The k2p blog

The influence of climatic change on the Late Bronze Age Collapse and the Greek Dark Ages by Brandon L. Drake, Department of Anthropology, University of New Mexico, Albuquerque

Abstract

Between the 13th and 11th centuries BCE, most Greek Bronze Age Palatial centers were destroyed and/or abandoned. The following centuries were typified by low population levels. Data from oxygen-isotope speleothems, stable carbon isotopes, alkenone-derived sea surface temperatures, and changes in warm-species dinocysts and formanifera in the Mediterranean indicate that the Early Iron Age was more arid than the preceding BronzeAge. A sharp increase in Northern Hemisphere temperatures preceded the collapseof Palatial centers, a sharp decrease occurred during their abandonment. Mediterranean Sea surface temperatures cooled rapidly during the Late Bronze Age, limiting freshwater flux into the atmosphere and thus reducing precipitation over land. These climatic changes could have affected Palatial centers that were dependent upon high levels of agricultural productivity. Declines in agricultural production would have made higher-density populations in Palatial centers unsustainable. The ‘Greek Dark Ages’ that followed occurred during prolonged arid conditions that lasted until the Roman Warm Period.

CO2 Science reviews the paper in an editorial:

….. What we found to be of most interest is something that has been known (by us and many others) about earth’s climate for quite some time now; and that is the long-term temperature record produced by the Greenland Ice Sheet Project (GISP2), which is depicted below, as plotted by Drake but based on data reported by Alley (2004).

The past 5,000 years of the GISP2 temperature history of the Greenland Ice Sheet, adapted from Drake (2012), who denoted the general locations of the Late Bronze Age (LBA), the Roman Warm Period (RWP) and the Medieval Warm Period (MWP) in their original work.

In viewing this history, it is most interesting to note (and know) that over its first 4,800 years (that’s 96% of the record) – when the temperature varied all over the place – the atmosphere’s CO2 concentration was extremely stable, hovering between about 275 and 285 ppm; while over the last 200 years (the remaining 4% of the record), when the temperature shows but a fraction of a degree warming, the air’s CO2 concentration rose by well over an extra 100 ppm.

Clearly, the air’s CO2 content is not a major driver of earth’s temperature. In fact, it may not even be a minor driver.