Saturday, September 25, 2010

Paper: Roman & Medieval Warming Period Temps Reached or Exceeded the 20th Century

A new paper utilizing "many" records never previously included in reconstructions of past temperatures finds that the Roman & Medieval Warming Period temperatures reached or exceeded those of the latter 20th century. Unfortunately, the paper still resorts to the old Michael Mann tactic of tacking on the instrumental thermometer record at the end for an apples and oranges comparison, but at least they are up-front about it.

Year AD on x axis, temp anomaly on y axis, added red line showing temp at year 2000, red dashed line is the tacked on thermometer record, MWP = Medieval Warming Period, RWP=Roman Warming Period
Geografiska Annaler: Series A, Physical Geography Volume 92, Issue 3, pages 339–351, September 2010
Article first published online: 6 SEP 2010 DOI: 10.1111/j.1468-0459.2010.00399.x

Abstract: A new temperature reconstruction with decadal resolution, covering the last two millennia, is presented for the extratropical Northern Hemisphere (90–30°N), utilizing many palaeo-temperature proxy records never previously included in any large-scale temperature reconstruction. The amplitude of the reconstructed temperature variability on centennial time-scales exceeds 0.6°C. This reconstruction is the first to show a distinct Roman Warm Period c. ad 1–300, reaching up to the 1961–1990 mean temperature level, followed by the Dark Age Cold Period c. ad 300–800. The Medieval Warm Period is seen c. ad 800–1300 and the Little Ice Age is clearly visible c. ad 1300–1900, followed by a rapid temperature increase in the twentieth century [doesn't look to me to be any more rapid than from 700 to 1000 AD]. The highest average temperatures in the reconstruction are encountered in the mid to late tenth century and the lowest in the late seventeenth century. Decadal mean temperatures seem to have reached or exceeded the 1961–1990 mean temperature level during substantial parts of the Roman Warm Period and the Medieval Warm Period. The temperature of the last two decades, however, is possibly higher than during any previous time in the past two millennia, although this is only seen in the instrumental temperature data and not in the multi-proxy reconstruction itself. Our temperature reconstruction agrees well with the reconstructions by Moberg et al. (2005) and Mann et al. (2008) with regard to the amplitude of the variability as well as the timing of warm and cold periods, except for the period c. ad 300–800, despite significant differences in both data coverage and methodology.

UPDATE: just noticed the NIPPC has a write up on this paper 

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