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2023 summer warmth unparalleled over the past 2,000 years


Including an exceptionally warm Northern Hemisphere summer1,2, 2023 has been reported as the hottest year on record3,4,5. However, contextualizing recent anthropogenic warming against past natural variability is challenging because the sparse meteorological records from the nineteenth century tend to overestimate temperatures6. 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 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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Fig. 1: 2023 in the context of the past 2,000 years.
Fig. 2: Forcing of modern-day temperatures.

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Data availability

The observational data, reconstruction and uncertainty estimates are available at

Code availability

None of the statistical tests applied were performed with environment-specific code.


  1. McKie, R. World experiences hottest week ever recorded and more is forecast to come. The Guardian (16 July 2023).

  2. Sands, L. This July 4 was hot. Earth’s hottest day on record, in fact. The Washington Post (5 July 2023).

  3. Poynting, M. & Rivault, E. 2023 confirmed as world’s hottest year on record. BBC (9 January 2024).

  4. Copernicus. 2023 is the hottest year on record, with global temperatures close to the 1.5 °C limit. Copernicus (9 January 2024).

  5. Bardan, R. NASA analysis confirms 2023 as warmest year on record. NASA (12 January 2024).

  6. Schneider, L., Konter, O., Esper, J. & Anchukaitis, K. J. Constraining the nineteenth-century temperature baseline for global warming. J. Climate 36, 6261–6272 (2023).

    Article  ADS  Google Scholar 

  7. Friedlingstein, P. et al. Global carbon budget 2023. Earth Syst. Sci. Data 15, 5301–5369 (2023).

    Article  Google Scholar 

  8. van Oldenborgh, G. J. et al. Defining El Niño indices in a warming climate. Environ. Res. Lett. 16, 044003 (2021).

    Article  ADS  Google Scholar 

  9. Rohde, R. Global Temperature Report for 2023 (Berkeley Earth, 2024).

  10. Zachariah, M. et al. Extreme heat in North America, Europe and China in July 2023 Made Much More Likely by Climate Change (World Weather Attribution, 2023).

  11. NOAA Climate Prediction Center. El Niño/La Niña Home (NOAA Climate Prediction Center, 2024).

  12. NOAA Global Monitoring Laboratory. Trends in Atmospheric Carbon Dioxide (Global Monitoring Laboratory, 2024).

  13. United Nations. 7. d Paris Agreement, Treaty Series, Vol. 3156, 79 (United Nations, 2015).

  14. Jones, P. The reliability of global and hemispheric surface temperature records. Adv. Atmos. Sci. 33, 269–282 (2016).

    Article  Google Scholar 

  15. Frank, D., Büntgen, U., Böhm, R., Maugeri, M. & Esper, J. Warmer early instrumental measurements versus colder reconstructed temperatures: shooting at a moving target. Quat. Sci. Rev. 26, 3298–3310 (2007).

    Article  ADS  Google Scholar 

  16. Parker, D. E. Effects of changing exposure of thermometers at land stations. Int. J. Climatol. 14, 1–31 (1994).

    Article  Google Scholar 

  17. Trewin, B. Exposure, instrumentation, and observing practice effects on land temperature measurements. Wiley Interdiscip. Rev. Clim. Change 1, 490–506 (2010).

    Article  Google Scholar 

  18. Masson-Delmotte, V. P. et al. (eds) Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge Univ. Press, 2021).

  19. Menne, M. J., Williams, C. N., Gleason, B. E., Rennie, J. J. & Lawrimore, J. H. The Global Historical Climatology Network monthly temperature dataset, version 4. J. Clim. 31, 9835–9854 (2018).

    Article  ADS  Google Scholar 

  20. Rohde, R. et al. A new estimate of the average Earth surface land temperature spanning 1753 to 2011. Geoinform. Geostat. 1, 1000101 (2013).

    Google Scholar 

  21. Osborn, T. J. et al. Land surface air temperature variations across the globe updated to 2019: The CRUTEM5 data set. J. Geophys. Res. Atmos. 126, e2019JD032352 (2021).

    Article  ADS  Google Scholar 

  22. Lenssen, N. J. L. et al. Improvements in the GISTEMP uncertainty model. J. Geophys. Res. Atmos. 124, 6307–6326 (2019).

    Article  ADS  Google Scholar 

  23. Büntgen, U. et al. The influence of decision-making in tree ring-based climate reconstructions. Nat. Commun. 12, 3411 (2021).

    Article  ADS  PubMed  PubMed Central  Google Scholar 

  24. Schneider, L. et al. Revising midlatitude summer temperatures back to A.D. 600 based on a wood density network. Geophys. Res. Lett. 42, 4556–4562 (2015).

