- High heat exposure will become a public health challenge, particularly affecting the elderly, outdoor workers, vulnerable health groups and those with lower incomes, warn experts.
- By 2100, many people living in tropical regions, such as India and sub-Saharan Africa, will be exposed to dangerously high heat levels during most days of the year, a study finds.
- Apart from short-term heat mitigation solutions, protecting or expanding green and blue spaces in cities, building city-specific heat action plans, climate-resilient urban planning and responsible heatwave communication, should become long-term strategies.
“When you switch the fan on, the air inside the room blows like fire,” 50-year-old Dolena Khatoon says with an emphasis on the word aagun which means ‘fire’ in the Bengali language. The ageing slum resident points to what appears to be a jumble of plastic tarpaulin, bamboo scaffolding, and tin, that makes up her home in the northern part of Kolkata, a metropolis in east India.
It is September and a short but intense evening spell has just preceded our chat outside her residence – one in a row of hundreds of such densely packed, matchbox-like shapes, haphazardly draped in heat-trapping materials like tin or plastic tarp.
Her neighbour, F. Khatoon, adds: “When we need some air, we move out and try to sit in the shade of a tree, because even in the evening the interiors seem to boil despite switching on the fan.” F. Khatoon’s is a family of 12 trying to cope with the high humidity and hot air trapped inside their window-less two-storey home, with four fans. Two are clasped to the ceiling and the rest are portable fans. “We got electricity connection only a couple of years ago; otherwise running a fan would have been a distant dream,” the 55-year-old says.
The Khatoons’ experience of heat stress is reflected in a series of recently published research on heat stress in elderly populations in a Kolkata (urban) slum and a rural village. “What it (the research) shows to me is that people living in those densely packed, low-rise housing in slums virtually bake all day long and all night long,” says American anthropologist and study co-author Charles Weitz, who studies the adaptability of humans to environmental stresses.
In their study on a Kolkata slum and a rural village 75 km from metropolis, Weitz and co-author Barun Mukhopadhyay found that the construction materials and the urban heat island effect combined to create hotter indoor and outdoor conditions throughout the day and particularly at night.
A public health challenge, particularly for the elderly
The authors of the heat stress study warn of a public health challenge given the decline in the human body’s capacity to deal with temperature-related stress with age, and with climate change making summer heat more extreme. According to a 2021 Lancet report, record temperatures in 2020 resulted in a new high of 3.1 billion more person days of heatwave exposure among older people than 65 years and 626 million more person days affecting children younger than one year, compared with the annual average of the 1986-2005 baseline.
“The physiological changes that occur with age are really quite profound. Elderly people are significantly less capable of retaining thermal equilibrium in hot or cold environments. We recently studied heat and that really produces significant problems for health. And particularly is a problem for people with existing comorbidities. So, people with diabetes with heart disease, which are all increased with age end up having a very difficult time managing in hot environments,” added Charles Weitz.
And stepping outside for relief from the heat could become even tougher in decades to come.
Why greenhouse gas emissions cuts are necessary
A new study projects that by 2100, many people living in tropical regions — such as India and sub-Saharan Africa — will be exposed to dangerously high heat levels on most days of each year. The findings suggest that carbon dioxide emissions from human activity could drive global increases in exposure to extreme temperatures in the coming decades, even if global warming is limited to 2˚C, in line with the Paris Agreement.
“So, just because of how much warming that we’ve baked into the system already, no matter what we do with emissions, there’s going to be exposure to unprecedented levels of heat stress, basically, no matter where you are in the world unless you’re at a very high latitude,” study co-author Lucas Vargas Zeppetello told Mongabay-India.
Without adaptation measures there may be large increases in the incidence of heat-related illnesses — particularly in the elderly, outdoor workers, and those with lower incomes — and more ambitious targets to reduce emissions are needed, the authors emphasise.
Zeppetello and colleagues estimated potential exposure to dangerous heat and humidity (using the United States’ Heat Index). A Heat Index above 103°F (39.4 degrees Celsius) is classified by the United States’ National Weather Service as ‘dangerous’ because of the likely onset of heat cramps and heat exhaustion. A Heat Index above 124°F (51.1 degrees Celsius) is classified as ‘extremely dangerous’ and can lead to heat stroke, a condition with a high mortality-case ratio that can lead to death within a matter of hours.
During the period 1979–1998, the dangerous Heat Index threshold (39.4 degrees Celsius) was exceeded on roughly five percent of the days each year, in the tropics and subtropics, and for 10–15% of the days each year, in subtropical Africa, the Indian subcontinent, and the Arabian Peninsula.
“Delhi had three days over that 20-year period, where the heat index got above this extremely dangerous level–it was bad enough to be extremely dangerous to be outside,” said Zepettelo, adding that such specifics are useful to policymakers.
What would happen if Indian cities crossed the 1.5˚C warming?
