The Medieval Warm Period in the Karakorum Mountains of Northern Pakistan
Treydte, K.S., Frank, D.C., Saurer, M., Helle, G., Schleser, G.H. and Esper, J. 2009. Impact of climate and CO2 on a millennium-long tree-ring carbon isotope record. Geochimica et Cosmochimica Acta 73: 4635-4647.
More specifically, as the authors describe it, they "present a millennium-long (AD 828-1998), annually resolved δ13C tree-ring chronology from high-elevation juniper trees in northern Pakistan [35.74-36.37°N, 74.56-74.99°W] together with three centennial-long (AD 1900-1998) δ13C chronologies from ecologically varying sites," in the process of which they "define an 'optimum' correction factor that is best suited to remove non-climatic trends from [their] high-elevation trees in the Karakorum," in order to "provide new regional temperature reconstructions derived from tree-ring δ13C, and compare those records with existing regional evidence."
The end result of the six scientists' analysis was that "the 1990s are substantially below MWP [Medieval Warm Period] temperatures," and they state that their reconstruction "provides additional suggestions that High Asian temperatures during the MWP might have exceeded recent conditions," which finding, in their words, is also suggested by "ring-width data from living trees (Esper et al., 2007)." Consequently, as they state in the abstract of their paper, they "find indications for warmth during the Medieval Warm Period" that imply summer temperatures "higher than today's mean summer temperature."
As ever more carefully analyzed data become available, it is becoming ever more difficult for climate alarmists to deny that the Medieval Warm Period was probably slightly warmer than the Current Warm Period has been to date. And this evolving consensus suggests that the magnitude and rate of 20th-century warming likely did not exceed the natural climate variability of the last millennium, which further suggests there is no compelling reason to attribute 20th-century warming to 20th-century anthropogenic CO2 emissions, especially since even greater warmth likely existed a thousand years ago, when there was over 100 ppm less CO2 in the air than there is today.
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