Guest opinion: Dr. Tim Ball
A favorite exam question in my first-year climate class was, “Why is the North Pole warmer than the South Pole? I changed it each year, to confuse students who looked at last year’s exam; “Why is the South Pole colder than the North Pole?” Most people have no idea about the geography of the Poles and assume they are climatically the same. They are literally polar opposites and that is important in understanding the significance for global climate.
The major driving force for atmospheric circulation is the temperature difference between the Poles and the Equator – the gradient. Theoretically, maximum heating at the Equator and minimum at the Poles creates a single cell circulation system (Figure 1).
Rotation is the major perturbation to this theoretical base, followed by surface differences, particularly land/water ratios.
Earth’s elliptical orbit round the Sun is a small factor in determining the temperature difference. Two important points are perihelion, when the earth is closest, and aphelion when it is furthest away. (Figure 2)
The current situation is as follows.
The Earth is closest to the Sun or at its Perihelion two weeks after the December solstice and farthest from the Sun or Aphelion, two weeks after the June Solstice. In 2015, the Earth will reach its Aphelion at 19:41 (7:41 pm) UTC on July 6, 2015.
All this changes as part of the larger Milankovitch Effect, but it means that at present the Earth is closer during the Northern Hemisphere winter and further away during the Southern Hemisphere Winter.
At the risk of stirring up solar specialists, here is one estimate of the insolation difference.
Aphelion Insolation = [(149,597,870.7 km) / (152,098,232 km)] = 0.9674
Perihelion Insolation = [(149,597,870.7 km) / (147,098,290 km)] = 1.0343
It’s approximately a 6.5 percent variance, which is a minor difference but one amplified by other factors.
Figure 3 shows that the North Pole is near the middle of the Arctic Ocean (approx. 16 million km2) almost totally surrounded by land that all lies within the Arctic Circle. It is essentially a flat plain at sea level.
The Arctic Ocean sits in an almost enclosed basin with only one deep channel in and out called the East Greenland Rift (Figure 4). (Soviet submarines used the channel during the Cold War). This means most water moving in or out of the Arctic Ocean is in the upper few hundred meters of the ocean. The Continental Shelf is vast and drops off to the deep ocean at 200 fathoms, instead of 100 fathoms like most others. The result is very large areas of relatively shallow water, visible as the light blue area in Figure 3 and the turquoise in Figure 4.
The essentially enclosed condition was a major part of the Ewing and Donn 1956 theory of the causes of Ice Ages. It led to alarmist headlines similar to those we see today, except it was The Coming Ice Age. (Is the author Betty Friedan of feminist fame?).
How a rising of the ocean waters may flood most of our port cities within the foreseeable future — and why it will be followed by the growth of a vast glacier which may eventually cover much of Europe and North America.
Albedo is high all year round because of the low angle of incidence. Reflected sunlight makes snow blindness a danger among people of the Arctic. They fashion snow goggles to combat the problem.
Note the very narrow slit.
Albedo changes significantly in the summer when some 10 million km2 of sea ice melts exposing low albedo, dark green, polar water.
This means that the influence of massive quantities of warm water on ice conditions are much more important. The other factor is the impact of the Polar Easterlies driving the sea ice in a constant rotation round the Pole. On Arctic survival with the Canadian Air Force, I learned that the winds were so consistent that the Inuit used the direction of snowdrifts for guides even under “white out” conditions.
Ice thickness was made an issue to add to the focus on sea ice melting. I wrote about the exploitation and misrepresentation of this in October 2012. Influx of warmer water is a major factor, as occurred in 1816. Another reason the North Pole is warmer than the South because of heat from this warm water moving through the ice to heat the atmosphere (Figure 5).
Source: Climatology (Oliver and Hidore)
The biggest problem for climate research in the Arctic is the lack of data. Figure 6 shows that there is no data for most of the basin.
Source: Arctic Climate Impact Assessment (ACIA).
Polynyas are large areas of open water and a unique feature in the Arctic Oceans that contribute heat directly to the Arctic atmosphere. Figure 7 shows Polynyas for the Canadian sector of the Ocean.
The net result is the North Pole is cold, but nowhere near as cold as the South Pole. That is all we can say precisely because actual conditions at the geographic North Pole are not measured. Wikipedia says,
Winter (January) temperatures at the North Pole can range from about −43 °C (−45 °F) to −26 °C (−15 °F), perhaps averaging around −34 °C (−29 °F). Summer temperatures (June, July, and August) average around the freezing point (0 °C (32 °F)). The highest temperature yet recorded is 5 °C (41 °F),
Temperature is important because it determines the density of the atmosphere and, therefore, the height of the Troposphere, which affects the circulation.
Little was known about the Antarctic continent until approximately 100 years ago, which is not surprising since the first confirmed landing occurred in 1895. Despite this, scientific interest triggered organization of an International Polar Year (IPY) in 1882-1883. The major advance in knowledge was the International Geophysical Year (IGY) in 1957, while scientific efforts to assess Antarctic climate began as recently as the third IPY in 2007.
The geography is directly opposite to the North with a continent surrounded by ocean (Figure 8). The entire area is above sea level with the South Pole at 2830 m (9,285 feet). The Tropopause is less than 8 km above Antarctica, so there is very limited atmosphere above the South Pole. The intensely cold air that drains down off the continent enhances the general circulation pattern of the Polar Easterlies. Known as a Katabatic flow, it generates remarkable winds. British Antarctic Survey reports
Port Martin (67°S 141°E) is an especially windy site with an annual mean wind speed of 17 ms-1 (33 kt — nearly gale force). The station has recorded a monthly mean wind speed of 28 ms-1 (54 kt — storm force 10) and a daily mean of 46 ms-1 (89 kt).
The Southern Ocean surrounds the continent and creates a dramatic contrast with the cold polar air. All these conditions combine to create a very powerful Circumpolar Vortex. Failure to understand or include these conditions was part of the misunderstanding and incorrect claim that CFCs were creating and enlarging the area of ozone thinning over Antarctica.
Figure 9 shows Polynyas (dark green) for the Antarctic for a specific day. They are defined as areas of thin ice or open water. Like the Arctic they are quite extensive. WUWT illustrated how Antarctic polynyas are primarily a result of katabatic winds. This was in response to a claim that they were going to disappear.
Sun angles are the same as in the Arctic, but the albedo is much higher because of the permanent snow and ice surfaces.
Net result of these differences means the North Pole is much warmer than the South. It is probably more accurate to say it is less cold. We only have an approximate difference because there are no instrumental readings for the North Pole. There are so few measures that application of the claim that a station represents everything in a 1200 km radius do not apply. Wikipedia says winter temperatures (January) range from -43°C to -26°C. South Pole records show winter temperature (July) range is from a mean daily minimum of -62.8°C to a mean daily high of -55.9°C. Regardless of specific accuracy, the difference is approximately 20°C difference, which is very significant in the fundamental driving force of atmospheric circulation.
Historically, this difference was amplified because a higher global mean temperature, such as during the Medieval Warm Period (MWP), had greater impact at the North Pole than the South. A 2°C change would have limited impact at the South Pole. It would have much greater impact at the North Pole altering conditions of the Arctic Basin including the sea ice, the snow line, the tree line, the albedo, and ocean circulation, among other conditions.