Twentieth-century hydroclimate changes consistent with human influence


Although anthropogenic climate change is expected to have caused large shifts in temperature and rainfall, the detection of human influence on global drought has been complicated by large internal variability and the brevity of observational records. Here we address these challenges using reconstructions of the Palmer drought severity index obtained with data from tree rings that span the past millennium. We show that three distinct periods are identifiable in climate models, observations and reconstructions during the twentieth century. In recent decades (1981 to present), the signal of greenhouse gas forcing is present but not yet detectable at high confidence. Observations and reconstructions differ significantly from an expected pattern of greenhouse gas forcing around mid-century (1950–1975), coinciding with a global increase in aerosol forcing. In the first half of the century (1900–1949), however, a signal of greenhouse-gas-forced change is robustly detectable. Multiple observational datasets and reconstructions using data from tree rings confirm that human activities were probably affecting the worldwide risk of droughts as early as the beginning of the twentieth century.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Regional fingerprints.
Fig. 2: Global fingerprints.
Fig. 3: Projections and time of emergence.
Fig. 4: Detection and attribution results.
Fig. 5: Aerosol attribution.
Fig. 6: Regional detection and attribution.

Data availability

All model data used in this paper are available through the Earth System Grid (see and freely available for download. All observational and reconstructed PDSI and soil moisture data are freely available for download from the indicated links. Data for NADA, MXDA, OWDA,; ANZDA,; MADA,; CRU,; DAI,; MERRA-2,; GLEAM,

Code availability

Analysis code written in Python is available at GitHub (


  1. 1.

    Cook, E. R., Seager, R., Cane, M. A. & Stahle, D. W. North American drought: reconstructions, causes, and consequences. Earth Sci. Rev. 81, 93–134 (2007).

    ADS  Article  Google Scholar 

  2. 2.

    Cook, E. R. et al. Megadroughts in North America: placing IPCC projections of hydroclimatic change in a long-term palaeoclimate context. J. Quaternary Sci. 25, 48–61 (2010).

    ADS  Article  Google Scholar 

  3. 3.

    Cook, E. R. et al. Old World megadroughts and pluvials during the Common Era. Sci. Adv. 1, e1500561 (2015).

    ADS  Article  Google Scholar 

  4. 4.

    Stahle, D. W. et al. The Mexican drought atlas: tree-ring reconstructions of the soil moisture balance during the late pre-Hispanic, colonial, and modern eras. Quat. Sci. Rev. 149, 34–60 (2016).

    ADS  Article  Google Scholar 

  5. 5.

    Cook, E. R. et al. Asian monsoon failure and megadrought during the last millennium. Science 328, 486–489 (2010).

    ADS  CAS  Article  Google Scholar 

  6. 6.

    Palmer, J. G. et al. Drought variability in the eastern Australia and New Zealand summer drought atlas (ANZDA, ce 1500–2012) modulated by the interdecadal pacific oscillation. Environ. Res. Lett. 10, 124002 (2015).

    ADS  Article  Google Scholar 

  7. 7.

    Cook, B. I., Anchukaitis, K. J., Touchan, R., Meko, D. M. & Cook, E. R. Spatiotemporal drought variability in the Mediterranean over the last 900 years. J. Geophys. Res. 121, 2060–2074 (2016).

    Google Scholar 

  8. 8.

    Griffin, D. & Anchukaitis, K. J. How unusual is the 2012–2014 California drought? Geophys. Res. Lett. 41, 9017–9023 (2014).

    ADS  Article  Google Scholar 

  9. 9.

    Cook, B. I., Seager, R. & Smerdon, J. E. The worst North American drought year of the last millennium: 1934. Geophys. Res. Lett. 41, 7298–7305 (2014).

    ADS  Article  Google Scholar 

  10. 10.

    Bindoff, N. et al. Detection and Attribution of Climate Change: from Global to Regional Vol. 10, 867–952 (Cambridge Univ. Press, Cambridge, 2013).

    Google Scholar 

  11. 11.

    Berg, A. & Sheffield, J. Climate change and drought: the soil moisture perspective. Curr. Clim. Change Rep. 4, 180–191 (2018).

    Article  Google Scholar 

  12. 12.

    Bonfils, C. et al. Competing influences of anthropogenic warming, ENSO, and plant physiology on future terrestrial aridity. J. Clim. 30, 6883–6904 (2017).

    ADS  Article  Google Scholar 

  13. 13.

    Milly, P. C. & Dunne, K. A. Potential evapotranspiration and continental drying. Nat. Clim. Change 6, 946–949 (2016).

    ADS  Article  Google Scholar 

  14. 14.

