By Balakrishna Pisupati, Head of the United Nations Environment Programme in India
By mid-afternoon, many schools in Chennai, India are heavy with heat. Spinning overhead fans are little match for spiking outdoor temperatures, which routinely hit 40C. Students rest their heads on their desks and clutch at water bottles. Few are learning.
Chennais pupils are among hundreds of millions of people around the world whose lives are being upended by an onslaught of extreme heat. From Bangkok to Paris to New York, scorching temperatures are throttling productivity, aggravating illnesses and taking lives.
These rising temperatures are creating a moment of reckoning for the worlds cities, some of which may soon verge on unlivable unless municipal officials can find ways to cool things down.
The epidemic of extreme heat has two main causes. First, as humans pump greenhouse gases into the atmosphere, the planet is warming 1.5C and counting. This climate change is leading to more frequent and more intense heat waves, like a record-smashing scorcher that engulfed India last month, pushing temperatures in many cities to over 45C.
The way cities are designed is inflaming the problem. Closely packed buildings and paved surfaces soak up the suns heat and radiate it outwards, like a poker just removed from the fire. In some cases this urban heat island effect, as its known, can make cities 5C to 10C warmer than the surrounding countryside.
You can feel this heat everywhere. It radiates off roads in the evening. It lingers inside cramped apartments long after sunset. It settles into buses, markets and shops with nowhere to escape.
And while extreme heat affects everyone, the burden lies heaviest on the poor.
Families living in slums swelter both day and night. Outdoor labourers chance heat stroke because missing work is not an option. School children, enduring fatigue and dehydration, struggle to focus.
The only obvious solution to many of these problems might seem to be air conditioning.
But its not.
Air conditioners are expensive and beyond the financial reach of many. They also consume enormous amounts of electricity most of which still comes from fossil fuels feeding the very climate crisis driving extreme heat. The United Nations Environment Programme (UNEP) estimates that cooling equipment, including refrigeration, could account for up to 10 per cent of greenhouse gas emissions by 2050.
So, if air conditioning is not the answer, what is? Well, there are three main things cities can do over the long term to counter rising temperatures.
First, municipal officials can enshrine so-called passive cooling strategies into their building codes. These often-simple hacks like planting trees to provide shade or painting rooftops white to reflect the suns rays can lower indoor temperatures by up to 8C. That is enough to turn a restless, sweat-soaked night into a comfortable slumber.
Second, cities can set an example in the buildings they erect by incorporating passive cooling techniques, installing fans, and if air conditioners are necessary, making sure they are energy efficient. These public procurement policies can be a powerful force for change.
Finally, cities can embrace the architecture styles and building materials of the past, which often do a much better job of shedding heat than todays glass-and-concrete monoliths.
Long before air conditioners existed, for example, homes across India were designed to cope with heat naturally. Mud walls, shaded courtyards, lime plasters and high ceilings helped buildings stay cool by improving airflow and reducing heat absorption.
These techniques evolved over generations in response to local climates. Yet many were abandoned in favour of concrete-heavy construction that often performs poorly in extreme heat.
In some places, the arithmetic is changing, though. In Chennai, for example, UNEP is helping schools in low-income neighbourhoods incorporate passive cooling. The work has lowered indoor temperatures by up to 3C and is on track to benefit 150,000 pupils. While the project is relatively small, it shows that change is possible. That is a lesson I hope government officials around the world take to heart.
The work in Chennai, incidentally, is part of a wider global push by UNEP, including through the 50@50 initiative, to help cities plan for and respond to extreme heat by reducing greenhouse gas emissions and scaling up sustainable, people-centred cooling solutions.
Extreme heat is already reshaping daily life in many places. And with greenhouse gas emissions continuing to rise, our cities are only going to get hotter. But we do not have to resign ourselves to a future of stifling days and nights. With a little ingenuity, we can ensure our cities remain vibrant, liveable places in the years to come.
About World Environment Day
World Environment Day, celebrated annually on 5 June, is one of the planet's largest platforms for environmental outreach and is led by the United Nations Environment Programme (UNEP). This year's iteration, hosted by Azerbaijan, will focus on the mushrooming climate crisis. See how you can get involved.
