How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

Two Thousand Years of Dust Deposition in the Aral Sea
Huang, X., Oberhansli, H., von Suchodoletz, H. and Sorrel, P. 2011. Dust deposition in the Aral Sea: implications for changes in atmospheric circulation in central Asia during the past 2000 years. Quaternary Science Reviews 30: 3661-3674.

What was done
Noting that dust storms are common features adjacent to the Aral Sea, the authors investigated the grain-size distributions of wind-blown sediments found in a core retrieved from that water body while "attempting to trace the variations in atmospheric dynamics in central Asia during the past 2000 years," and in doing so, they focused on variations observed at the transition from the Medieval Warm Period to the Little Ice Age, since this period, in their words, "is the most pronounced climatic transformation during the last millennium," in support of which statement they cite the studies of Yang B. et al. (2002), Trouet et al. (2009) and Chen et al. (2010).

What was learned
Huang et al. report that the history of dust deposition in central Asia can be divided into five distinct periods on the basis of their observations: "a remarkably low deposition during AD 1-350, a moderately high value from AD 350-720, a return to a relatively low level between AD 720 and AD 1400 (including the Medieval Warm Period), an exceptionally high deposition from AD 1400 to [the] 1940s and an abnormally low value since [the] 1940s." Most interestingly in this regard, we note that the first of these "distinct periods" coincides with the Roman Warm Period, the second with the Dark Ages Cold Period, the third (as Huang et al. make a point of noting) with the Medieval Warm Period, the fourth with the Little Ice Age, and the fifth with the Current Warm Period. Thus, it was no surprise that they found that the temporal variation in dust deposition they observed was consistent with the "mean atmospheric temperature of the Northern Hemisphere during the past 2000 years, with low/high annual temperature anomalies corresponding to high/low dust supplied in the Aral Sea sediments, respectively [italics added]."

What it means
Based on the four researchers' detailed graphs of their wind intensity/dust storm data, we note that the minimum values of these inverted measures of annual temperature during the Roman Warm Period, the Medieval Warm Period and the Current Warm Period were all about the same. And it is thus quite clear that there is nothing unusual, unnatural or unprecedented about earth's current level of warmth, which is merely an expected consequence of the millennial-scale cycling of climate that is a natural expression of one of the ways in which earth's climate system operates in its particular location within our solar system and the galaxy that hosts it.

Chen, F.H., Chen, J.H., Holmes, J., Boomer, I., Austin, P., Gates, J.B., Wang, N.L., Brooks, S.J. and Zhang, J.W. 2010. Moisture changes over the last millennium in arid central Asia: a review, synthesis and comparison with monsoon region. Quaternary Science Reviews 29: 1055-1068.

Trouet, V., Esper, J., Graham, N.E., Baker, A., Scourse, J.D. and Frank, D.C. 2009. Persistent positive north Atlantic oscillation mode dominated the medieval climate anomaly. Science 324: 78-80.

Yang, B., Brauning, A., Johnson, K.R. and Shi, Y.F. 2002. General characteristics of temperature variation in China during the last two millennia. Geophysical Research Letters 29: 10.1029/2001GL014485.

Reviewed 7 March 2012