The Indian summer this year has been a story of extreme heatwaves. These began as early as April, when a severe humid heatwave gripped most parts of India. And earlier this month, between 14-20 June, Uttar Pradesh and Bihar was struck by a sweltering heatwave. The effects of this was severe enough that schools were shut in Bihar. In Uttar Pradesh’s Ballia district, a deadly cocktail of high temperature (43 degrees Celsius on 18 June) and high humidity resulted in the deaths of at least 68 people.
Scientists and commentators had suspected that the heat event was the result of climate change. Now, a new analysis by the New Jersey-based climate organization Climate Central has confirmed the role played by global warming in the catastrophic event. The analysis found that climate change dramatically increased the likelihood of the heat event's occurrence. For the analysis, Climate Central scientists used the Climate Shift Index (CSI), which quantifies the contribution of climate change to daily temperatures. The index is calibrated between the values of -5 and 5, where a value of 1 and over indicates a climate change signal.
According to the scientists, the June heat event reached the CSI value of 3, which means that the high temperatures were made at least three times more likely due to the effects of climate change. However, since the CSI measures the impact of global warming only on temperature, the added high humidity would have made the temperatures during the heat event even more unbearable.
This combination of heat and humidity is commonly known as wet-bulb temperature. As a Lounge cover story on India’s tryst with humid heat in 2020 (Is Extreme Heat Making India Unlivable?) noted, “Human beings, even those who have adapted to high heat, find it difficult to carry out normal activities in a wet-bulb temperature of 32 degrees Celsius. The survivability threshold of the human body is reached at the wet-bulb temperature of 35 degrees. At that level, even if a human being is in the shade, the results are fatal.” And this lethal combination is growing in India due to climate change.
According to the Indian Meteorological Department (IMD), the relative humidity in Ballia on 18 June was 31%, while the maximum temperature reached 43.2 degrees Celsius. This resulted in a Heat Index or a “real feel” of 51 degrees Celsius. This is deadly heat that is difficult for a human being to survive. India has a severe problem.