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Aerosol forcing of the position of the intertropical convergence zone since AD 1550.

Ridley, Harriet E. and Asmerom, Yemane and Baldini, James U. L. and Breitenbach, Sebastian F. M. and Aquino, Valorie V. and Prufer, Keith M. and Culleton, Brendan J. and Polyak, Victor and Lechleitner, Franziska A. and Kennett, Douglas J. and Zhang, Minghua and Marwan, Norbert and Macpherson, Colin G. and Baldini, Lisa M. and Xiao, Tingyin and Peterkin, Joanne L. and Awe, Jaime and Haug, Gerald H. (2015) 'Aerosol forcing of the position of the intertropical convergence zone since AD 1550.', Nature geoscience., 8 (3). pp. 195-200.

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 contrasts1, 2. The release of aerosols by human activities may have resulted in a southward shift of the intertropical convergence zone since the early 1900s (refs 1, 3, 4, 5, 6) by muting the warming of the Northern Hemisphere relative to the Southern Hemisphere over this interval1, 7, 8, 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.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1038/ngeo2353
Date accepted:02 January 2015
Date deposited:24 February 2015
Date of first online publication:09 February 2015
Date first made open access:No date available

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