By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt
(Translated/edited by P Gosselin)
On April 29 German ARD public television presented a report on a Canadian sea ice reconstruction using coral algae growth. The report (in German) can be seen at the ARD-Mediathek in the Internet (begins at the 16:38 mark).
German researcher Jochen Halfar of the University of Toronto found a coral algae type in Canada’s Arctic Ocean that forms annual rings. During the polar nights of winter, photosynthesis stops. In the spring it reactivates again and the algae starts to grow, and does so much better when there is less ice to block out the sunlight. This allows the sea ice cover to be reconstructed over the past several centuries.
It is truly a documentary worth seeing.
But it does has one point that deserves to be criticized. Beginning at the the 27:10 mark, Halfar shows a reconstruction for northern Canada with a strongly receding ice cover since 1850 (Figure 1). Thus the algae growth has increased greatly since 1850 because the shrinking ice cover allowed more light to find its way to the algae.
Fig. 1: Curve for sea ice cover over the past 200 years in North America was reconstructed from coral algae growth, which is shown in the above chart. The strong upward trend means reduced sea ice cover. Screenshot from ARD documentary at 27:20 mark.
The problem is that Halfar blames the effect solely on the industrialization that started in 1850 and the rise of atmospheric CO2 concentration. Here it would have been more real if he had brought up the Little Ice Age – the coldest phase of the last 10,000 years – a natural climate variation. He must have forgotten about it. But things got interesting shortly thereafter when Halfar claimed that such a reduction in sea ice had never occurred during the examined pre-industrial time. But then the camera moved in on the curve for the past 600 years (Fig. 2):
Fig. 2: Coral algae curve for northern Canada over the past 600 years, which allows sea ice cover to be reconstructed. The upward trend line on the right side supposedly corresponds to what Halfar said was an unprecedented sea ice reduction. Screenshot from ARD documentary at the 27:37 mark.
Lo and behold, the data immediately refuted Halfar’s claim. Between 1430 and 1470 there were multiple algae growth spurts which would mean a sea ice reduction.
So what could have caused these earlier warm phases? Here the solar active phase between the Wolf and Spörer Minima may have played a role. But maybe it was due to the AMO or PDO.
In any case Halfar succeeded in documenting significant pre-industrial fluctuations which were flat out ignored on Germany’s flagship ARD public television.
The elephant in the room is plain to see: If one goes back some hundreds of years into the Medieval Warm Period (MWP) when Arctic sea ice also melted, we find that sea ice cover was about what it is today.
We have documented the Medieval ice melt very well within the scope of our ongoing MWP Mapping Project We have to assume that Halfar is very familiar with this literature. It remains a mystery as to why he left out this important climate-historical context in the documentary.