Observations show that summer rainfall over large parts of South Asia has declined over the past five to six decades. It remains unclear, however, whether this trend is due to natural variability or increased anthropogenic aerosol loading over South Asia. Here we use stable oxygen isotopes in speleothems from northern India to reconstruct variations in Indian monsoon rainfall over the last two millennia. We find that within the long-term context of our record, the current drying trend is not outside the envelope of monsoon' s oscillatory variability, albeit at the lower edge of this variance. Furthermore, the magnitude of multi-decadal oscillatory variability in monsoon rainfall inferred from our proxy record is comparable to model estimates of anthropogenic-forced trends of mean monsoon rainfall in the 21st century under various emission scenarios. Our results suggest that anthropogenic-forced changes in monsoon rainfall will remain difficult to detect against a backdrop of large natural variability.
Bibliographical noteFunding Information:
We gratefully acknowledge the Chinese National Science Foundation grants to H.C. (NBRP 2013CB955902 and NSFC 41230524) and the National Science Foundation grants to A.S. (ATM: 0823554), R.L.E. and H.C. (1211299, 1103403 and 1337693) for funding this research. S.F.M.B. acknowledges financial support from the Swiss National Foundation (Sinergia grant CRSI22-132646/1). We thank Lowell Stott, Miguel Rincon and Tannia Ochoa for the stable isotopic measurements.
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