Extreme terrestrial heat in 2023

Extreme terrestrial heat in 2023 | Nature Reviews Earth & Environment

Multiple relentless heatwaves occurred in 2023, with much of the world experiencing at least 20 more heatwave days than the 1991–2020 average. Prominent and record-breaking events included exceptional wintertime and spring heat in South America, large heatwaves over Europe, Africa and Asia, and a prolonged event over south-eastern USA and Central America.

Key points

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Persistent heatwaves across much of the globe were synonymous with the hottest year on record.
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Many 2023 heatwaves exhibited record-smashing extreme temperatures, including a widespread heatwave spanning Thailand to Northern China that featured the worst April heatwave in South China on record.
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South America saw many prominent heat events, with exceptional heat in winter and early spring that broke all-time summertime records.

2023 was the hottest year on record. The global average temperature was 1.45 °C above pre-industrial (1850–1900) values, beating the previous record, which was set in 2016, by 0.16 °C (ref. 1). Behind this remarkable anomaly were many global temperature records, including: the hottest month and season ever recorded (July and June–August; both approaching 17 °C, which is 0.72 °C and 0.66 °C above average, respectively); daily instances of global temperatures 2 °C above pre-industrial levels; and 23% of land regions setting new extreme heat records 2. However, these figures hide the plethora of extraordinary daily and regional-scale terrestrial heat extremes, each linked to a combination of large- and local-scale drivers and feedbacks, such as anthropogenic climate change, persistent atmospheric blocking, droughts, adjacent marine heatwaves and the developing El Niño 1, 2.

Here, we summarize extreme terrestrial heat events during 2023 using ERA5 reanalysis 3. Not all events — of which there are many — are discussed, and Australia is omitted, since record-breaking heat extremes over this continent were minimal. Throughout, anomalies are calculated with respect to 1991–2020.

South America

During 2023, much of South America experienced anomalously warm temperatures; anomalies of 0.5–1 °C were observed over Peru, northern Bolivia and Brazil, while stronger anomalies of 1–3 °C were apparent over Chile, Bolivia, Paraguay and Argentina 2. All months were above average, with record conditions experienced for March and all months from July to December 4. Accordingly, heatwave events occurred across the continent, with central Brazil, parts of Colombia, Venezuela, Guyana, Suriname and French Guiana experiencing 110–150 heatwave days (anomalies of 80–110 days) and southern regions experiencing ~50–70 heatwave days (anomalies of ~40 days) (Fig. 1; Supplementary Fig.

a, Number of heatwave days (a day is considered part of a heatwave when it is one of at least three consecutive days where the daily maximum temperature is above the local 90th percentile computed from a 15-day moving window relative to 1991–2020), calculated using ERA5 (ref. 3). b, Average daily maximum temperature anomalies for South America during 17th–26th September 2023. c, As in b, but for Central and North America during 2nd–31st July 2023. d, As in b, but for Europe and North Africa during 15th–25th July 2023. e, As in b, but for Asia during 15th–22nd April 2023. Much of the globe experienced a substantial number of heatwaves during 2023, with numerous regional events resulting in very extreme temperatures.

Widespread extreme heatwaves occurred across numerous countries in the southern half of the continent during austral winter (July and August). Several periods of intense, summer-like heat occurred, breaking numerous local-scale all-time records (although observations are generally only two or three decades long). In particular, average daily maximum temperature anomalies during 1st–7th August reached 9 °C in Argentina and 3–7 °C in Paraguay, Uruguay, Bolivia and parts of Brazil (Supplementary Fig. 2a).

Extreme heat also followed into spring. A record-breaking heatwave occurred in mid-September over Brazil and bordering locations (Fig. 1b), with central-southern regions experiencing the warmest start to spring in at least 63 years. Here, temperatures exceeded 43 °C, corresponding to daily maximum temperature anomalies of 5–8 °C (Fig. 5.