    Swann, A. L., Hoffman, F. M., Koven, C. D. & Randerson, J. T. Plant responses to increasing CO2 reduce estimates of climate impacts on drought severity. Proc. Natl Acad. Sci. USA 113, 10019–10024 (2016).

    ADS  CAS  Article  Google Scholar 

  15. 15.

    Taylor, K. E., Stouffer, R. J. & Meehl, G. A. An overview of CMIP5 and the experiment design. Bull. Am. Meteorol. Soc. 93, 485–498 (2012).

    ADS  Article  Google Scholar 

  16. 16.

    Martens, B. et al. GLEAM v3: satellite-based land evaporation and root-zone soil moisture. Geosci. Model Dev. 10, 1903–1925 (2017).

    ADS  Article  Google Scholar 

  17. 17.

    Reichle, R. H. et al. Assessment of MERRA-2 land surface hydrology estimates. J. Clim. 30, 2937–2960 (2017).

    ADS  Article  Google Scholar 

  18. 18.

    Santer, B. et al. Separating signal and noise in atmospheric temperature changes: the importance of timescale. J. Geophys. Res. 116, D22105 (2011).

    ADS  Article  Google Scholar 

  19. 19.

    Santer, B. D. et al. Ocean variability and its influence on the detectability of greenhouse warming signals. J. Geophys. Res. 100, 10693–10725 (1995).

    ADS  Article  Google Scholar 

  20. 20.

    Santer, B. D. et al. Identifying human influences on atmospheric temperature. Proc. Natl Acad. Sci. USA 110, 26–33 (2013).

    ADS  CAS  Article  Google Scholar 

  21. 21.

    Marvel, K. & Bonfils, C. Identifying external influences on global precipitation. Proc. Natl Acad. Sci. USA 110, 19301–19306 (2013).

    ADS  CAS  Article  Google Scholar 

  22. 22.

    van Vuuren, D. P. et al. The representative concentration pathways: an overview. Clim. Change 109, 5–31 (2011).

    Article  Google Scholar 

  23. 23.

    Cook, B. I., Smerdon, J. E., Seager, R. & Coats, S. Global warming and 21st century drying. Clim. Dyn. 43, 2607–2627 (2014).

    Article  Google Scholar 

  24. 24.

    Dai, A. Characteristics and trends in various forms of the Palmer drought severity index during 1900–2008. J. Geophys. Res. 116, D12115 (2011).

    ADS  Article  Google Scholar 

  25. 25.

    van der Schrier, G., Briffa, K., Jones, P. & Osborn, T. Summer moisture variability across Europe. J. Clim. 19, 2818–2834 (2006).

    ADS  Article  Google Scholar 

  26. 26.

    Stott, P. A. & Tett, S. F. Scale-dependent detection of climate change. J. Clim. 11, 3282–3294 (1998).

    ADS  Article  Google Scholar 

  27. 27.

    Marvel, K. et al. External influences on modeled and observed cloud trends. J. Clim. 28, 4820–4840 (2015).

    ADS  Article  Google Scholar 

  28. 28.

    Baek, S. H. et al. Precipitation, temperature, and teleconnection signals across the combined North American, monsoon Asia, and Old World drought atlases. J. Clim. 30, 7141–7155 (2017).

    ADS  Article  Google Scholar 

  29. 29.

    Santer, B. D. et al. Identification of human-induced changes in atmospheric moisture content. Proc. Natl Acad. Sci. USA 104, 15248–15253 (2007).

    ADS  CAS  Article  Google Scholar 

  30. 30.

    Santer, B. D. et al. Human and natural influences on the changing thermal structure of the atmosphere. Proc. Natl Acad. Sci. USA 110, 17235–17240 (2013).

    ADS  CAS  Article  Google Scholar 

  31. 31.

    Hegerl, G. C. et al. Good Practice Guidance Paper on Detection and Attribution Related to Anthropogenic Climate Change (IPCC, 2010).

  32. 32.

    Mastrandrea, M. D. et al. Guidance Note for Lead Authors of the IPCC Fifth Assessment Report on Consistent Treatment of Uncertainties (IPCC, 2010).

  33. 33.

    Dai, A. & Zhao, T. Uncertainties in historical changes and future projections of drought. Part I: estimates of historical drought changes. Clim. Change 144, 519–533 (2017).

    ADS  Article  Google Scholar 

  34. 34.

    Skeie, R. et al. Anthropogenic radiative forcing time series from pre-industrial times until 2010. Atmos. Chem. Phys. 11, 11827–11857 (2011).

    ADS  CAS  Article  Google Scholar 

  35. 35.

    Miller, R. L. et al. CMIP5 historical simulations (1850–2012) with GISS ModelE2. J. Adv. Model. Earth Syst. 6, 441–478 (2014).

    ADS  Article  Google Scholar 

  36. 36.

