassic transition of East Greenland

Flood basalt volcanism has been implicated in several episodes of mass extinctions and environmental degradation in the geological past, including at the Triassic–Jurassic (Tr–J) transition, through global warming caused by massive outgassing of carbon dioxide. However, the patterns of biodiversity loss observed are complicated and sometimes difficult to reconcile with the effects of global warming alone. Recently, attention has turned to additional volcanic products as potential aggravating factors, in particular sulphur dioxide (SO2). SO2 acts both directly as a noxious environmental pollutant and indirectly through forming aerosols in the atmosphere, which may cause transient global dimming and cooling. Here, we present a range of morphological changes to fossil plant leaf cuticle surfaces of hundreds of Ginkgoales and Bennettitales specimens across the Tr–J boundary of East Greenland. Our results indicate that morphological structures of distorted cuticles near the Tr–J boundary are consistent with modern cuticle SO2-caused damage and supported by recent leaf-shape SO2 proxy results, thus identifying cuticle surface morphology as a potentially powerful proxy for SO2. Recording the timing and duration of SO2 emissions in the past may help distinguish between the driving agents responsible for mass extinction events and thus improve our understanding of the Earth System.

The Global Energy Balance Archive (GEBA) version 2017: a database for worldwide measured surface energy fluxes

Abstract. The Global Energy Balance Archive (GEBA) is a database for the central storage of the worldwide measured energy fluxes at the Earth's surface, maintained at ETH Zurich (Switzerland). This paper documents the status of the GEBA version 2017 dataset, presents the new web interface and user access, and reviews the scientific impact that GEBA data had in various applications. GEBA has continuously been expanded and updated and contains in its 2017 version around 500 000 monthly mean entries of various surface energy balance components measured at 2500 locations. The database contains observations from 15 surface energy flux components, with the most widely measured quantity available in GEBA being the shortwave radiation incident at the Earth's surface (global radiation). Many of the historic records extend over several decades. GEBA contains monthly data from a variety of sources, namely from the World Radiation Data Centre (WRDC) in St. Petersburg, from national weather services, from different research networks (BSRN, ARM, SURFRAD), from peer-reviewed publications, project and data reports, and from personal communications. Quality checks are applied to test for gross errors in the dataset. GEBA has played a key role in various research applications, such as in the quantification of the global energy balance, in the discussion of the anomalous atmospheric shortwave absorption, and in the detection of multi-decadal variations in global radiation, known as global dimming and brightening. GEBA is further extensively used for the evaluation of climate models and satellite-derived surface flux products. On a more applied level, GEBA provides the basis for engineering applications in the context of solar power generation, water management, agricultural production and tourism. GEBA is publicly accessible through the internet via http://www.geba.ethz.ch. Supplementary data are available at https://doi.org/10.1594/PANGAEA.873078.

Aerosols characteristics, trends and their climatic implications over Northeast India and adjoining South Asia

ABSTRACTAerosol characteristics and climatic implications derived for selected locations of the north‐eastern region of India and adjoining locations Thimphu (THM), Dhaka (DAC) and Banmauk between 22–30°N and 88–98°E are reported. The region is found to reveal a distinct spatio‐temporal variability in aerosol distribution, with highest climatological mean aerosol optical depth at 550 nm (AOD550) at DAC (0.65 ± 0.07) and lowest at the high altitude location THM (0.19 ± 0.02). Seasonally the maximum AOD550 is observed in the pre‐monsoon season. Moderate resolution imaging spectroradiometer Level‐3 Collection 6 AOD550 and Ångström exponent (AE) exhibit a significant and simultaneous increasing trend in the range of ∼0.003 year−1 to 0.012 year−1 and ∼−0.001 year−1 to 0.020 year−1, respectively, during the period 2001–2014. Together with AE, increasing trend of total ozone mapping spectrometer and ozone monitoring instrument‐retrieved aerosol index (∼0.001 year−1 to 0.007 year−1 during 1979–2014) signifies an increase in anthropogenic aerosol loading, leading to an increase in number density of cloud condensation nuclei and decrease/increase of cloud effective radius /cloud optical depth (COD). This is further associated with overall decreasing trends of rainfall rate over this complex monsoon region. A slow increase in maximum temperature (Tmax) (∼0.008 °C year−1 to 0.049 °C year−1) compared to that in minimum temperature (Tmin) (∼0.007 °C year−1 to 0.068 °C year−1) is attributed to solar dimming due to increasing aerosol loading and COD (∼0.056 year−1 to 0.15 year−1). A decrease in high‐level cloud (CODhigh) counteracts decreasing trends of ground reaching solar radiation over a few locations, including Dibrugarh. This study is important from an aerosol radiation interaction and aerosol cloud interaction viewpoint, which facilitates in reaching a closure of model simulated present day climate change and future climate projections.

