Extreme temperatures have become the new normal, with 2023 being the hottest year in over a century and 2024 on track to surpass it. Prolonged periods of extreme heat and elevated humidity levels are serious public health risks including heat exhaustion, stroke, heart attack, chronic kidney disease, cognitive impairment, and death from internal overheating.
These effects are unequally distributed across world populations and regional vulnerabilities related to social, class, economic, and gender disparities. Extreme heat, especially when coupled with high humidity, is projected to displace 1-3.5 billion people worldwide by 2070.
Critical health risks
“The IECC 2024 Heat Stress Primer highlights the critical health risks posed by exposure to extreme heat, especially for outdoor workers in low-latitude regions like India. Exposure to higher temperatures and higher humidity levels impairs the body’s natural cooling processes, leading to heat-induced exhaustion, illness, and death. As 49% of India’s workforce is exposed to these hazardous conditions, IECC’s research stresses the urgent need for improved heat stress assessments and protective measures. Without swift action, hundreds of millions of workers, children, and older adults too, will face increasing exposure to life-threatening heat stress,” warn Primer authors Dr. Ashok Gadgil, Head of Research, Resilience to Climate Impacts at IECC and Elif Kilic.
Measuring Heat Stress
The two most widely used metrics for measuring heat stress are the wet bulb temperature and the heat index.
Recent research by Romps and Lu at UC Berkeley highlights that the National Weather Services approximation is biased low by approximately 10°C (approximately 20°F) during the peaks of severe heat waves in the US. The researchers extended the heat index to temperature and humidity combinations that were not accounted for in the earlier used Steadman model and allowed their model to include a reduction in metabolic rate and dripping sweat.
The extended heat index is valuable in assessing the risks of hyperthermia and fatality under extreme environmental conditions, as the previous heat indexes did not apply. However, this extension still only applies to healthy young American adults.
More data is needed for measuring heat stress on humans without access to shade and water, who are performing hard labor, in sunlight, and also those who are less than in optimal health, such as the elderly, sick, injured or populations in the developing nations.
Heatwaves Put Vulnerable Populations at Risk
People in developing countries in the tropics and subtropics generally do not meet the fitness levels, living conditions and/or occupations assumed in the Steadman model or the extended Lu and Romps model.
Climate vulnerabilities are unequally distributed, especially affecting regions like India, where a large portion of the workforce is exposed to extreme heat without adequate infrastructure for protection.
Heatwaves in India are starting earlier, lasting longer, and getting more intense. Between April and June 2024, India saw around 40,000 suspected cases of heatstroke and dozens of heat-related deaths. With a 3-degree celsius increase in global temperature, 197 cities will have more than 150 very hot days a year. More than half of these cities (103) are located in India. In the last five decades, India has experienced over 700 heatwaves, claiming the lives of more than 17,000 people.
Inadequate Warnings
Governments in nations facing extreme temperatures are currently left with highly imperfect tools to issue useful heat stress warnings to adequately protect outdoor workers and vulnerable groups. Accurate model predictions of physiological stress are crucial for protecting public health, guiding urban planning, and building climate resilience. Enhancing the extended heat index is an essential first step for addressing the growing threat of extreme heat events. Improvements on the extended heat index will be practically applicable in contextualizing and developing heat action plans, producing more accurate heat advisories and warnings that guide individuals to take necessary precautions during extreme heat events.
Impact of Extreme Heat on India’s Workforce
India has more than 350 million people working as informal labor with direct exposure to heat, while less than 10% of households have access to air-conditioning. The scorching temperature plus humidity conditions pose immediate health risks and threaten labor productivity and livelihoods.
More than 230 million people of India’s current working population are employed in the unorganized sector, in outdoor jobs such as in agriculture, construction, street vending, etc. They are exposed to the weather, and commonly also without shade from the sun.
After migrating from villages, many settle in urban slums where plastic and corrugated iron shelters trap heat, creating oven-like conditions, exacerbated by cities’ heat island effect and concrete’s poor insulation.
Summer daytime temperatures in mid- and northern regions regularly exceed 40°C (104°F), occasionally reaching 50°C (122°F). These temperatures are above the human tolerance limit of 36°C (96.8°F), beyond which conditions can become fatal. India’s infrastructure is insufficient to provide relief or protection from extreme weather events for a large fraction of its current population.
Heat Action Plans
“While the National Disaster Management Authority (NDMA) in India has issued guidelines for the prediction and management of heatwaves, these guidelines focus solely on dry heat, as the official definition of a heatwave does not account for the combined impact of temperature and relative humidity (heat index),” says Piyush Narang, Policy Analyst at IECC.
“Although around 19 states in India have prepared Heat Action Plans (HAPs) in response to NDMA guidelines, the HAPs do not adequately plan for long-term infrastructure interventions to prevent heat deaths, nor do these outline sufficient funding mechanisms for scaling up adaptation efforts. Another significant gap is the absence of heat waves from the list of notified natural disasters, implying that heat waves do not receive the same level of emergency response, funding, or resource allocation as floods or cyclones leaving rural and agricultural populations, already disproportionately affected by extreme heat, without adequate support for cooling centers, public awareness campaigns, or necessary infrastructure improvements,” says Narang.
Berkeley Institute Works With Indian Policymakers
The India Energy and Climate Center (IECC) collaborates with Indian policymakers and business leaders towards a tech-informed policy design, capacity building, a leadership dialogue platform, and south-to-south collaboration.
Given its geography, population, and socio-economic characteristics, India is highly vulnerable to extreme heat. By 2100, it is projected that India’s average surface temperature will be 3.4°C higher than pre-industrial levels.
“We have a clear strategy on heat resilience in India, now that we understand the gaps in the ecosystem,” says Shruti M. Deorah, Executive Director, IECC, Goldman School of Public Policy, UC Berkeley.
According to the Lethal Humidity Global Council , of all the dangerous impacts of the climate crisis, humid heat waves are one of the nearest dangers we face according to major scientific consensus.
While it is clear that strong climate change mitigation efforts are needed, it is also clear that extreme heat is already here and impacting people, especially vulnerable people in India and other developing countries in the tropics and the subtropics. We need to adapt to extreme heat fast.
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