Heat waves in India: A scorching indication of where inaction on climate change crisis will lead

Editor's note: From May 2017, Firstpost is featuring a fortnightly column by Mridula Ramesh, titled 'Climate Conversations'. In this column, we take a look at pressing issues pertaining to climate change — in an accessible way.

Not a one-size-fits-all heat wave

When I stepped out this morning, my eyes squinted to shut out the glare from the sun. After a minute or so, the top of my head prickled, and I began to pant. A few minutes later, I began to feel parched and a little dizzy, and so went indoors, swigged some water and cooled off.

When our body temperatures rise above 38 degrees Celsius, we begin to suffer from heat exhaustion, and our physical and mental functions begin to falter. When our body temperatures cross 41 degrees Celsius, our organs start to collapse, and the risk of death rises sharply.

Our skin temperatures, at 35 degrees Celsius, are about two degrees centigrade cooler than our core body temperature. When the outside temperatures begin to cross this skin temperature threshold, we take adaptive action – we move to the shade, drink plenty of water and we sweat. But not all of us can take this action. What if the only job available at hand involves working in the hot sun? What if one’s body could not cool itself down effectively, or if one were too weak to cope – or too sick perhaps? Or too old or too young?

These are not theoretical questions.

For the fortunate, higher temperatures may just mean higher air-conditioning bills. For others, midday commutes will have to be rethought, summer work hours will need to change, and factories, schools and offices will need to cool their insides as the mercury keeps rising. The additional cost this entails will need to be factored and managed. For the poor, heat stress may well prove to be fatal. For one, the jobs available to the poor – agriculture and urban manual jobs – require exertion while being exposed to the elements. And the poor cannot afford to refuse these jobs because there are precious few alternatives available.

Climate change and heat stress

As the climate has warmed, the death toll from heat exposure has been increasing – marching steadily upwards in lockstep with rising temperatures.

 Heat waves in India: A scorching indication of where inaction on climate change crisis will lead

Figure 1: Decadal death toll from heat waves (EMDAT database,http://www.emdat.be/) * 2011-2020 projected from 2011-2017 data

Add humidity to the heat and you have a prescription for disaster. Our body cools itself by sweating, and by the evaporation of that sweat. But if the environment is too humid, then the sweat cannot evaporate, and the body cannot cool itself.

Scientists define two temperature or heat thresholds — dangerous heat and fatal heat. Let’s start with dangerous heat: This happens when the wet bulb temperature exceeds 31 degrees Celsius.

What is wet bulb temperature? To understand this, take a regular mercury thermometer. Wrap the bulb in a wet muslin cloth and take the temperature of a room. This is called the wet bulb temperature. Now, if you repeated the same exercise with a perfectly dry thermometer you would get another reading, which will typically be higher than the wet bulb reading. As the humidity, or the water vapour present in the air increases, the wet bulb temperature approaches the dry bulb temperatures.

This is important from our body’s point of view. Because, as the humidity in the air increases, our body will find it harder and harder to cool itself, because it becomes harder for that sweat to evaporate. Which means at high humidity levels, health hazards happen at lower temperatures. Keep in mind that while today, temperatures in the hottest parts of our planet cross 50 degrees Celsius in the peak of summer, wet bulb temperatures have rarely exceeded 31 degrees Celsius, even in the hottest summers.

But that is going to change. By the end of this century, large parts of India are projected to experience these deadly humid heat waves. If we continue with our current pace of emissions, about three-quarters of our population is projected to experience a dangerous level of humid heat, compared to about 15 percent today.

Fatal heat is when wet bulb temperatures cross 35 degrees Celsius. Experts reckon this has not happened in recent times in our planet. But it is likely to happen in the coming decades and centuries if human-caused warming continues.

We make it worse – the urban heat island effect


Even if all countries reduce their emissions as per their commitments in the Paris Agreement, temperatures will still move up from where we stand today. Reuters

Experts project that a quarter of the world’s cities could warm by more than 7 degrees Celsius by the end of this century. That’s insane! But global warming per se contributes only part of this more-than-7-degrees warming. Our city planning contributes the other part – through what is called the urban heat island effect – that is, replacing our green spaces and water bodies with concrete. This extra heat will increase the demand supply gap in many cities’ water. It will increase demand, because when it is hotter, we need to drink more water and use it more in cooling our spaces. It will lower supply because a higher proportion of water will evaporate – meaning lower water levels in the reservoirs and canals. This only means ‘Day Zero’ will spread to more and more cities.

Also read on Firstpost: Cape Town's water crisis and lessons for Bengaluru: Resource management is the answer

But there is good news hidden in this depressing projection: we can cool our cities even while global warming continues, if we reverse the urban heat island effect. Hold that thought, we will come back to it.

What does this mean for India?

Even if all countries reduce their emissions as per their commitments in the Paris Agreement, temperatures will still move up from where we stand today.

This means, large parts of the Indian subcontinent will be become unfriendly to human life, at least during some parts of the year. South Asia is projected to see an internal migration of 35.7 million people by 2050, if we continue with business-as-usual. These millions would leave Bangladesh, the northern Indo-Gangetic plains, the corridor between Delhi and Lahore, and coastal regions such as Mumbai, Chennai and Dhaka.

Is this a big deal?

To answer that question, let us ask how many migrants are there today. India already sees about 9 million migrants a year. The Economic Survey of 2017 has an interesting map that shows most migrants today tend to come from Uttar Pradesh and Bihar and head to Delhi. But what happens when Delhi falls under the too-hot-to-live-in category? Where will the migrants then go?

Moreover, today’s migrants are predominantly young and able individuals who come to work. Climate refugees will be less productive and more dependent. Out-of-state migrants may be welcomed to perform chores that States cannot get people from within their own borders to do. But will climate refugees be welcomed?

The next question to ask is, where will these 36 million climate refugees head to?

Bengaluru and interior Chennai are two ‘in-migration’ hotspots. When I spoke about this to some people from Bengaluru and Chennai, one person asked, ‘Will we have enough water to accommodate millions more?’

Probably not.

But that will not stop the millions from pouring in...unless we can solve some of their problems, in their place of residence. The good news is there is so much we can do – including increasing the green spaces in our cities and renewing urban water bodies to reverse the urban heat island effect. Given that we actively conspire with the warming climate to worsen its effects, that is possible to do. And unless we want to change the very fabric of our country, it is what we must do.

The writer is the founder of the Sundaram Climate Institute, cleantech angel investor and author of The Climate Solution - India's Climate Crisis and What We Can Do About It published by Hachette in June. Follow her work on her website; on Twitter; or write to her at cc@climaction.net

Updated Date: May 10, 2018 13:43:46 IST