Shading Contributes to the Reduction of Stem Mechanical Strength by Decreasing Cell Wall Synthesis in Japonica Rice (Oryza sativa L.).

Low solar radiation caused by industrial development and solar dimming has become a limitation in crop production in China. It is widely accepted that low solar radiation influences many aspects of plant development, including slender, weak stems and susceptibility to lodging. However, the underlying mechanisms are not well understood. To clarify how low solar radiation affects stem mechanical strength formation and lodging resistance, the japonica rice cultivars Wuyunjing23 (lodging-resistant) and W3668 (lodging-susceptible) were grown under field conditions with normal light (Control) and shading (the incident light was reduced by 60%) with a black nylon net. The yield and yield components, plant morphological characteristics, the stem mechanical strength, cell wall components, culm microstructure, gene expression correlated with cellulose and lignin biosynthesis were measured. The results showed that shading significantly reduced grain yield attributed to reduction of spikelets per panicles and grain weight. The stem-breaking strength decreased significantly under shading treatment; consequently, resulting in higher lodging index in rice plant in both varieties, as revealed by decreased by culm diameter, culm wall thickness and increased plant height, gravity center height. Compared with control, cell wall components including non-structural carbohydrate, sucrose, cellulose, and lignin reduced quite higher. With histochemical straining, shading largely reduced lignin deposition in the sclerenchyma cells and vascular bundle cells compared with control, and decreased cellulose deposition in the parenchyma cells of culm tissue in both Wuyunjing23 and W3668. And under shading condition, gene expression involved in secondary cell wall synthesis, OsPAL, OsCOMT, OsCCoAOMT, OsCCR, and OsCAD2, and primary cell wall synthesis, OsCesA1, OsCesA3, and OsCesA8 were decreased significantly. These results suggest that gene expression involved in the reduction of lignin and cellulose in both sclerenchyma and parenchyma cells, which attribute to lignin and cellulose in culm tissue and weak mechanical tissue, consequently, result in poor stem strength and higher lodging risks.Highlights:(1) Shading decreases the stem mechanical strength of japonica rice by decreasing non-structural carbohydrate, sucrose, lignin, and cellulose accumulation in culms.(2) The decrease of carbon source under shading condition is the cause for the lower lignin and cellulose accumulation in culm.(3) The expression of genes involved in lignin and primarily cell wall cellulose biosynthesis (OsCesA1, OsCesA3, and OsCesA8) at the stem formation stage are down-regulated under shading condition, inducing defective cell wall development and poor lodging resistance.

