1. Seidel, D. J., Fu, Q., Randel, W. J. & Reichler, T. J. Widening of the tropical belt in a changing climate. Nat. Geosci. 1, 21–24 (2008).

2. Seager, R. & Vecchi, G. A. Greenhouse warming and the 21st century hydroclimate of southwestern North America. Proc. Natl Acad. Sci. USA 107, 21277–21282 (2010).

3. Lucas, C., Timbal, B. & Nguyen, H. The expanding tropics: a critical assessment of the observational and modeling studies. Wiley Interdiscip. Rev. Clim. Change 5, 89–112 (2014).

4. Lucas, C. & Nguyen, H. Regional characteristics of tropical expansion and the role of climate variability. J. Geophys. Res. Atmos. 120, 6809–6824 (2015).

5. Lu, J., Chen, G. & Frierson, D. M. W. Response of the zonal mean atmospheric circulation to El Niño versus global warming. J. Clim. 21, 5835–5851 (2008).

6. Allen, R. J., Norris, J. R. & Kovilakam, M. Influence of anthropogenic aerosols and the Pacific Decadal Oscillation on tropical belt width. Nat. Geosci. 7, 270–274 (2014).

7. Nguyen, H., Evans, A., Lucas, C., Smith, I. & Timbal, B. The Hadley circulation in reanalyses: climatology, variability, and change. J. Clim. 26, 3357–3376 (2013).

8. D’Agostino, R. & Lionello, P. Evidence of global warming impact on the evolution of the Hadley circulation in ECMWF centennial reanalyses. Clim. Dyn. 48, 3047–3060 (2017).

9. Adam, O., Schneider, T. & Harnik, N. Role of changes in mean temperatures versus temperature gradients in the recent widening of the hadley circulation. J. Clim. 27, 7450–7461 (2014).

10. Hu, Y., Tao, L. & Liu, J. Poleward expansion of the Hadley circulation in CMIP5 simulations. Adv. Atmos. Sci. 30, 790–795 (2013).

11. Allen, R. J., Sherwood, S. C., Norris, J. R. & Zender, C. S. Recent Northern Hemisphere tropical expansion primarily driven by black carbon and tropospheric ozone. Nature 485, 350–354 (2012).

12. Wang, H., Xie, S.-P. & Liu, Q. Comparison of climate response to anthropogenic aerosol versus greenhouse gas forcing: distinct patterns. J. Clim. 29, 5175–5188 (2016).

13. Polvani, L. M., Waugh, D. W., Correa, G. J. P. & Son, S.-W. Stratospheric ozone depletion: the main driver of twentieth-century atmospheric circulation changes in the Southern Hemisphere. J. Clim. 24, 795–812 (2011).

14. Garfinkel, C. I., Waugh, D. W. & Polvani, L. M. Recent Hadley cell expansion: the role of internal atmospheric variability in reconciling modeled and observed trends. Geophys. Res. Lett. 42, 10824–10831 (2015).

15. Johanson, C. M. & Fu, Q. Hadley cell widening: model simulations versus observations. J. Clim. 22, 2713–2725 (2009).

16. Lu, J., Deser, C. & Reichler, T. Cause of the widening of the tropical belt since 1958. Geophys. Res. Lett. 36, L03803 (2009).

17. Brönnimann, S. et al. Southward shift of the northern tropical belt from 1945 to 1980. Nat. Geosci. 8, 969–974 (2015).

18. Davis, N. & Birner, T. On the discrepancies in tropical belt expansion between reanalyses and climate models and among tropical belt width metrics. J. Clim. 30, 1211–1231 (2017).

19. Davis, N. & Birner, T. Climate model biases in the width of the tropical belt. J. Clim. 29, 1935–1954 (2016).

20. Compo, G. P. et al. The twentieth century reanalysis project. Q. J. R. Meteorol. Soc. 137, 1–28 (2011).

21. Oort, A. H. & Yienger, J. J. Observed interannual variability in the Hadley circulation and its connection to ENSO. J. Clim. 9, 2751–2767 (1996).

22. Nguyen, H. et al. Variability of the extent of the Hadley circulation in the southern hemisphere: a regional perspective. Clim. Dyn. 50, 129–142 (2018).

23. Horel, J. D. & Wallace, J. M. Planetary-scale atmospheric phenomena associated with the Southern Oscillation. Mon. Weather Rev. 109, 813–829 (1981).

24. Li, J. et al. El Niño modulations over the past seven centuries. Nat. Clim. Change 3, 822–826 (2013).

25. Liu, Y. et al. Recent enhancement of central Pacific El Niño variability relative to last eight centuries. Nat. Commun. 8, 15386 (2017).

26. Liu, Z. et al. Pacific North American circulation pattern links external forcing and North American hydroclimatic change over the past millennium. Proc. Natl Acad. Sci. USA 114, 3340 (2017).

27. D’Arrigo, R. & Wilson, R. On the Asian expression of the PDO. Int. J. Climatol. 26, 1607–1617 (2006).

28. Haigh, J. D., Blackburn, M. & Day, R. The response of tropospheric circulation to perturbations in lower-stratospheric temperature. J. Clim. 18, 3672–3685 (2005).

29. Sigl, M. et al. Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature 523, 543–549 (2015).

30. Robock, A. Volcanic eruptions and climate. Rev. Geophys. 38, 191–219 (2000).

31. Iles, C. E., Hegerl, G. C., Schurer, A. P. & Zhang, X. The effect of volcanic eruptions on global precipitation. J. Geophys. Res. Atmos. 118, 8770–8786 (2013).

32. Wilson, R. et al. Last millennium Northern Hemisphere summer temperatures from tree rings. Part I: The long term context. Quat. Sci. Rev. 134, 1–18 (2016).

33. Luterbacher, J. & Pfister, C. The year without a summer. Nat. Geosci. 8, 246 (2015).

34. Emile-Geay, J., Seager, R., Cane, M. A., Cook, E. R. & Haug, G. H. Volcanoes and ENSO over the past millennium. J. Clim. 21, 3134–3148 (2008).

35. Clement, A. C., Seager, R., Cane, M. A. & Zebiak, S. E. An ocean dynamical thermostat. J. Clim. 9, 2190–2196 (1996).

36. Grove, J. The Little Ice Age (Methuen, London, 1988).

37. Mann, M. E. et al. Global signatures and dynamical origins of the Little Ice Age and medieval climate anomaly. Science 326, 1256–1260 (2009).

38. Denniston, R. F. Expansion and contraction of the Indo-pacific tropical rain belt over the last three millennia. Sci. Rep. 6, 34485 (2016).

39. Ridley, H. E. et al. Aerosol forcing of the position of the intertropical convergence zone since ad 1550. Nat. Geosci. 8, 195–200 (2015).

40. Lechleitner, F. A. et al. Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw. Sci. Rep. 7, 45809 (2017).

41. Stahle, D. W. et al. Tree-ring data document 16th century megadrought over North America. Eos Trans. AGU 81, 121–125 (2000).

42. Touchan, R., Akkemik, Ü., Hughes, M. K. & Erkan, N. May–June precipitation reconstruction of southwestern Anatolia, Turkey during the last 900 years from tree rings. Quat. Res. 68, 196–202 (2007).

43. Shen, C., Wang, W.-C., Hao, Z. & Gong, W. Exceptional drought events over eastern China during the last five centuries. Clim. Change 85, 453–471 (2007).

44. Stahle, D. W., Cleaveland, M. K., Blanton, D. B., Therrell, M. D. & Gay, D. A. The lost colony and Jamestown droughts. Science 280, 564 (1998).

45. Xoplaki, E. et al. Modelling climate and societal resilience in the eastern Mediterranean in the last millennium. Hum. Ecol. 46, 363–379 (2018).

46. Cai, W. et al. Increased frequency of extreme La Niña events under greenhouse warming. Nat. Clim. Change 5, 132–137 (2015).

47. Allen, R. J. & Ajoku, O. Future aerosol reductions and widening of the northern tropical belt. J. Geophys. Res. Atmos. 121, 6765–6786 (2016).

48. Caldeira, K., Bala, G. & Cao, L. The science of geoengineering. Annu. Rev. Earth. Planet. Sci. 41, 231–256 (2013).

49. Ricke, K. L., Morgan, M. G. & Allen, M. R. Regional climate response to solar-radiation management. Nat. Geosci. 3, 537 (2010).

50. Jones, A. C. et al. Impacts of hemispheric solar geoengineering on tropical cyclone frequency. Nat. Commun. 8, 1382 (2017).

51. Studholme, J. & Gulev, S. Concurrent changes to Hadley circulation and the meridional distribution of tropical cyclones. J. Clim. 31, 4367–4389 (2018).

52. Donat, M. G. et al. Reanalysis suggests long-term upward trends in European storminess since 1871. Geophys. Res. Lett. 38, L14703 (2011).

53. Harris, I., Jones, P. D., Osborn, T. J. & Lister, D. H. Updated high-resolution grids of monthly climatic observations—the CRU TS3.10 Dataset. Int. J. Climatol. 34, 623–642 (2014).

54. Trouet, V. & Van Oldenborgh, G. J. KNMI Climate Explorer: a web-based research tool for high-resolution paleoclimatology. Tree-Ring Res. 69, 3–13 (2013).

55. Rayner, N. A. et al. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res. 108, 4407 (2003).

56. Zhang, Y., Wallace, J. M. & Battisti, D. S. ENSO-like interdecadal variability: 1900–93. J. Clim. 10, 1004–1020 (1997).

57. Mantua, N. J., Hare, S. R., Zhang, Y., Wallace, J. M. & Francis, R. C. A Pacific interdecadal climate oscillation with impacts on salmon production. Bull. Am. Meteorol. Soc. 78, 1069–1079 (1997).

58. Trouet, V. A tree-ring based late summer temperature reconstruction (ad 1675–1980) for the Northeastern Mediterranean. Radiocarbon 56, S69–S78 (2014).

59. Frank, D., Esper, J. & Cook, E. R. On variance adjustments in tree-ring chronology development. Tree Rings Archaeol. Climatol. Ecol. TRACE 4, 56–66 (2006).

60. Cook, E. R., Meko, D. M., Stahle, D. W. & Cleaveland, M. K. Drought reconstructions for the continental United States. J. Clim. 12, 18 (1999).

61. Esper, J. et al. Long-term drought severity variations in Morocco. Geophys. Res. Lett. 34, L17702 (2007).

62. Briffa, K. R. et al. Fennoscandian summers from ad 500: temperature changes on short and long timescales. Clim. Dyn. 7, 111–119 (1992).

63. Jenkins, G. & Watts, D. Spectral analysis and its applications. Louvain Econ. Rev. 36, 554–554 (1970).

64. Torrence, C. & Compo, G. P. A practical guide to wavelet analysis. Bull. Am. Meteorol. Soc. 79, 61–78 (1998).

65. Bunn, A. G. A dendrochronology program library in R (dplR). Dendrochronologia 26, 115–124 (2008).

66. Crowley, T. J. & Unterman, M. B. Technical details concerning development of a 1200 yr proxy index for global volcanism. Earth Syst. Sci. Data 5, 187–197 (2013).

67. Gao, C., Robock, A. & Ammann, C. Volcanic forcing of climate over the past 1500 years: an improved ice core-based index for climate models. J. Geophys. Res. 113, D23111 (2008).

68. Sigl, M. et al. A new bipolar ice core record of volcanism from WAIS Divide and NEEM and implications for climate forcing of the last 2000 years. J. Geophys. Res. Atmospheres 118, 1151–1169 (2013).