Scorching and humid conditions also extended later into spring. Notably, extreme heat was observed throughout Brazil, Bolivia and Paraguay from the 7th to the 19th November. Daily maximum temperature anomalies reached 9 °C in parts of southern Brazil and ~7 °C across much of the rest of the country (Supplementary Fig. 2b), making it one of the hottest and most widespread heatwaves ever recorded in Brazil’s history. This heatwave included both days on which the global average temperature anomaly surpassed 2 °C relative to pre-industrial temperatures 1.

Central and North America

Like South America, annual temperatures across Central America and North America were above average; anomalies were generally 1–2 °C above average over most of the USA (except in central and south-eastern regions) and southern Canada, and well over 2 °C above average in northern Canada 2. Accordingly, the USA experienced its warmest year on record 4. Moreover, much of the continent experienced unparalleled long and intense heat extremes, with 50–60 heatwave days (anomalies of 20–40 days) being commonplace (Fig. 1a; Supplementary Fig. 1).

Continuing the record-breaking heat of 2022, the Pacific Northwest experienced extreme heat during May. Here, daily maximum temperature anomalies reached 9–12 °C from the 12th to the 17th May (Supplementary Fig. 2c), breaking multiple temperature records across British Columbia and Alberta.

Exceptionally persistent and record-breaking heat conditions also affected much of the south-western United States and Mexico throughout July (Fig. 1c). From the 2nd to the 31st July, average daily maximum temperature anomalies reached 1–5 °C over the south-western United States and into Mexico, and 3–8 °C in north-western Canada and Alaska (Fig. 6— various records were also broken. For instance, Phoenix reached a daily maximum temperature of 48 °C multiple times, and all days in the month were above 43 °C, surpassing the previous record for consecutive days above this threshold by 13 (ref. 7). Death Valley similarly recorded its hottest daytime and night-time temperatures of 53.3 °C and 48.8 °C, respectively, on July 16th (ref.

Heat events also continued in late summer and into autumn. For example, twenty states experienced heat conditions in the Midwest and southern and south-western USA in late August, where maximum daily temperature anomalies reached ~7–8 °C (Supplementary Fig. 2d). During this event, New Orleans experienced a maximum temperature of 39 °C on the 23rd August (the joint hottest day on record for the city), while Sioux Falls in South Dakota also experienced a night-time temperature of 27 °C, equalling the local record.

Extreme heat persevered well into autumn. Average daily maximum temperature anomalies of 10–12 °C were observed in Ontario and neighbouring provinces (Supplementary Fig. 2e) such that seasonal records were broken, including Montreal surpassing its October maximum temperature record by 2.6 °C. This heat also extended south into the north-eastern USA, where anomalies of 3–8 °C (Supplementary Fig.

Europe and Africa

2023 ranked as the hottest and second-hottest year on record for Africa and Europe, respectively 2. Average temperatures were generally 1 °C warmer than average, with all months (except May for Europe) experiencing anomalous warmth at the continental scale for both locations 4. The Mediterranean was among the regions with the highest number of heat days, experiencing ~50–70 heatwave days (anomalies of ~20–40 days) (Fig. 1; Supplementary Fig.

As for other continents, extreme heat was experienced well before summer. For instance, the Iberian Peninsula and northern Africa registered temperatures more typical of early summer by the end of April, with daily maximum temperature anomalies of 3–9 °C apparent throughout much of the region (Supplementary Fig. 2f). In fact, scorching temperatures up to 20 °C higher than normal broke monthly national records in Portugal (reaching 36.9 °C) and Spain (reaching 38.8 °C), as well as several local records in Morocco (reaching >41 °C).

The summer was also sweltering, with many regions experiencing more than two weeks of heat. During mid to late July, for example, an exceptional heatwave hit southern Europe and northern Africa, with local daily maximum temperature anomalies of up to 8 °C (Fig. 1d); accordingly, July was the hottest month ever recorded in southern Europe 2. This extreme heat subsequently spread from Spain to the Balkans and northern Africa, breaking several daily records: Tunisia and Algeria exceeded 49 °C, and Spain, Italy and Greece recorded temperatures above 45 °C, including 48.2 °C on July 24 in Sardinia, Italy, approaching the European record 1. This July heatwave would have been virtually impossible without anthropogenic climate change 6.