    Article  ADS  Google Scholar 

  25. Stoffel, M. et al. Estimates of volcanic-induced cooling in the Northern Hemisphere over the past 1,500 years. Nat. Geosci. 8, 784–788 (2015).

    Article  ADS  CAS  Google Scholar 

  26. Wilson, R. et al. Last millennium Northern Hemisphere summer temperatures from tree rings: Part I: the long term context. Quat. Sci. Rev. 1–18 (2016).

  27. Guillet, S. et al. Climate response to the Samalas volcanic eruption in 1257 revealed by proxy records. Nat. Geosci. 10, 123–128 (2017).

    Article  ADS  CAS  Google Scholar 

  28. Büntgen, U. et al. Prominent role of volcanism in Common Era climate variability and human history. Dendrochronologia 64, 125757 (2020).

    Article  Google Scholar 

  29. Büntgen, U. et al. Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 ad. Nat. Geosci. 9, 231–236 (2016).

    Article  ADS  Google Scholar 

  30. Esper, J. et al. Large-scale, millennial-length temperature reconstructions from tree-rings. Dendrochronologia 50, 81–90 (2018).

    Article  Google Scholar 

  31. Esper, J. et al. European summer temperature response to annually dated volcanic eruptions over the past nine centuries. Bull. Volcanol. 75, 736 (2013).

    Article  ADS  Google Scholar 

  32. Esper, J., Büntgen, U., Hartl-Meier, C., Oppenheimer, C. & Schneider, L. Northern Hemisphere temperature anomalies during the 1450s period of ambiguous volcanic forcing. Bull. Volcanol. 79, 41 (2017).

    Article  ADS  Google Scholar 

  33. Esper, J. et al. Orbital forcing of tree-ring data. Nat. Clim. Change 2, 862–866 (2012).

    Article  ADS  Google Scholar 

  34. Cai, W. et al. ENSO and greenhouse warming. Nat. Clim. Change 5, 849–859 (2015).

    Article  ADS  Google Scholar 

  35. Huang, B. et al. Extended Reconstructed Sea Surface Temperature, version 5 (ERSSTv5): upgrades, validations, and intercomparisons. J. Clim. 30, 8179–8205 (2017).

    Article  ADS  Google Scholar 

  36. Columbia Climate School. ENSO forecast. Columbia Climate School (20 May 2024).

  37. Kumar, A. & Hoerling, M. P. The nature and causes for the delayed atmospheric response to El Niño. J. Clim. 16, 1391–1403 (2003).

    Article  ADS  Google Scholar 

  38. Bluth, G. J., Doiron, S. D., Schnetzler, C. C., Krueger, A. J. & Walter, L. S. Global tracking of the SO2 clouds from the June, 1991 Mount Pinatubo eruptions. Geophys. Res. Lett. 19, 151–154 (1992).

    Article  ADS  CAS  Google Scholar 

  39. Parker, D. E., Wilson, H., Jones, P. D., Christy, J. R. & Folland, C. K. The impact of Mount Pinatubo on world‐wide temperatures. Int. J. Climatol. 16, 487–497 (1996).

    Article  Google Scholar 

  40. Self, S. & Rampino, M. R. The 1963–1964 eruption of Agung volcano (Bali, Indonesia). Bull. Volcanol. 74, 1521–1536 (2012).

    Article  ADS  Google Scholar 

  41. Francis, P. & Oppenheimer, C. Volcanoes 2nd edn (Oxford Univ. Press, 2004).

  42. Medhaug, I., Stolpe, M. B., Fischer, E. M. & Knutti, R. Reconciling controversies about the ‘global warming hiatus’. Nature 545, 41–47 (2017).

    Article  ADS  CAS  PubMed  Google Scholar 

  43. Karl, T. R. et al. Possible artifacts of data biases in the recent global surface warming hiatus. Science 348, 1469–1472 (2015).

    Article  ADS  CAS  PubMed  Google Scholar 

  44. Wild, M. et al. Global dimming and brightening: a review. J. Geophys. Res. Atmos. 114, D00D16 (2009).

    Article  ADS  Google Scholar 

  45. Stern, D. I. Reversal of the trend in global anthropogenic sulfur emissions. Glob. Environ. Change 16, 207–220 (2006).

    Article  Google Scholar 

  46. Allan, R. P. in Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (eds Masson-Delmotte, V. et al.) (Cambridge Univ. Press, 2021).

