A period of intense warmth 125 to 90 million years ago, known as the mid-Cretaceous super greenhouse, was marked by substantially different tropical and subtropical atmospheric circulation compared with earlier, cooler times, suggests an analysis of Cretaceous desert distribution.
Hitoshi Hasegawa of the University of Tokyo and colleagues tracked the location of Cretaceous-aged deserts in Asia as well as the prevailing wind direction indicated by the aeolian features preserved in the desert deposits. Today, deserts develop where dry air downwells in the subtropical limb of the Hadley circulation cell, around 30° N and 30° S. The authors' reconstruction of Cretaceous wind systems suggests that during the moderately warm climates of the early and late Cretaceous, the Hadley circulation expanded by about three to six degrees of latitude. However, during the extreme mid-Cretaceous heat, the circulation contracted dramatically, with the descending limb located at about 25° N. Such a contraction is supported by the contemporaneous appearance of arid environments in relatively low-latitude locations around the globe.
The Hadley cell has generally expanded in response to rising atmospheric CO2 concentrations and global temperatures. The authors suggest that a climatic threshold may exist beyond which the cell will contract.
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Newton, A. Circulation shrinkage. Nature Geosci 5, 682 (2012). https://doi.org/10.1038/ngeo1604
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DOI: https://doi.org/10.1038/ngeo1604
