The world’s largest capitals are experiencing more extremely hot days than ever before, according to a new study, revealing the dangerous trend is being driven by scorching temperatures in Asia as the climate crisis worsens.
The world’s 20 most populous cities – home to more than 300 million people – have seen a 52 percent increase in the number of days above 35 degrees Celsius (95 degrees Fahrenheit) over the past three decades, according to an analysis by the International Institute for Environment and Development (IIED), published Friday.
The research shows that major capitals, from Buenos Aires in Argentina to the French capital Paris and Cairo, Egypt, are experiencing more extremely hot days every decade as man-made greenhouse gas emissions increase. This poses a threat to human health, economy and infrastructure.
“Climate change is not just a future threat – it is already happening and getting worse,” IIED senior researcher Tucker Landesman said in a press release.
“In just one generation, there has been an alarming increase in the number of days of extreme heat affecting some of the world’s largest capitals – exacerbated by the urban heat island effect,” which occurs when cities replace natural land with roads and buildings that require more retain heat.
Asian cities, which make up about half of the world’s most populous capitals, saw some of the biggest temperature increases – a trend evident in recent heat waves across the continent, from Southeast Asia to China and India. Asia is uniquely vulnerable to climate risks, due to its high population density, poverty and the percentage of people living in low-lying areas prone to flooding, sea level rise and other natural disasters.
New Delhi topped the list of hottest cities, with 4,222 days above 35 degrees Celsius in the past three decades – more than any other city analyzed. Between 2014 and 2023, just under half (44%) of days in India’s capital met that threshold, compared to 35% from 1994 to 2003 and 37% from 2004 to 2013.
The capital region is only getting hotter. In late May, part of Delhi reached 49.9 degrees Celsius (121.8 degrees Fahrenheit) – the highest temperature ever recorded in the city, putting pressure on India’s electricity grid and power supply. The heat also continued at night, giving residents little respite.
“We have been living in this area for 40 years, but we have never experienced a summer like this,” Kalyani Saha, a 60-year-old resident of Lajpat Nagar in southeast Delhi, told CNN.
“We only get water once a day and it’s boiling hot. Unless you fill a bucket and let it cool all day before using it, you can’t bathe in this water.”
A Delhi rickshaw driver told CNN he had seen fewer passengers as people preferred air-conditioned taxis to open-air transport.
“My body can’t handle it, but I have to keep cycling,” said Sagar Mandal, 39. “We are used to physical labor, we don’t complain about that. But this heat is not normal, something has to change.”
Indonesia’s capital Jakarta saw one of the biggest jumps in the number of days above 35 degrees Celsius in the past thirty years, from 28 days between 1994 and 2003 to 167 days between 2014 and 2023.
Seoul, South Korea and Beijing, China have also experienced a significant increase in extremely hot days. In 2018, Seoul saw 21 days above 35 degrees Celsius — more than the previous 10 years combined. The number of days above 35 degrees in Beijing has increased by 309% since 1994.
Cities are also seeing longer periods of high temperatures as governments fail to meet climate goals and sufficiently limit emissions. In October 2023, Jakarta had 30 consecutive days of temperatures above 35 degrees Celsius — more days than in the entire period between 1994 and 2003.
Extreme heat can be deadly, especially for vulnerable groups who may not have access to cool areas. Between June 11 and June 19, there were 192 heatwave-related deaths among the homeless population in Delhi, a record high compared to the same period in the past five years, according to a report by the NGO Center for Health Development India.
Young children, the elderly and pregnant people are at greater risk during heat waves, which can also have a devastating impact on informal and hourly workers, who may face work stoppages or the choice between staying home unpaid or working in hazardous conditions.
Heat also harms economies, damaging crops and livestock and reducing labor productivity, especially in places without air conditioning, as workers need more breaks to rest and rehydrate.
And extreme heat strains infrastructure, including highways, roads, power lines and railways, causing supply chain disruptions, power outages and illness.
According to a 2022 Dartmouth College study, extreme heat has cost the global economy trillions of dollars since the early 1990s. The poorest countries in the world and countries with the lowest emissions suffer the most from the consequences.
“Responding to the challenge of extreme heat requires bold action from policymakers, including serious investments to adapt to this new reality,” said Landesman of the IIED.
“For many cities, it is not a lack of knowledge, capacity or resources that prevents large-scale action to tackle climate change, but rather a lack of political will and governance tools.”
CNN’s Esha Mitra and Kathleen Magramo contributed reporting.
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