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TitleSupplementary data, code, and information for ‘Interhemispheric antiphasing of neotropical precipitation during the past millennium’ (PNAS, Steinman et al. 2022)
AbstractUncertainty about the influence of anthropogenic radiative forcing on the position and strength of convective rainfall in the Intertropical Convergence Zone (ITCZ) inhibits our ability to project future tropical hydroclimate change in a warmer world. Paleoclimatic and modeling data inform on the timescales and mechanisms of ITCZ variability; yet a comprehensive, long-term perspective remains elusive. Here, we quantify the evolution of neotropical hydroclimate over the pre-industrial past millennium (850 to 1850 CE) using a synthesis of 48 paleo-records, accounting for uncertainties in paleo-archive age models. We show that an interhemispheric pattern of precipitation anti-phasing occurred on multi-century timescales in response to changes in natural radiative forcing. The conventionally-defined "Little Ice Age" (1450 to 1850 CE) was marked by a clear shift toward wetter conditions in the southern neotropics and a less distinct and spatiotemporally complex transition toward drier conditions in the northern neotropics. This pattern of hydroclimatic change is consistent with results from climate model simulations indicating that a relative cooling of the Northern Hemisphere caused a southward shift in the thermal equator across the Atlantic Basin and a southerly displacement of the ITCZ in the tropical Americas, with volcanic forcing as the principal driver. These findings are at odds with proxy-based reconstructions of ITCZ behavior in the western Pacific basin, where changes in ITCZ width and intensity, rather than mean position, appear to have driven hydroclimate transitions over the last millennium. This reinforces the idea that ITCZ responses to external forcing are region-specific, complicating projections of the tropical precipitation response to global warming.
MetadataClick here for full metadata
Data DOIdoi:10.26208/87ba-yh40

Steinman, B. A.
Penn State Department of Meteorology
Stansell, N.
Northern Illinois University
Mann, M. E.
Penn State Department of Meteorology
Cooke, C. A.
University of Alberta
Abbott, M. B.
University of Pittsburgh
Vuille, M.
SUNY Albany
Bird, B. W.
Indiana University-Purdue University, Indianapolis
Lachniet, M. S.
University of Nevada, Las Vegas
Fernandez, A.
University of Minnesota Duluth

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Steinman, B.A., Stansell, N., Mann, M.E., Cooke, C.A., Abbott, M.B., Vuille, M., Bird, B.W., Lachniet, M.S., Fernandez, A., Interhemispheric antiphasing of neotropical precipitation during the past millennium, Proc. Nat. Acad. Sci., 2022 (in press)