In the model context, the forced warming trend can be estimated by averaging all 84 members. Since observations only correspond to one possible realization of climate, it is challenging to identify the underlying forced warming trend. It is unclear to what extent this ‘warming hole’ behaviour is forced or due to variability 18, 19, 20 (Extended Data Fig. Heat extremes observed over North America also show no clear trend in the last decades 17, 18. In the corresponding model realization the trend in Tx7d before 2019 is seemingly small.
1a, simulated in a 84-member Community Earth System Model version 1.2 (CESM1.2) ensemble forced with representative concentration pathway RCP 8.5 ( Methods), the hottest week ( Tx7d Methods) over Central North America exceeds the previous record in the respective simulation by >5 σ. 1a), with record margins much larger than the ones of recent heatwaves (Extended Data Fig. Nevertheless, large climate model ensembles simulate individual events in the near future that shatter previous records set over a period of 175 yr (Fig. In a gradually warming climate with a century of observations, one would not necessarily expect previous temperature records to be broken by large margins. It is known that the signal-to-noise ratio is high for seasonal averages leading to rapid increase in record-breaking seasonal events 16 but changes in record-shattering events at typical synoptic time scales of heatwaves of about 1–2 weeks are unknown. Climate models suggest that record-breaking monthly and seasonal events increase particularly over low latitudes 16. Most of the literature focuses on moderate extremes that occur several times a year, or every few years, or record-breaking events that often only marginally exceed previous events 12, 13, 14, 15. There is a lack of methods to quantify whether record-shattering events of much higher intensities than observed are possible or plausible today and in the near future. We argue that the record-shattering nature of extremes has not received much attention but is very relevant for impacts, as there is a tendency to adapt at most to the highest anomalies experienced during a lifetime 9, 10, 11 or documented in observational or historical archives. Events that break previous local records by large margins are hereafter defined as record-shattering extremes and their intensity quantified as the standardized anomaly by which the previous record is exceeded. In contrast to most of the scientific literature, we here take a complementary perspective and do not define the intensity of extremes as anomalies relative to pre-industrial or present-day climates but specifically focus on the margin by which previous records are exceeded, with the records being updated with every occurrence. Such unprecedented events need to be taken into account when designing critical infrastructure, such as power plants, or heatwave preparedness strategies. 1) and thereby literally ‘shattered’ previous records by a large margin. Week-long temperature maxima during the latter heatwaves exceeded previous records by more than two standard deviations ( σ) (Extended Data Fig. Society has often been surprised by the magnitude by which recent climate extremes exceeded previous observed records, such as during the extreme rainfall of Hurricane Harvey 1, 2, 3, the 2020 warm anomaly over Siberia 4 or the 2003 European and 2010 Russian heatwaves 5, 6 that caused tens of thousands of heat-related fatalities 6, 7, 8. In 2051–2080, such events are estimated to occur about every 6–37 years somewhere in the northern midlatitudes. In high-emission scenarios, week-long heat extremes that break records by three or more standard deviations are two to seven times more probable in 2021–2050 and three to 21 times more probable in 2051–2080, compared to the last three decades. We demonstrate that their probability of occurrence depends on warming rate, rather than global warming level, and is thus pathway-dependent. These record-shattering extremes, nearly impossible in the absence of warming, are likely to occur in the coming decades. Here, we show models project not only more intense extremes but also events that break previous records by much larger margins. Such extremes unprecedented in the observational period often have substantial impacts due to a tendency to adapt to the highest intensities, and no higher, experienced during a lifetime. Recent climate extremes have broken long-standing records by large margins.