    Biasutti, M. & Giannini, A. Robust Sahel drying in response to late 20th century forcings. Geophys. Res. Lett. 33, L11706 (2006).

    ADS  Article  Google Scholar 

  37. 37.

    Polson, D., Bollasina, M., Hegerl, G. & Wilcox, L. Decreased monsoon precipitation in the Northern Hemisphere due to anthropogenic aerosols. Geophys. Res. Lett. 41, 6023–6029 (2014).

    ADS  Article  Google Scholar 

  38. 38.

    Bollasina, M. A., Ming, Y. & Ramaswamy, V. Anthropogenic aerosols and the weakening of the South Asian summer monsoon. Science 334, 502–505 (2011).

    ADS  CAS  Article  Google Scholar 

  39. 39.

    Wilcox, L. J., Highwood, E. J. & Dunstone, N. J. The influence of anthropogenic aerosol on multi-decadal variations of historical global climate. Environ. Res. Lett. 8, 024033 (2013).

    ADS  Article  Google Scholar 

  40. 40.

    Pincus, R., Forster, P. M. & Stevens, B. The radiative forcing model intercomparison project (RFMIP): experimental protocol for CMIP6. Geosci. Model Dev. 9, 3447–3460 (2016).

    ADS  Article  Google Scholar 

  41. 41.

    Zelinka, M. D., Andrews, T., Forster, P. M. & Taylor, K. E. Quantifying components of aerosol–cloud–radiation interactions in climate models. J. Geophys. Res. 119, 7599–7615 (2014).

    Google Scholar 

  42. 42.

    Ekman, A. M. Do sophisticated parameterizations of aerosol-cloud interactions in CMIP5 models improve the representation of recent observed temperature trends? J. Geophys. Res. 119, 817–832 (2014).

    Google Scholar 

  43. 43.

    Gelaro, R. et al. The modern-era retrospective analysis for research and applications, version 2 (MERRA-2). J. Clim. 30, 5419–5454 (2017).

    ADS  Article  Google Scholar 

  44. 44.

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

    ADS  CAS  Article  Google Scholar 

  45. 45.

    Kosaka, Y. & Xie, S.-P. Recent global-warming hiatus tied to equatorial Pacific surface cooling. Nature 501, 403–407 (2013).

    ADS  CAS  Article  Google Scholar 

  46. 46.

    England, M. H. et al. Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus. Nat. Clim. Change 4, 222–227 (2014).

    ADS  Article  Google Scholar 

  47. 47.

    Schmidt, G. A., Shindell, D. T. & Tsigaridis, K. Reconciling warming trends. Nat. Geosci. 7, 158–160 (2014).

    ADS  CAS  Article  Google Scholar 

  48. 48.

    Johansson, D. J. A., O’Neill, B. C., Tebaldi, C. & Häggström, O. Equilibrium climate sensitivity in light of observations over the warming hiatus. Nat. Clim. Change 5, 449–453 (2015).

    ADS  CAS  Article  Google Scholar 

  49. 49.

    Risbey, J. S. et al. A fluctuation in surface temperature in historical context: reassessment and retrospective on the evidence. Environ. Res. Lett. 13, 123008 (2018).

    ADS  Article  Google Scholar 

  50. 50.

    Trenberth, K. E., Fasullo, J. T., Branstator, G. & Phillips, A. S. Seasonal aspects of the recent pause in surface warming. Nat. Clim. Change 4, 911–916 (2014).

    ADS  Article  Google Scholar 

  51. 51.

    Palmer, W. C. Meteorological Drought. Research Paper No. 45 (US Department of Commerce, 1965).

  52. 52.

    Guttman, N. B. Comparing the Palmer drought index and the standardized precipitation index. J. Am. Water Resour. Assoc. 34, 113–121 (1998).

    ADS  Article  Google Scholar 

  53. 53.

    Vicente-Serrano, S. M., Beguería, S. & López-Moreno, J. I. A multiscalar drought index sensitive to global warming: the standardized precipitation evapotranspiration index. J. Clim. 23, 1696–1718 (2010).

    ADS  Article  Google Scholar 

  54. 54.

    Trenberth, K. E. et al. Global warming and changes in drought. Nat. Clim. Change 4, 17–22 (2014).

    ADS  Article  Google Scholar 

  55. 55.

    Williams, A. P. et al. Contribution of anthropogenic warming to California drought during 2012–2014. Geophys. Res. Lett. 42, 6819–6828 (2015).

    ADS  Article  Google Scholar 

  56. 56.

    Seneviratne, S. I. et al. Investigating soil moisture–climate interactions in a changing climate: a review. Earth Sci. Rev. 99, 125–161 (2010).

    ADS  CAS  Article  Google Scholar 

  57. 57.