Thermodynamic and dynamic responses of the hydrological cycle to solar dimming

Abstract. The fundamental role of the hydrological cycle in the global climate system motivates a thorough evaluation of its responses to climate change and mitigation. The Geoengineering Model Intercomparison Project (GeoMIP) is a coordinated international effort to assess the climate impacts of solar geoengineering, a proposal to counteract global warming with a reduction in incoming solar radiation. We assess the mechanisms underlying the rainfall response to a simplified simulation of such solar dimming (G1) in the suite of GeoMIP models and identify robust features. While solar geoengineering nearly restores preindustrial temperatures, the global hydrology is altered. Tropical precipitation changes dominate the response across the model suite, and these are driven primarily by shifts of the Hadley circulation cells. We report a damping of the seasonal migration of the Intertropical Convergence Zone (ITCZ) in G1, associated with preferential cooling of the summer hemisphere, and annual mean ITCZ shifts in some models that are correlated with the warming of one hemisphere relative to the other. Dynamical changes better explain the varying tropical rainfall anomalies between models than changes in relative humidity or the Clausius–Clapeyron scaling of precipitation minus evaporation (P − E), given that the relative humidity and temperature responses are robust across the suite. Strong reductions in relative humidity over vegetated land regions are likely related to the CO2 physiological response in plants. The uncertainty in the spatial distribution of tropical P − E changes highlights the need for cautious consideration and continued study before any implementation of solar geoengineering.

81‐2: Visual Quality of Global Dimming Backlight with High Contrast Liquid Crystal Panel for High Dynamic Range Displays

Using an RGB OLED display to emulate LC display systems, we compared the video quality of global dimming 4000:1 contrast with local dimming 1000:1 contrast displays. The 4000:1 contrast system with global dimming was equal or more preferred to the 1000:1 system in 90% of the clips tested.

Competing influences of greenhouse warming and aerosols on Asian Summer Monsoon circulation and rainfall.

In this paper, we have compared and contrasted competing and amplifying influences on the global and regional drivers, circulation and rainfall responses of the Asian monsoon under global greenhouse warming (GHG) and aerosol forcing, based on CMIP5 historical simulations. Under GHG-only forcing, the land warms much faster than the ocean, magnifying the pre-industrial climatological land-ocean thermal contrast and hemispheric asymmetry, i.e., warmer northern than southern hemisphere. A steady increasing warm-ocean-warmer-land (WOWL) trend has been in effect since the 1950's substantially increasing moisture transport from adjacent oceans, and enhancing rainfall over the Asian monsoon regions. However, under GHG warming, increased atmospheric stability due to strong reduction in mid-tropospheric and near surface relative humidity coupled to an expanding subsidence areas, associated with the Deep Tropical Squeeze (DTS, Lau and Kim, 2015b) strongly suppress monsoon convection and rainfall over subtropical and extratropical land, leading to a weakening of the Asian monsoon meridional circulation. The inclusion of aerosol emissions strongly masks WOWL, by over 60% over the northern hemisphere, negating to a large extent the rainfall increase due to GHG warming, and leading to a further weakening of the monsoon circulation, through increasing atmospheric stability, most likely associated with aerosol solar dimming and semi-direct effects. Overall, we find that GHG exerts stronger positive rainfall sensitivity, but less negative circulation sensitivity in SASM compared to EASM. In contrast, aerosols exert stronger negative impacts on rainfall, but less negative impacts on circulation in EASM compared to SASM.

Efficacy of global dimming backlight and high‐contrast liquid crystal panel for high‐dynamic‐range displays

AbstractUsing an RGB organic light‐emitting diode display to emulate liquid crystal display systems, we examined the efficacy of different global dimming strategies for cinematic content. A global dimming solution with smoothed transitions was preferred over solutions using a static backlight level or the highly aggressive frame‐by‐frame backlight adjustment scheme. We compared two such smoothing approaches, one making use of causal data, and another using future information (which could be available via latency or dynamic metadata) and did observe some opportunities for an improved experience, but found the causal data to be a competitive approach. We also evaluated the importance of native panel contrast and how global dimming compares to local dimming approaches. For most content tested, a global dimming display with a high‐contrast liquid crystal panel was judged as being equivalent or more preferred to a full‐array local dimming display with a low‐contrast panel. These results build on the existing evidence that native panel contrast remains one of the strongest predictors of high‐dynamic‐range image quality even as backlight technologies continue to improve.

