@article{0968eb8f5b6f4fa08c802e38065e2e44,
title = "Aerosol forcing of the position of the intertropical convergence zone since ad 1550",
abstract = "The position of the intertropical convergence zone is an important control on the distribution of low-latitude precipitation. Its position is largely controlled by hemisphere temperature contrasts. The release of aerosols by human activities may have resulted in a southward shift of the intertropical convergence zone since the early 1900s (refs,) by muting the warming of the Northern Hemisphere relative to the Southern Hemisphere over this interval, but this proposed shift remains equivocal. Here we reconstruct monthly rainfall over Belize for the past 456 years from variations in the carbon isotope composition of a well-dated, monthly resolved speleothem. We identify an unprecedented drying trend since ad 1850 that indicates a southward displacement of the intertropical convergence zone. This drying coincides with increasing aerosol emissions in the Northern Hemisphere and also marks a breakdown in the relationship between Northern Hemisphere temperatures and the position of the intertropical convergence zone observed earlier in the record. We also identify nine short-lived drying events since ad 1550 each following a large volcanic eruption in the Northern Hemisphere. We conclude that anthropogenic aerosol emissions have led to a reduction of rainfall in the northern tropics during the twentieth century, and suggest that geographic changes in aerosol emissions should be considered when assessing potential future rainfall shifts in the tropics.",
author = "Ridley, {Harriet E.} and Yemane Asmerom and Baldini, {James U.L.} and Breitenbach, {Sebastian F.M.} and Aquino, {Valorie V.} and Prufer, {Keith M.} and Culleton, {Brendan J.} and Victor Polyak and Lechleitner, {Franziska A.} and Kennett, {Douglas J.} and Minghua Zhang and Norbert Marwan and Macpherson, {Colin G.} and Baldini, {Lisa M.} and Tingyin Xiao and Peterkin, {Joanne L.} and Jaime Awe and Haug, {Gerald H.}",
note = "Funding Information: rates); increased bedrock carbon contributions; and reduced soil bioproductivity, all contributing to a more positive δ13C. Conversely, wetter conditions result in more negative δ13C (see Supplementary Information). This interpretation is supported by the remarkable, demonstrably annual δ13C cycle reflecting seasonal water recharge conditions, as well as by interpretations of other Belizean stalagmite δ13C records as reflecting rainfall, notably ref. 15, linking pronounced δ13C increases to El Ni{\~n}o-related rainfall reductions, and ref. 16 linking δ13C shifts over the past 3,300 years to rainfall. We note that these two studies represent the two published speleothem records from cave sites closest to Yok Balum Cave (ATM Cave, ∼100 km to the north, and Macal Chasm, ∼80 km to the north), and that both used δ13C as a palaeorainfall proxy (Supplementary Fig. 4). The similarity between the YOK-G δ13C record and the Cariaco Basin record ITCZ rainfall record10 also strongly supports this interpretation. We stress that δ18O is also an extremely useful complementary rainfall proxy17 (see Supplementary Information), but we believe that under the conditions at our site, δ13C is more sensitive to subtle shifts in recharge. Publisher Copyright: {\textcopyright} 2015 Macmillan Publishers Limited.",
year = "2015",
month = mar,
day = "4",
doi = "10.1038/ngeo2353",
language = "English (US)",
volume = "8",
pages = "195--200",
journal = "Nature Geoscience",
issn = "1752-0894",
publisher = "Nature Publishing Group",
number = "3",
}