As the global climate has warmed, the number of "hot days" that China is experiencing has been on the rise, shown in the figure below.
Change in the average annual number of "hot days" - days at or above 35 °C - at meteorological stations in China, relative to the 1991-2020 average. Data is taken from a chart in the CMA's 2024 Annual Climate Bulletins. Chart by Carbon Brief.
The year 2022 set a new record, with meteorological stations in China recording an average of 16.4 hot days. This was 7.3 more than the average for 1991-2020. The year 2024 came close to this record, with 15.6 hot days. These two years have also seen China's hottest summers on record.
In 2022, more than 1,000 meteorological stations in China reported heatwaves, with 441 breaking "historical records". For 2024, 74 stations reported "consecutive high temperature days" and 81 of them broke records.
Xiao said at a press conference in 2023 that "continuous high temperatures" in China's central and eastern regions lasted for 79 days in the summer of 2022. The provinces of Gansu and Xinjiang in north-west China, Hubei in central China and Sichuan in south-west China all reported their "highest temperatures since 1961".
In addition, the "maximum daily temperature [in the summer of 2022] at 361 national meteorological stations - accounting for 14.9 per cent of the total number of stations in the country - reached or exceeded historical extremes", Xiao added.
The CMA has also highlighted that summer is arriving earlier for much of China. In 2024, for example, summer in regions including most of Hainan province in south China, central Yunnan province in south-west China as well as central and southern Xinjiang province in north-west China arrived more than 20 days earlier than average.
"If a year's spring and summer are longer, the potential heatwaves...will also be longer," Prof Wenjia Cai, from the department of earth system science of Tsinghua University, tells Carbon Brief.
Cai notes that there are more ways to define heatwaves than CMA's absolute threshold of 35 °C.
For example, a heatwave can also be defined by how long the hot weather persists, or based on "the daily maximum temperature, daily average temperature, or even nighttime temperature", she tells Carbon Brief.
However, regardless of the definition used, the "number of heatwave days is definitely increasing as a result of climate change", she adds.
What role does human-caused climate change play?
A field of climate science called "attribution" has emerged over the past two decades to establish the role that human-caused warming plays in individual extreme weather events, including heatwaves, floods, droughts and storms.
Attribution studies can also be used to find the "fingerprint" of human-caused climate change in longer-term trends, such as the gradual increase in surface temperatures over multiple decades.
Heat is the most-studied extreme event in attribution literature, as it is mainly driven by thermodynamic influences - in other words, it is relatively easy to study.
In contrast, storms and droughts are more strongly affected by complex atmospheric dynamics and, as such, can be trickier to simulate in a model. Cai tells Carbon Brief:
"High temperature is the most obvious trend against the background of climate change. Heatwaves, in comparison to events such as rainfall and typhoons, are also more predictable."
Carbon Brief has produced an interactive map showing every attribution study published up to November 2024. In total, 114 extremes and trends in China have been the subject of an attribution study, including more than 20 relating specifically to extreme heat.
One study included on the map looks at the change in the intensity and frequency of extreme temperatures across China over 1951-2018. The authors say that, over this time period, "more intense and more frequent warm extremes" were observed across "most regions" in China - and that "greenhouse gas forcing plays a dominant role" in this.
Looking at individual extreme events, one analysis by the "rapid attribution" group World Weather Attribution investigates the then-record-breaking heat across China in July 2023. The analysis says that temperatures exceeded 50 °C in north-west China, adding that Sanbao, in Xinjiang, hit 52.2 °C on 16 July of that year.
The study finds that, in a world without climate change, such an extreme heat event would have been "extremely rare" and would only have happened once every 250 years. However, in today's climate, as a result of human-caused climate change, a heatwave of this intensity is now expected once every five years.
This means China's extreme heat of July 2023 was 50 times more likely due to climate change. The study also finds that in a world without climate change, the heatwave over China would have been 1 °C cooler.
A separate study finds that human-caused climate change also caused a more than 60-fold increase in the likelihood of the extremely warm 2013 summer, compared to the early 1950s.
It adds that other factors such as urbanisation and changes in atmospheric circulation patterns can also make heat extremes more intense and frequent.
What impact are these heatwaves having?
Heatwaves have a wide variety of impacts on human activities, such as public health, crop yields and economic output.
Older people are particularly vulnerable to extreme heat. The 2024 report from the Lancet Countdown on Health and Climate Change found that, in 2023, demographic changes alone could have driven a 65 per cent increase in heat-related deaths among over-65s, compared to the 1990-99 average.
Cai, who is also the lead author of the Lancet Countdown's China report, tells Carbon Brief that older people are the "most commonly mentioned vulnerable group" and that the number of people affected by heatwaves will grow as societies age.
However, heatwaves also "affect outdoor activities" regardless of age group, she adds, as well as having impacts on sleep and allergies:
"We don't want anyone to think they are in a group of people unaffected by heatwaves."
Cai says that heat exposure can increase the incidence of certain dangerous behaviours, such as domestic violence, as well as a wide range of diseases - including cardiovascular diseases and respiratory diseases - and mental health disorders.
In 2023, more than 30,000 deaths were related to heatwaves in China - 1.9 times higher than the average over 1986-2005, according to Cai and her colleagues' China report.
This was a result of increased heat exposure - the average number of "heatwave exposure days" per person reached 16 days in 2023, more than three times the historical average (1986-2005), the report adds.
A 2022 attribution study on China notes that extreme heat can also increase the risk of preterm births. The authors find that over 2010-20, an average of 13,262 premature births were recorded in China due to heatwave exposure. The study linked one-quarter of these early births to climate change.
Another profound impact of heatwaves is that they can exacerbate droughts, with knock-on impacts for agriculture.
Reuters reported last June that "China's agriculture ministry said...searing temperatures have adversely impacted summer planting and that fighting drought and protecting summer planting were arduous tasks".
Droughts in 2024 hit more than 11 million people in China, with more than 1.2m hectares of affected crops and direct economic losses topping nearly 8.4 billion yuan (US$1.2 billion), the Ministry of Emergency Management said in early 2025.
Heat-related economic losses could reach nearly 5 per cent of China's GDP by 2060, according to a recent guest post for Carbon Brief. Authors Prof Guan Dabo and doctoral student Sun Yida from Tsinghua University wrote:
"By 2060, China's heat-induced economic losses could total about 1.5 per cent of total GDP under 1.5 °C of global warming, 3 per cent under 2 °C of warming and 4.9 per cent under 2.5 °C of warming."
Those predicted losses include "indirect economic losses", which "could be due to changes in production, consumption or employment" in the global supply chain, including crop failures and labour slowdowns, they explained.
The figure below, based on their study, shows Chinese GDP losses under three different scenarios of future emissions, called "shared socioeconomic pathways" (SSPs).
The SSP1-1.9, SSP2-4.5 and SSP5-8.5 scenarios project average global temperature rises of around 1.5 °C, 2 °C and 2.5 °C by mid-century, respectively.
Economic losses are split into indirect losses (dark blue), labour losses (blue) and health losses (light blue).