Assessment of Biofuels in Aviation Industry for Environmental Sustainability

The world has come to increasingly accept that conventional sources of fuel and energy are being depleted since the process of forming fossil fuels takes millions of years longer than the rate that it is rapidly consumed. Aircraft engines cause noise pollution and emit gases and particulates that reduce air quality and contribute to global warming and global dimming, where dust and ash from natural and industrial sources block the sun to create a cooling effect. This paper looks into the working of biofuel as to how it can be the solution towards solving fuel price and energy crisis in the aviation industry. It reviews the usage of biofuel in the aviation industry by airlines in the world focusing on strategies conducted by Virgin Atlantic Airways and some other selected airlines. The understanding of low carbon fuels has developed rapidly over the last decade and Virgin Atlantic are closer than ever before to bringing a sustainable product to the market for commercial use. The paper also considers the biofuel impact on sustainability of the environment and how such usage of biofuel can be adopted into Malaysian aviation industry using available biofuel resources in Malaysia. With many technologies designed for aviation industry, biofuel has come to be utilised in many countries, including the Malaysian Aviation industry. Biofuel ensures the lower emissions of Greenhouse Gas (GHG) as well as sustainability against depleting fossil fuels. It has been estimated that if greenhouse gas emissions continue at the present rate, Earth's surface temperature could exceed historical values as early as 2047, with potentially harmful effects on ecosystems, biodiversity and the livelihoods of people worldwide. Recent estimates suggest that on the current emissions trajectory the Earth could pass a threshold of 2 °C global warming, which the United Nations' IPCC designated as the upper limit for dangerous global warming, by 2036. By prioritising research and deployment of advanced technologies that can convert sustainable waste into biofuel, future aviation industry can witness new development.

Gradual Solar Coronal Dimming and Evolution of Coronal Mass Ejectionin the Early Phase

Abstract We report observations of a two-stage coronal dimming in an eruptive event of a two-ribbon flare and a fast coronal mass ejection (CME). Weak gradual dimming persists for more than half an hour before the onset of the two-ribbon flare and the fast rise of the CME. It is followed by abrupt rapid dimming. The two-stage dimming occurs in a pair of conjugate dimming regions adjacent to the two flare ribbons, and the flare onset marks the transition between the two stages of dimming. At the onset of the two-ribbon flare, transient brightenings are also observed inside the dimming regions, before rapid dimming occurs at the same places. These observations suggest that the CME structure, most probably anchored at the twin dimming regions, undergoes a slow rise before the flare onset, and its kinematic evolution has significantly changed at the onset of flare reconnection. We explore diagnostics of the CME evolution in the early phase with analysis of the gradual dimming signatures prior to the CME eruption.

Impact of the GeoMIP G1 sunshade geoengineering experiment on the Atlantic meridional overturning circulation

We analyze the multi-earth system model responses of ocean temperatures and the Atlantic Meridional Overturning Circulation (AMOC) under an idealized solar radiation management scenario (G1) from the Geoengineering Model Intercomparison Project. All models simulate warming of the northern North Atlantic relative to no geoengineering, despite geoengineering substantially offsetting the increases in mean global ocean temperatures. Increases in the temperature of the North Atlantic Ocean at the surface (∼0.25 K) and at a depth of 500 m (∼0.10 K) are mainly due to a 10 Wm−2 reduction of total heat flux from ocean to atmosphere. Although the AMOC is slightly reduced under the solar dimming scenario, G1, relative to piControl, it is about 37% stronger than under abrupt4 × CO2. The reduction of the AMOC under G1 is mainly a response to the heat flux change at the northern North Atlantic rather than to changes in the water flux and the wind stress. The AMOC transfers heat from tropics to high latitudes, helping to warm the high latitudes, and its strength is maintained under solar dimming rather than weakened by greenhouse gas forcing acting alone. Hence the relative reduction in high latitude ocean temperatures provided by solar radiation geoengineering, would tend to be counteracted by the correspondingly active AMOC circulation which furthermore transports warm surface waters towards the Greenland ice sheet, warming Arctic sea ice and permafrost.

