For the first time in recorded meteorological history, the diurnal temperature cycle has collapsed across large swathes of India. Night-time temperatures in Delhi, Jaipur, and Lucknow failed to drop below 38°C on Tuesday, with daytime peaks hitting 47°C. The UK Met Office has raised its heat health warning to the highest level, citing an 'extreme risk to life' for over 400 million people.
This is not a heatwave in the conventional sense. A heatwave implies a temporary aberration, a spike above the climatological mean. What we are witnessing is a structural breakdown of the land-atmosphere feedback loop. Normally, solar radiation heats the surface by day, and longwave radiation cools it by night. But with soil moisture depleted to less than 10% of normal in the Indo-Gangetic Plain, the ground behaves like a dry brick: it absorbs heat rapidly and re-radiates it continuously. Without evaporation to cool the surface, the night offers no reprieve.
The UK Climate Office's Hadley Centre models have been projecting this scenario for years. Their latest set of probabilistic forecasts, updated last week, showed a 72% chance of heat index values exceeding 55°C in parts of Uttar Pradesh by 2030. That threshold, once considered theoretical, is now a near-term reality. The human body cannot cool itself when wet-bulb temperatures exceed 35°C for more than six hours. Tuesday's wet-bulb readings in Lucknow hit 32.4°C. At this rate, the survivability window is closing.
What worries me as a climate physicist is the compounding effect on energy infrastructure. As night-time temperatures remain high, air conditioning demand does not fall. The Indian grid is already strained: coal-fired plants are running at 98% capacity, but coal stockpiles at 40% of normal due to heat-disrupted rail transport. Solar farms, ironically, produce less power in extreme heat because photovoltaic efficiency drops by roughly 0.5% per degree above 25°C. At 47°C, that is a 11% efficiency loss. Renewable backup fails when it is needed most.
We are seeing a positive feedback loop accelerate. Higher temperatures dry out soil, which reduces evaporative cooling, which amplifies heat. This is not a weather event: it is a climate regime shift. The UK Met Office's 'extreme risk' flag is usually reserved for storms that can be evacuated from. But you cannot evacuate 400 million people from a hemisphere-scale heat dome.
Technological solutions exist: district cooling, reflective roofs, sub-surface geothermal heat pumps. But these require infrastructure investment on a timescale of decades. We are losing time at a rate of roughly 0.4°C per decade in this region. The question is no longer whether the planet is warming. It is whether we can adapt fast enough to avoid the collapse of the thermal safety net that has allowed human civilisation to flourish for the past 10,000 years.
Dr Helena Vance, Science & Climate Correspondent, London.
