If war at sea changes the climate, such an event would have tremendous political implications. If there are significant political implications in 2006,there must have been in 1939 too, but unfortunately no one knew what was at stake at that time.

On the 1st of September 1939, Germany launched land, air and sea attacks on Poland. Soon, the Nazis deployed 5,000 planes upon Poland. On the 25th of September 1939, 240 German planes bombed Warsaw, dropping 560 tons of bombs (including the first bomb of 1,000 kg). 30 transport aircrafts dropped 70 tons of firebombs.

This investigation is not concerned with naval history but with global warming, respectively climate changes. Describing military events in Europe since September 1939 would require any historical writer to make the distinction between activities on land, in the air and at sea. Military aspects interest us only as far as they affect the climate.

Dimension does matter if one considers the effect of stirring the soup in a bowl with a spoon. In oceanic terms, the enclosed seas of Northern Europe represent only 0.2% of global sea surface and a mere drop with respect to the total volume of the seas around the world (0.0026%). Nevertheless, they play a crucial role as their size represents roughly one-third of North-western Europe. As for the effect of the ‘turning about’ of the sea areas, their depths are of considerable importance.

By December 1939, the number of main naval ships belonging to Germany, Great Britain, France, Italy, the Soviet Union and Italy amounted to more than 1,000 vessels (including submarines, torpedo boats, etc.), with a total tonnage of 2.8 million plus at least another thousand smaller vessels and boats serving as mines sweepers, etc.

As far as Britain was concerned, shipping activity was of utmost importance, so no effort was spared in order to maintain this. Atlantic supremacy should ensure sufficient supply to Great Britain at any time. Allies introduced the convoy system without delay, this strategic display having been very successful during WWI. The convoy system was supported by the First Lord of the Admiralty Winston Churchill who once said that it was \"the dominating factor all throughout the war… Battles might be won or lost, enterprises might succeed or miscarry, territories might be gained or quitted, but dominating all our power to carry on the war, or even to keep ourselves alive lay our mastery of the ocean routes and the free approach and entry to our ports\".

British submarines had the difficult task of intercepting well protected German shipping around Northern Europe by direct torpedo attacks or by mine laying missions. Although Britain never managed to operate in the Baltic Sea during WWII, Royal Navy submarines took its heavy toll of German troop transporters, supply ships and escort vessels, quickly forcing the Germans to adopt the system of defensive convoys when operating in the North Sea or, since 1940, in the Norwegian waters. During the Second World War, British submarines were credited with the sinking of 475 merchant ships, 105 warships and 36 submarines, and with the damaging of many others.

This section is about ASW, namely anti-submarine-warfare. A depth charge is a ‘drum’ containing explosives with a fuse which is detonated at a preset depth and which is based on hydrostatic pressure. Developed in 1916, during WWI, a depth charge could detonate up to 100m depth and carried 150 kg of explosives. There was little development for this weapon between the wars except for a 300kg variant. At the start of WWII, depth charges were essentially the same weapon as it existed at the end of WWI. This situation changed quickly. In September 1939, The New York Times wrote about the procedures of U-boat hunting: “Once a submarine is located, British naval plans, so far as they were known before the war, call for attack by familiar methods of an enclosing diamond pattern of depth bombs, supplemented, of course, by shell fire and ramming if the submarine could be forced to the surface. In the diamond-pattern attack, the destroyer goes at full speed to the spot where the submarine, slow and clumsy under water, is thought to be. One depth bomb is charged just before the spot is reached. A few seconds’ later two more are lobbed out by a Y-gun so that they land out on either side of the destroyer’s wake. In the front part of the diamond pattern, another depth bomb is dropped over the stern, some distance ahead of where the Y-gun fired. This way a large area of the sea is covered by this diamond pattern. The effect is further increased by the fact that the bombs are timed to go off at different levels, so that the area is covered not only horizontally but vertically as well. The bursting area of a modern depth bomb is considerable”.

Neither the German navy nor the British one had a fully operational aerial arm at the beginning of WWII. The German Navy never got one. British Royal Air Force Coastal Command became operational in 1940. However, airplanes charged with bombing missions were operating frequently (British airplanes in the Helgoland Bight and German airplanes on England’s East coast) or were attacking the enemy in the open sea. On the 3rd of September 1939, Britain was in possession of a fully operational unit of 2,600 aircrafts; the Germans had nothing less. A few out of many hundred events are listed below in order to offer you an outline of what happened during the first few months of the WWII.

Between 100,000 and 200,000 sea mines have been laid during the few autumn months of 1939. Most of the mines were placed in the North Sea and a substantial number in the Baltic Sea.