Unprecedented temperatures continued during autumn. In early September, daily maximum temperature anomalies of 7–10 °C were reported across several north-western European countries (Supplementary Fig. 2g). Many countries reported their hottest days of 2023 during this time, with local temperatures approaching 39 °C in France and 33 °C in the United Kingdom.

By late November, a record-breaking heatwave also affected large areas of southern Africa. Across Botswana, southern Mozambique and Namibia, and central and eastern South Africa, local heatwave conditions lasted 10 days, with anomalies of 3–8 °C (Supplementary Fig. 2h), pushing daily maximum temperatures above 40 °C in several locations.

Asia

Much of Asia similarly experienced average temperatures above normal. Anomalies of at least 0.5 °C were observed throughout central, southern and eastern Asia, while anomalies >1 °C were observed in western Asia 2, both contributing to Asia’s second-warmest year on record 4. At the country scale, China recorded its hottest year on record (0.82 °C above average 8), and Japan experienced its hottest March, July, and August since 1898 (2.75 °C, 1.91 °C and 2.16 °C above average, respectively). Similarly, most of Asia experienced ~40–60 heatwave days during 2023 (anomalies of ~20 days) (Fig. 1a; Supplementary Fig. 1).

April saw a particularly extreme heatwave throughout Southeast Asia and south-west China. This event, which peaked between the 15th and the 22nd, was the worst April heatwave on record, with maximum daily anomalies of 2–6 °C being commonplace (Fig. 1e). During the event, several record-breaking maximum temperatures reaching between 41 °C and 45 °C (and above) occurred over Lao PDR and Thailand. Bangladesh and north-eastern India were also badly hit, with temperatures of 40 °C to over 44 °C recorded. Because of anthropogenic climate change, April temperatures over the greater Asian region were 2 °C warmer relative to pre-industrial values 9.

Summer also saw scorching conditions in East Asia. The first regional high-temperature event hit eastern and southern China from 28th May to the 5th June (Supplementary Fig. 2i) — more than two weeks earlier than the traditional heatwave season — producing average daily maximum temperature anomalies of 3–8 °C (Supplementary Fig. 8). A subsequent heatwave across China from the 5th to the 18th July also experienced daily maximum temperatures of 2–6 °C (Supplementary Fig. 2j), with the event being 1.1 °C warmer because of climate change 6.

Summertime heat also enveloped India during August. The region experienced heatwave conditions wherein daily maximum temperature anomalies reached 2–3 °C at the end of the month (Supplementary Fig. 2k); given the tropical climate of southern India, such anomalies are quite extreme. The region’s average August maximum temperature of 32.66 °C was the highest since 1901 (ref. 10).

Summary

Extreme heat during 2023 was incomparable, with exceptional and record-shattering heatwaves experienced around the world and at all times of the year. Notably, relentless record-breaking heat occurred concurrently over multiple Northern Hemisphere continents during boreal summer, as well as multiple wintertime heatwaves in South America that rivalled extreme summertime heat. However, previously implausible heat was also prevalent during shoulder seasons across many locations. Attribution studies indicate that climate change was behind the outstanding intensity and frequency, despite the occurrence of El Niño. Given how close 2023 was to the ominous 1.5 °C anthropogenic warming threshold 1, 2, it is imperative that we prepare for previously unthinkable and unseasonal heat extremes.
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Acknowledgements

We thank the Copernicus Climate Change Service for publicly providing the ERA5 reanalysis in near real time.

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Perkins-Kirkpatrick, S., Barriopedro, D., Jha, R. et al. Extreme terrestrial heat in 2023. Nat Rev Earth Environ (2024). https://doi.org/10.1038/s43017-024-00536-y
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DOI: https://doi.org/10.1038/s43017-024-00536-y