Analysis: India’s fatal sweltering heat in June linked to climate change

June 22, 2023

New analysis by Climate Central shows that a three-day extreme heat event over Uttar Pradesh from June 14-16, 2023 was made at least 2 times more likely by human-caused climate change. In Ballia, a district in Uttar Pradesh, temperatures reached 42.2°C on June 16 and at least 34 fatalities occurred over the three-day event. 

The analysis uses a metric called Climate Shift Index (CSI), which quantifies the contribution of climate change to daily temperatures. CSI levels over 1 indicate a clear climate change signal, while levels between 2 and 5 mean that climate change made those temperatures between 2 and 5 times more likely. The methodology used to calculate the CSI is based on peer-reviewed science.

In addition to Uttar Pradesh, most locations across India experienced significant CSI levels during the same period. The heat wave affected hundreds of millions of people in India. 

Attribution analysis: how did climate change influence these temperatures?

• In Uttar Pradesh, CSI levels peaked on June 14th, decreasing over the following two days. Certain parts of the state reached CSI levels of 3, indicating temperatures that were made at least three times more likely because of climate change.

• The current CSI applies only to temperature. The fact that these extreme temperatures occurred along with high humidity is unusual and contributed to the severity of the event.

• This extreme event comes after the deadly humid heat wave in April of 2023, which was made more than 30 times more likely by human-caused climate change.

What impacts were experienced?

• At least 34 fatalities in Uttar Pradesh were reported as part of this heat event [1] 

• Primary and secondary schools closed in Bihar, India [2]

Context on heat waves

• Heat waves are amongst the deadliest natural hazards with thousands of people dying from heat-related causes each year and many more suffering other severe health and livelihood consequences. However, the full impact of a heat wave is often not known until weeks or months later, once death certificates are collected, or scientists can analyse excess deaths. As many places lack good recordkeeping of heat-related deaths, the currently available global mortality figures are likely an underestimate.

• While people in the affected regions are used to hot and humid temperatures, those who are more physiologically susceptible to heat (e.g. due to pre-existing conditions, age, and disability) and/or are more exposed due to their occupation (e.g. outdoor workers, farmers) are at the highest risk of heat-related health impacts. Such exposure and vulnerability are intensified by societal disadvantage based on factors such as socio-economic status, religion, caste, gender, migration, and living conditions. On top of this, factors such as air pollution, the urban heat island effect, and wildfires further compound health impacts, particularly among the most vulnerable populations.

What do experts say?

Dr. Friederike Otto, a researcher at Imperial College London and co-lead of World Weather Attribution (WWA) said:

“We see again and again that climate change dramatically increases the frequency and intensity of heat waves, one of the deadliest weather events that exist. Our most recent WWA study has shown that this has been recognised in India, but implementation of heat action plans is slow. It needs to be an absolute priority adaptation action everywhere.”

Dr. Mariam Zachariah, a researcher at Imperial College London and WWA, said:
“The combination of extreme heat and humidity is particularly dangerous for humans, even more so in urban contexts where the 'heat island' effect can further increase temperatures. Unless carbon emissions are rapidly reduced, these life-threatening events will become more frequent and intense."