The British successfully mined their East coast from Dover to Orkneys during the first few months of the war. In September 1939 alone, the British minelayers Adventure and Plover laid 3,000 mines across the Strait of Dover. In the second half of September, the barrage was completed with 3,636 U-boat mines, which soon paid results, Germany losing three U-boats in October. The British set up the East Coast Barrier, a mine barrage between twenty and fifty miles wide, from Scotland to the Thames, leaving a narrow space for navigation between the barrage and the coast. In early January 1940 The New York Times reported: “British naval vessels are sowing some of the last mines needed to complete Great Britain’s 30,000,000-pounds protective shield for east-coast shipping, which is the most extensive mine field ever laid.” If one assumes that the weight of those mines varied between 300 and 1,200 pounds, the number of mines laid in autumn along the east coast alone would be between 25,000 and 100,000 mines.

At the beginning of the war, the German Navy laid a large mine field starting from the Nethelands’ coastal waters (near Terschelling island) and going northwards across the Helgoland Bight up to the entrance of the Skagerrak, at a distance between 50 and 100 km off the coast of Schleswig-Holstein and Denmark. This barrage was known under the name of “Westwall”. For about three weeks, a flotilla of at least 25 naval vessels was engaged in laying mines along this “Westwall”. The number of mines laid during the period in question could be somewhere between 20,000 and 200,000. But as the distance from Terschelling to 56° 30’ North is of about 350 kilometres (170 sea miles) and the 25 naval vessels charged with this task were able to lay thousands of mines per day, it seems reasonable to assume that, by the end of the year, the Reichsmarine could have placed somewhere between 50,000 and 100,000 mines.

War had just started when the 1,555-ton, Greek ship Kosti hit a German mine, two miles south of Falsterbo/Sweden, on the 4th of September, and sank after a terrible explosion in the minefield in the south of the Great Belt and the west of the Danish island of Zealand. Danish Government made public its plans of planting mines in its own waters. From the very first days of the war, the Germans had laid about 1,000 mines at the entrance in the Danish waters and they continued to lay mines during autumn as well. In the early November, gales had loosened several hundred mines from the German mine field, drifting them off the Copenhagen shore, where some of them exploded, breaking windows and frightening citizens with the terrific noise of their detonations.

Minesweeping activities were another particularly effective means of churning and turning huge sea areas day-by-day, since the war started. A standard mine was the moored contact mine, a buoyant material filled with up to 1,000 kg of explosive. To avoid detonation, special ships used distant means to cut the mooring chain or wire attached to the mines to keep them afloat. Sometimes, the mines exploded before reaching the surface and if they surfaced they were blown up with rifle shots. In November 1939, magnetic mines entered the scene. They could only be destroyed through forced explosion. From the climatic point of view, this was the worst case scenario. The mine was exploding in its location, at a depth of 20 or 50 metres, producing the biggest possible “stirring” effect in the water column reaching above. The countermeasure was to deactivate the ship’s ‘magnetism’ so that it could pass near the mine without activating it.

War destruction at sea is usually counted in sunken merchant tonnage or destroyed enemy naval ships. During autumn 1939 already the total loss of merchant ships was of about 380 with a tonnage of 1 million, out of which the British, Allied and Neutral forces counted 320 vessels and about 900,000 tons. We are all aware of the attention paid today to the drama of only one ship that happens to sink in the sea. Well, imagine that during the autumn 1939 there were three sunken ships per day and that this terrible situation lasted for four months.

Although physical laws are the same for hot soup and for the “stirred” seas, things tend to become more complex when naval activities occur in the North and Baltic Seas. This happens because the location, seasons and acting forces are different and would not matter so much if science had organized a comprehensive and sufficient coverage of the temperature measurements throughout a seawater body, a long time ago. But such a system was not available before WWII and it is still not available today. Only a few coastal stations recorded sea surface temperatures for a longer period of time. This is by far too insignificant for the climate research. Only a complete picture of the interior of seas and oceans would help us detect and understand the climate course and changes. But when the seas are the ones who determine the pace of weather and of climate, one can turn ‘the table around’ by using meteorological data and by citing deviations from usual atmospheric wintertime conditions, deviations which are due to the turning about of waters of the North and Baltic Seas.

The North Sea is one of the principal factors in European climatology. On one hand, the North Sea is part of the North Atlantic Ocean and has the aspect of a big bight. On the other hand, it draws a curve into the landmasses of the European continent. Climatic conditions are therefore transitory and its climate is neither maritime nor continental. Nevertheless, due to its geographical location, prevailing westerly winds travelling through the hemisphere within a zone of 2,000 kilometres width, usually ensure a temperate humid climate.

Due to the shallowness and tidal forces of the water body, its temperature structure can be described as a homogeneous one (from surface to the bottom), with small variations as the average temperatures indicate: December (8.5°C), January (6.5-7°C), February (5.5°C), March (5°C), April (6.5°C), suggesting that water very close to the coasts has lower temperatures during the winter season.

