In 2023, the planet experienced its hottest summer on record.

According to the latest data from the European Union’s Copernicus Climate Change Service, the global average temperature from June to August reached 16.77 degrees Celsius, beating the record set in the summer of 2019 by nearly 0.3 degrees Celsius.

“Our planet has just endured a season of simmering — the hottest summer on record. Climate breakdown has begun,” said António Guterres, Secretary-General of the United Nations.

China has also fallen in line with this climate trend. During this summer, multiple places across the country were hit by extreme weather conditions. Beijing, for instance, experienced 14 scorching days in June with temperatures over 35 degrees Celsius, as well as the largest rainstorm in its 140-year history in August. Temperature and precipitation records were shattered across the board.

The record-breaking heat this summer is in line with Guterres’ warning back in July that “the era of global warming has ended” and “the era of global boiling has arrived.”

Previous rankings of the hottest cities, based solely on temperature, no longer accurately describe the current situation. Sixth Tone’s sister publication, The Paper, compiled a new list to gauge the “boiling degrees” of different cities in China based on peak temperature, diurnal temperature range, body temperature, and precipitation as recorded by Chinese authorities since 1951.

Drawing data from 31 provincial capitals and four municipalities, this special report gives a simplified overview of climate change trends to offer insights into this sweltering summer.

Fiercer heat

Many people may wonder why summers used to be bearable, even without air conditioning, whereas nowadays turning on the AC is a summertime necessity. The truth is that summer is becoming hotter with each passing year.

Across most cities in China, summers have been intensifying in recent years. To begin with, the summer season is getting longer. A case in point is Fuzhou, the provincial capital of the southeastern Fujian province. In 2020, compared to data from 1960, the city saw an increase of 22 days with temperatures exceeding 35 degrees Celsius, eight days surpassing 38 degrees Celsius, and 2.8 days exceeding 40 degrees Celsius. Fuzhou also experienced temperatures surpassing 35 degrees Celsius for more than 46 days between June and August 2020.

In addition to the prolonged hot days, records for daily high temperatures are also being shattered. Since 1960, Chengdu, the capital of the southwestern Sichuan province, has seen its temperature records broken 12 times, with half of them occurring after 2016. In 2022, Jianyang, a county-level city under the administration of Chengdu, witnessed its highest-ever recorded temperature, when it soared to a scorching 43.4 degrees Celsius.

What’s worse is that heatwaves are not only becoming more frequent and intense — they’re also arriving much earlier. Meteorological data spanning over half a century shows that nearly 90% of major cities are experiencing their first high-temperature day earlier than before.

In the 1960s, the first high-temperature day reaching 35 degrees Celsius in Guangzhou typically fell around July 19. However, in the 2010s, it came a month earlier.

The early onset of scorching heat in June has brought unrelenting heatwaves to northern China. In June, the Beijing Meteorological Bureau issued one red heat alert, three orange alerts, seven yellow alerts, and one blue alert, with degrees descending in severity from red to blue. The observatory station in the city’s southern suburbs even recorded an unprecedented total of 14 high-temperature days.

Boiling cities

As heatwaves increase in frequency and intensity, even nicknames like “furnace cities” fail to capture the severity of the extreme heat that Chinese cities are enduring. Instead, “boiling” seems to be a more fitting description.

This newly compiled list by The Paper identifies the most “boiling” cities in different decades in China. Changsha, Chongqing, and Fuzhou consistently secure the top three spots for cities with the highest temperatures, while Hangzhou, Nanchang, and Wuhan frequently find themselves in the top 10 rankings.

The competition for the not-so-coveted top spot has grown fiercer over the years. Over 64 years, the number of high-temperature days for the city ranked first has surged by 19 days, with the average daily high temperature rising by 2.1 degrees Celsius.

In the 1960s, the reigning champion, Changsha, in the central Hunan province, had 31 high-temperature days with an average daily high of 38.4 degrees Celsius, while the leader on the 2020s list, Fuzhou, recorded 50 days of high temperatures with an average of 40.5 degrees Celsius.

