Enhancement of life cycle assessment (LCA) methodology to include the effect of surface albedo on climate change: Comparing black and white roofs (original) (raw)
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Environmental Impact Assessment Review, 2019
Land use affects the global climate through greenhouse gas and aerosol emissions, as well as through changes in biophysical properties of the surface. Anthropogenic land use change over time has caused substantial climate forcing related to albedo, i.e. the share of solar radiation reflected back off the ground. There is growing concern that albedo change may offset climate benefits provided by afforestation, bioenergy or other emission reduction measures that affect land cover. Conversely, land could be managed actively to increase albedo as a strategy to combat global warming. Albedo change can be directly linked to radiative forcing, which allows its climate impact to be compared with that of greenhouse gases in Life Cycle Assessment (LCA). However, the most common LCA methods are static and linear and thus fail to account for the spatial and temporal dependence of albedo change and its strength as a climate forcer. This study sought to develop analytical methods that better estimate radiative forcing from albedo change by accounting for spatial and temporal variations in albedo, solar irradiance and transmission through the atmosphere. Simplifications concerning the temporal resolution and aggregation procedures of input data were evaluated. The results highlight the importance of spatial and temporal variations in determining the climate impact of albedo change in LCA. Irradiance and atmospheric transmittance depend on season, latitude and climate zone, and they co-vary with instantaneous albedo. Ignoring these dependencies led to case-specific errors in radiative forcing. Extreme errors doubled the climate cooling of albedo change or resulted in warming rather than cooling in two Swedish cases considered. Further research is needed to understand how different land use strategies affect the climate due to albedo, and how this compares to the effect of greenhouse gases. Given that albedo change and greenhouse gases act on different time scales, LCAs can provide better information in relation to climate targets if the timing of flows is considered in life cycle inventory analysis and impact assessment. counterproductive land-based mitigation measures (
The urban environment is characterized by multiple interactions between its parts, and any change can determine a modification in its metabolism. Typically life cycle assessment (LCA) takes into account only part of the interactions. The main aim of this study was to present a hybrid analysis for enhancing the spatial resolution of LCA, focusing on surface albedo evaluation.In this article the substitution in New York City, New York, USA, of traditional roofs with a mean albedo of 0.32 with white roofs with an albedo of 0.9 has been hypothesized. A multiscale approach was used to evaluate the impact of variation in urban albedo, since it can influence the urban heat island (UHI), energy use, and atmospheric chemistry, affecting radiative forcings. The impact on global climate has been translated, through the use of a climatological model, into equivalents of carbon dioxide and added to the impact of the white roof. The effect of the summer UHI mitigation on human health has been assessed through the use of a hybrid model. Finally, the environmental burdens of a square meter of roof have been evaluated by considering the elementary flows—excluding the energy use—and added to the results deriving from the evaluation of the effects on human health and on climate change. In time horizons of 50 and 100 years, it shows that the increase in rooftop albedo plays an important role in decreasing the impact of rooftops on the climate-change and human health impact categories.
Comparative Life Cycle Assessment of Standard and Green Roofs
Environmental Science & Technology, 2006
Life cycle assessment (LCA) is used to evaluate the benefits, primarily from reduced energy consumption, resulting from the addition of a green roof to an eight story residential building in Madrid. Building energy use is simulated and a bottom-up LCA is conducted assuming a 50 year building life. The key property of a green roof is its low solar absorptance, which causes lower surface temperature, thereby reducing the heat flux through the roof. Savings in annual energy use are just over 1%, but summer cooling load is reduced by over 6% and reductions in peak hour cooling load in the upper floors reach 25%. By replacing the common flat roof with a green roof, environmental impacts are reduced by between 1.0 and 5.3%. Similar reductions might be achieved by using a white roof with additional insulation for winter, but more substantial reductions are achieved if common use of green roofs leads to reductions in the urban heat island.
The International Journal of Life Cycle Assessment, 2010
Purpose Climate change impacts in life cycle assessment (LCA) are usually assessed as the emissions of greenhouse gases expressed with the global warming potential (GWP). However, changes in surface albedo caused by land use change can also contribute to change the Earth's energy budget. In this paper we present a methodology for including in LCA the climatic impacts of land surface albedo changes, measured as CO 2-eq. emissions or emission offsets. Methods A review of studies calculating radiative forcings and CO 2-equivalence of changes in surface albedo is carried out. A methodology is proposed, and some methodological issues arising from its application are discussed. The methodology is applied in a practical example dealing with greenhouse agriculture in Southern Spain. Results The results of the case study show that the increase in surface albedo due to the reflective plastic cover of greenhouses involves an important CO 2-eq. emission offset, which reduces the net GWP-100 of tomato production from 303 to 168 kg CO 2-eq. per ton tomato when a 50-year service time is considered for the agricultural activity. This example shows that albedo effects can be very important in a product system when land use plays an important role, and substantial changes in surface albedo are involved. Conclusions Although the method presented in this work can be improved concerning the calculation of radiative forcing, it constitutes a first operative approach which can be used to develop regionalized characterization factors and provide a more complete evaluation of impacts on the climate change impact category. Keywords Climate change. Global warming potential (GWP). Greenhouse agriculture. Land transformation. Land use change. Life cycle impact assessment (LCIA). Radiative forcing Responsible editor: Llorenc Milà i Canals.
