These people were the victims of the worst natural calamity that hit France, and probably the first recorded victims of climate change. Temperatures were over 40°C for nearly two months, even reaching 41.1°C at some parts of the country.

At the time, this was perceived as a one-off event.

But a study — Global, regional, and national burden of mortality associated with non-optimal ambient temperatures from 2000 to 2019: a three-stage modelling study — published in July 2021 found that 9.4% of global deaths each year are attributable to heat or cold exposure, equivalent to 74 extra deaths per 100,000 people.

And extreme weather events are only now starting to hold our attention.

“Central Asia Heat Wave: Another brutally hot day with 48.7C in Iran and crazy hot at high elevations: Tabas (710m) 29.5/46.7 Bam (920m) 33.6/45.7 Khor (921m) 46.4 2 days ago 44C in Tajikistan,45C in China,38C in Siberia Next day's Tajik national heat record will be threatened,” tweeted Maximiliano Herrera, a climatologist and weather historian, on June 19.

These temperatures are after the Earth recorded its third warmest May since measurements began in 1850, according to Berkeley Earth.

However, for India, the threat appears more urgent.

Over the last week, more than 100 people have died in three eastern states -- Uttar Pradesh, Bihar, and Odisha. The reason: Officially, yet to be found; unofficially, heat stress.

Doctors in the region said that extreme temperatures aggravated pre-existing ailments among the victims who were mostly over 60 years of age.

One of the doctors, from Uttar Pradesh's Ballia district hospital, was later shunted out and circumstances of his transfer remained unclear. But, one must look at what stands out in the doctors' statements: Extreme heat aggravated pre-existing ailments.

First, the extreme heat.

While high temperatures raise the risk of hyperthermia or heatstroke, even lower temperatures, when coupled with high humidity, can be dangerous as the body struggles to cool down through perspiration.

Temperatures, combined with relative humidity and wind speed, represent the heat index or the “feels like temperature”, which is a more accurate tool to assess risk.

On Sunday, when UP's Ballia district reported 14 more deaths, a maximum temperature of 45.5 degrees C was recorded, along with a relative humidity of 31%. This means that HI actually stood at around 51 degrees Celsius.

Prolonged exposure to a heat index between 40-54°C is associated with heatstroke.

According to India Met Department (IMD's) Climatological Tables, climate normals for the period 1991-2020, the mean daily maximum temperature for the district is 37.3 degrees Celsius and mean relative humidity is 63%.

Thus, the district was under a scorching heatwave, recording maximum temperatures at least four degrees above normal for most of last week.

And these are temperatures that do not consider the Urban Heat Island effect. 

Urban Heat Islands occur when cities replace natural land cover with dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat. (Think malls where once it was an unkempt forested wasteland.)

The sun’s heat and light reach the rural and the urban areas the same way. The difference in temperatures, thus, has to do with how the surfaces in each area absorb and hold heat.

And as the saying goes, it is no rocket science that plants absorb heat better than cement, steel, and glass.

Now, on to the second part of the doctors' statements: aggravation of pre-existing ailments. There are several ways extreme heat affects the human body.

Skin: Excessive exposure to the sun's ultraviolet rays can cause sunburn, and the more the body is subjected to it, the more likely to lead to skin cancer.

Brain: Hot weather has been linked to reduced cognitive function and a higher risk of occupational injury.

Perspiration: The hypothalamus acts as the body's thermostat, sensing temperature changes, and making adjustments to keep it near 37C. It works by signalling blood vessels near the skin to dilate, which increases the amount of blood at the surface of the skin from where heat can thus be lost. However, this only works if the ambient air temperature is less than the body temperature. If not, sweat glands secrete sweat on the surface of the skin, where evaporation has a cooling effect. But, if a person is already dehydrated due to extreme heat, the body can no longer cool itself by sweating.

Lungs: High temperatures are accompanied by still air which allows pollutants to stagnate. This increases the quantity of ground-level ozone -- a gas produced when pollutants react chemically with sunlight. This ozone can reduce lung function.

Heart: As the body heats and blood vessels dilate, blood pressure falls. If the blood pressure drops too far, the risk of heart attacks rises.

Fatigue: When the body reaches abnormally high temperatures, it goes into a state of hyperthermia. But there are stages to it. The first is heat exhaustion, when the muscles start to slow down and fatigue sets in. It graduates to a heat syncope, when dizziness, visual disturbances, intense thirst, and nausea lead to fainting. The final, and often fatal, stage is heatstroke. This kicks in at 40C and symptoms include dry, hot skin and mental dysfunction.

Heatstroke often affects the functioning of organs, its effects persisting for up to a week, and has a mortality rate of 30-40%.

However, there is no way to quantify the human toll of extreme heat.

As in UP’s Ballia, the health machinery in India does not record heat-related deaths as such. Only the victim’s comorbidity is added as the factor and not the extreme heat that worsened it.

“There is no record of all-cause mortality. If we employed statisticians, and recorded all-cause mortality for a specific area, we will be able to tell when there is an uptick in deaths and correlate it with the extreme weather,” said Dr Dileep Mavalankar, director, Indian Institute of Public Health, Gandhinagar.

A large number of these deaths are preventable.

“We are not adequately perceiving the threat of extreme heat by not recording mortality. If we did, we could prepare infrastructure in advance,” Dr Mavalankar said. And the cure is simple. In most cases, patients only need ice packs, fanning, and cold water. In more severe cases, IV fluids.

The gap in implementation may also have to do with investment in health infrastructure.

According to a World Health Organization Global Health Expenditure database, India's expenditure on health dropped from 4% of its GDP in 2000, to 2.96% in 2020.

The central and state governments’ budgeted expenditure on healthcare touched 2.1% of GDP in the last financial year, according to the Economic Survey 2022-23.

Dr Mavalankar also cited the example of Cyclone Biparjoy, which hit the Gujarat coast on June 15, and involved activating the full might of the government machinery. According to official records, there were no casualties after the cyclone made landfall as most of the people in vulnerable areas were evacuated much in advance following IMD alerts.

IMD does not only issue cyclone alerts.

On June 12, the Met department issued an alert for “heat wave conditions over Uttar Pradesh, east and north peninsular India during next five days”. And there was little preparation for these warnings.

“Severe heat wave conditions very likely to continue in isolated pockets over Chhattisgarh, Odisha, and coastal Andhra Pradesh during next two days... Heat wave conditions very likely to continue in isolated pockets over south Uttar Pradesh, Gangetic West Bengal, Bihar, Jharkhand during next five days,” the bulletin said.

“Eastern India is under one of the worst heat waves in its history: Not only daytime but night temperatures are setting records including in Kolkata. Today Tmins (minimum temperatures) were 32C/33C in many stations," Herrera tweeted on June 17.

However, there is the issue of these alerts not reaching the most vulnerable: the manual workers slogging out in the sun, and the elderly suffering comorbidities.

For this, Dr Mavalankar says, “Activate your local networks. Issue alerts in the newspaper, give out ads on the radio, have speakers installed on rickshaws with people making announcements.”