In a 2˚C warming scenario, Delhi could see eight days each year with extremely dangerous days when the Heat Index goes above 51.1 degrees Celsius (124 degrees Fahrenheit). In a worst-case scenario in which emissions remain unchecked until 2100 (roughly equivalent to a 3˚C warming), Delhi may have up to 30 days per year when it can get extremely dangerous to be outside.
In the same period (1979-1998), Kolkata, experienced roughly one event (day) every 2 years when the heat index soared above the extremely dangerous threshold (above 51.1 degrees Celsius). In a 2˚C warming there could be nine days each year when it is extremely dangerous to be outside while for the 3˚C warming, the extremely dangerous hot days could be 33 per year.
Zeppetello says that the difference between a two- and three-degree warming means “three times the exposure to extremely dangerous” heat waves that are still relatively uncommon in India (except Kolkata, where these events happen about once every two years).
Anthropologist Barun Mukhopadhyay says research on heat health effects on humans is necessary to build up the evidence base for policymakers to act on.
Another analysis of daily temperature and humidity data from April to July spanning 1990 to 2019 for four cities-Kolkata, Delhi, Mumbai and Chennai–reveals that extreme discomfort during heat or non-heatwave period was higher in Kolkata and Chennai than in other cities. “While the number of heat wave events in the Delhi region is higher than Kolkata, Chennai, and Mumbai for the study period, the risk of extreme heat stress is more in Kolkata and Chennai due to a combination of higher temperature and high humidity,” says earth system scientist Arun Chakraborty.
Chakraborty and colleagues at IIT-Kharagpur’s Centre for Oceans, Rivers, Atmosphere and Land Sciences used Humidity Index (HD) to evaluate the degree of discomfort and the Universal Thermal Climate Index (UTCI) to categorise the level of heat stress.
“The number of heat wave events in the Delhi region is significantly more than in Kolkata, Chennai and Mumbai but the possibility of extreme heat stress and dangerous-heat strokes in the Chennai region is higher than other metropolitan cities in both heatwave and non-heatwave periods,” Chakraborty says.
Climate change adaptation expert and IPCC (Intergovernmental Panel on Climate Change) lead author Chandni Singh says the findings in Zeppetello’s study are also corroborated by the IPCC Sixth Assessment reports. “We are already at average warming of 1.1 degree Celsius globally and approximately 0.7 degree Celsius (on average) in India. We know that even 1.5˚C global warming will increase extreme heat, hot nights, and humid heat severely across the Indian subcontinent, affecting poor and vulnerable populations disproportionately,” Singh at Indian Institute for Human Settlements, told Mongabay-India.
Apart from short-term strategies, including heat-proofing vulnerable livelihoods such as outdoor workers (through cooling shelters, altered work timings) or indoor workers (better ventilation) and deploying mitigation measures such as protecting/expanding green and blue spaces in cities, building city-specific heat action plans, enforcing measures around climate-resilient urban planning and building design, building institutional capacities around holistic heat management (that focusses not only on heat but second-order impacts on water, agriculture, industry sectors) can underline longer-term measures.
“It is important to understand that the best form of adaptation to heat is often mitigation, i.e. reducing greenhouse gas emissions that drive heating in the first place,” Singh notes.
Responsible communication is important for effective adaptation
Heatwave communication is also “an important part of effective adaptation”, say researchers studying social science dimensions of climate variability and change at University of Exeter, UK.
Saffron O’Neill who specialises in visual communication of climate change investigated the visual news coverage of the 2019 heatwaves in France, Germany, the Netherlands and the UK, using content and visual critical discourse analysis. The dominant type of images in all countries were photographs of people having fun in or by water.
Such disparity between the text and the visuals is problematic because by displacing concerns of vulnerability, it “marginalises the experiences of those vulnerable to heatwaves and these visual discourses exclude opportunities for imagining a more resilient future,” adds O’Neill, an associate professor in geography at the university.
Manju Bura, who is with O’Neill’s research group and is analysing heatwave visuals on Google Images in the Global South said initial observations point to a lot more stress on people coping with extreme heat. “What stood out was the fact that when it comes to Google Images, the most common images for heat waves in India and Kenya – countries that are highly vulnerable to the impacts of climate change but are considered to have lower readiness for adaptation – were generally of impacts of heat on daily life, but also on infrastructure,” said Bura.
These are images of roads melting and other images of people adapting to heat such as people under the tree and people with water sources or workers in helmets and protective covering.
“What we see in the Indian heatwave (the April-May 2022 spell) are images of people coping, just surviving in the extreme heat. So, it would be good to open up to other kinds of images to help move the conversation on from just coping, to options for adaptation,” O’Neill concluded.
Banner Image: Dolena Khatoon stands by the entrance of her home in Kolkata. Photo by Sahana Ghosh/Mongabay