  47. Anchukaitis, K. J. & Smerdon, J. E. Progress and uncertainties in global and hemispheric temperature reconstructions of the Common Era. Quat. Sci. Rev. 286, 107537 (2022).

    Article  Google Scholar 

  48. Morice, C. P. et al. An updated assessment of near‐surface temperature change from 1850: the HadCRUT5 data set. J. Geophys. Res. 126, e2019JD032361 (2021).

    Article  ADS  Google Scholar 

  49. Esper, J., Frank, D. C., Wilson, R. J. S. & Briffa, K. R. Effect of scaling and regression on reconstructed temperature amplitude for the past millennium. Geophys. Res. Lett. 32, L07711 (2005).

    Article  ADS  Google Scholar 

  50. Ohmura, A. Observed decadal variations in surface solar radiation and their causes. J. Geophys. Res. Atmos. 114, D00D05 (2009).

    Article  ADS  Google Scholar 

  51. Wild, M. Decadal changes in radiative fluxes at land and ocean surfaces and their relevance for global warming. Wiley Interdiscip. Rev. Clim. Change 7, 91–107 (2016).

    Article  Google Scholar 

  52. Rohde, R. A. & Hausfather, Z. The Berkeley Earth land/ocean temperature record. Earth Syst. Sci. Data 12, 3469–3479 (2020).

    Article  ADS  Google Scholar 

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This study was supported by the ERC Advanced projects MONOSTAR (AdG 882727), the ERC Synergy project SYNERGY-PLAGUE (101118880), the Czech Science Foundation grant HYDRO8 (23-08049 S), the co-funded EU project AdAgriF (CZ.02.01.01/00/22_008/0004635) and the Centre for Interdisciplinary Research (ZiF) in Bielefeld, Germany. We thank C. Oppenheimer, J. Quaas and M. Wild for their discussions of volcanic and solar radiation forcings.

Author information

Authors and Affiliations



J.E., M.T. and U.B. designed the study. J.E. and M.T. conducted the analyses with support from U.B. The paper was written by J.E. together with M.T. and U.B.

Corresponding author

Correspondence to Jan Esper.

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Nature thanks Gabriele Hegerl and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Instrumental temperature records.

a, Comparison of 30–90°N JJA land only temperatures from Berkeley Earth extending back to 1850 CE (red)20, CRUTEM5 back to 1878 CE (blue)21 and GISTEMP4 back to 1883 CE (grey)22. b, Frequency distributions of the three observational records. All data shown as anomalies with respect to 1883–1912 CE means.

Extended Data Fig. 2 Observational temperatures averaged over different spatiotemporal domains.

a, Northern Hemisphere JJA land only temperatures (red) shown together with global annual land and sea surface temperatures from 1850–2023 CE (black)20. The latter represents a combination of Berkeley Earth land and HadSST3 sea surface temperatures52. b, Frequency distributions. Data shown as anomalies with respect to their 1850–1900 CE means.

Extended Data Fig. 3 Early instrumental temperature offset.

Comparison of Berkeley Earth 30–90°N JJA land only observational temperatures20 with ensemble mean reconstructed JJA temperatures23 since 1850 CE. Bold horizontal lines emphasize the 1850–1900 CE offset of 0.24 °C between the two records. The reconstruction was scaled against the observations from 1901–2010 CE and both timeseries then displayed as anomalies with respect to the 1850–1900 CE reconstruction mean.

Extended Data Fig. 4 Ensemble reconstruction climate signals.

Field correlations of the ensemble mean23 against GISTEMP4 JJA land (a, b) and land and sea surface temperatures (c, d) from 1850–2010 CE. Maps produced using the KNMI Climate Explorer at

Extended Data Fig. 5 Reconstruction verification.

Ensemble mean shown together with other NH extra-tropical summer temperature reconstructions (ref. 24. is Sch15, ref. 25. is Sto15, ref. 26. is Wil16, ref. 27. is Gui17, ref. 28. is Bün20) since 500 CE. All records scaled from 1901–2010 CE against 30–90°N JJA land temperatures (red) and shown as anomalies from 1850–1900 CE.

Extended Data Fig. 6 Reconstructed temperature extremes.

Comparison of temperature anomalies in the four warmest (246, 282, 1061, 986 CE) and four coldest summers (535, 627, 1601, 1642 CE) identified in ensemble mean reconstruction (see Table 1) with estimates from other NH extra-tropical reconstructions. “x” indicates if values are missing due to limited reconstruction lengths.

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Esper, J., Torbenson, M. & Büntgen, U. 2023 summer warmth unparalleled over the past 2,000 years. Nature 631, 94–97 (2024).

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