From 13.4℃ in 2016 to 14.5℃ in 2024, and Yangsan's 41.6℃ in 2026 — Confirming South Korea's Temperature Rise and Summer Peak Temperature Changes Through Data

South Korea's summer is no longer what it used to be. According to observation data released by the Korea Meteorological Administration (KMA), temperature records on the Korean Peninsula have been rewritten year after year over the past few years. In particular, with 2023 to 2025 marking three consecutive years in the top three for highest annual average temperatures on record, expressions like "record-breaking heat" are shifting from exceptions to the everyday norm. This trend is closer to a structural tendency than a temporary anomaly. In fact, in the summer of 2026, even the domestic all-time high temperature record was broken, elevating the intensity of the heat a step further. This article summarizes how South Korea's temperatures have changed over the past decade and how high summer peak temperatures have climbed, based on official observation data.

The Past Decade: Annual Average Temperatures Continue to Rise

According to KMA data, South Korea's annual average temperature reached 14.5℃ in 2024, ranking first on record, followed by 13.7℃ in 2025 for second place, and 13.7℃ in 2023 for third place. In other words, the past three years side-by-side occupy the top tier of the hottest years since observations began. Here, the term "on record" refers to rankings since 1973, when the nationwide meteorological observation network was significantly expanded, calculated based on the average values of 62 observation points nationwide. The key point is that the records do not spike in a single isolated year, but are concentrated in the upper ranks across multiple recent years.

Not only short-term records but long-term trends are also clear. The "Korea Climate Crisis Assessment Report 2025," jointly published by the Ministry of Environment and the KMA, presented the temperature rise rate on the Korean Peninsula as 0.18℃ per decade based on the 1912–2017 period, and 0.21℃ per decade based on the 1912–2024 period. This means that as the observation period extends closer to the present, the rate of increase itself has accelerated. The report analyzed that the warming trend has intensified, particularly over the past seven years since 2018. In short, South Korea's heat is estimated to have entered a phase of "increasingly steep" rather than "slow and steady" progression.

It is also worth noting that the "normal baseline value"—the standard used to judge temperatures—continues to rise. The normal baseline currently in use is the 30-year average from 1991 to 2020, and this baseline itself is set higher than the preceding 30 years. In other words, even the normal baseline we refer to when saying "it was hotter than normal year" has risen compared to the past, meaning recent high temperatures are manifesting in a form that surpasses an already elevated standard.

Another characteristic of recent changes is that the heat is no longer confined to the three summer months. According to the KMA, in 2025, monthly average temperatures ranked 1st or 2nd on record for five consecutive months from June to October, and the nationwide average temperature for the autumn season also rose to 16.1℃, ranking second on record. The trend of spring and autumn becoming shorter and the hot period extending on both ends is becoming distinct.

The Temperature Curve of the Past Decade by Year

Examining the past decade year by year highlights the upward trend at a glance. The year 2016 recorded a nationwide annual average temperature of 13.4℃, ranking first at the time and peaking the mid-2010s heat. Afterward, 2019 and 2021 both ranked high at 13.3℃, while 2020 recorded 13.0℃. A year to note is 2018, remembered for the worst heatwave in history. That summer left an all-time record temperature of 41.0℃ in Hongcheon and 31.0 nationwide heatwave days, but because the winter was extremely cold, the annual average temperature itself remained in the middle tier at 12.8℃. This is an example showing that extreme summer heat and annual averages do not always move in the same direction.

The upward trend sharply resumed starting in 2023. The annual average temperature jumped to 13.7℃ in 2023, and in 2024, it surged to 14.5℃, surpassing 14 degrees for the first time since observations began and breaking the all-time record. Subsequently, 2025 also recorded 13.7℃, ranking second on record. The very fact that 13.4℃—which was the record for the "hottest year" just a decade ago—is now pushed out of the top tier concisely illustrates how fast the temperature baseline has climbed over the past decade. Looking at the summer season alone, the change is even more vivid. The historical rankings for nationwide average summer temperatures are 25.7℃ in 2025, 25.6℃ in 2024, and 25.3℃ in 2018, with the top three years all concentrated within the past eight years. For 2026, annual statistics are still being compiled, but as shown later, summer peak temperatures are already setting new all-time records.

