Impact assessment of human health and energy consumption caused by urban climate change

The air temperature in Tokyo has increased by 3.0 ° C for the past 100 years and it seems to continue to increase by global warming in the future. This urban air temperature increase poses various environmental impacts in our society, such as hyperthermia, increase in the use of air conditioning, and so on. An effective air temperature reduction measure, which is one of the countermeasures against urban heat islands and adaptation measures for global warming, varies by time and location. In order to reduce the environmental impacts reasonably and totally, we need to grasp magnitude of various impacts by time and location in the past and the future with the same criteria.

For this purpose, we developed an environmental impact assessment model based on the endpoint-type life cycle impact assessment (LCIA) methodology to evaluate various environmental impacts with single index defined in LIME 1 (Itsubo and Inaba, 2005). Using this model, we assessed four kinds of impacts, namely heat-related disease including hyperthermia, cold-related disease, and energy consumption for heating/cooling, which are considered to be large and quantifiable. The previous survey showed that sleep disturbance is recognized to be the most significant problem caused by warming air temperature among Japanese residents (NIES, 2003). Therefore, we added sleep disturbance as the fifth impact.

The relationships among thermal/cold stress (including severe hyperthermia), sleep disturbance, and energy consumption with diurnal and nocturnal air temperature were quantified within the developed model as follows:

• Thermal/cold stress expressed among people of aged 65 and over was based on a previous research about the relationship between mortality rate and daily maximum air temperature by Honda et al (1998). We assumed that the years of life lost (YLL) by heat/cold stress would be 2 years as well the estimation of those caused by global warming (Itsubo and Inaba, 2005). 1 disability-adjusted life year (DALY) was estimated as 9.76 million Yen in LIME.
• There are no previous studies on thermal/cold stress among people under 65. But only severe hyperthermia was analyzed by Ono (2009). In this study, only severe hyperthermia among people under 65 was evaluated as thermal/cold stress among people under 65. YLL of an average person under 65 who died by hyperthermia was estimated to be 47.8 years.
• There are no available statistics about sleep disturbance caused by air temperature increase. With reference to the Japanese version of the Pittsburgh Sleep Quality Index (PSQI-J) (Doi et al, 2000), we surveyed relationship between quantitative sleep quality and nocturnal air temperature (Okano et al, 2008). Calculating years lived with disability (YLD) requires disability duration and disability weight of sleep disturbance. We assumed 1 day and 0.05 as these values, respectively.
• The relationship between various energy consumption and air temperature were referred to Narumi et al (2007). Those various energy consumptions also pose increases in emission of environmental burden including CO₂, SO_x, and NO_x. These events have impacts on our society such as depletion of resources, global warming, air pollution, and so on. We analyzed the environmental impact by energy consumption using life cycle inventory (LCI) analysis and LCIA on AIST-LCA ver.4, which mounts LIME as an LCIA calculating method and is the most widely used LCA software in Japan (JEMAI, 2007).

Additionally, we predicted air temperature in Tokyo in the next 70 years under IPCC SRES A2 scenario with pseudo global warming technique (Kimura and Kitoh, 2007) from a global circulation model (GCM)'s future prediction (Nozawa et al, 2007).

Using the above LCIA model and the air temperature data in Tokyo in the past and the future prediction, the environmental impacts by the increase in air temperature in Tokyo were evaluated.

Firstly, regarding the present environmental impacts caused by air temperature rise from 1973 to 2003, we found that sleep disturbance, which is small impact per capita but wide-spread in our society, has had large impact on our society. The air temperature increase in Tokyo during the recent 30 years brought 8.43 × 10⁸ Yen damage on heat stress of people aged 65 and over, 1.87 × 10⁹ Yen on heat stress of people under 65 (hyperthermia), -7.86 × 10⁹ Yen on cold stress (only people aged 65 and over), 1.35 × 10¹⁰ Yen on sleep disturbance, 3.28 × 10⁷ Yen on energy use in hot, -5.87 × 10⁷ Yen on energy use in cold (Negative values mean merits). Total damage is 8.31 × 10⁹ Yen. The damage on sleep disturbance is the most remarkable, while we obtain merit from reduction in cold stress from October to May.

Secondarily, we found that the next 70-year air temperature increase will give about five times more damage on our society than the present. Particularly, because diurnal air temperature will also increase while nocturnal air temperature largely increased in the past, heat stress including severe hyperthermia will significantly increase. Concretely, the air temperature increase of August in the future 70 years under IPCC SRES A2 scenario brought 1.80 × 10⁹ Yen damage on heat stress of people aged 65 and over (while the past 30-year air temperature increase brought 2.99 × 10⁸ Yen), 3.48 × 10⁹ Yen (4.95 × 10⁸ Yen) on heat stress of people under 65, - 3.12 × 10⁸ Yen ( -6.58 × 10⁷ Yen) on cold stress (only people aged 65 and over) , 6.89 × 10⁹ Yen (1.99 × 10⁹ Yen) on sleep disturbance, 2.14 × 10⁷ Yen (4.15 × 10⁶ Yen) on energy use in hot. Total damage is 4.99 × 10⁹ Yen (7.32 × 10⁸ Yen).

From the above result, it can be said that air temperature reduction measures to reduce nocturnal air temperature except reduction of air temperature in winter is effective for our society in the past and for the future. However, the impacts caused by diurnal air temperature increase may become more serious in the future. This study assessed only five kinds of impacts, so our findings are limited. The assessment on fatigue, mild hyperthermia, torrential rain, and biota, which are also considered to have large impacts, are the future tasks.