Summary

Extreme heat that elevates core body temperatures has a significant impact on humans. It induces excess mortality, fatigue, and affects cognition. Extreme heat events are increasing in frequency, intensity, and length around the world.
South Asia is particularly at risk due to its high population density and low level of existing adaptations. Naively extrapolating present trends, under RCP 4.5, extreme heat will be responsible for 13.8M DALYs and reduce GDP by 2.4 to 4.5% by 2050.
Heat adaptation is a relatively neglected and underfunded area in South Asia and a potential funder can contribute to tractable solutions such as air conditioning and infrastructure adaptations to alleviate impacts in the short run. They can also fund research to improve measurement and forecasting of extreme heat events and find more efficient cooling solutions to limit additional GHG emissions.

Introduction

“In the morning the sun again rose like the blazing furnace of heat that it was, blasting the rooftop and its sad cargo of wrapped bodies. Every rooftop and, looking down at the town, every sidewalk too was now a morgue. The town was a morgue, and it was as hot as ever, maybe hotter. The thermometer now said 42 degrees, humidity 60 percent…People were dying faster than ever. There was no coolness to be had.” — Ministry for the Future, Kim Stanley Robinson

Kim Stanley Robinson’s climate fiction book, Ministry for the Future, opens with a devastating heat wave in India. A disastrous combination of heat and humidity yields wet-bulb temperatures beyond what the human body can handle, even in the shade. In the most densely populated region in the world, the heat wave kills over 20M people.

Severe South Asian heat waves are not a cli-fi fantasy. I read Ministry for the Future while in Delhi this April, when India and Pakistan experienced the hottest “spring” months since 1901. It was nearly impossible to stand in the sun for more than a few minutes between 10am and 5pm. Outdoor activities, the primary source of income for over 75% of the workforce, were restricted to the shade or to the slim windows near dawn and dusk. For weeks, temperatures over the South Asian plains, home to over 400M people, averaged at over 37°C. Some areas reported peaks of over 45°C.
Figure 1: Climate change will induce extreme heat waves around the world and over highest concentration of people in South Asia

Source: NASA GEOS-5, April 2022 (Map via @jscarto)

As climate change accelerates, South Asia will also face more frequent and longer periods of increasingly extreme heat. Effects are already being seen–in northwestern India, the number of days exceeding 40°C has increased from 25 / year in the 1970s to 45 / year in the 2010s. Though severe heat waves are also expected in other parts of the world, South Asia is home to deadly combinations of dense populations, high poverty rates, limited existing cooling infrastructure, and compounding effects of air pollution and water scarcity. ^[1]

One may ask: Heat waves have been a part of the weather cycle throughout history, so why are they a problem now? In particular, why can’t we expect humans to adapt to these changes, as they have throughout history?

Adaptation will be limited by the:

Intensity of climate change-induced heat (mean annual temperatures greater than 29°C).
Geographic scale and population densities impacted (one-third of the global population).
Incompatibility of urban societies with historical adaptations to extreme heat (nomadic and pastoral lifestyles of desert tribes).

Humans have only experienced such heat at significantly smaller scales in the past. The vast majority of humans throughout history have lived in a “narrow climatic envelope” characterized by a mean annual temperature (MAT) between 11 and 15°C. Under RCP 8.5, one-third of the global population will reside under MAT > 29°C, previously only found on 0.8% of the Earth’s surface, in the Sahara. Further, for the first time in history, the majority of the world’s population lives in urban areas. The urban heat island effect and crowding will further exacerbate the effects of extreme heat.

Nearly 300M South Asians live in extreme poverty. They predominantly engage in outdoor labor and don’t have access to air conditioning. Heat will directly increase their mortality risk and cause significant cognitive and health impairments, which will in turn impact well-being, productivity, and human capital accumulation.

These effects will set the region back on social and economic progress. South Asia’s growth trajectory has been slower than East Asia’s, which pulled large swathes of their population out of poverty on the back of economic liberalization. In South Asia, large scale economic growth has only taken place since economic liberalization in the 1990s. There has been significant progress on social indicators—female empowerment, education, minority rights—but most South Asians remain far from enjoying fundamental freedoms development must wrought.^[2] Under extreme heat, students’ learning outcomes will be demonstrably worsened. Intense temperatures will further limit already low female mobility in the region, as it will become too hot to step out during the day and too unsafe to do so after dark. Compounded across nearly a billion people, these effects will have disastrous consequences for the region’s development trajectory, potentially putting the countries permanently off the path of growth.