Summer Average Temperatures Break All-Time Highs Back-to-Back

Among the seasons, the change is most dramatic in summer. According to KMA analysis, the nationwide average temperature for the summer season (June–August) of 2025 was 25.7℃, surpassing the previous record of 25.6℃ set in 2024 and breaking the all-time high since 1973. This figure is 2.0℃ higher than the normal baseline (the 30-year average from 1991 to 2020). A 2.0℃ higher average temperature means not just feeling a few days of heat, but that the entire three months of summer were thoroughly hotter than usual.

An even more notable indicator is daytime temperatures. The average daily maximum temperature for the summer of 2025 recorded an all-time high of 30.7℃. The fact that mid-day summer temperatures averaged over 30 degrees demonstrates that heatwaves are no longer isolated exceptions of a few days, but have established themselves as the baseline for the entire summer. Starting from mid-June, the North Pacific high pressure expanded faster than usual, triggering early heat, and the characteristic feature was that this heat wave lasted for a long time until late August. Such heat—starting early and ending late—further increases the burden on cooling demand, outdoor activities, and health management.

All-Time High Temperature Record Broken Again in the Summer of 2026

For a long time, South Korea's official all-time high temperature record was 41.0℃ observed in Hongcheon, Gangwon Province, on August 1, 2018. This broke Daegu's 40.0℃ record from 1942 after 76 years. However, that peak was rewritten once more in the summer of 2026. On July 31, 2026, the daytime high temperature in Yangsan, South Gyeongsang Province, rose to 41.4℃, surpassing the Hongcheon record, and just the next day on August 1, Yangsan recorded 41.6℃, breaking the record again in a single day. This is the highest temperature recorded domestically since modern meteorological observations began, as well as since the nationwide weather observation network was established in 1973.

Yangsan recorded daytime temperatures exceeding 40℃ for four consecutive days starting July 29, which is also the first time in domestic observation history that temperatures exceeded 40 degrees for three consecutive days or more. This extreme heatwave is analyzed to have occurred as the North Pacific high pressure and the Tibetan high pressure blanketed the Korean Peninsula in a double layer, combined with a Foehn effect where winds crossing the Sobaek Mountains became hot and dry in the Yeongnam region. However, as the heat was still ongoing even at the time of writing in early August 2026, the extreme value records may change again thereafter.

What deserves attention is that the "duration during which high temperatures are maintained" is rapidly increasing alongside the "peak temperature extremes." This is because enduring late-30s heat throughout the entire summer imposes a far heavier burden on the human body and society than a single day of extreme temperature. Indeed, recent heatwaves are exhibiting heightened simultaneous qualities of extreme momentary records, persistence, and wide scope.

Heatwaves and Tropical Nights Become the Norm, Not the Exception

The normalization of extreme heat is clearly evident in the number of heatwave days and tropical nights. Based on "heatwave days" where the daily maximum temperature is 33℃ or higher, the nationwide average number of heatwave days in the summer of 2025 was 28.1 days, ranking third on record following 2018 (31.0 days) and 1994 (28.5 days). Broadening the view to an annual basis, the ranking goes 2018 (31.0 days), 2024 (30.1 days), and 2025 (29.7 days), with recent years concentrated at the top.

Nighttime heat is even more severe. Seoul's tropical night days in the summer of 2025 reached 46 days, the highest since observations began in 1908. This means that daytime heat failed to cool down at night, resulting in nearly a month and a half where nighttime minimum temperatures did not drop below 25℃. In particular, with high nighttime temperatures of around 27–28℃ repeating almost daily centered around Seoul and the Gangwon Yeongdong region, evaluations suggest that tropical nights have practically become a default condition of summer. Furthermore, in 2025, Daegwallyeong experienced heatwaves for the first time since observations began in 1971, expanding the heatwave zone even to high-altitude regions that were previously far removed from extreme heat. In Seogwipo, Jeju, a tropical night appeared in mid-October—the latest timing since observations began in 1961—confirming the tendency of heat not only starting earlier but also lingering later.

