Temperature-related mortality and climate change in Australia
Authors: Thomas Longden
Journal: The Lancet Planetary Health (2019)

Temperature-related mortality is one of the main measures used to assess the costs and benefits associated with climate change. Some assessments have found a net benefit of climate change due to reduced cold temperature deaths offsetting increases in heat-related deaths.1Gasparrini A Guo Y Sera F et al.Projections of temperature-related excess mortality under climate change scenarios.Lancet Planet Health. 2017; 1: e360-e367Summary Full Text Full Text PDF PubMed Scopus (354) Google Scholar, 2Guo Y Li S Li Liu D Chen D Williams G Tong S Projecting future temperature-related mortality in three largest Australian cities.Environ Pollut. 2016; 208: 66-73Crossref PubMed Scopus (54) Google Scholar, 3Vicedo-Cabrera AM Guo Y Sera F et al.Temperature-related mortality impacts under and beyond Paris Agreement climate change scenarios.Clim Change. 2018; 150: 391-402Crossref PubMed Scopus (81) Google Scholar Antonio Gasparrini and colleagues1Gasparrini A Guo Y Sera F et al.Projections of temperature-related excess mortality under climate change scenarios.Lancet Planet Health. 2017; 1: e360-e367Summary Full Text Full Text PDF PubMed Scopus (354) Google Scholar and Vicedo-Cabrera and colleagues3Vicedo-Cabrera AM Guo Y Sera F et al.Temperature-related mortality impacts under and beyond Paris Agreement climate change scenarios.Clim Change. 2018; 150: 391-402Crossref PubMed Scopus (81) Google Scholar found a net benefit of climate change for Australia, a surprising outcome given that other regions that experience cooler weather were associated with a net cost of climate change. Examples of the regions that were associated with a net cost of climate change in Gasparrini and colleagues'1Gasparrini A Guo Y Sera F et al.Projections of temperature-related excess mortality under climate change scenarios.Lancet Planet Health. 2017; 1: e360-e367Summary Full Text Full Text PDF PubMed Scopus (354) Google Scholar and Vicedo-Cabrera and colleagues'3Vicedo-Cabrera AM Guo Y Sera F et al.Temperature-related mortality impacts under and beyond Paris Agreement climate change scenarios.Clim Change. 2018; 150: 391-402Crossref PubMed Scopus (81) Google Scholar reports include North America, Central America, central Europe, southeast Asia, South America and southern Europe. In comparison to these regions, why Australia would have a net benefit from climate change is unclear, as it is a country associated with extreme heat rather than extreme cold. In 2018, I reported that Australian cities were adversely impacted by heat and had little cold-temperature mortality in an article published in Climatic Change.4Longden T Measuring temperature-related mortality using endogenously determined thresholds.Clim Change. 2018; 150: 343-375Crossref Scopus (8) Google Scholar The corresponding temperature-mortality relationship is a J-shaped curve, rather than the U-shaped curves reported by Gasparrini and colleagues.5Gasparrini A Guo Y Hashizume M et al.Mortality risk attributable to high and low ambient temperature: a multicountry observational study.Lancet. 2015; 386: 369-375Summary Full Text Full Text PDF PubMed Scopus (20) Google Scholar This J-curve relationship implies that climate change is likely to increase the number of deaths in Australian cities in the future. A J-shaped curve has been reported before6Dang TN Seposo XT Duc NHC et al.Characterizing the relationship between temperature and mortality in tropical and subtropical cities: a distributed lag non-linear model analysis in Hue, Viet Nam, 2009–2013.Glob Health Action. 2016; 9: 28738Crossref PubMed Scopus (33) Google Scholar, 7Lee W Kim H Hwang S Zanobetti A Schwartz JD Chung Y Monte Carlo simulation-based estimation for the minimum mortality temperature in temperature-mortality association study.BMC Med Res Methodol. 2017; 17: 137Crossref PubMed Scopus (19) Google Scholar, 8Egondi T Kyobutungi C Kovats S Muindi K Ettarh R Rocklöv J Time-series analysis of weather and mortality patterns in Nairobi's informal settlements.Glob Health Action. 2012; 5: 19065Crossref Scopus (62) Google Scholar, 9Cui Y Yin F Deng Y et al.Heat or cold: which one exerts greater deleterious effects on health in a basin climate city? Impact of ambient temperature on mortality in Chengdu, China.Int J Environ Res Public Health. 