Hot air. Damp sheets. A restless turn. A distant horn. A barking dog. A ceiling fan that does nothing but push the same heat around the room. Time stretches. Sleep fractures. The night refuses to soften.
Morning comes anyway and with it, the slow accumulation of everything the night could not fix.
Across cities, the day begins already strained. The roads fill early. Horns layer over one another — first as signals, then as impatience. A driver wipes sweat from his neck, misses a signal, and brakes too late. Another leans out, shouts. It escalates quickly. No one quite knows why.
Heat, now, is no longer just a discomfort people endure. It is quietly reshaping how they sleep, how they think, how they react. A growing body of research points to a clear pattern: rising temperatures are disrupting sleep, weakening cognitive performance, and lowering emotional thresholds — with consequences that spill into everyday life, and increasingly, onto the roads.
It begins at night, in rooms that never quite cool. Studies show warmer nights are consistently linked to shorter, poorer sleep. Even a slight rise in temperature, around 27°C, can reduce sleep by 15–17 minutes, increasing the likelihood of getting fewer than six hours. As the body struggles to cool itself, sleep becomes lighter, more fragmented and easily disrupted, with the deficit building night after night.
What changes is not just how long people sleep, but how deeply. Research by Alain Buguet, Manny W Radomski, Jacques Reis and Peter S Spencer shows that heatwaves reduce deep and REM sleep — the stages essential for recovery — turning sleep from restoration into another form of stress.
Through the day, it surfaces in small but telling ways. Attention blurs at the edges. Memory falters. Decisions take longer, feel heavier. Emotional balance weakens. Even brief exposure to extreme heat can reduce cognitive performance, while longer stretches deepen the strain — sometimes tipping into bad mood and depression.
Work does not escape it. In heat-exposed environments, productivity can drop by 30% to 60%. Outdoor and labour-intensive sectors feel it first, but indoor work is not spared. Performance rises to a point, then steadily declines as temperatures climb.
On the roads, the change is harder to ignore. Drivers honk more. Wait less. React quicker than they mean to. In cities where heat lingers in concrete and asphalt, even ordinary commutes begin to feel charged. Fatigue, delayed reactions, and irritability converge — and moments that should pass quietly escalate instead.
At the physiological level, the explanation is direct.
AIIMS resident Dr SM Turab explained, ““Heat disrupts sleep patterns, making it harder to fall asleep and causing frequent awakenings. The ideal bedroom temperature is 18–22°C, and any deviation affects sleep quality and duration. It also triggers the release of stress hormones like adrenaline and cortisol, increasing irritability, restlessness and conflicts such as road rage. Heat drains energy, leading to dehydration, cognitive impairment, and low enthusiasm and motivation.”
But the effects are not just physical, they are behavioural, layered, cumulative.
Zoya Ahmed, a psychologist, said, “Extreme heat places the body under constant strain, disrupting sleep and behaviour. Warm nights lead to lighter, fragmented sleep, which over time weakens emotional regulation, reduces impulse control and increases irritability. Heat also contributes to dehydration, fatigue and cognitive overload, affecting attention and reaction times.”
She added, “In high-pressure settings like traffic, these effects lower tolerance. People are not necessarily more aggressive during heatwaves, but they are more likely to react impulsively, leading to a rise in road rage and conflicts.”
Neurologists explained that when sleep is disrupted, activity in the prefrontal cortex — which governs impulse control and decision-making — decreases, while the amygdala becomes more reactive. This imbalance increases irritability and impulsive behaviour, lowering tolerance in high-stress situations like traffic and raising the likelihood of aggression, including road rage.
Beyond the cities, the same heat settles differently, but no less heavily. In rural India, where livelihoods depend on land and weather, the strain extends beyond discomfort. It seeps into uncertainty, into loss, into mental health.
Dr Nanda Kishore Kannuri, an associate professor at UoH, told TNIE that the TOLAKARI project examines how rising temperatures affect farmers’ health, particularly mental health and depression. Using participatory research and weather-linked data, it aims to co-develop and test a heat-informed mental health intervention. The five-year study focuses on vulnerable farming communities in Telangana, Andhra Pradesh and Karnataka.
Experts say the impact is not felt equally. Older adults, children, outdoor workers, and those without access to cooling face a greater burden. In cities that retain heat long after sunset, and in villages where relief depends on uncertain rain, the strain remains constant, even if uneven.
They suggest simple measures such as staying hydrated, taking frequent breaks, using air conditioning where possible, and ensuring proper ventilation to reduce the effects.
At a broader level, responses are beginning to take shape — from cooling centres and heat alerts to shaded spaces, and shifts in how work is organised and cities are designed. There is a growing recognition that heat is not just an environmental issue, but a behavioural, economic and deeply human one.
Yet it rarely feels like a crisis. It arrives quietly — one restless night, one irritable morning at a time — slipping into routine almost unnoticed. And when exhaustion becomes familiar, when strain begins to feel normal, at what point does it stop feeling like change?