The list also has its limitations. The cities’ heat levels are measured by the total number of days exceeding 35 degrees Celsius, which may not fully account for the impact of extremely high temperatures. For example, in the summer of 2022, Chongqing saw 17 scorching days over 40 degrees Celsius, a notably extreme temperature occurrence.

Some cities find no relief from relentless heatwaves even during the night. Residents of many southern cities have to endure sweltering summer nights with temperatures exceeding 30 degrees Celsius.

In Nanchang, the capital of Jiangxi province, the number of nights with temperatures over 28 degrees Celsius was 9.5 in 1960. By 2020, this figure had surged to 29, subjecting residents to an additional 20 unbearable nights.

Chongqing and Hangzhou have also steadily climbed the ranks in recent decades, coming in second and fifth, respectively, in 2020.

For southern cities, relying solely on temperature figures is insufficient to gauge the intensity of the heat felt by people, as high humidity exacerbates the discomfort.

In 2023, Guangzhou experienced 19 days with temperatures exceeding 35 degrees Celsius. However, when factoring humidity and wind speed to assess perceived body temperatures, the count soared to 85 days.

Moist heat often proves more intolerable than dry heat. According to China’s climate livability index, the human body perceives the same air temperature differently depending on humidity and wind speed. Residents in cities with high humidity, such as Guangzhou, Haikou, and Nanning, endured a more searing summer from June to August this year.

Taking these factors into account, Shijiazhuang in the northern Hebei province, while ranking high in terms of high-temperature days, does not feel as scorching. Its dry climate, large diurnal temperature range, and ample rainfall have mitigated the impact on people’s perceived body temperature. In other words, it doesn’t feel as hot.

An escalating trend

The issue of “boiling” temperatures has been a global concern, with consequences extending beyond just hotter summers.

Global warming has heightened the frequency and intensity of extreme weather events, including heatwaves, heavy precipitation, and droughts, according to a report by the Intergovernmental Panel on Climate Change (IPCC).

Higher temperatures also lead to increased heavy rainfall. An analysis of the causes behind the severe rainstorm in Zhengzhou, Henan province, on July 20, 2021, by the Chinese Academy of Sciences found that warmer and moister climates doubled the probability of this type of natural disaster and caused a 7.5% surge in rainfall intensity.

Over the past 70 years, most cities have experienced a consistent increase in annual rainfall, with Shanghai, Nanchang, Nanjing, and Hefei showing an upward trend.

According to China’s official weather forecast website, northeast China and north China have experienced more substantial rainfall and an increase in extreme rainstorms in recent years due to climate change.

Excessive heat poses a significant threat to both health and life.

A sleep survey by the University of Copenhagen, involving 48,000 adults across 68 countries, found that warmer temperatures cause people to go to bed later and wake up earlier, resulting in a shorter length of time spent asleep. When nighttime temperatures exceed 30 degrees Celsius, adults sleep approximately 14 minutes less per night. In the long run, this warming trend could reduce annual sleep hours by about 44.

Heatwaves are characterized by a sequence of three hot days with temperatures surpassing 35 degrees Celsius, and they have become a recurring extreme weather phenomenon globally. The WHO reported that in Europe alone, at least 15,000 people died of heat-related causes in the three summer months of 2022.

According to the IPCC, as of 2019, the Earth’s surface has warmed by an average of 1.1 degrees Celsius compared to pre-industrial levels in the late 19th century, marking the highest temperature increase in the past 100,000 years. Even this modest temperature rise has already exposed humans to extreme weather events such as heatwaves and torrential rains, and experts have warned that excessive heat, droughts, and floods will hit our planet more frequently in the future.

Reported by Chen Zhifang, Chen Liangxian, Wei Yao, and Kong Jiaxing.

A version of this article originally appeared in The Paper. It has been translated and edited for brevity and clarity, and is republished here with permission.

Translator: Wu Yichen; editors: Xue Ni, Luo Yahan, and Elise Mak.

(Header image: A boy sweats on a hot day in Beijing, June 2023. Hao Yi/Beijing Youth Daily/VCG, reedited by Sixth Tone)