The effects of global dimming on the wheat crop grown in the Yangtze Basin of China simulated by SUCROS_LL, a process-based model

Low light spell, one of the major causes of reduction in global radiation (global dimming), has become a new challenge to crop production. For assessing impacts of low light spells on wheat yield, we proposed a low light index (LLI) and quantified the effects of low light spell conditions occurring at different development stages on five key crop parameters of wheat (leaf photosynthetic capacity, photosynthetic initial light-use efficiency, specific leaf area, dry matter partitioning index for green leaf and harvest index) as functions of LLI using data from field experiments with different levels (50%, 66% and 84% of reduction in incident radiation from ambient) and durations (2d, 4d, 6d and 8d) of shading treatments. These functions were then incorporated into the generic process-based crop growth model SUCROS97 to develop a model, called SUCROS_LL hereafter, for assessing potential yield loss of wheat caused by low light spells. SUCROS_LL was validated and tested using independent data from field shading experiments and 19 agro-meteorological experimental stations, and then used for assessing the potential yield loss of wheat caused by low light spells in the Middle-Lower Reaches of Yangtze River Basin during 1961–2010. Our field experimental data showed that responses of wheat parameters and yield to low light depended on not only LLI, but also the development stages. Plant adaptive responses cannot fully mitigate the negative effects of short-term substantial reduction in incident radiation on wheat crop yield. Compared with SUCROS97, SUCROS_LL significantly improved prediction accuracy of wheat yield by 37% under field shading experimental conditions and 29% under natural low light spell conditions at the 19 agro-meteorological experimental stations. The simulated potential yield loss of wheat caused by low light spells averaged over 1961–2010 increased from the North (below 10%) to the South (above 40%) in the studied region. Potential yield loss averaged over the whole studied region was estimated to increase from the 1960s to the 1990s by 2.9% per decade, but decrease in the 2000s by 9.1% per decade. Although potential wheat yield loss caused by low light spells has been decreased in the past decade in the studied region, the trends of global dimming suggests that breeding/choice of cultivars with better morphological plasticity in response to light availability is in need to mitigate the negative effects of reduction in incident radiation on wheat growth and yield.

Solar Radiation over Four Cities of India: Trend analysis using Mann-Kendall Statistical Test

The present work deals with the study of the solar radiation trend over four major cities of India. The four cities Jodhpur, New Delhi, Nagpur, and Kolkata, represent different climate types: arid, semi-arid, sub-humid and humid, respectively. For trend analysis, we have used over forty years (1957/60-2003) global solar radiation (R G ) and thirty-one years (1973-2003) diffuse solar radiation (R D ) observational data. Based on the Mann-Kendall test (MKT) a significant declining trend in R G (solar dimming) has been observed at the all the stations at p<0.05 during 1957/60-2003. The decresaing trend in R G in past decades indicates the increasing atmospheric load over the four cities of India. Maximum solar dimming has been observed over Jodhpur (-1.54 Wm -2 y -1 ) for the period 1960-2003, followed by New Delhi (-0.98 Wm -2 y -1 , 1957-2003), Nagpur (-0.79 Wm -2 y -1 , 1960-2003), and Kolkata (-0.35 Wm -2 y -1 , 1957-2003). R D has shown the increasing trend in all the station-Jodhpur (0.08 Wm-2y-1), New Delhi (0.05 Wm -2 y -1 ), Nagpur (0.21 Wm -2 y -1 ) and Kolkata (0.04 Wm -2 y -1 ) for the period 1973-2003.The increase in R D indirectly hinted the increase in scattering of insolation by aerosols and clouds. However, in the later decades (after 1990s) R G has shown an increasing trend (solar brightening) in Jodhpur (1.14 Wm -2 y -1 ) and New Delhi (2.24 Wm -2 y -1 ) for the period 1991-2003. The present results show that solar dimming is the global phenomena, but solar brightening is the local phenomena.