Heat will further exacerbate existing effects from air pollution and water scarcity in the region. South Asian air pollution accounts for 71.4M disability-adjusted life years (DALYs) annually, 3% of the global total. Water pollution alone contributes to 0.5M annual deaths in India. 68 to 84% of water sources in the region are contaminated and over 130M people lack access to safe drinking water. In combination, South Asians will experience extreme heat and they won’t be able to breathe or drink to save themselves.

Measurements

Zhao et al (2021) estimate there are over 110,000 annual deaths due to extreme heat in South Asia. Assuming 30 years of life lost per premature death, extreme heat already accounts for 3.4M DALYs per year in South Asia.

Under RCP 4.5, 55% of the population in South Asia is expected to experience maximum wet bulb temperatures exceeding 31°C by 2050, up from 15% currently. Extrapolating current trends, this will lead to 13.8M DALYs attributable to extreme heat annually. This figure is a naive extrapolation of the impact of excess mortality. Continuous exposure to extreme heat is also likely to increase the years of life lost due to disability across a wider range of the population and the true magnitude of DALYs is likely higher.

McKinsey & Co estimate that outdoor working hours lost will increase by 15% by 2030, leading to a $150-250B decline in GDP in India. A similar analysis of lost GDP due to reduced outdoor work estimates India, Pakistan, and Bangladesh will lose 3.2, 2.8, and 3.0% of their GDP respectively, amounting to over $530B in lost output across the subcontinent every year. McKinsey & Co estimates it would cost $110B to provide air conditioning to India’s heat-exposed population, pointing to a greater than 10-20x ROI over a decade of averted GDP loss.

Importance

Heat directly affects the human body, agriculture, infrastructure and the environment, though causal research remains patchy because it is difficult to distinguish heat’s impact from other channels.

The following analyses focus on the impact of heat on human mortality and cognition and makes contextual deductions necessary to understand the societal implications of these impacts. A more thorough estimation of total impact should also consider the impact of heat on agricultural yields, biodiversity, infrastructure sustainability etc.

The majority of research and evidence from South Asia focuses on India but I expect this will be broadly applicable to the South Asian region, and particularly to Bangladesh and Pakistan due to similarities in development trajectories, geography, climate, and culture.

I borrow from Turek-Hankins et al. (2021) to explore the impact of heat across three orders

Primary impacts in direct response to heat including excess morality, loss of productivity
Secondary impacts in response to primary impacts such as lost income, reduced population health outcomes
Third order impacts at an economy and society wide level such as societal inequity, decrease in economic growth

Primary impacts

Mortality

Human bodies have evolved to function in a narrow range of temperature. Extreme heat pushes the body to the brink by hindering its ability to thermoregulate, resulting in seizures, exhaustion, cardiovascular stress, and ultimately death. It exacerbates underlying health issues and disproportionately hurts the most vulnerable.

The human body’s upper limit for heat exposure depends on a potent mix of high air temperature and high humidity, which limits thermoregulation and reduces the effectiveness of typical adaptations like air conditioning. This mix of heat and humidity is captured through the “wet-bulb” temperature, while most news reporting relies on “dry-bulb” or “air” temperature which measures heat but not humidity. Wet-bulb temperature is measured through a “thermometer covered in water-soaked cloth over which air is passed.” At less than 100% relative humidity, the wet-bulb temperature is lower than dry-bulb temperature due to evaporative cooling.

Wet-bulb temperatures above the average human skin temperature (35°C) are considered hazardous as the humidity acts as the proverbial “cloth over the thermometer” preventing the human body from thermoregulating. Exposure to such temperatures for 6 hours is expected to cause mortality even in healthy young adults. However, the actual threshold for wet-bulb survivability might be even lower, dropping to as low as wet-bulb temperatures of 25°C (low relative humidity) in conditions where air temperatures exceed 50°C.

