Alberto Salvo, Associate professor at the Department of Economics, Faculty of Arts and Social Sciences, National University of Singapore/ Today Online
News reports of a study I authored, published in Nature Communications last month, have put the spotlight on how different segments of society may be affected by climate change.
What can we infer from the findings given that the global climate is changing and researchers and policymakers are trying to understand the impacts of rising temperatures on societies around the world?
Scientists use unseasonal weather fluctuations — say a warmer versus cooler summer — to examine how heat affects a range of socioeconomic variables that we care about, such as public health, worker productivity, industrial output, commuter behaviour, school test scores, and so on.Specifically, consider the ways in which people protect themselves from excess heat.
Earlier studies have credited the energy-hungry air conditioner with a decline in heat mortality in the United States over the past century, as well as lower heat mortality in the US than in poorer India, where adoption of air conditioning remains low.In Europe, fewer excess deaths during 2018’s hot summer compared to an earlier heat wave in 2003 may be due to increased adoption of air conditioners during the 15 interim years.
Another study by my colleagues, published this month in the Proceedings of the National Academy of Sciences, quantifies a large response to heat by residential electricity consumers in Shanghai, China.
On warm days (above 25 °C), a 1 °C increase in daily temperature raises household electricity use by a staggering 15 per cent.Shanghai is one of China’s richest cities, with a near 100 per cent penetration rate of air conditioners in residences, comparable to 90 per cent in the US and Japan.The price of buying and operating an air conditioner has fallen so fast relative to incomes that Shanghai households do not
hesitate to turn their appliances on when temperatures rise.Households need to protect themselves from environmental stress as best they can, yet it is ironic that increased electricity demand to cope with heat often leads to more burning of fossil fuels to supply the electricity, which in turn leads to greater greenhouse gas emissions and higher temperatures in the future.In contrast to rich areas in Asia and the US, only 8 per cent of the three billion people living in the tropics currently have access to air conditioning.This brings us to the question, absent air conditioners, how do households seek relief from heat?
To study this question, I examined the combined electricity, water and town gas bills of about 130,000 anonymous households in Singapore over more than three years.Daily temperatures in Singapore range between 24 and 31 °C, depending on the time of the year, and relative humidity averages 76 per cent.
Tropical Singapore is unique in that, despite its overall wealth, not everyone has an air conditioner at home.
For example, less than 20 per cent of households in 1-room and 2-room flats had an air conditioner during the period of study.I found that households in 1-room and 2-room flats — which tend to have lower per-capita incomes compared with households in other types of dwelling — significantly increase their water consumption when temperatures rise.A 1 °C increase in daily temperature raises these households’ water use by 1-4 per cent. Specifically, a +1 °C heat shock induces an increase in water use equivalent to one additional daily shower for every 2.3 households living in 1-room flats.In comparison, households in dwelling types with higher mean per-capita incomes, such as 5-room flats and condominiums, do not respond to heat stress by raising water demand.As in the Shanghai study, it is their electricity consumption that shows a steep response to temperature. Needless to say, air conditioners are prevalent among more affluent households.