Optical and radiative properties of aerosols over Abu Dhabi in the United Arab Emirates

The present study is on the aerosol optical and radiative properties in the short-wave radiation and its climate implications at the arid city of Abu Dhabi (24.42 ∘N, 54.61 ∘E, 4.5 m MSL), in the United Arab Emirates. The direct aerosol radiative forcings (ARF) in the short-wave region at the top (TOA) and bottom of the atmosphere (BOA) are estimated using a hybrid approach, making use of discrete ordinate radiative transfer method in conjunction with the short-wave flux and spectral aerosol optical depth (AOD) measurements, over a period of 3 years (June 2012–July 2015), at Abu Dhabi located at the south-west coast of the Arabian Gulf. The inferred microphysical properties of aerosols at the measurement site indicate strong seasonal variations from the dominance of coarse mode mineral dust aerosols during spring (March–May) and summer (June–September), to the abundance of fine/accumulation mode aerosols mainly from combustion of fossil-fuel and bio-fuel during autumn (October–November) and winter (December–February) seasons. The monthly mean diurnally averaged ARF at the BOA (TOA) varies from −13.2 Wm−2 (∼−0.96 Wm−2) in November to −39.4 Wm−2 (−11.4 Wm−2) in August with higher magnitudes of the forcing values during spring/summer seasons and lower values during autumn/winter seasons. The atmospheric aerosol forcing varies from + 12.2 Wm−2 (November) to 28.2 Wm−2 (June) with higher values throughout the spring and summer seasons, suggesting the importance of mineral dust aerosols towards the solar dimming. Seasonally, highest values of the forcing efficiency at the surface are observed in spring (−85.0 ± 4.1 W m−2 τ −1) followed closely by winter (−79.2 ± 7.1 W m−2 τ −1) and the lowest values during autumn season (−54 ± 4.3 W m−2 τ −1). The study concludes with the variations of the atmospheric heating rates induced by the forcing. Highest heating rate is observed in June (0.39 K day −1) and the lowest in November (0.17 K day −1) and the temporal variability of this parameter is linearly associated with the aerosol absorption index.

Speculative promise as a driver in climate engineering research: The case of Paul Crutzen’s back-of-the-envelope calculation on solar dimming with sulfate aerosols

In this paper, I study the generative role of speculative promise in climate engineering research. My analysis operationalizes Alfred Nordmann’s call for a ‘forensics of wishing’, a variety of technology assessment which scrutinizes the politics of anticipation in technoscience. Using scientific articles and reports as primary sources I trace the uptake and contestation of bold claims made by atmospheric scientist Paul Crutzen a decade ago. In 2006, Crutzen called for dedicated research on stratospheric albedo enhancement as a method to cool the planet. A back-of-the-envelope calculation invoking the eruption of the Mount Pinatubo volcano as a case to be mimicked served to illustrate the method. In the paper, I concentrate on the reception of this idea by fellow climate scientists. Besides fundamental objections being made to Crutzen’s climate paradigm, less idealized models appeared to produce much less promising calculations. The initial claims however kept re-appearing as well and continue to exert influence as idealized models take the idea further. Speculation thus continues to be an important driver of the research. In the conclusion, I discuss aspects of the worldview underlying the proposal, drawing on environmental humanities literature on the human condition in the Anthropocene.

A new look at solar dimming and brightening in China

AbstractPublished estimates on the magnitude of solar dimming and brightening in China show large discrepancies and inconsistencies in its seasonal variations. A nationwide reorganization of the surface solar radiation (SSR) network during 1990–1993 contributed to these uncertainties, which is reflected in a sudden upward jump in the published composite SSR time series. This jump is found to be prevalent in 23 out of 130 stations due to both natural (7 stations) and operational factors (16 stations). After eliminating the stations containing artifacts and discontinuous records, a new magnitude of solar dimming and brightening was estimated for China, and seasonal trends were determined. A transition from dimming to brightening remains in the SSR trend in China after excluding the affected stations and associated jump, in line with the global SSR trend.