2023 summer warmth unparalleled over the past 2,000 years

• Published in: Nature (London) Vol. 631; no. 8019; pp. 94 - 97
• Main Authors: Esper, Jan, Torbenson, Max, Büntgen, Ulf
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04-07-2024; Nature Publishing Group
• Subjects: 704/106/413; 704/106/694; Agreements; Air temperature; Anthropocene; Anthropogenic factors; Archives & records; Carbon emissions; Climate variability; Cold; El Nino; Emissions; Emissions control; Greenhouse gases; Humanities and Social Sciences; Ice ages; International agreements; multidisciplinary; Natural variability; Northern Hemisphere; Science; Science (multidisciplinary); Sulfur; Summer; Surface temperature; Surface-air temperature relationships; Temperature; Northern Hemisphere; Europe
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/s41586-024-07512-y

Including an exceptionally warm Northern Hemisphere summer
1
,
2
, 2023 has been reported as the hottest year on record
3
–
5
. However, contextualizing recent anthropogenic warming against past natural variability is challenging because the sparse meteorological records from the nineteenth century tend to overestimate temperatures
6
. Here we combine observed and reconstructed June–August surface air temperatures to show that 2023 was the warmest Northern Hemisphere extra-tropical summer over the past 2,000 years exceeding the 95% confidence range of natural climate variability by more than 0.5 °C. Comparison of the 2023 June–August warming against the coldest reconstructed summer in
ce
536 shows a maximum range of pre-Anthropocene-to-2023 temperatures of 3.93 °C. Although 2023 is consistent with a greenhouse-gases-induced warming trend
7
that is amplified by an unfolding El Niño event
8
, this extreme emphasizes the urgency to implement international agreements for carbon emission reduction.
Observations and a reconstruction of the June–August surface air temperatures show that 2023 was the warmest summer over the past 2,000 years exceeding the 95% confidence range of natural climate variability by more than 0.5 °Cs.