In March, the lowest annual average temperatures at the surface of the water ranged between 7°C in the northwest (Atlantic water) and 4.5°C in the southeast (Dutch coast). At the end of August, the highest average temperatures at the surface of the water ranged correspondingly (NW and SE) between 13°C and 17.5°C in the Helgoland Bight. From May until August, a horizontal thermo-cline builds up, but declines during the autumn months. Temperature level increases at lower water levels (e.g. 20m, 40m) in autumn and decreases at the bottom (60m). It is therefore possible for the whole water body to be warmer in September than in August. Even if, after calculating the ‘monthly averages’, we get only an approximate figure, this gives us an indication about the monthly decrease in temperature (or energy release) which takes place in small quantities: from 11°C in August to 4.5°C in March, i.e. on an average it could be as little as only one degree per month.

In terms of size, the Baltic Sea is a mere ‘drop’ of water in the world’s oceans, but thanks to its strategic location and specific features it represents a ‘significant’ force and influences the weather in the countries surrounding it. It is an excellent location for the climatology study. The total area of the Baltic Sea is of 400,000 square kilometres, with an average depth of 55m (including the Gulf of Bothnia, 55-294m and the Gulf of Finland, 30m). Except for the eastern part (Gdynia Bight with a maximum of 114m), the southern Baltic Sea is less than 50m deep. An important climatic feature of this sea is a 2,500m high mountain ridge going from the north to the south of Norway and drawing a sharp line between maritime and continental areas. Continental and polar air has much easier access behind this barrier than it has in areas where the Atlantic air travels east at a lower level. This mainly guarantees warm summers to Baltic countries by significantly delaying the arrival of continental winter conditions. There is hardly any other sea in the northern hemisphere which can convincingly illustrate the importance of the heat storage and release process throughout all seasons the way the Baltic Sea does.

The western European weather is famous for the predominant flow of wind blowing from the North Atlantic above the Euro-Asian landmasses (from west to east). The wind brings warm air from the depression but soaked up with humidity from the ocean. In contrast, anticyclones influence the weather conditions through high air pressure combined with dry and cold air masses.

North and Baltic Seas play their role according to the physical laws. By the end of August, they had reached the highest seasonal heat capacity. At this time, the upper water column (down to 30 meters depth) is about 10°C warmer than six months later, in March. If no unnatural phenomena come up to stir the seas, then only usual winter winds and storms make waves and only the internal currents exchange the cold water with warm water at the surface of the sea. In this case, seasonal cooling (from September to December and to March) occurs gradually, but close to long term statistical average. That is what climatology tells ever since: “climate is average weather over a long period of time”.

In the previous section, we offered an overview of the winds changing direction and blocking cyclone influence in Western Europe. We saw how excessive evaporation determined air to flow in from north-east. But what happened with the increased humidity of the air? What chain of physical phenomena was set in motion?

First and most important picture: when there is less humidity in the air, it is easier for the cold air to take control. During the winter season, when the Northern Atmosphere is drier, general circulation decrease makes it easier for the polar air to travel to southern latitudes and to determine lower temperatures in many other regions. Some may even wonder about the appearance of such arctic conditions. January 1940 reflected this exact situation. North America, China and Europe froze under extreme low temperatures and there was plenty of snow everywhere. We will first deal with the excessive rain in Western Europe and then, in a subsequent section of this chapter, with the situation of North America in autumn 1939 and January 1940. However, the record winter of 1939/40 in North Europe was ‘homemade’ due to naval warfare in its seas and to the forming of ‘dry air’, which may have been responsible for the extreme cold month of January 1940 throughout the Northern Hemisphere.

One can discuss the matter under two aspects: 1. where did so much water vapor come from? 2. how was it brought down?

The ‘rainmaking’ in Europe had a very interesting consequence on the other side of the globe. In the late autumn of 1939, the U.S.A. ‘fell dry’ after receiving only a small percentage of normal precipitation: in October 78%, in November 44% and in December 71%. On the 7th of January 1940, The New York Times reported that November was an unusual month because of its dry air. According to US Weather Bureau “the fall season was extremely dry over large areas. From the Rocky Mountains eastward it was the driest fall on record considering the area as a whole.”

Icing along the Danish, German and Finnish coasts started early and sea ice conditions lasted longer than in dozens of previous years. This proves that the sea water along all coasts was too cold for that time of the year.

While the previous chapter described the severity of war winter 1939/40 on one hand, and the naval activities during four pre-war months on the other, this chapter attempted to link anthropogenic causes with corresponding reactions in regional environment. As navies churned huge sea areas about, the evaporation of the seas increased and eventually changed the prevailing winds, declined the movement of the Atlantic depression on common routes and caused record deviations of the sea water temperatures. At least in one case, the build-up of sea ice conditions in the North and Baltic Seas demonstrates several aspects of the naval war and of its implication in environmental issues.