This trend became even more pronounced heading into 2026. In June 2026, the KMA overhauled the heatwave advisory system for the first time in 18 years, subdividing it into a three-tier system by adding a "severe heatwave warning" to the existing two tiers of advisories and warnings. The highest-level severe warning is issued when the apparent temperature is expected to reach 38℃ or higher, or the temperature 39℃ or higher; the first severe warning of the summer was issued for Gyeongsan and Pohang in North Gyeongsang Province on July 12. Nighttime heat also persisted, with the nationwide average tropical night days as of late July compiled at the highest level on record. Combined with a lack of precipitation in the southern provinces, this created a compound disaster pattern where heatwaves and droughts occurred simultaneously.

The Toll of Heatwaves Confirmed Through Health Damages

Temperature rises do not stop at statistical numbers but manifest directly as harm to human health. According to the operation results of the Korea Disease Control and Prevention Agency's (KDCA) emergency room surveillance system for heat-related illnesses, heat-related patients totaled 4,460 during the summer of 2025. This is the highest level since 2018 (4,526 cases), which had the most under the surveillance system. Among them, fatalities stood at 29, making the scale of deaths the fourth highest following 2018 (48 deaths), 2024 (34 deaths), and 2023 (32 deaths). The fact that more than half of the deceased were elderly individuals aged 60 and older shows that heatwaves pose an even greater risk to vulnerable populations.

While these figures have limitations as provisional statistics based on sentinel surveillance, the fact that the top ranks for heat-related patients and deaths in recent years are all concentrated after 2018 implies that the intensity of the heat is directly linked to health risks.

In 2026, these risks arrived even earlier. The KDCA launched the operation of its heat-related illness emergency room surveillance system on May 15, earlier than usual, and on that very first day, a man in his 80s in Seoul died from a presumed heat-related illness, marking the earliest first fatality case since the introduction of the surveillance system. With record-breaking heatwaves overlapping in late July afterward, heat-related illness casualties also increased rapidly, reflecting the trend of heatwaves starting earlier and persisting stronger directly in health statistics.

Why Is It Getting So Hot?

Increasing greenhouse gas concentrations and rising sea surface temperatures are pointed to together as the backdrop for these changes. According to the "Korea Climate Crisis Assessment Report 2025," carbon dioxide concentrations observed domestically in 2024 exceeded the global average, such as 430.7 ppm in Anmyeondo, and the annual average sea surface temperature of the seas surrounding the Korean Peninsula also rose to the highest level in the past decade. When the ocean warms, water vapor in the atmosphere increases, and summer high-pressure systems develop more strongly, creating a structure where heatwaves and torrential rains repeat. In fact, the annual average sea surface temperature of the seas surrounding South Korea in 2025 was 17.7℃, the second highest in the past decade, with the first being 2024 at 18.6℃. In particular, the autumn sea surface temperature was 22.7℃, showing the largest increase at 1.4℃ higher than the past decade's average.

However, because a given year's temperature is determined by fluctuating factors such as that year's pressure patterns and ocean currents superimposed on the long-term trend of warming, records are projected to rise with deviations rather than being monotonically broken every single year.

How Rising Temperatures Are Changing Industry and Daily Life

Temperature rises hold implications that go beyond statistics. The increase in heat-related illnesses due to heatwaves, electrical loads from soaring cooling demand, changes in agricultural and fishery crop yields and productivity, and the deterioration of outdoor working environments in construction and logistics are already manifesting as real-world problems. In particular, rising ocean water temperatures lead to changes in catchable fish species and damage to fish farms, lowering fishery productivity, while heatwaves burden crop growth and livestock management. The "Korea Climate Crisis Assessment Report 2025" also forecasted major social impacts, such as an increase in heat-related illnesses and a decline in fishery productivity due to heatwaves. For corporations, this serves as a risk factor structurally raising summer energy costs and safety management expenses, while conversely opening new demands and markets in the fields of cooling, climate adaptation, renewable energy, and data-driven climate forecasting.

Ultimately, South Korea's temperature rise is a socio-economic variable that goes beyond a "hotter summer." The direction shown by the data is clear. The records of the past decade are not exceptional anomalies but a new baseline, and how we prepare and adapt upon this baseline remains a task for the future. For individuals, heatwave response has become a living condition repeating every year rather than a summer-time trick, and corporations and society are tasked with redesigning cooling, safety, and energy infrastructures on a permanent standard. In an era where records are broken every year, the phrase "this summer was unusually hot" is projected to repeat more frequently and earlier. The summer of 2026, which rewrote the all-time high temperature record, is confirming that outlook before our very eyes.