Arctic Warming 1918–1939 by Human Activities?
The concern about the Arctic concerns since several decades. A recent paper “Rapid reductions and millennial-scale variability in Nordic Seas sea ice cover during abrupt glacial climate changes” by researcher Henrik Sadatzki, et al. (1) from the Niels Bohr Institute, at the University of Copenhagen, claims that abrupt climate change occurred as a result of widespread decrease of sea ice. By analyzing the last glacial period, app. 10,000–110,000 years ago the Northern Hemisphere was covered in glacial ice and extensive sea ice, covering the Nordic seas. But as soon as the Nordic Seas changed abruptly from ice covered to open sea, the energy from the warmer ocean water was released to the cold atmosphere, leading to amplification of sudden warming of the climate. The study concludes, that sea ice is a “tipping element” in the tightly coupled ocean-ice-climate system. This is particularly relevant today, as the still more open ocean to the north can lead to similar abrupt climate change.
The paper assumes that scientific evidence for abrupt climate change in the past has finally been achieved. Doubts are justified. Sea ice is an element between the interaction of ocean and atmospheric energy, but also a “tipping point”? A much more recent warming event, the so called Early Arctic Warming (EAW) from 1918 to 1939 certainly followed other rules. It has caused the most pronounced warming of the Northern Hemisphere since the end of the Last Little Ice Age (~1850), lasting in North America until about 1933, and in Europe until winter 1939/40. The EAW was primarily related to a sharp rise in winter temperature since 1918, gradually decreasing subsequently, which is a strong indication that the warmth derived for the Nordic Seas and related currents that flow into the Arctic Ocean.
To summarize the problem, it follows an excerpt from the Book : “How Spitsbergen Heats the World — The Arctic Warming 1919–1939”, Chapter 2C, (2):
The early arctic warming and modern assessments
Many scientists confirm broadly the early two decade long warming period (WHEN) but fall short of identifying the exact time period and location, of which a few are here presented exemplary:
- The warming in the 1920s and 1930s is considered to constitute the most significant regime shift experienced in the North Atlantic in the 20th century (Drinkwater, 2006).
- The huge warming of the Arctic that started in the early 1920s and lasted for almost two decades is one of the most spectacular climate events of the 20th century (Bengtsson, 2004).
- At least Polyakov (2002) get the timing right: The period from 1918 to 1922 displays exceptionally rapid winter warming not only in the circum-Arctic region northward of 62oN. (Polyakov, 2002).
- A meridional pattern was also seen in the late 1930s with anomalous winter (DJFM) SAT, at Spitsbergen (Overland, 2008).
- Average Arctic temperatures increased at almost twice the global average rate in the past 100 years. Arctic temperatures have high decadal variability, and a warm period was also observed from 1925 to 1945. (IPCC, 2007)
When it comes to explaining the causation of the warming (WHY), the matter seems rather sketchy than well founded. Here only two examples:
- Natural variability is the most likely cause (Bengtsson, 2004);
- We theorize that the Arctic warming in the 1920s/1930s was due to natural fluctuations internal to the climate system (Johannessen, 2004).
The EAW had defiantly been a climatic shift, the most pronounced since 1850, only followed by the a severe global cooling from 1940 to the mid-1970s. In both cases neither an increase or decline in sea-ice cover, show up as significant contributor. As the sun can be excluded concerning the EAW during the winter season in the higher Northern Hemisphere, the only cause remaining is a substantial shift in the structure of the Nordic Seas, which are likely to have caused by two factor.
First reason: Shift in the Arctic Ocean structure since the end of the LIA
A shift within the Arctic Ocean was underway since the 19th Century. During his Arctic voyage with his ship “FRAM”, from 1893–1896, Fridjof Nansen, observed (see image) that the colder sea-cover layer (and lower salinity), over a warmer and saltier water layer, was thinning. The lower level, several hundred meters thick, was Atlantic water carried into the Arctic Basin. While in Nansen’s time had been in a slow process, it accelerated three decades later due to human activities at sea.
Second reason: Naval War, 1914 to 1918, a force to recon
Around the years of the 1910s, nature had run its normal course. No “natural” event, which could have affected the natural commons, had been observed in the North Atlantic or Arctic region, or at a global level. There was no significant earthquake, no eruption of a forceful volcano, no tsunami, no sunspots, and no big meteorite fell on the continent or into the sea. But with the commencement of the First World War (WWI) the situation changed.
