Guest post by David Middleton
The recent return of the Warming Island AGW myth inspired me to build a climate reconstruction for the Greenland Sea region.
I performed a GISS station search centered on 71.4 N latitude, 23.5 W longitude and downloaded the 12 GISS/GHCN instrumental records with at least 60 years of continuous data up to 2011.
Next I calculated a temperature anomaly relative to 1961-1990 for each of the 12 stations and then averaged them together to create a temperature reconstruction. The climate in the Warming Island area is statistically indistinguishable from that of the 1930’s.
Then I took that reconstruction back to 1000 AD with the GISP2 ice core d18O data (Kobashi et al., 2010)…
The Modern Warming is also statistically indistinguishable from the Medieval Warm Period in the Warming Island / Greenland Sea region.
Arctic Sea Ice Reconstruction
It occurred to me that there might just be a relationship between the temperature anomaly and the Arctic sea ice extent. So I went to Wood for Trees and downloaded the historical NSIDC Arctic Sea Ice Index. Then I cross plotted an annual 13-month running average of the sea ice index against the average of the station anomalies and the GISP2 reconstruction (Kobashi et al., 2010) and found a pretty good correlation (R-squared = 0.67)…
Using the equation “Sea Ice Index = (-0.5976 * Temp. Anom.)+12.374” I calculated a Model Sea Ice Index.
The “Model Sea Ice Index” (white curve) is very similar to the measured sea ice index (cyan curve)…
Using the same equation, I extrapolated the Model Sea Ice Index back to 1000 AD using the GISP2 temperature data from Kobashi et al., 2010…
The model suggests that Arctic sea ice had been steadily expanding from ca. 1150 AD up until ca. 1800 AD and has been declining since ca. 1800 AD.
Next, I carried the model back to the Early Holocene using the Alley, 2000 GISP2 reconstruction…
This suggests that the sea ice contraction during the instrumental era (1979-2011) is not particularly remarkable.
Calibrating the Model
Realizing that my model has been extrapolated about 8,000 years away from real data, I decided to compare it to some real data. McKay et al., 2008 demonstrated that the modern Arctic sea ice cover is anomalously high and the Arctic summer sea surface temperature is anomalously low relative to the rest of the Holocene…
Modern sea-ice cover in the study area, expressed here as the number of months/year with >50% coverage, averages 10.6 ±1.2 months/year… Present day SST and SSS in August are 1.1 ± 2.4 8C and 28.5 ±1.3, respectively… In the Holocene record of core HLY0501-05, sea-ice cover has ranged between 5.5 and 9 months/year, summer SSS has varied between 22 and 30, and summer SST has ranged from 3 to 7.5 8C (Fig. 7).
My GISP2 (Alley, 2000) sea ice model is generally consistent with McKay et al., 2008…
“Move along, there’s nothing to see here.” The Arctic sea ice has “been there and done that” many times over the last 10,000 years without any anthropogenic assistance.
Alley, R.B. 2000. The Younger Dryas cold interval as viewed from central Greenland. Quaternary Science Reviews 19:213-226.
Kobashi, T., J.P. Severinghaus, J.-M. Barnola, K. Kawamura, T. Carter, and T. Nakaegawa. 2010. Persistent multi-decadal Greenland temperature fluctuation through the last millennium. Climatic Change, Vol. 100, pp. 733-756.
McKay, J.L., A. de Vernal, C. Hillaire-Marcel, C. Not, L. Polyak, and D. Darby. 2008. Holocene fluctuations in Arctic sea-ice cover: dinocyst-based reconstructions for the eastern Chukchi Sea. Can. J. Earth Sci. 45: 1377–1397
Michaels, P. 2008. “Warming Island”—Another Global Warming Myth Exposed.World Climate Report.