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Sustain to gain: March 2013 Archives

Our cities heat up. Urbanization and changes in natural environment, such as substitution of urban vegetation with impervious surfaces, formation of urban canyons and decrease in natural albedo can lead to an increase in urban temperature: the so called urban heat island (UHI) effect (Landsberg, 1981). In summer, the increase in urban temperature affects people with physical and social vulnerability (WHO, 2009) increasing the heat-related mortality (Basu and Samet, 2002). Urban adaptation strategies - such as the increase in urban albedo - can contribute to decrease urban summer temperatures and to prevent from summer weather-related mortality.

Life Cycle Assessment (LCA) is considered a useful tool for decision-makers. However, in its current use, it does not consider the contribution of the interaction between surface albedo and urban environment among the environmental burdens. The variation in albedo is able to affect global climate (i.e., radiative forcing), local climate (i.e., UHI adaptation) and micro-scale (i.e., life cycle inventory of the roofs).

A new study by Tiziana Susca (2012a) proposes an enhancement of the current use of LCA considering a multiscale approach. It includes the evaluation of the potential change in impact on global, meso and micro-scale due to the increase in urban albedo. In particular, the author developed a methodology to include in LCA the effect that the decrease in temperature - due to the citywide albedo - has on human health. The theoretical framework was applied to the case study of the New York City´s rooftops. New York City is plagued by a UHI of about 2°C (Susca et al., 2011) and it is the most populous city in the U.S. This means that the decrease in summer temperature can positively affect a large number of people.

The main aim of the research was to evaluate the contribution of surface albedo in affecting the impact on global climate and on human health. A functional unit of one square meter of white roof was evaluated in the time-horizons of 50 and 100 years. An increase in the urban-wide rooftop albedo from 0.32 to 0.9 - the maximum value that a surface albedo can reach - was proposed. Through the use of an existing climatological model developed by Oleson and colleagues (2010) the mitigation in urban summer temperature in the City was evaluated. The effect on human health was evaluated through the use of both statistical (i.e., life expectancy for different classes of age) and epidemiological data (i.e., risk ratio related to the number of deaths for natural cause in New York City). The mitigation in summer mean temperatures was translated in Disability Adjusted Life Years, the metric that LCA uses for the evaluation of the impact of products, services and goods on human health. The impact on global climate related to the variation in rooftop albedo was calculated through the use of a time-dependent climatological model developed by the same author (Susca, 2012b).

The results of the study show that surface albedo decreases the impact on climate change of one square meter of roof by approximately 84% and on human health of about 3% in a time-frame of 50 years. Besides, in a time-horizon of 100 years the estimation of the effect of surface albedo respectively on global climate and on human health shows a decrease in the impact of 70% and 6%.

The study shows that surface albedo is an important optical characteristic that should be considered in LCA application. Furthermore, the study highlights the importance of the use of a multi-scale approach in LCA that considers the multiple interactions with the urban environment.   

References:

Basu, R. and J. M. Samet. 2002. Relation between elevated ambient temperature and mortality: A review of then epidemiologic evidence. Epidemiologic Reviews 24: 190-202

Landsberg, H. E. 1981. The urban climate. International Research Series, Vol. 28. New York, NY, USA: Academic Press

Oleson, K. W., G. B. Bonan, and J. Feddema. 2010. Effects of white roofs on urban temperature in a global climate model. Geophysical Research Letters 37. doi:10.1029/2009GL042194

Susca, T. 2012a. Multiscale Approach to Life Cycle Assessment Evaluation of the Effect of an Increase in New York City´s Rooftop Albedo on Human Health, Journal of Industrial Ecology, 16 (6), 951-962

Susca, T. 2012b. Enhancement of life cycle assessment methodology to include the effect of surface albedo on climate change: Comparing black and white roofs. Environmental Pollution 163: 48-54

Susca, T., S. R. Gaffin, and G. R. Dell'Osso. 2011. Positive effects of vegetation: Urban heat island and green roofs. Environmental Pollution 159 (8-9): 2119-2126

WHO (World Health Organization). 2009. Protecting health from climate change. Connecting science, policy and people. Accessed May 2011 http://whqlibdoc.who.int/publications/2009/9789241598880_eng.pdf.