2016; 13: 1225Crossref Scopus (17) Google Scholar, 10Sim G Kim H Zanobetti A Schwartz J Chung Y Non-parametric Bayesian multivariate metaregression: an application in environmental epidemiology.J R Stat Soc Ser C Appl Stat. 2018; 67: 881-896Crossref Scopus (3) Google Scholar and is more appropriate for a country known for having winters that are much milder than those in North America and central Europe. Although Gasparrini and colleagues1Gasparrini A Guo Y Sera F et al.Projections of temperature-related excess mortality under climate change scenarios.Lancet Planet Health. 2017; 1: e360-e367Summary Full Text Full Text PDF PubMed Scopus (354) Google Scholar used a statistically determined minimum mortality temperature to distinguish between heat-related and cold-related mortality, this reference temperature can be quite warm. For example, the minimum mortality temperature for Melbourne was very high and equal to the 90th percentile (ie, an average daily temperature of 22·4°C compared with the mean average daily temperature of 18·1°C reported for Australia).1Gasparrini A Guo Y Sera F et al.Projections of temperature-related excess mortality under climate change scenarios.Lancet Planet Health. 2017; 1: e360-e367Summary Full Text Full Text PDF PubMed Scopus (354) Google Scholar A high minimum mortality temperature could mean that deaths during average temperatures are associated with cold-related mortality rather than being treated as deaths during moderate (usual) temperatures. By contrast, in my article4Longden T Measuring temperature-related mortality using endogenously determined thresholds.Clim Change. 2018; 150: 343-375Crossref Scopus (8) Google Scholar I used endogenous threshold regressions and a temperature measure that accounts for acclimatisation to distinguish between heat-related and cold-related mortality. This Excess Heat Index that accounts for acclimatisation (EHI_A) is part of the Excess Heat Factor produced by the Australian Bureau of Meteorology. It is the 3-day average temperature minus the 30-day average temperature. The measure has a mean of 0°C, which is a useful reference temperature that can be compared with 3-day periods that are hotter or colder than the previous 30 days. To distinguish between heat-related and cold-related mortality, I used the thresholds determined by this estimation technique to classify the estimated mortality into the number of deaths during cold temperatures (EHI_A at <−3·51°C), moderate temperatures (EHI_A at ≥−3·51°C and <1·95°C), hot temperatures (EHI_A at ≥1·95°C and <7·26°C), and extreme heat (EHI_A at ≥7·26°C). Consistent with the thresholds estimated, most temperature-related deaths in Australia were associated with high and extremely high temperature events. In some regressions a negative relationship with cold temperatures was apparent, which is plausible given that winters in Australia are quite mild. My article indicated that the risk from future temperature events in Australian capital cities will be associated with extreme heat and hot temperature events rather than cold temperature events, in contrast to the previous results.1Gasparrini A Guo Y Sera F et al.Projections of temperature-related excess mortality under climate change scenarios.Lancet Planet Health. 2017; 1: e360-e367Summary Full Text Full Text PDF PubMed Scopus (354) Google Scholar, 3Vicedo-Cabrera AM Guo Y Sera F et al.Temperature-related mortality impacts under and beyond Paris Agreement climate change scenarios.Clim Change. 2018; 150: 391-402Crossref PubMed Scopus (81) Google Scholar, 5Gasparrini A Guo Y Hashizume M et al.Mortality risk attributable to high and low ambient temperature: a multicountry observational study.Lancet. 2015; 386: 369-375Summary Full Text Full Text PDF PubMed Scopus (20) Google Scholar I believe that further analysis is warranted to confirm whether the reference temperatures used to distinguish between heat-related and cold-related mortality are appropriate given the prevailing climate in Australia. I declare no competing interests. Projections of temperature-related excess mortality under climate change scenariosThis study shows the negative health impacts of climate change that, under high-emission scenarios, would disproportionately affect warmer and poorer regions of the world. Comparison with lower emission scenarios emphasises the importance of mitigation policies for limiting global warming and reducing the associated health risks. Full-Text PDF Open AccessTemperature-related mortality and climate change in Australia – Authors' replyWe thank Thomas Longden for his Correspondence, in which he offers insightful comments on some publications from our research team on temperature-related mortality projections under climate change scenarios.1,2 His letter provides us with the opportunity to discuss some aspects in more detail, and to clarify specific debated issues. Full-Text PDF Open Access