This new paper uses a rather unique proxy; high-resolution samples micromilled from archaeological shells of the European limpet, Patella vulgata. Mr. Limpet would be proud.
A paper published this week in the journal 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 scientists in the Medieval Warm Period Project showing that the global Medieval Warming Period was warmer than the current warming period.
Highlights:
► We investigated oxygen isotope ratios of Viking Age limpet shells.
► Seasonal SST was reconstructed for the early MCA (10th-12th centuries).
► Early MCA winters were cooler and summers were warmer than late 20th century.
► MCA seasonality was almost twice that of the late 20th century.
The paper is titled:
- Donna Surge, University of North Carolina, Department of Geological Sciences, 104 South Road, CB #3315, Chapel Hill, North Carolina, USA, James H. Barrett, McDonald Institute for Archaeological Research, University of Cambridge, Downing Street, Cambridge, CB2 3ER, UK
- Received 1 March 2012. Revised 2 July 2012. Accepted 8 July 2012. Available online 15 July 2012. http://dx.doi.org/10.1016/j.palaeo.2012.07.003
Here’s the Abstract:
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.
h/t to “The Hockey Schtick”
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Didn’t read all the comments but…
Caleb says:
July 17, 2012 at 8:02 am
We’re expected to believe that Greenland and Greenland alone warmed enough to farm!
When did science take over from recorded history? 400 years of warming in Greenland and we’re supposed to believe the rest of the World was cooler to compensate with no movement of that energy? History says no!
DaveE.
From the actual paper itself:
“Our findings are consistent with Mann et al. (2009)…”
So much for “another paper refutes Mann”.
JJ,
I’ve now read the paper, and you’re right.
The study specifically resolves only the highest summer temperatures and the lowest winter temperatures. They conclude that early MCA seasonality was almost twice that of late 20th century. Early MCA winters were cooler and summers warmer than the late 20th century.
So I was wrong to suggest that this paper can be interpreted as giving an average annual temperature in the early MCA very close to that of the 1960-1990 period. However, it does clearly state that to conclude that the early MCA was 1C above 1960-1990 would be biased to the high side. They don’t give any estimate of by how much.
So a correct interpretation of their results would be that (as well as the primary finding about increased peak to trough seasonal range) the early MCA average temperature was somewhat less than 1C above the 1960-1990 period.
Anthony’s headline of MCA being 1C above current temperatures remains wrong.
As for refuting Mann’s work, the authors say:
According to this Guardian article iron age Britons were eating olives in the first century BC, i.e. during the Roman Warm Period:
http://www.guardian.co.uk/uk/2012/jul/19/olive-stone-pre-roman-britain
Of course the article assumed that the olives were imported from the Mediterranean. But is this likely – transit time would be a little long methinks? Perhaps they were home-grown?
Kevin MacDonald says:
July 18, 2012 at 4:05 am
Smokey says:
July 17, 2012 at 8:08 pm
“There is ample evidence [far beyond any reasonable doubt] showing that the MWP was global, and warmer than current temperatures.”
Yet you’ve never been able to provide any, instead posting an interminable number of links to regional reconstructions.
What has happened to logic these days? Regional evidence for the MWP from all the earth’s continents = evidence for a global MWP. Hellooo! – anyone at home???
So I guess you were among the first to criticise the tree-ring hockey-stick of Mann, Briffa et al for also being regional??