This study examines observed regional and global trends in heatwave characteristics using the Berkeley Earth temperature dataset and key heatwave metrics. Heatwaves have increased in intensity, frequency, and duration, with these trends projected to worsen under enhanced global warming. The study finds that heatwave frequency demonstrates the most rapid and significant change across almost all regions. Cumulative heat has shown significant increases almost everywhere since the 1950s, mainly driven by heatwave days. Trends in heatwave frequency, duration, and cumulative heat have accelerated since the 1950s, and due to the high influence of variability, regional trends are assessed over multiple decades. The study provides comparable regional observed heatwave trends on spatial and temporal scales necessary for understanding impacts. Heatwaves are defined as prolonged periods of excessive heat and have many adverse impacts, including on human health, agriculture, workplace productivity, wildfire frequency and intensity, and public infrastructure. The inequality of heatwave impacts has been assessed, adversely affecting developing nations due to a lack of adaptive capacity, as well as varying cultural constraints. These impacts will increase under enhanced global warming, where more rapid heatwave trends will likely produce more severe and possibly irreversible impacts in some sectors. The study uses the Berkeley Earth observational dataset and compares it with the HadGHCND dataset to assess heatwave trends. The results show that heatwave frequency demonstrates the most widespread and significant increase of the characteristics analysed. Heatwave duration has significant trends restricted to South America, Africa, the Middle East, and Southwest Asia. Significant heatwave intensity trends are non-existent for most of the globe, the exception being southern Australia and small areas of Africa and South America. Significant cumulative heat trends are comparable in space to heatwave frequency, with mainly positive magnitudes. The largest trends are seen over the Middle East and parts of Africa and South America, where the extra heat produced by heatwaves is increasing by 10°C decade⁻¹. Regional trends in heatwave characteristics show that the largest trends were mainly over low-latitude regions. At least one extra heatwave day has occurred each decade over the majority of regions between 1950 and 2017. Heatwaves have increased in length by between 0.2 to over 1 day decade⁻¹. Regional trends beginning in a later decade can be larger in magnitude, which is at least in part due to greater overall warming of the global climate in later decades. However, later regional trends also bear less significance due to the influence of internal climate variability at shorter timescales. The study recommends a period of at least 3–4 decades to robustly assess changes in heatwaves, which is considerably longer than that proposed for average temperature trends. The cumulative heat—or the extra heat experienced during heatwaves—has markedly increased both globally and regionally. The study demonstrates this is largely driven by increases in the overall number of heatwave days, although over some regions slight increases in average intensity also contributeThis study examines observed regional and global trends in heatwave characteristics using the Berkeley Earth temperature dataset and key heatwave metrics. Heatwaves have increased in intensity, frequency, and duration, with these trends projected to worsen under enhanced global warming. The study finds that heatwave frequency demonstrates the most rapid and significant change across almost all regions. Cumulative heat has shown significant increases almost everywhere since the 1950s, mainly driven by heatwave days. Trends in heatwave frequency, duration, and cumulative heat have accelerated since the 1950s, and due to the high influence of variability, regional trends are assessed over multiple decades. The study provides comparable regional observed heatwave trends on spatial and temporal scales necessary for understanding impacts. Heatwaves are defined as prolonged periods of excessive heat and have many adverse impacts, including on human health, agriculture, workplace productivity, wildfire frequency and intensity, and public infrastructure. The inequality of heatwave impacts has been assessed, adversely affecting developing nations due to a lack of adaptive capacity, as well as varying cultural constraints. These impacts will increase under enhanced global warming, where more rapid heatwave trends will likely produce more severe and possibly irreversible impacts in some sectors. The study uses the Berkeley Earth observational dataset and compares it with the HadGHCND dataset to assess heatwave trends. The results show that heatwave frequency demonstrates the most widespread and significant increase of the characteristics analysed. Heatwave duration has significant trends restricted to South America, Africa, the Middle East, and Southwest Asia. Significant heatwave intensity trends are non-existent for most of the globe, the exception being southern Australia and small areas of Africa and South America. Significant cumulative heat trends are comparable in space to heatwave frequency, with mainly positive magnitudes. The largest trends are seen over the Middle East and parts of Africa and South America, where the extra heat produced by heatwaves is increasing by 10°C decade⁻¹. Regional trends in heatwave characteristics show that the largest trends were mainly over low-latitude regions. At least one extra heatwave day has occurred each decade over the majority of regions between 1950 and 2017. Heatwaves have increased in length by between 0.2 to over 1 day decade⁻¹. Regional trends beginning in a later decade can be larger in magnitude, which is at least in part due to greater overall warming of the global climate in later decades. However, later regional trends also bear less significance due to the influence of internal climate variability at shorter timescales. The study recommends a period of at least 3–4 decades to robustly assess changes in heatwaves, which is considerably longer than that proposed for average temperature trends. The cumulative heat—or the extra heat experienced during heatwaves—has markedly increased both globally and regionally. The study demonstrates this is largely driven by increases in the overall number of heatwave days, although over some regions slight increases in average intensity also contribute