Saturday, July 21, 2012

Medieval Warming Period One Degree Warmer

What this emphatically does is establish that the Orkneys were one degree warmer during the Medieval Warming period than they are at present. This is not much of a difference for the latitude involved but certainly supports the idea not recognized yet that we have in fact reentered the same part of the climatic cycle.

I suspect that we have entered the beginning of a four hundred year era comparable to the MWP and part of a 1200 year cycle that includes temperature collapses and is driven by deep shifts in the deep and adjustment of current volumes and location all of which is presently only hinted at let alone measured. I have found indications of such a cycle going back at least three such cycles and suspect that the cycle can be established as real once we figure out how to investigate it clearly.

It ultimately stabilizes the Holocene.

A paper published today in Palaeogeography, Palaeoclimatology, Palaeoecology finds that the Medieval Warming Period "was warmer than the late 20th century by ~1°C." The paper adds to the peer-reviewed publications of over 1000 scientistsshowing that the global Medieval Warming Period was warmer than the current warming period.

Marine climatic seasonality during early medieval times (10th to 12th centuries) based on isotopic records in Viking Age shells from Orkney, Scotland

MONDAY, JULY 16, 2012

    Donna Surgea, James H. Barrettb,
    15 July 2012

Seasonal sea-surface temperature (SST) variability during the Medieval Climate Anomaly (MCA), which corresponds to the height of Viking exploration (800–1200 AD), was estimated using oxygen isotope ratios (δ18O) obtained from high-resolution samples micromilled from archaeological shells of the European limpet,Patella vulgata. Our findings illustrate the advantage of targeting SST archives from fast-growing, short-lived molluscs that capture summer and winter seasons simultaneously. Shells from the 10th to 12th centuries (early MCA) were collected from well-stratified horizons, which accumulated in Viking shell and fish middens at Quoygrew on Westray in the archipelago of Orkney, Scotland. Their ages were constrained based on artifacts and radiocarbon dating of bone, charred cereal grain, and the shells used in this study. We used measured δ18OWATER values taken from nearby Rack Wick Bay (average 0.31 ± 0.17‰ VSMOW, n = 11) to estimate SST from δ18OSHELL values. The standard deviation of δ18OWATER values resulted in an error in SST estimates of ± 0.7 °C. The coldest winter months recorded in the shells averaged 6.0 ± 0.6 °C and the warmest summer months averaged 14.1 ± 0.7 °C. Winter and summer SST during the late 20th century (1961–1990) was 7.77 ± 0.40 °C and 12.42 ± 0.41 °C, respectively. Thus, during the 10th to 12th centuries winters were colder and summers were warmer by ~ 2 °C and seasonality was higher relative to the late 20th century. Without the benefit of seasonal resolution, SST averaged from shell time series would be weighted toward the fast-growing summer season, resulting in the conclusion that the early MCA was warmer than the late 20th century by ~ 1 °C. This conclusion is broadly true for the summer season, but not true for the winter season. Higher seasonality and cooler winters during early medieval times may result from a weakened North Atlantic Oscillation index.

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