The heatwaves that preceded the ongoing monsoon, with Odisha in particular witnessing a series of heat-related deaths, are likely to get deadlier and more frequent as temperatures rise across the globe. Two new studies, one of these specific to India, present an alarming picture of growing populations being exposed to heatwaves, with a greater likelihood of death.
The India-specific study, published in Science Advances on June 7, has found that even a small rise in temperature can make mass heat-related mortality events several times more likely. A rise of just half a degree in summer mean temperatures, it found, raises the probability of 100 or more heat-related deaths 2½ times.
The other study, published in Nature Climate Change Sunday, has found that almost a third of the world’s population is currently exposed to deadly climatic conditions for at least 20 days a year. This is going to get worse: even if greenhouse gas emissions are drastically reduced, half the world’s population will be exposed to such conditions for 20 days a year by 2100. And if the emissions continue to grow, it will expose three-fourths of the population.
Mass deaths likelier
The first study used data from the India Meteorological Department to analyse changes in summer temperatures and heat-related deaths between 1960 and 2009. Mean temperatures across India have risen by more than 0.5°C over this period, the study notes, and uses a probabilistic model to correlate that with deaths. When mean temperatures rise from 27°C to 27.5°C, it found the probability of mass heat-related mortality — more than 100 deaths — rises from 13% to 32%, or 2½ times (figure 1a).
Additionally, when the average number of heatwave days across India increases from six to eight days, the study found that the probability of mass heat-related deaths rises from 46% to 82%, or by 78% (figure 1b).
“Small increases in global temperatures can lead to large increases in the frequency and intensity of extreme events, including heatwaves, cold waves, droughts, and floods,” lead author Omid Mazdiyasni, a civil and environmental engineer at the University of California, Irvine, told The Indian Express. “Measurements of small increases in temperatures refer to the entire globe over several years; however, at a local and daily scale, you will see much greater fluctuations in extreme temperature and other climatic events.”
The publication of the study coincided with the Donald Trump administration’s decision to pull the United States out of the Paris climate agreement to cut down on emissions. “Of course, addressing climate change requires major commitments by all countries, and it is appearing to be a daunting task,” said earth system scientist Amir AghaKouchak, Mazdiyasni’s university colleague and co-author of the study, in reply to a question.
The other authors include a civil engineer each from IITs Bombay and Delhi.
“While it would be great if all countries can work together on the solution,” AghaKouchak told The Indian Express, “still all countries can work toward their own adaptation plans including raising awareness (e.g., people should be educated on what they should and should not do during extreme events), and improving local infrastructure to cope with extremes (e.g., access to air-conditioning in case of heatwaves).”
Larger populations vulnerable
The newer study analysed reports published between 1980 and 2014, and found 783 cases of excess heat-related mortality from 164 cities in 36 countries.
Based on the climatic conditions of those events, the researchers identified a global threshold beyond which temperature and humidity levels become deadly. Using a web-based app, the researchers counted the number of days in a given year when climatic conditions cross this threshold.
In Delhi, for example, the app forecasts that the threshold will be crossed on 81 days in 2100 even if strong mitigating circumstances come into play (figure 2a). In 2000, Delhi had crossed the threshold on 63 days. In the absence of any reduction in emissions, it will cross the threshold on 131 days in 2100 (figure 2b).
Worldwide in 2000, over 30% of the world’s population was exposed to 20 or more days when conditions surpassed the deadly threshold. In 2100, 47% of the population will be so exposed in the most aggressive mitigation scenario, which will go up to 74% if emissions continue to grow.
“Our attitude towards the environment has been so reckless that we are running out of good choices for the future,” said lead author Camilo Mora, a geographer at the University of Hawaii, who provided The Indian Express with materials of the study.
“Many people around the world are already paying the ultimate price of heatwaves, and while models suggest that this is likely to continue to be bad, it could be much worse if emissions are not considerably reduced,” the university website quotes Mora.