Study objectives: The widely discussed warming of the arctic during the last decades is comparable to the warming period that commenced in the late 1910s and lasted until the early 1940s (Fig.: I_Arctic_1918-1940). The most significant difference between these two periods is the sea ice cover. In stark contrast to the annual sea ice losses during the last two decades, the seasonal sea ice cover during the former period from 1920-1940 remained on the whole unaltered. Although understanding the earlier arctic warming may provide valuable clues on what has caused the current situation in the Arctic, recent research papers offer little hindsight in this respect. For example, Lennart Bengtsson et al. regard this event as “one of the most puzzling climate anomalies of the 20th century” (“The Early Twentieth-Century Warming in the Arctic—A Possible Mechanism”, Journal of Climate, October 2004, page 4045-4057), and assume: “that natural variability is the most likely cause”; ditto: James E. Overlandand Ola M. Johannessen, et al. (Reference details: Chapter B at: http://www.arctic-warming.com).As the notion “natural variability” is of little help for understanding the current situation in the Arctic, the paper aims at identifying the main parameters of the sudden warming in the first half of the 20th century, respectively to answer the question: Why are the maximum climate fluctuations confined to the Atlantic sector of the Arctic?” V.F. Zakharov raised in1997 (in ‘Sea Ice in the Climate System’, Arctic Climate System Study, WMO/TD-No. 782, 1997; p. 71.)
Concept: As there are only few temperature data series, limited sea ice data, and not any sufficient arctic marine data series available for the time in question, the research aims to overcome this deficiencies with a two fold approach concerning:
the timing (Winter 1918/19), the location (Spitsbergen) and source (West Spitsbergen Current respectively the sea), (Fig.: II_Manley_1944) , and
confining the research to the winter season, when air and sea water temperatures are only marginal directly influenced by sun ray or sun spots, and the impact of the sea ice, culminating in April, strongly minimise any interchange between the sea and the atmosphere.
Focus and Method: The investigation is using historical data and information, which will prove sufficient to draw principle conclusions, as a number of eminent scholars discussed the matter back in the 1930s. Starting point is the air temperature taken at Spitsbergen since 1912, which suddenly ‘exploded’ in winter 1918/19. B.J. Birkeland (1930) regarded this temperature rise, as “probably to be the greatest yet known on earth”; A. W. Ahlmann (1946) called the warming period a ‘climatic revolution’; R. Scherhag could demonstrate that the early warming during the first warming decade (1920-1930) was most pronounced in the Arctic region, which was according Ola M. Johannessen, et al. (2004) mainly confined to the Arctic-Atlantic sector (Fig.: III_Johannesen_2004); J. Schokalsky, 1936, (in: The Scottish Geographical Magazine, Vol. 52, No.2, p. 73-84) already noted that the cover layer of cold water, which was measuring 200 meters in the 1890s, was reduced to less than 100 meters in the 1920s; (References in detail at: http://www.arctic-warming.com/). Based on these parameters the investigation will demonstrate that the warming started at Spitsbergen in winter 1918/19 (Fig.: II_Manley_1944), while locations in Greenland and other close-by areas followed with a time lag of 12 months or more. In Greenland the warming lasted only until about 1933, while the region from Spitsbergen to Franz Josef-Land/Novaya Zemlya continued with warming until the early 1940s. Due to the seasonal sea ice cover at Spitsbergen, the Greenland Sea, and the Barents Sea, (Fig.: IV_April_1914), and due to the increasing warming over this time period and across the wider region, it is possible to draw a pointed picture of the possible sources that caused the two decade warming, namely the West-Spitsbergen Current, respectively water from the Gulf Current, reaching the Arctic Ocean westwards of Spitsbergen or via the Barents Sea. The center of the arctic warming during the winters was the open sea area in the west of Spitsbergen, an ice free sea area formed like a tongue, reaching up to the Arctic Ocean (Fig.: IV_April_1914).
Conclusion: It is possible to demonstrate along historical data and the physical feature of the Arctic that the two decades arctic warming from winter 1918/19 to ca. 1940 has been caused and sustained by the sea, particularly the West-Spitsbergen-Current. This solution would not only answer V.F. Zakharov’s question (see above), but would be of significant help for a more in-depth understanding of the current situation, respectively may lead to the comprehension that much more ocean research in the northern North Atlantic, the Barents Sea, and the Arctic Ocean is required.
The Abstract was written and submitted in October 2008