A third of heat-related deaths from 1991 to 2018 can be attributed to climate change. Globally, 0.5M annual deaths are estimated to occur due to heat-related causes, though this figure may be prone to underreporting as heat may be a trigger for other direct causes of mortality (e.g. heart attack). Most LMICs also lack quality all-cause mortality data as many deaths often occur outside of formal hospital settings. ^[3]

Estimates of excess mortality due to heat are thus hard to find and most existing studies focus on European settings which have very different baseline levels of adaptation compared to South Asia. However, extreme heat can have significant mortality impacts even in areas adapted to high temperatures. In Ahmedabad, Gujarat–a city where the daily mean summer temperature in May is 34.3°C–a 2010 heat wave pushed temperatures to 46.8°C leading to an approximately 40% increase in mortality for the time of the year.^, A longer term analysis of weather patterns in Varanasi found daily mortality increased by approximately 12% during heatwaves, defined as periods of three or more consecutive days where daily mean temperatures exceeded the 95th percentile of the annual mean (34.5°C).

Human capital

In addition to inducing excess mortality, heat directly increases the human body’s core temperature which induces fatigue and hampers cognition. A third of all global workers exposed to episodes of extreme heat experience persisting negative health effects. This limits human capital accumulation and productivity, which in turn has broader ramifications for economy and society.

Seemingly small changes in the body’s core temperature can lead to declines in several aspects of performance and coordination:

0.06°C: task performance requiring vigilance
0.2°C: multitasking ability
0.9°C: neuromuscular coordination
1.3°C: simple mental performance
3°C: dangerous heat stroke
5°C: death

Studies have uncovered a strong inverse relation between student’s learning outcomes and long-term heat exposure. For instance, Goodman et al (2020) measured the impact of heat exposure on a sample of 10 M students retaking the PSAT. They found that a 1°F hotter school year reduces that year’s learning by 1%, absent air conditioning.

South Asia’s population pyramid skews younger–70% of the subcontinent is below 30 years old. While this age structure has been hailed as the region’s “demographic dividend,” the region continues to see high unemployment rates, low skill accumulation, and slow structural transformation of the economy. Heat will further slow down human capital accumulation. The region’s schools are already under-resourced and rates of stunting (30.7%) and wasting (14.1%) amongst children are significantly higher than global averages (22% and 6.7%respectively).

The detrimental cognitive effects of heat also hurt the working age population by increasing rates of worker injury and reducing productivity. Park et al (2017) studied workers compensation claims in California from 2001 to 2018 and found that hotter temperatures lead to approximately 20,000 additional injuries per year. Heat’s direct effects on cognition limit concentration and lead to injuries in hazardous workplace environments. Reduced labor productivity also increases the opportunity cost of time on the clock, leading to cutting corners on safety protocols. They estimate that the annual financial costs of heat-related injuries in California alone may be between $0.75 and $1.25B, across health care expenditures, lost wages and productivity, and disability claims.

Over 75% of the labor force in India (and likely higher in other South Asian countries) is employed in informal, heat-exposed work. Such work is estimated to produce about 50% of GDP. Given the informal nature of most labor, these 400M people work in hazardous and hot industrial settings or outdoors, with little regulation and oversight. Extreme heat exposure will lead to lasting negative health effects and reduce worker productivity. As noted above, reduced outdoor worker hours will result in up to $530B lost output every year in the region by 2050.

Other impacts

Humans are not the only beings that will be affected by extreme heat. High temperatures hurt biodiversity, impact migratory patterns, lead to drought and contribute to further destabilizing fragile natural ecosystems.

Extreme heat will directly reduce agricultural productivity, contributing to lower yields and food insecurity. For instance, wheat yields can decrease up to 20% for every 1°C rise in temperature above 30°C during the reproductive phase. The 2022 heat wave in India reduced the wheat harvest by 4%, breaking a streak of increasing output for 5 years. Successive years of such temperatures will drastically reduce food stocks and create conditions for extreme food scarcity in the region.

Extreme heat events can also be direct triggers for “cascading impacts” across multiple systems, as in the case of India in 2003 and 2009 when concurrent heat waves and droughts impacted “agriculture, health, and economic sectors and caused water storage losses and electricity shortages.”

Secondary impacts

As outlined above, the poorest sections of society will be most impacted by extreme heat. They will face higher incidence of heat exhaustion and mortality, decreasing their ability to engage in outdoor manual labor demanded by the informal economy, resulting in lost income. Day-time mobility for people reliant on non-airconditioned modes of transport will also decrease during extreme heat episodes, further exacerbating inequalities and loss of potential income.

Worsened health and human capital outcomes from extreme heat will compound existing impacts of air pollution, which is also known to affect cognitive capacity and mortality. A study in California found that days of extreme heat and air pollution increased risk of mortality by 21%. Air pollution alone results in 71.4M DALYs annually, 3% of the global total.

Rapid adaptation to extreme heat through widespread air conditioning will also pose a double edged sword to overall health outcomes. Nearly 70% of South Asia’s energy is derived from fossil fuels and 15% of PM 2.5 emissions can be attributed to coal power plants. The energy system faces significantly higher loads in summer months, even as only 12% of households currently have air conditioning. As air conditioning expands and energy use increases, South Asia is likely to meet this demand through increased burning of fossil fuels which will further exacerbate the air pollution problem in the country.

Tertiary impacts

Heat’s impact on human capital will have devastating economy-wide consequences. In the short-term, the heat will lead to drastic losses in productivity. According to McKinsey & Co. estimates, India and Pakistan’s GDP could fall by 8 to 13% by 2050 due to the impact on outdoor labor. In the long-term, heat will successively reduce learning outcomes and human capital accumulation across generations delaying the regions’ structural transformation into the “knowledge economy.”

These economy-wide impacts will not be felt evenly. Costly adaptations to extreme heat will allow the richest segments of society to continue their lives largely unaffected — as they continue to operate in indoor, air conditioned spaces, while the majority of the working class population will bear the brunt of extreme heat. We can expect situations somewhat analogous to India’s experience with the Covid-19 shutdowns in 2020, which triggered the largest migrant crisis in the country’s history since Partition. Though the government implemented strict measures to ostensibly prevent the spread of Covid, only the most privileged had the luxury of sheltering in place while seasonal workers walked home over several days as economic activities in cities grinded to a halt.

In addition to lower income populations, women will be disproportionately affected by extreme heat. Women’s mobility and labor force participation is already severely circumscribed by strict gender norms and gender-based violence. Even as female literacy in India rose from 53.67% in 2001 to 65.46% in 2011 and GDP grew at 6 to 10% during this period, female labor force participation decreased from 35% in 2005 to 26% in 2018. Extreme heat will further limit women’s mobility, rendering them unable to leave the house during the day due to heat and at night due to lack of safety.

Even as South Asia is home to the largest population of people in extreme poverty, the region also has a growing incidence of obesity, high blood pressure, and heart disease. ~20% of the population is overweight or obese with higher rates in urban areas. Extreme heat will further reduce outdoor mobility and increase sedentariness in the population.

Neglectedness

Only 12% of households in India have access to air conditioning and under 5% of those earning less than $1000 USD (Figure 2). Air conditioning adoption correlates with hotter climatic conditions but is tempered by urbanicity and availability of electricity. Pavanello et al (2021) observe that while cooling degrees day values (a measure of days with wet bulb temperatures exceeding 24°C) are highest in West Bengal, Assam, Uttar Pradesh, and Orissa, these states do not see the highest rate of air-conditioning use due to rurality and lack of electricity, which also drives down the rate of refrigerator ownership.

Though 99% of Indian households are now “on the grid”, more than 23% of the population (304M) lacks reliable access to electricity, and rolling blackouts across swathes of the country are especially common in the summer. The burden of paying for electricity in India is also relatively high, with households spending 3.4-4.5% of their monthly expenditure on electricity.

Further, philanthropic funding for climate change interventions in South Asia focuses on clean energy. Climate change adaptations and interventions for cooling are negligibly funded, despite the high potential for cost-effective impact as outlined below.

There has also been relatively little work on exploring novel adaptations to extreme heat exposure or implementing heat action plans at scale. Additionally, most research studies that seek to empirically measure the impact of heat exposure are based in Western countries which tend to have more widely available data but may also lack local adaptations that exist in tropical regions and LMICs.

Figure 2: Climate, air-conditioning, and income characteristics in four selected emerging economies

Source: Pavanello et al, 2021

Tractability and Speed

Adapting to heat exposure is highly tractable in the short run through wider adoption of air conditioning. Air conditioning can demonstrably reduce the mortality impact of extreme heat, as observed over the 20th century in the US where heat-related mortality fell by 75% on days with mean temperatures higher than 27°C. No effects were observed on days with lower temperatures or deaths due to factors unrelated to heat like infectious disease, indicating that air conditioning was likely responsible for this decline.

In addition to air conditioning, heat action plans can also help combat heat in the short to medium run. Heat action plans are typically instituted by local governance authorities or disaster response bodies and involve multifaceted approaches to mitigating the impacts of heat exposure including:

Public awareness and behavioral changes: increasing awareness on signs of heat exposure, changing work and school schedules to minimize time outside in extreme heat
Emergency aid: drinking water supplied to outdoor workers, emergency air conditioning shelters
Small-scale infrastructure investments: applying heat-reflecting paint to roads, install cool roofs (reduce indoor temperatures by 2 to 5°C)

Additional structural changes may seem less immediately tractable, but can also directly reduce the impact of extreme heat in the longer term:

Large scale infrastructure investments: Improved urban planning and building codes to reduce the urban heat island effect and improve “shade, ventilation, and insulation” in existing buildings and new construction; Heat-reflectance at large scale (e.g. roads, pavements).
Research and development of higher efficiency cooling: Air conditioning, while extremely impactful in the short-run, may have compounding negative effects by exacerbating greenhouse gas emissions and the urban heat island effect (further details below). Investment in developing highly efficient ways of cooling will limit the cycle of continuous heating and cooling.
Strengthening healthcare systems: South Asia continues to have significant disparities in access to health care along lines of urbanicity (only 28% of Indian doctors are based in rural areas), socio-economic status, and caste. A stronger healthcare system will enable preventative treatments and emergency interventions in case of extreme heat events, driving down excess mortality and disabilities.
Structural transformation of economy to reduce reliance on outdoor labor: Reducing the proportion of South Asians engaged in outdoor labor will directly reduce population-wide exposure to extreme heat. Speedening the transition to the knowledge economy will enable more of the labor force to work indoors. However, extreme heat will also slow down the human capital growth required to realize this change, meriting earlier interventions in education and upskilling.

Potential Areas for Funding

Measuring wet-bulb temperatures and predicting extreme heat events
- Interventions are only as effective as our ability to forecast and prepare for extreme heat events. Current classification of “heat waves” largely relies on dry bulb temperatures which may not provide a complete picture of risk. Heat and humidity interact in complex and dynamic ways, often counteracting each other. There can also be significant local variation in wet-bulb temperatures based on the urban landscape, presence of water bodies etc. Investments to better measure and predict wet bulb temperatures can enable better targeting of interventions and increase preparedness through improved forecasting.
Improving air conditioning
- While air conditioning is an effective intervention against the impacts of extreme heat in the short-run, it also has the potential to exacerbate underlying issues increasing emissions of carbon and ozone-depleting hydrofluorocarbons (HFC) and increasing local urban temperatures
- 70% of South Asian energy is still generated from fossil fuels and air conditioning accounts for 40-60% of the energy load during peak summers in urban centers.^, There are currently approximately 30M installed room AC units in India, projected to increase to 55 to 124M by 2030. Extrapolating current trends, an increase in air conditioning will require 200TWh of electricity and emit 1.4B tons of CO₂ into the atmosphere by 2030.
- Additionally, while air conditioners cool the indoors, they also increase outdoor local temperatures by up to 1°C at night time. In highly dense urban areas, this will compound the urban heat island effect and further increase local temperatures in the event of a heat wave.
- The Rocky Mountain Institute estimates that a 5x more efficient air conditioning solution (which has 1/5th the climate impact of current air conditioners through reduced electricity use and lower emissions) is realizable at scale and can globally save over $1.4 trillion in investments required to meet the energy demand at current trends. A grantmaker can help supercharge these initiatives by funding additional research, especially localized to the energy and climate contexts of South Asia. For instance, RMI funded a “Global Cooling Prize” along with the Indian government to create a platform for innovation and collaboration from major companies in the space. Grantmakers can also fund lobbying for regulatory changes to increase the speed of market adaptation to greater efficiency.
Support and prioritization of existing cooling action plans
- There is already an expansive body of research on cooling and adaptation in India (with learnings potentially transferable to other South Asian countries), with a particularly notable national Indian Cooling Action Plan released by the Government of India in 2019. A grantmaker can support additional research to identify the highest impact and cost-effective interventions and fund their deployment at scale through local partners.
Protecting the most vulnerable
- As outlined above, South Asia’s most vulnerable will face disproportionate risk from extreme heat. McKinsey & Co estimates it would cost $110B to provide air conditioning to India’s heat-exposed population. A grantmaker in the area can fund the construction of air conditioned emergency shelters to combat short-term impacts in high-risk areas.
- South Asia also has a history of rights-based social welfare, codified in India through the rights to food, employment, and information. There may be additional scope for codifying a “right to cooling” to fuel prioritization of interventions to enable universal access to cooling such as updated housing codes, subsidies, distribution programs etc.^[4]
Increasing rate of substitution to clean energy
- To pre-empt increased emissions from air conditioning, a grant maker can fund programs that help add renewable energy capacity rapidly and at scale, though this area has relatively more attention in South Asia and is unlikely to be significantly neglected.