WWI had destructive effects on men and on the environment, but nothing changed the commons of nature as much as the naval war did. This notion derives from understanding that the oceans, together with the sun, determine the status of the atmosphere on a short, medium or long term. Human war activities at sea penetrate and churn the sea surface layers of 50 meters and lower depth. Huge water masses in Western Europe seas were churned upside-down by naval war activities. The Norwegian Current transports these water masses northwards, to Spitsbergen. The temperature and salinity structure of the water had certainly changed its composition.
The total loss of the Allies ship tonnage during WWI is of about 12,000,000 tons, namely 5,200 vessels. The total loss of the Allies together with the Axis naval vessels (battle ships, cruisers, destroyers, sub-marines, and other naval ships) amounted to 650, respectively 1,200,000 tons. Most ships that were sunk transported a variety of cargo, and all of them had equipment and provisions on board. The total number could be somewhere in the range of 10–15 million tons. It has been never quantified how much cargo and provisions surfaced and traveled with the currents towards the Arctic region and how the sea and sea-ice interacted with all that stuff — a matter that should not be ignored outright.
The naval war from1914 to 1918 can be considered as the most comprehensive single event in the 1910s that has altered the common sea body structure around Great Britain through a huge variety of activities and means. All naval activities around Britain had changed the water structure that moved on toward the North. The distance between Spitsbergen and the main naval battleground was of about 2000 km. But this distance is not very significant in this case. The currents moving along the Norwegian coast consist of water from the North Sea and of water from the Golf Current, flowing at a medium speed of 0.1 km/hour. At the sea surface, the current is up to 10 times faster.
The branch of the North Atlantic Current has temperatures exceeding 6°C and salinity greater than 35. The main arm is well below the sea surface and in quite a distant to the coast of Norway. The Norwegian Coastal Current flows closer to the coast of Norway in the upper 50–100 m of the water column with lower temperatures than the Atlantic branch and low-salinity water, less than 34.8.
What does a system shift mean in respect to the Spitsbergen/Arctic region? The main answer is simple. The incoming warm water of the West Spitsbergen Current was “positioned” in a manner that it could release more heat into the atmosphere. This can happen in two ways: I.) the sea ice forming during the winter season diminishes, which would not explain the suddenness of the shift; or II.) the thickness of cold sea water layer above the warm water was suddenly substantially reduced so that the air temperatures could immediately benefit from warmer water close to the sea surface. This was actually the case. In the mid-1930s it had been already discovered and published, that since the FRAM expedition in 1893–1896 the cold surface layer had grossly weaken, observed the Russian oceanographer J. Schokalsky, 1936 (3):
“The branch of the North Atlantic Current which enters it by way of the edge of the continental shelf around Spitsbergen has evidently been increased in volume, and has introduced a body of warm water so great, that the surface layer of cold water which was 200 meters tick in Nansen’s time, has now been reduced to less than 100 meters in thickness.”
What further evidence is required to attribute the EAW from 1918 to the 1930s to naval war activities during WWI? This knowledge is necessary in order to better understand the mechanisms between sea, sea ice, atmosphere and human influence on processes in the Arctic. The sudden shift into the EAW, was a significant climatic change event, strongly enhanced by naval war activities.
Instead of analyzing the last glacial period, app. 10,000–110,000 years ago, a thorough understanding of what the WWI caused changes in the North Atlantic and Arctic Ocean and subsequently on weather and climate is urgently required. Henrik Sadatzki, et al. conclusion that sea ice is a “tipping element” in the tightly coupled ocean-ice-climate system, would certainly require a revised and more convincing classification.
(1) Henrik Sadatzki, et al.; 2020; “Rapid reductions and millennial-scale variability in Nordic Seas sea ice cover during abrupt glacial climate changes” ; first published November 9, 2020; https://doi.org/10.1073/pnas.2005849117; dito: https://www.pnas.org/content/117/47/29478
(3) Schokalsky, J. (1936); ‚Recent Russian researches in the Arctic Sea and the in mountains of Central Asia’, in: The Scottish Geographical Magazine, Vol. 52, №2, March 1936, p. 73–84. See: http://www.arctic-heats-up.com/chapter_8.html