New paper finds South Pacific precipitation variability over past 600 years was entirely natural

A new paper published in Climate of the Past reconstructs rainfall in the tropical South Pacific over the past 600 years and shows precipitation levels at the end of the record in 2000 were at the mean of the past 600 years, and that 20th century precipitation was by no means unusual, unprecedented, or unnatural in comparison to the past 600 years. The authors attribute the extreme, abrupt, and periodic changes in rainfall entirely to natural variability and rule out external forcing including AGW and natural forcings as a cause.

The authors

"present evidence for large (~1.5 m), abrupt, and periodic changes in total annual rainfall amount on decadal to multidecadal timescales since 1423 ± 5 CE (Common Era) in the Solomon Islands." 

"The Solomons record of PDV [Pacific Decadal Variability] is not associated with variations in external forcings, but rather results from internal [natural] climate variability. The 600 yr Solomon Islands stalagmite δ18O record indicates that decadal oscillations in rainfall are a persistent characteristic of SPCZ-related climate variability."

Top graph is a precipitation proxy and shows 20th century precipitation was by no means unusual, unprecedented, or unnatural. The dashed horizontal orange lines are 1 standard deviation from the 600-year mean, and precipitation levels at the end of the record in 2000 were at the mean of the past 600 years. 

Clim. Past, 10, 1319-1332, 2014 www.clim-past.net/10/1319/2014/ doi:10.5194/cp-10-1319-2014 Persistent decadal-scale rainfall variability in the tropical South Pacific Convergence Zone through the past six centuries

C. R. Maupin^1,2, J. W. Partin¹, C.-C. Shen³, T. M. Quinn^1,2, K. Lin³, F. W. Taylor¹, J. L. Banner², K. Thirumalai^1,2, and D. J. Sinclair^4
1Institute for Geophysics, Jackson School of Geosciences, University of Texas, Austin, Texas 78758, USA
²Department of Geological Sciences, Jackson School of Geosciences, University of Texas, Austin, Texas 78705, USA
³High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, Taipei 106, Taiwan
⁴Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey 08901, USA
Abstract. Modern Pacific decadal variability (PDV) has global impacts; hence records of PDV from the pre-instrumental period are needed to better inform models that are used to project future climate variability. We focus here on reconstructing rainfall in the western tropical Pacific (Solomon Islands; ~ 9.5° S, ~160° E), a region directly influenced by PDV, using cave deposits (stalagmite). A relationship is developed between δ¹⁸O variations in the stalagmite and local rainfall amount to produce a 600 yr record of rainfall variability from the South Pacific Convergence Zone (SPCZ). We present evidence for large (~1.5 m), abrupt, and periodic changes in total annual rainfall amount on decadal to multidecadal timescales since 1423 ± 5 CE (Common Era) in the Solomon Islands. The timing of the decadal changes in rainfall inferred from the 20th century portion of the stalagmite δ¹⁸O record coincides with previously identified decadal shifts in PDV-related Pacific ocean–atmosphere behavior (Clement et al., 2011; Deser et al., 2004). The Solomons record of PDV is not associated with variations in external forcings, but rather results from internal [natural] climate variability. The 600 yr Solomon Islands stalagmite δ¹⁸O record indicates that decadal oscillations in rainfall are a persistent characteristic of SPCZ-related climate variability.