    Yin, D., Roderick, M. L., Leech, G., Sun, F. & Huang, Y. The contribution of reduction in evaporative cooling to higher surface air temperatures during drought. Geophys. Res. Lett. 41, 7891–7897 (2014).

    ADS  Article  Google Scholar 

  58. 58.

    Dai, A. Increasing drought under global warming in observations and models. Nat. Clim. Change 3, 52–58 (2013).

    ADS  Article  Google Scholar 

  59. 59.

    Feng, S., Trnka, M., Hayes, M. & Zhang, Y. Why do different drought indices show distinct future drought risk outcomes in the US great plains? J. Clim. 30, 265–278 (2017).

    ADS  Article  Google Scholar 

  60. 60.

    Dai, A., Trenberth, K. E. & Qian, T. A global dataset of Palmer drought severity index for 1870–2002: relationship with soil moisture and effects of surface warming. J. Hydrometeorol. 5, 1117–1130 (2004).

    ADS  Article  Google Scholar 

  61. 61.

    Hasselmann, K. Optimal fingerprints for the detection of time-dependent climate change. J. Clim. 6, 1957–1971 (1993).

    ADS  Article  Google Scholar 

  62. 62.

    Smith, S. J. et al. Anthropogenic sulfur dioxide emissions: 1850–2005. Atmos. Chem. Phys. 11, 1101–1116 (2011).

    ADS  CAS  Article  Google Scholar 

Download references


We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups (listed in Supplementary Table 3) for producing and making available their model output. For CMIP, the US Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provided coordinating support and led development of the software infrastructure in partnership with the Global Organization for Earth System Science Portals. We thank K. Taylor, G. Schmidt and R. Pincus for discussions. K.M. and C.J.W.B. were supported by the US Department of Energy Biological and Environmental Research Grant DE-SC0014423. K.M., B.I.C. and A.P.W. were supported for this work by the NASA Modeling, Analysis, and Prediction program (NASA 80NSSC17K0265). J.E.S. was supported in part by US National Science Foundation (NSF) grants AGS-1243204 and AGS-1602581; J.E.S. and A.P.W. were further supported by NSF grant OISE-1743738 and A.P.W. was supported by NSF grant AGS-1703029. P.J.D. was supported through PCDMI SFA funding from the DOE Regional and Global Model Analysis Program. Work at LLNL was performed under the auspices of the US Department of Energy under contract DE-AC52-07NA27344.

Reviewer information

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

Author information




K.M. and B.I.C. designed the study. K.M. performed the analyses with contributions from B.I.C. C.J.W.B. contributed to developing and applying the detection and attribution methodology. A.P.W. provided the code to calculate PSDI from CMIP5 model data. J.E.S. and A.P.W provided guidance on interpretation of the drought atlas data. P.J.D. provided the code to download and access CMIP5 data. K.M. and B.I.C. wrote the manuscript with contributions from all authors.

Corresponding author

Correspondence to Kate Marvel.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Noise estimates.

Distributions of overlapping (all possible) 50-year trends in the projection of preindustrial reconstructions (1400–1850) of the drought atlas onto the fingerprints shown in Fig. 1a–e. Best-fit Gaussian distributions are overlaid for visual clarity.

Extended Data Fig. 2 Trends in the GDA.

Linear trends in the multi-model mean CMIP5 historical simulations extended to 2100 with RCP8.5. Trends are calculated for each grid cell using ordinary least-squares regression. The pattern is extremely similar to the fingerprint shown in Fig. 2a, with the pattern correlation exceeding 99%.

Extended Data Figure 3 Models with and without aerosol indirect effects.

a, b, The approximated aerosol fingerprint for models with (a) and without (b) aerosol indirect effects, defined as the leading EOF of the multi-model average historical simulations over the years 1950–1975. Models are grouped according to the previously reported classifications39. c, d, Associated principal components for the fingerprints shown in a and b.

Extended Data Figure 4 Noise time dependence.

The standard deviation of all 50-year trends in projections of the drought atlas for 1400–1850 onto the fingerprints in Fig. 1a–e were calculated from years early (x axis) and late (y axis) in the preindustrial record. There is no evidence for a systematic difference in noise estimates across drought atlas regions.

Supplementary information

Supplementary Table 1

S/N ratios and percentiles relative to tree ring noise and forced (H85) simulations for individual drought atlases and combinations of drought atlases

Supplementary Table 2

For the CMIP5 models, the number of soil layers and approximate depths used for the calculation of surface and root zone soil moisture indices from variable mrlsl

Supplementary Table 3

Modeling group information for the CMIP5 models used in this study

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Marvel, K., Cook, B.I., Bonfils, C. et al. Twentieth-century hydroclimate changes consistent with human influence. Nature 569, 59–65 (2019).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing