Two shifts in Arctic sea ice conditions indicate how it came about.
Arctic Sea ice is a big concern in the climate change debate. During the last 100 years three major shifts occurred. Less sea ice from 1918 to 1939; more sea ice formed from 1940 to about 1980, and retread again thereafter. Meanwhile the ice situation in 1939/40 is close to the conditions today, as just published paper by Guillian Van Achter et.al. , assumes (see image).
While the latter point is important to recognize, the authors fail taking in account what happened in the last century, with the high probability that the two major shifts have been caused by two devastation naval wars.
Instead of looking for anthropogenic links authors merely relate the Arctic sea ice retreat and thinning to greenhouse gas emissions and natural variability. Their introduction put it as it follow:
“On long timescales (a few decades or more), retreating and thinning are projected to continue as greenhouse gas emissions are expected to rise.
However, on shorter timescales (1–20 years), internal climate variability, defined as the variability of the climate system that occurs in the absence of external forcing and caused by the system’s chaotic nature, limits the predictability of climate (Deser et al., 2014) and represents a major source of uncertainty for climate predictions (Deser et al., 2012). In this context, greater knowledge of Arctic SIT (sea ice thickness) internal variability and of its drivers is essential to document the true evolution of the Arctic atmosphere–ice–ocean system and to predict its future changes.”
To understand future changes, it seems foremost necessary to understand historical observations for which sufficient data and information are available as the G. Van Achter’s image shows (above). Required is to take the oceans into account. They are the main driver of climate, and the North Atlantic alone, and together with the Gulf Current, the main source of the Arctic sea ice conditions. How the three mentioned shifts did came about:
The story of World War I is simple. On the west coast of England, an arm of the Gulf Stream flows northwards to Svalbard and into the Arctic Ocean. A fierce naval war took place around the United Kingdom for 4 years, in the North Sea and also over the Gulf Stream. This messed up the “natural sea water structure” in terms of temperature and salinity and all these water masses ended up high up in the north. This caused a change in the water structure there. The mighty, cold, thick surface layer became thinner and so the warm Gulf Stream water could give off much more heat to the atmosphere. For two decades significant higher air temperature was observed in the Northern Hemisphere, ending suddenly with the beginning of World War II in September 1939.
The story of WWII is very different, but it is also not particularly complicated. In this case it is about the whole North Atlantic, north of the Straits of Gibraltar, the Strait of Florida and up to the North Cape. The sea area is several thousand meters deep and has a temperature of below 4 ° C. For more than six years there was fierce fighting in large parts. Whole sea areas were literally tumbled over many dozen meters deep, several thousand ships were sunk. There were huge explosions above, on and below sea level. This resulted in huge ‘shifts’ in the water structure which took years to return to the old ‘equilibrium’. A large part of it circulated the central North Atlantic (clockwise, lasting around 4 years). A smaller moved to the Arctic Ocean , which caused more sea ice over two dozen years. The more known result was a marked global cooling from 1940 to around mid-1970, the only global cooling since the end of the Little Ice Age (LIA), around 1850.
The story on Arctic sea ice after the 1980s is by far the easiest to explain. The overall conditions in the North Atlantic and Arctic Ocean indicate that a seven decade long period was required “to heal the sea from the wound WWII had inflicted”. About 3 to 4 decades to turn the cooling and increased sea ice trend back to a warming trend. And 3 to 4 decades to reach the same level as it existed in the late 1930s. In so far it is to note, that the lowest point was about 2012, but the sea ice is today back to the extent in 2005, in other word, the situation has stabilized during the last decade.
Finally, a comment on the overall situation. After the LIA ended in the middle of the 19th century, the trend had to go towards less Arctic sea ice for a longer period of time. Aside from the fact that many factors for sea ice changes from human activities in the oceans and the Arctic have never been addressed, but two of the most distinctive and unique trend changes cannot be explained without the two world wars. Even if the contribution could only be in a lower percentage range (which is very unlikely), it is irresponsible not to worry about an explanation as quickly as possible. That is forcing by man and has nothing to do with a “chaotic nature” but with physic.
Link to two books on Climate Change and Naval War: