Facing the Heat: India's Escalating Battle Against Rising Temperatures

The past year, 2023 was the hottest year on record with mean temperature nearing the critical 1.5⁰ Celsius threshold over 12 months and the trend continued in the first two months of this year. For India, 2023 was the second warmest year on record in the country since 1901. Projections reveal the current year may surpass this record as apart from April, the next two months may become unbearable in western, northern and eastern parts of India. Moreover, the coastal cities with high humidity and desert regions may give a feeling of anything around 42 to 45 degrees Celsius.

Given the forecast, Prime Minister Modi called a meeting last week to take stock of the preparedness for heatwave conditions and advised that governments at central, state and district levels must work in synergy.

The annual ‘State of Climate Report’of World Meteorological Organisation(WMO), says the global mean temperature in 2023 was 1.45⁰C -- 0.2 degree Celsius above the 1850-1900 average, turning it the warmest year in the 174-year history of record keeping. Besides, it broke records in all climate indicators, including greenhouse gas levels, ocean heat, sea level rise, Antarctica sea ice loss and glacier retreat.

It’s distressing touching the critical 1.5⁰Celsius threshold so early has negated the projection of the Paris Agreement, hailed globally. “Never have we been so close to the 1.5⁰ C limit of the Paris Agreement on climate change”, observed WMO Secretary-General Celeste Saulo, sounding the red alert to the world. Thus, the question now would be whether warming would reach 2 or 2.5⁰ C in the next two decades.

India observed a significant mean temperature increase of 0.15 degrees C per decade since 1950, according to a 2020 Ministry of Earth Sciences assessment. The observed warming is not occurring evenly across India. Warm days and warm nights have also increased at about seven and three days per decade, respectively, during 1951 to 2015 and even later. Currently, 23 States, mainly of plain and coastal regions, are considered more vulnerable to widespread heat impact. However, that doesn’t mean hilly states are safe. Although their maximum temperatures do not reach heatwave threshold levels of 45 degrees C, the population is experiencing higher temperatures compared to previous decades. 

The warming has been in focus for quite some time. A UN report about two years back, says India would become the worst climate-affected region in the world, specially applicable to the cities. Even this report could not contemplate that global warming of 1.5 degrees centigrade would be reached by 2023.

At the same time, the report predicted various trends which include: Rise in weather and climate extremes led to some irreversible impacts as natural and human systems are pushed beyond their ability to adapt; Approximately 3.3 to 3.6 billion people live under climate threat; Beyond 2040, climate change will lead to numerous risks and multiple climate hazard will occur simultaneously; Coastal cities are under severe climate risk which includes Mumbai, Chennai, Kolkata, Bhubaneswar etc.

Human health exposure to severe or continuous heat, leads to heat stress. When uncompensated, heat stress manifests as heat-related illnesses. Such illnesses range from superficial/mild and manageable (e.g. prickly heat, heat-related swelling, heat cramps, heat exhaustion) to a medical emergency (i.e. heat stroke). Heat stroke is the most severe of heat-related illnesses as it impairs brain function (i.e. stroke) due to uncontrolled body heating. It may turn into a critical condition that often turns fatal if there is a delay or failure in reducing body temperature by rapid, active cooling. Besides neurological impairment, high core body temperature (at least 40 degrees C), or hot, dry skin are other heat stroke symptoms.

Heat-related illnesses are not the only cause of emergency or mortality during hot summer days. Normal human body temperature stays within a narrow range of 36.3-37.3 degrees C. It maintains thermal balance through radiation (40%), evaporation (30%), convection (27%), and conduction (3%). Any external or internal condition that increases body temperature invokes various physiological responses changing cardiovascular, kidney, and metabolic systems, driven by increased blood flow to the skin and dehydration. Various studies have indicated that 90% of India is found to be vulnerable to heatwave impact.

Epidemiologically, it is important to note; in current scenario, whichever threshold is used to announce heatwaves, the health impacts of heat do not begin to occur only after those threshold temperature levels are crossed. Health impacts begin much before, even at moderate temperature levels. In terms of external factors, humidity plays a crucial role in creating heat stress by limiting our body’s major cooling mechanism: sweating.

Even at moderate temperatures, like 35 or 36 degrees C, if the relative humidity is 70%, it will feel like 50 degrees C to us. In terms of internal factors, heat’s impacts depend on the acclimatisation and build-up of heat stress in the human body. Acclimatisation is a gradual physiological adaptation (short-term) that increases heat tolerance as a person incrementally exerts in a hot setting for a few days. Air conditioning and comorbidities reduce our heat tolerance. Similarly, long-term adaptation occurs in people living in hotter regions over the years. Therefore, tourists from colder regions are particularly at risk of heat stroke.

The Union Health Ministry cautioned amid weather forecasts of excess days of heat waves across the country during Lok Sabha elections. The National Programme on Climate Change and Human Health (NPCCHH) advisory on extreme heat underlined that physical exertion, direct sun exposure and difficult access to shade and water may worsen the health of vulnerable people. Infants, and young children and people with cardiovascular diseases or high blood pressure are among the vulnerable populations. Not just stroke but heat related illnesses include heat rash, heat oedema (swelling of hands, feet and ankles) and fainting.

A study conducted in Kolkata for2021-22 summer found that indoor heat index levels in urban slum dwellings were 5.29 degrees C higher than outdoors. Dangerously high heat and humidity (at least 45 degrees C) remained for an average of about nine hours/day in urban slum dwellings compared to 2 hours a day in rural houses. These differences were particularly notable at night. During the coolest time of night, the insides of urban dwellings recorded a 6.4 degrees C higher heat index than outdoors, while the insides of rural houses recorded 1.3 degrees C above outdoor levels. Cement walls, clay tiles, corrugated tin roofs, fewer rooms, and crowding made urban slums dangerously hot.

Similarly, a study from Ahmedabad recorded an average 6.7 degrees C higher heat index at the locations where patients with acute heat illnesses were picked up by emergency medical services compared to what was recorded by the nearest weather station during the summer of 2016. At city level, such differences translate into an increase in all-cause mortality with daily city temperature. Hence, city-level temperature-mortality studies has become vital for heat-health action planning.

Adaptation measures to extreme heat are essential as the situation has the potential to change the course of irreversible planetary consequences. Due to rise in greenhouse gases, global warming has reached alarming levels. Even with all the commitments made by different nations and the very recent aim of targeting net zero emissions, large numbers of people in tropical countries, including India, will find it hard to live. Thus, every sector should seriously follow a health-centric adaptation focus to tackle the ongoing heat wave. This will also help us stay on course for the achievement of the SDGs

(This article is authored by Dhurjati Mukherjee)