Posted by Jeff Condon on July 3, 2009
From Science Daily where I read fairly often, I found this headline.
The title makes you instantly skeptical because sea ice isn’t at it’s lowest even in the last two years. Of course we then have to wonder how they determined sea ice levels back 800 years.
ScienceDaily (July 2, 2009) — New research, which reconstructs the extent of ice in the sea between Greenland and Svalbard from the 13th century to the present indicates that there has never been so little sea ice as there is now. The research results from the Niels Bohr Institute, among others, are published in the scientific journal, Climate Dynamics.
What do you know it’s another tree ring study in noise blending.
There are of course neither satellite images nor instrumental records of the climate all the way back to the 13th century, but nature has its own ‘archive’ of the climate in both ice cores and the annual growth rings of trees and we humans have made records of a great many things over the years – such as observations in the log books of ships and in harbour records. Piece all of the information together and you get a picture of how much sea ice there has been throughout time.
If someone has a copy of the PDF for this paper, I would appreciate it. In the meantime, I’ve copied the abstract below. It sounds straight from the team bendahockeystick playbook. The abstract can be found HERE
Abstract We reconstructed decadal to centennial variability of maximum sea ice extent in the Western Nordic Seas for A.D. 1200–1997 using a combination of a regional tree-ring chronology from the timberline area in Fennoscandia and δ18O from the Lomonosovfonna ice core in Svalbard. The reconstruction successfully explained 59% of the variance in sea ice extent based on the calibration period 1864–1997. The significance of the reconstruction statistics (reduction of error, coefficient of efficiency) is computed for the first time against a realistic noise background. The twentieth century sustained the lowest sea ice extent values since A.D. 1200: low sea ice extent also occurred before (mid-seventeenth and mid-eighteenth centuries, early fifteenth and late thirteenth centuries), but these periods were in no case as persistent as in the twentieth century. Largest sea ice extent values occurred from the seventeenth to the nineteenth centuries, during the Little Ice Age (LIA), with relatively smaller sea ice-covered area during the sixteenth century. Moderate sea ice extent occurred during thirteenth–fifteenth centuries. Reconstructed sea ice extent variability is dominated by decadal oscillations, frequently associated with decadal components of the North Atlantic Oscillation/Arctic Oscillation (NAO/AO), and multi-decadal lower frequency oscillations operating at ~50–120 year. Sea ice extent and NAO showed a non-stationary relationship during the observational period. The present low sea ice extent is unique over the last 800 years, and results from a decline started in late-nineteenth century after the LIA.
The effect of the calibration is almost certainly the same as the one demonstrated in this post:
The math of calibration creates a reduced amplitude historic signal in comparison to the calibration range almost guaranteeing an unprecidented whatever you’re looking for. The reason I’m confident is because they use uncalibrated tree ring data, combined with a partial calibration range to calculate their results. I’ve yet to see a calibration study which compensates for the temperature scale distorting effect of the noise on the data.