As we grapple with the escalating climate crisis, it's crucial to recognize that its impacts extend far beyond environmental changes. The extreme weather events we're witnessing are not just disrupting ecosystems; they're taking a devastating toll on human health and lives. This summer of 2024 has brought this reality into sharp focus, as scorching temperatures spiral out of control, teaching us harsh lessons about how heat can kill.
In Delhi alone, by the end of June 2024, we estimate that around 270 people have died due to extreme heat. However, I caution against taking this number at face value. The true toll is likely much higher, as heat often exacerbates existing health conditions like cardiovascular or kidney diseases. Many more may have succumbed to heat this summer, but their deaths are attributed to underlying conditions rather than heat stress.
The most vulnerable are those exposed to heat due to their work conditions, construction workers, farmers, and the poor who lack access to electricity and cooling appliances. Tragically, their deaths are often recorded as due to poverty, old age, or "unknown causes," rather than heat stress. This underscores a critical gap in our health reporting system: heat is not listed among the notifiable diseases in our country, meaning there's no requirement to record or report heat-related deaths for further action.
Recent research, however, is shedding light on the dynamics of deadly heat. A 2022 study published in The Lancet found that the relative mortality risk on days with hot nights could be 50% higher than on days with cooler night temperatures. This is because heat disrupts sleep and prevents the body from repairing itself, exacerbating health stress. Additionally, we now understand that when humidity rises beyond 75%, known as the wet bulb phenomenon, our bodies' natural cooling mechanism through evaporation becomes ineffective.
Alarmingly, our cities are seeing an increasing trend in all three killer factors: temperatures rising beyond human tolerance, increasing humidity, and rising night-time heat. A recent report by my colleagues at CSE tracked heat trends across major Indian cities and found that ambient air temperatures are increasing faster in cities compared to the national average. Cities like Hyderabad, Delhi, Mumbai, Kolkata, and Chennai are experiencing more humid summers, with a 5-10% increase in the last decade compared to 2001-2010.
Moreover, our cities are not cooling down at night as they used to. The report notes that the difference between day and night temperatures is decreasing across all climatic zones. Hyderabad has seen a 13% decrease in this temperature difference, Delhi 9%, and Bengaluru 15%. Kolkata, already known for its small day-night temperature difference, is now worse off due to higher humidity levels.
This urban heat crisis is a result of a double whammy. On one hand, we have a warming planet breaking all previous high-temperature records. On the other, our cities are experiencing dramatic changes in microclimate due to the heat island effect, as concrete replaces open and green spaces, and traffic and energy use for cooling add to the heat trapped in the air.
As we face this existential crisis, it's crucial to understand that climate change will continue to surprise us with its impacts on human health. The science in this area is still not fully understood, but what we do know is that climate change is bringing its impacts closer to our bodies and our health. This is why planetary health is fundamentally about human health.
This summer has taught us new lessons in heat stress, and we must heed them. It's time we made the connection between climate change and human health explicit. It's time we understood why climate change is truly an existential crisis - it is literally about life and death.
As we move forward, we must prioritize research, policy-making, and public awareness around the health impacts of climate change. Only by understanding and addressing these challenges can we hope to protect vulnerable populations and ensure a healthier future for all in the face of our changing climate.
