Abstract
Including an exceptionally warm Northern Hemisphere (NH) summer1,2, 2023 has been reported as the hottest year on record3-5. Contextualizing recent anthropogenic warming against past natural variability is nontrivial, however, because the sparse 19th century meteorological records tend to be too warm6. Here, we combine observed and reconstructed June-August (JJA) surface air temperatures to show that 2023 was the warmest NH extra-tropical summer over the past 2000 years exceeding the 95% confidence range of natural climate variability by more than half a degree Celsius. Comparison of the 2023 JJA warming against the coldest reconstructed summer in 536 CE reveals a maximum range of pre-Anthropocene-to-2023 temperatures of 3.93°C. Although 2023 is consistent with a greenhouse gases-induced warming trend7 that is amplified by an unfolding El Niño event8, this extreme emphasizes the urgency to implement international agreements for carbon emission reduction.
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Esper, J., Torbenson, M. & Büntgen, U. 2023 summer warmth unparalleled over the past 2,000 years. Nature (2024). https://doi.org/10.1038/s41586-024-07512-y
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DOI: https://doi.org/10.1038/s41586-024-07512-y
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