Recent extreme heatwaves are no match for future events

In recent years, record-breaking heatwaves have occurred over many regions of the Earth causing serious impacts to human and natural systems. Here we show that recently observed exceptional heatwaves are no match to potential future 21^st century events based on multiple metrics. For several observed heatwaves, this holds even under low- and medium-emissions scenarios. In a high- to very high-emissions future, many regions are projected to experience heatwaves that generate several times more cumulative heat and are many times longer (up to several months) than the observed heatwaves. Should the Nationally Determined Contributions under the Paris Agreement not be implemented, in most regions a concerningly large proportion of projected heatwaves exceeds all analyzed heatwave characteristics at once. Our results underscore the crucial need for substantial emissions reduction and have important implications for adaptation measures, as a substantial proportion of projected heatwaves is well outside the recent lived experience.