An increase in mean temperature of 0.5 degrees Celsius over 50 years may seem trivial, but it more than doubles the probability of a heat wave in India that could kill more than 100 people.

This is according to recent research from the University of California – Irvine (UCI).

Using data gathered by the India Meteorological Department over the past 50 years, the research team analyzed changes in summer temperatures, along with the frequency, severity, and duration of heat waves. They also used data on the number of heat-related deaths.

They found that when mean summer temperatures in India went from 27 to 27.5 degrees Celsius, the probability of a heat wave killing more than 100 people increased by 146 percent.

This could have dire implications for the future, particularly in low- and mid-latitude countries like those in South Asia, Africa, the Middle East, and South America, because mean temperatures are projected to rise by 2.2 to 2.5 degrees Celsius by the end of the century.

“The impact of global climate change is not a specter on the horizon. It’s real, and it’s being felt now all over the planet,” said UCI associate professor Amir AghaKouchak, a co-author of the study. “It’s particularly alarming that the adverse effects are pummeling the world’s most vulnerable populations.”

What does all this mean in real numbers? In 1975, when the mean summer temperature was about 27.4 degrees Celsius, there were only 43 heat-related deaths. However, at least 1,600 people died in 1998 during a heat wave when the mean summer temperature was higher than 28 degrees Celsius.

Nearly a quarter of India’s 1.3 billion people live on less than $1.25 a day, and they have little or no access to electricity. That means most of them can’t even use an electric fan to move the air around them when a heat wave hits.

“In addition to India, populations in other developing countries in low- to mid-latitude regions are especially hard hit by these extreme heat events,” said study lead author Omid Mazdiyasni, a UCI graduate student. “They lack air conditioning that people in richer countries rely on when the heat is unbearable, and they don’t have the funds to escape to cooler climates.”

The study authors say their findings should be a wake-up call for everyone about the reality of global climate change. But with the U.S.’s withdrawal from the Paris Agreement, they acknowledge that it would be difficult to build a broad-based coalition to deal with the issue.

“Given the quantifiable impacts of climate change in India and other developing nations in the coming decades, both rich and poor countries should be ramping up our efforts to combat global climate change instead of turning our backs on commitments we have made to the international community,” said study co-author Steven J. Davis, a UCI associate professor of Earth system science.

Photo: People living in slums like this one in Mumbai, India, face a much greater risk of heat deaths from even a small increase in mean temperature. Credit: Jan S. /