Extreme heat events and global temperature records
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Global Temperature Records and Extreme Heat Events: Trends and Drivers
Rising Global Temperatures and Record-Breaking Events
Recent years have seen a dramatic increase in global temperature records, with 2023 and early 2024 standing out as every month from June 2023 to June 2024 set new global temperature records. The annual average temperature in 2023 approached 1.5°C above pre-industrial levels, a result of both long-term warming and natural climate variability, such as El Niño. The magnitude of these anomalies was unprecedented and surprised the scientific community, but they can be explained by the ongoing warming trend combined with a peak in internal variability .
The Link Between Warming Trends and Extreme Heat
Research shows that the number of record-breaking heat events increases roughly in proportion to the rate of warming compared to short-term temperature fluctuations. In other words, as the climate warms, the likelihood of setting new heat records rises, while short-term variability can slightly reduce this effect. For very extreme events, the relationship with the warming trend becomes highly nonlinear, meaning that even small increases in average temperature can lead to a much larger increase in the number of extreme events. For example, global warming has raised the expected number of new global temperature records in the last decade from 0.1 to 2.8 .
Probability and Intensity of Record-Shattering Extremes
Climate models project not only more frequent but also more intense heat extremes in the future. Events that break previous records by large margins—so-called "record-shattering" extremes—are expected to become much more common. The probability of these events depends on how quickly the world warms, not just the total amount of warming. Under high-emission scenarios, week-long heat extremes that break records by three or more standard deviations could become two to seven times more likely by mid-century, and up to 21 times more likely by 2080, compared to recent decades . By the end of the century, if greenhouse gas emissions continue unchecked, high monthly mean temperature records could be set in about 58% of the world every year, with even higher rates in the least developed countries and small island states .
Attribution of Recent Extreme Heat Events
Studies of recent extreme heatwaves, such as the 2021 Pacific Northwest event, show that such events would have been virtually impossible without human-caused climate change. The observed temperatures were so far outside historical ranges that, under current climate conditions, they are estimated to be about 1-in-1000-year events. Without human-induced warming, these events would have been at least 150 times less likely. Furthermore, these heatwaves are now about 2°C hotter than similar events would have been in the late 19th century. If global warming reaches 2°C, such extreme events could become even more frequent and intense Philip2022Philip2021.
Challenges in Defining and Measuring Extreme Heat
There are significant challenges in defining and measuring extreme heat events globally. Different datasets and definitions can lead to discrepancies, especially in tropical regions where there is little agreement on the timing and frequency of extreme heat events. This highlights the need for locally tailored heatwave metrics and careful comparison of different data sources to accurately assess heat-health risks .
Human and Societal Impacts
The increase in extreme temperature events has significant consequences for human health and society. Historical analysis shows a genuine rise in the occurrence of extreme temperature events, with mortality trends less certain but potentially higher for heat events, especially when major heatwaves are included. Reporting biases and data limitations mean that the true human impact may be underestimated, particularly in less developed countries . The disruption caused by more frequent and intense heat events can push communities and ecosystems beyond their ability to cope, emphasizing the urgent need for adaptation and mitigation strategies Power2019Horton2016Zhang2023.
Conclusion
Extreme heat events and global temperature records are increasing in frequency and intensity due to ongoing climate warming. The probability of record-shattering heat events is rising, and recent extremes would have been nearly impossible without human influence. As the world continues to warm, the risks associated with extreme heat will grow, making adaptation and mitigation efforts more critical than ever. Accurate measurement and local understanding of heat events are essential for effective response and protection of vulnerable populations.
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