Volume 15, Number 46: 14 November 2012
In an attempt to rewrite earth's climatic history, certain scientists have long contended that the relative coldness of the Little Ice Age and the relative warmth of the Medieval Warm Period were not particularly great in extent (spatial coverage of the earth) nor in magnitude (degree of deviation from the long-term mean), in order to make the global warming of the latter part of the 20th century appear highly unusual, which they equate with anthropogenic-induced, which they associate with the historical rise in the air's CO2 content, which provided them a reason to call for dramatic reductions in the use of fossil fuels, such as coal, gas and oil, which reductions we believe to be unwarranted. Consequently, we weekly peruse the most recent scientific literature for newly-discovered real-world paleoclimatic evidence related to the question of whether or not the Little Ice Age and Medieval Warm Period were truly global phenomena. And we here discuss the findings of one such paper (Simms et al., 2012) that provides evidence for the Little Ice Age occurring on a portion of Antarctica - the South Shetland Islands (SSI) - at essentially the same time as it occurred in the Northern Hemisphere.
Very briefly, the five researchers used a new approach to dating remnants of raised beaches in the SSI of the northern Antarctic Peninsula, in order "to bracket the age of a Neoglacial advance that occurred between 1500 and 1700 AD." This approach, as they describe it, was based on measurements of the "optically stimulated luminescence of the underside of buried cobbles to obtain the age of beaches previously shown to have been deposited immediately inside and outside the moraines of the most recent Neoglacial advance." In addition, they demonstrated that their results "mark the timing of an apparent change in the rate of isostatic rebound thought to be in response to the same glacial advance within the SSI," using "a Maxwell viscoelastic model of glacial-isostatic adjustment to determine whether the rates of uplift calculated from the raised beaches are realistic." And they did find them to be realistic, as they fell "within the range of uplift rates from similar settings such as Alaska."
Although Simms et al. write that initial studies on ice cores "suggested that the timing of the most recent Neoglacial advance in West Antarctica may have been out of phase with the Little Ice Age in the Northern Hemisphere (Mosley-Thompson and Thompson, 1990)," they report that other ice core records from East Antarctica and elsewhere in West Antarctica support an in-phase relationship between climate events in the two hemispheres, citing the work of Li et al. (2009) and Bertler et al. (2011). And they add that the marine record provides ample evidence "for cooler conditions around ~250-550 calBP (1400-1700 AD)," citing the studies of Domack and Mayewski (1999), Brachfeld et al. (2003), Yoo et al. (2009), Hass et al. (2010) and Shevenell et al. (2011).
Clearly, the greater weight of real-world evidence in this controversy resides with Simms et al. and the many other researchers who have identified and dated a Little Ice Age in various parts of Antarctica that coincides in time with the Little Ice Age of the Northern Hemisphere. And that dating of the Little Ice Age, plus the comparing of its temperature with the temperatures that both preceded and followed it, also pretty much confirms the existence of the Medieval and Current Warm Periods in Antarctica, which are thus found to have occurred contemporaneously with the Medieval and Current Warm Periods in the Northern Hemisphere. And when viewed in this global and oscillatory context (and when extended even further back in time through the Dark Ages Cold Period and the Roman Warm Period), it becomes ever more clear that there is nothing unusual, unnatural or unprecedented about the global warming of the 20th century. Nor is there any need to invoke atmospheric CO2 enrichment as the driver of 20th-century warming, as previous equivalent ups and downs in earth's surface temperature occurred during times of both low and relatively constant values of the air's CO2 content.
Sherwood, Keith and Craig Idso
Bertler, N.A.N., Mayewski, P.A. and Carter, L. 2011. Cold conditions in Antarctica during the Little Ice Age - Implications for abrupt climate change mechanisms. Earth and Planetary Science Letters 308: 41-51.
Brachfeld, S., Domack, E.W., Kissel, C., Laj, C., Leventer, A., Ishman, S., Gilbert, R., Camerlenghi, A. and Eglinton, L.B. 2003. Holocene history of the Larsen-A Ice Shelf constrained by geomagnetic paleointensity dating. Geology 31: 749-752.
Domack, E.W. and Mayewski, P.A. 1999. Bi-polar ocean linkages: evidence from late-Holocene Antarctic marine and Greenland ice-core records. The Holocene 9: 247-251.
Hass, H.C., Kuhn, G., Monien, P., Brumsack, H.-J. and Forwick, M. 2010. Climate fluctuations during the past two millennia as recorded in sediments from Maxwell Bay, South Shetland Islands, West Antarctica. In: Howe, J.A., Austin, W.E.N., Forwick, M. and Paetzel, M. (Eds.). Fjord Systems and Archives, Vol. 344. Geological Society of London, London, United Kingdom, pp. 243-260.
Li, Y., Cole-Dai, J. and Zhou, L. 2009. Glaciochemical evidence in an East Antarctica ice core of a recent (AD 1450-1850) neoglacial episode. Journal of Geophysical Research 114: 10.1029/2008JD011091.
Mosley-Thompson, E. and Thompson, L.G. 1990. Spatial and temporal characteristics of the Little Ice Age: the Antarctic ice core record. In: Proceedings of the International Conference on the Role of the Polar Regions in Global Change, June 11-15, 1990. University of Alaska, Fairbanks, Alaska, USA.
Shevenell, A.E., Ingalls, A.E., Domack, E.W. and Kelly, C. 2011. Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula. Nature 470: 250-254.
Simms, A.R., Ivins, E.R., DeWitt, R., Kouremenos, P. and Simkins, L.M. 2012. Timing of the most recent Neoglacial advance and retreat in the South Shetland Islands, Antarctic Peninsula: insights from raised beaches and Holocene uplift. Quaternary Science Reviews 47: 41-55.
Yoo, K.-C., Yoon, H.I., Kim, J.-K. and Khim, B.-K. 2009. Sedimentological, geochemical and palaeontological evidence for a neoglacial cold event during the late Holocene in the continental shelf of the northern South Shetland Islands, West Antarctica. Polar Research 28: 177-192.