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The Little Ice Age in Mesoamerican Tropical Lowlands
Reference
Lozano-Garcia, Ma. del S., Caballero, M., Ortega, B., Rodriguez, A. and Sosa, S. 2007. Tracing the effects of the Little Ice Age in the tropical lowlands of eastern Mesoamerica. Proceedings of the National Academy of Sciences, USA 104: 16,200-16,203.

What was done
The authors conducted a high-resolution multi-proxy analysis of pollen, charcoal particles and diatoms found in the sediments of Lago Verde (1836'46" N, 9520'52"W) -- a small closed-basin lake on the outskirts of the Sierra de Los Tuxtlas (a volcanic field on the coast of the Gulf of Mexico) -- which covered the past 2000 years.

What was learned
The five Mexican researchers say their data "provide evidence that the densest tropical forest cover and the deepest lake of the last two millennia were coeval with the Little Ice Age, with two deep lake phases that follow the Sporer and Maunder minima in solar activity." In addition, they suggest that "the high tropical pollen accumulation rates limit the Little Ice Age's winter cooling to a maximum of 2C," and they conclude that the "tropical vegetation expansion during the Little Ice Age is best explained by a reduction in the extent of the dry season as a consequence of increased meridional flow leading to higher winter precipitation."

What it means
In the words of Lozano-Garcia et al., "the data from Lago Verde strongly suggest that during the Little Ice Age lake levels and vegetation at Los Tuxtlas were responding to solar forcing and provide further evidence that solar activity is an important element controlling decadal to centennial scale climatic variability in the tropics (Polissar et al., 2006) and in general over the North Atlantic region (Bond et al., 2001; Dahl-Jensen et al., 1998)."

References
Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, G. 2001. Persistent solar influence on North Atlantic climate during the Holocene. Science 294: 2130-2136.

Dahl-Jensen, D., Mosegaard, K., Gundestrup, N., Clow, G.D., Johnsen, S.J., Hansen, A.W. and Balling, N. 1998. Past temperatures directly from the Greenland Ice Sheet. Science 282: 268-271.

Polissar, P.J., Abbott, M.B., Wolfe, A.P., Bezada, M., Rull, V. and Bradley, R.S. 2006. Solar modulation of Little Ice Age climate in the tropical Andes. Proceedings of the National Academy of Sciences USA 103: 8937-8942.

Reviewed 23 January 2008