Effects of heat on human health

Researchers at the Barcelona Institute for Global Health (ISGlobal) has recently published 3 studies on the relationship between heat and human health. Two of the studies focused on analysing the relationship between temperatures and mortality. A third study developed a theoretical framework for estimating heat-related deaths.

“Understanding the factors that reduce susceptibility to extreme temperatures is crucial to inform health adaptation policies and combat the negative effects of climate change on our health”, says Hicham Achebak, researcher at the French Inserm and ISGlobal.

Heat and mortality

The conclusion of the first study is that heat increases the risk of mortality in patients hospitalised for respiratory diseases. Although the number of hospitalisations for these pathologies is higher in winter, the highest mortality occurs in summer. Heat was responsible for 16% and 22.1% of all fatal hospitalisations for respiratory diseases in Madrid and Barcelona, respectively, between 2006 and 2019. “Without effective adaptation measures in hospitals, global warming could increase the mortality burden of patients hospitalised for respiratory diseases during the summer period”, says Achebak, first author of the study.

“Without effective adaptation measures in hospitals, global warming could increase the mortality burden of patients hospitalised for respiratory diseases during the summer period”

Hicham Achebak, ISGlobal

A second study has found that air conditioning has reduced mortality from high temperatures in Spain by a third. The study uses mortality, demographic and socio-economic data from 48 Spanish provinces between January 1980 and December 2018. It concludes that air conditioning reduced heat deaths by 28.6% and extreme heat deaths by 31.5% between the late 1980s and early 2010s. Heating systems, on the other hand, reduced cold-related deaths by 38.3% and extreme cold-related deaths by 50.8% over the same period, despite an ageing population that has an increased vulnerability to temperature. According to the study, the reduction in mortality is more related to socio-economic development than to interventions such as heat-wave warnings.

Air conditioning has reduced mortality from high temperatures in Spain by a third

These data underline the importance of thermal comfort systems as an adaptation measure to climate change. They also highlight the problem of energy poverty among some population groups who cannot afford air conditioning or heating. The researchers note that there are large differences between provinces in the use of these systems. They also point out that these technologies can be dependent on energy sources that can contribute to global warming, and that it is therefore necessary to think about other thermal regulation strategies, such as the expansion of green and blue spaces in cities.

Global warming impact monitoring tools

For the development of adaptation strategies to global warming, studies that develop theoretical frameworks for studying, and also projecting, the relationship between rising temperatures and human health are also important. A third ISGlobal study analysed the best method for estimating temperature-related deaths.

The new theoretical framework was refined using data from 147 regions in 16 European countries between 1998 and 2004. The study concludes that the use of weekly or monthly temperature and mortality data leads to an underestimation of the impact of heat. For more accurate results, it is necessary to use daily data, as this helps to better establish the relationship between temperature and mortality.

This new model using daily data was used to re-estimate the mortality caused by record temperatures in 2022. The results show that mortality has been underestimated by 10.28%. Using daily data, the estimated number of heat-related deaths in Europe in 2022 is more than 70,000.

“These estimates can help design sustainable climate-based health early warning systems using publicly available data”

Rachel Lowe, Head of the Global Health Resilience Group at BSC

However, according to Joan Ballester Claramunt, ISGlobal researcher leading the EARLY-ADAPT project funded by the European Research Council, “in cases where daily data are not available, the use of weekly time series, which are easily accessible in real time at the European scale, provides a good approximation to the estimates obtained in the daily data model”. These estimates can help design “sustainable climate-based health early warning systems using publicly available data”, says Professor Rachel Lowe, Head of the Global Health Resilience Group at BSC.