Even if several studies and researches have demonstrated that green roofs significantly contribute to energy saving, indoor thermal comfort, urban heat island mitigation, rain-water management and air pollution reduction, environmental benefits of green roofs mainly depend on use of primary energy, natural resources or raw materials used in the construction. A green roof is usually a more or less complex aggregation of different layer addressing each one to a specific characteristic and performance. Results of previous LCA researches, based on a cold climate scenario, have demonstrated the highest influence that some specific layers have on the overall impact of the green roofs and to what extent the global impact changes when insulation and the substrate layers vary in density and quality. Starting from results of these similar EU researches, this study aims to evaluate the variation of the overall impact in hot climates where insulation is less strategic than heat capacity. LCA has been applied to assess and compare the environmental impacts of four different green roof solutions compared to a standard clay pitched roof, based on the functional unit of 1m 2 with the same reference service life, where layers have been selected according to local practice and market. Despite a general equivalence in environmental impacts of all the roofing elements, results have highlighted a general lack in specific life cycle inventory information that leads to a potential inaccuracy 647 Caterina Gargari et al. / Agriculture and Agricultural Science Procedia 8 (2016) 646 – 656 of the assessment especially when recycled material are used in the growing medium or when disposal scenario includes recycle processes.
Bright is the new black—multi-year performance of high-albedo roofs in an urban climate
Environmental Research Letters, 2012
High-albedo white and cool roofing membranes are recognized as a fundamental strategy that dense urban areas can deploy on a large scale, at low cost, to mitigate the urban heat island effect. We are monitoring three generic white membranes within New York City that represent a cross section of the dominant white membrane options for US flat roofs: (1) an ethylene-propylene-diene monomer (EPDM) rubber membrane; (2) a thermoplastic polyolefin (TPO) membrane; and (3) an asphaltic multiply built-up membrane coated with white elastomeric acrylic paint. The paint product is being used by New York City's government for the first major urban albedo enhancement program in its history. We report on the temperature and related albedo performance of these three membranes at three different sites over a multi-year period. The results indicate that the professionally installed white membranes are maintaining their temperature control effectively and are meeting the Energy Star Cool Roofing performance standards requiring a three-year aged albedo above 0.50. The EPDM membrane shows evidence of low emissivity; however this had the interesting effect of avoiding any 'winter heat penalty' for this building. The painted asphaltic surface shows high emissivity but lost about half of its initial albedo within two years of installation. Given that the acrylic approach is such an important 'do-it-yourself', low-cost, retrofit technique, and, as such, offers the most rapid technique for increasing urban albedo, further product performance research is recommended to identify conditions that optimize its long-term albedo control. Even so, its current multi-year performance still represents a significant albedo enhancement for urban heat island mitigation.
Effects of white roofs on urban temperature in a global climate model
Geophysical Research Letters, 2010
1] Increasing the albedo of urban surfaces has received attention as a strategy to mitigate urban heat islands. Here, the effects of globally installing white roofs are assessed using an urban canyon model coupled to a global climate model. Averaged over all urban areas, the annual mean heat island decreased by 33%. Urban daily maximum temperature decreased by 0.6°C and daily minimum temperature by 0.3°C. Spatial variability in the heat island response is caused by changes in absorbed solar radiation and specification of roof thermal admittance. At high latitudes in winter, the increase in roof albedo is less effective at reducing the heat island due to low incoming solar radiation, the high albedo of snow intercepted by roofs, and an increase in space heating that compensates for reduced solar heating. Global space heating increased more than air conditioning decreased, suggesting that end-use energy costs must be considered in evaluating the benefits of white roofs. Citation: Oleson, K. W., G. B. Bonan, and J. Feddema (2010), Effects of white roofs on urban temperature in a global climate model, Geophys. Res. Lett., 37, L03701,
Effects of Urban Surfaces and White Roofs on Global and Regional Climate
Land use, vegetation, albedo, and soil-type data are combined in a global model that accounts for roofs and roads at near their actual resolution to quantify the effects of urban surface and white roofs on climate. In 2005, ;0.128% of the earth's surface contained urban land cover, half of which was vegetated. Urban land cover was modeled over 20 years to increase gross global warming (warming before cooling due to aerosols and albedo change are accounted for) by 0.06-0.11 K and population-weighted warming by 0.16-0.31 K, based on two simulations under different conditions. As such, the urban heat island (UHI) effect may contribute to 2%-4% of gross global warming, although the uncertainty range is likely larger than the model range presented, and more verification is needed. This may be the first estimate of the UHI effect derived from a global model while considering both UHI local heating and large-scale feedbacks. Previous data estimates of the global UHI, which considered the effect of urban areas but did not treat feedbacks or isolate temperature change due to urban surfaces from other causes of urban temperature change, imply a smaller UHI effect but of similar order. White roofs change surface albedo and affect energy demand. A worldwide conversion to white roofs, accounting for their albedo effect only, was calculated to cool population-weighted temperatures by ;0.02 K but to warm the earth overall by ;0.07 K. White roof local cooling may also affect energy use, thus emissions, a factor not accounted for here. As such, conclusions here regarding white roofs apply only to the assumptions made.
IOP Conference Series: Materials Science and Engineering
In cities vegetated roofs are becoming more popular because they can mitigate Urban Heat Island phenomena by decreasing the outdoor air temperature in summer. This decrease reduces the electric energy demand for climatization of buildings, which, in front of a milder climate, will recur less to mechanical tools for guaranteeing thermal comfort conditions to occupants. Cities can registered another indirect positive effect: the reduced cooling energy demand, limits the heat released by the climatization systems' external unities toward the urban open spaces, thus lowering the outdoor air temperature. Therefore, the outdoor surface temperature of green, as well as cool roofs, can be assumed as an important design parameter for guaranteeing the sustainability of buildings and their approach toward an nZEB path. Obviously, designers and city planners must have at their disposal simple and effective tools for evaluating the economic feasibility of these two choices. This paper proposes a simple method to assess the economic effectiveness of green or cool roofs. It relies on the appraisal of the number of hours during which a building requires a cooling mechanical support for maintaining the indoor comfort conditions. This duty period of the cooling system is then simply converted into the cost of the needed electric energy.