Medieval Warm Period and Little Ice Age

[marchesarosa]

Interesting wide ranging film about the Mediaeval Warm Period and the Little Ice Age which followed it


[youtube]http://www.youtube.com/watch?v=QFQHTdn8egw&feature=player_embedded
[/youtube]

[marchesarosa]

New paper using various Northern Hemisphere proxies demonstrates the MWP and the LIA.

The title of the paper is, “The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability,” by B Christiansen of the Danish Meteorological Institute and F C Ljungqvist of Stockholm University.
www.clim-past.net/8/765/2012/cp-8-765-2012.html

The authors conclude that previous climate reconstructions “seriously underestimate” variability and trends in the climate record of the past two millennia.

This new analysis shows that the warming we have seen in the late-20th century is not unprecedented, as can be seen in figure 5 (from the paper). Seen in the reconstruction is a well-defined peak of temperature between 950–1050 AD. They also find that the first millennium is warmer than the second.

The researchers conclude:

“The level of warmth during the peak of the MWP (Medieval Warm Period) in the second half of the 10th century, equaling or slightly exceeding the mid-20th century warming, is in agreement with the results from other more recent large-scale multi-proxy temperature reconstructions.”


Fig. 5. Reconstruction of the extra-tropical NH mean temperature (C) based on the gray-shaded proxies in Table 1 reaching back to at least 300 AD. Calibration period 1880–1960AD. Only proxies with positive correlations and a p-value less than 0.01 are used. The included proxies are given in the legend. Thin curves are annual values; thick curves are 50-yr smoothed. Red curves show bias and confidence intervals for the 50-yr smoothed values. From ensemble pseudo-proxy studies mimicking the reconstructions, we have calculated the distribution of 50-yr smoothed differences between reconstructions and target. The biases and the upper and lower 2.5% quantiles are calculated from these distributions. In the figure the biases (full red curves) have been added to the real-world reconstructions. Likewise, the upper and lower quantiles have been added to the real-world reconstructions (dashed red curves). The green curve shows the observed extra-tropical (>30 N) annual mean temperature. The yellow curve show the temperature average over grid-cells with accepted proxies. Both curves have been centered to zero in 1880–1960 AD.

[mrsonde]

Thanks Marchesa, very interesting. Note the apparent (by eye) rhymicity of c600 years, with a seemingly p-shape curve, almost like a heartbeat.

[marchesarosa]

Another paper, by Esper et al published in the Journal of Global and Planetary Change, shows that not only were the summers of the MWP equal or greater than our current warmth, but that the summers of the Roman Warm Period of 2000 years ago were significantly warmer than today.

Variability and extremes of northern Scandinavian summer temperatures over the past two millennia

Jan Esper, Ulf Büntgen, Mauri Timonen, David C. Frank
www.sciencedirect.com/science/article/pii/S0921818112000070

Abstract

Palaeoclimatic evidence revealed synchronous temperature variations among Northern Hemisphere regions over the past millennium. The range of these variations (in degrees Celsius) is, however, largely unknown. We here present a 2000-year summer temperature reconstruction from northern Scandinavia and compare this timeseries with existing proxy records to assess the range of reconstructed temperatures at a regional scale. The new reconstruction is based on 578 maximum latewood density profiles from living and sub-fossil Pinus sylvestris samples from northern Sweden and Finland.

The record provides evidence for substantial warmth during Roman and Medieval times, larger in extent and longer in duration than 20th century warmth.





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Good coverage of this paper on WUWT here wattsupwiththat.com/2012/10/18/yet-another-paper-demonstrates-warmer-temperatures-1000-years-ago-and-even-2000-years-ago/#more-72568