Sources of Uncertainty & Areas for Further Investigation

This document is closest to a “shallow” investigation and requires significant additional research to provide clearer guidance on paths to impact in this area and evaluate the cost-effectiveness of various interventions in this area.

Key uncertainties and additional areas for investigation are related to the following questions:

How truly neglected is adaptation to heat exposure in South Asia? A range of actors, ranging from individuals and communities to governmental and international institutions, participate in climate change adaptation every day. These adaptations often occur implicitly, as actions are in response to discrete triggers (e.g. heatwaves, inability to function during peak daytime hours etc.) but fall into a larger pattern of adaptation across the continent, with vast aggregate effects. It’s difficult to measure the existing levels of such adaptation. Is additional funding or exploration needed in the area or will the force of the heat automatically lead to all actors prioritizing adaptation urgently?
How will extreme heat affect ecological and infrastructural systems? I focused on the direct impacts of extreme heat on humans, as measured through DALYs and reduction in GDP. What will be the impact of extreme heat on non-human animals and ecosystems? Are there any effective interventions to prevent potential ecosystem collapse? How does extreme heat strain the built environment and infrastructure? Can it trigger large-scale cascading effects across infrastructure? E.g., what is the risk of a large power grid outage or dam collapse due to extreme temperatures?
What is the threshold of human tolerance? As David Wallace Wells writes, South Asia has already witnessed some heat waves that in theory “should” have caused catastrophic mortality but did not, likely because these heat waves were “dry” and wet bulb temperatures did not exceed the threshold for tolerance. It is also possible that we are significantly underestimating the threshold of human tolerance to extreme heat and it will take much greater increases in temperature to cause a mass mortality event. However, as discussed above, mortality is only one of several dimensions of impact and the decrease in human capital accumulation is also likely to cause irreversible economic and societal damage.
What is the likelihood of there being highly effective, novel cooling interventions that are yet to be discovered? This cause exploration has largely focused on traditional cooling interventions such as air conditioning. What is the likelihood of their being a completely new cooling paradigm that is not being widely considered yet? Are there any unique interventions that are not already being explored or significantly resource constrained? Can South Asian countries consider controlled geo-engineering interventions?
Are resources better used in climate mitigation or adaptation? Existing work on climate change interventions aim to address the root cause and limit warming. Is it more valuable to double down on such geoengineering and mitigation interventions or begin to channel resources to adaptation?

^
For example, while the Gulf countries already experience extraordinarily high temperatures, most households have had air conditioning for decades reducing the impending costs to adapt to climate change induced temperature extremes.
^
Sen, Amartya, 1933-. Development as Freedom. New York :Anchor Books, 2000.
^
Similar issues have plagued attempts to count Covid-19 deaths in South Asia. While the Government of India has reported 0.5M Covid-19 deaths, the WHO estimated over 4M excess, pandemic-related deaths occurred in the country between 2020 and 2021.
^
The Government of India has a history of providing targeted subsidies to households for cooking gas, water, and electricity. Such programs can be used as a platform to advocate for a right to cooling as well.

Cause Exploration: Adapting to Extreme Heat Exposure in South Asia