A popular movie this past summer, March of the Penguins, mentions that Antarctica is the coldest, driest, windiest, darkest, and highest continent. Which of the these adjectives is incorrect?

It's astounding what Emperor Penguins must endure to rear their broods. They march from the edge of the sea ice for tens of miles to familiar but forlorn breeding grounds, and after a single egg has been laid, It's incubated (by the male) for weeks on end, despite lack of food and sunlight. Moreover, they're essentially out in the open, exposed to jarring winds and bitter cold temperatures that often drop below -40 degrees F (-40 degrees C). It seems almost as though they're trying to subject themselves to the most extreme conditions on Earth -- and they've pretty well succeeded in doing so.

Antarctica is a land of superlatives. With an average elevation of approximately 7,544ft (2,300 meters) above sea level, Antarctica is by far the highest continent. It's closest competitor is Asia, which in spite of its claim to Mt. Everest and the Himalayas, has an average elevation of a mere 3,000 ft (914 m). While Antarctica doesn't have the loftiest peaks on the globe nor the most impressive ranges, it's highest point, the Vinson Massif (16,067 ft or 5,140 m), is higher than any pinnacle in either the Alps or the Rockies, and the Transantarctic Mountain Range (1,800 miles or 2,880 km long) rivals that of the Andes in length. However, it's not the amount of rock that gives Antarctica the distinction of "highest," it's the amount of ice. Only the tallest mountains can penetrate the massive ice sheets, which average well over a mile in thickness (6,600 ft or 2,012 m), and in east Antarctica, the ice reaches a depth of nearly 3 miles (4.8 km)! Around 90% of the world's ice and 70% of its fresh water is stored on this frozen continent.

The huge ice deposits can't be attributed to an abundance of snowfall. Even though it's covered in ice, most of Antarctica receives a pittance of moisture, getting just slightly more precipitation than the Sahara Desert. It's essentially the largest desert on Earth. Over the past several million years, snow has accumulated with little melting, and even if only a few inches of snow falls each year, after several centuries, the ice noticeably thickens and thus the elevations substantially increase.

Antarctica is also the windiest continent. There's little to buffer the wind (no trees, for example), so the bottom of the world is frequently wracked by fierce gales. These winds are particularly hard along coastal edges. Antarctica is more or less dome shaped (owing largely to the accumulation process of ice over millions of years), and as a result, air flows down-stream from the higher elevations in the interior toward the coasts. This down-stream or down-slope drainage produces strong katabatic winds. In places, these wicked winds blow constantly and can be felt over distances of hundreds of miles. At Cape Denison, the average monthly wind speed is an amazing 56 mph or 90 km per hour.

It should come as no surprise that the lowest temperatures on Earth have been recorded in Antarctica. Meteorological records have been kept at the South Pole since 1957, and the temperature has only risen above zero on a handful of occasions! The average daily temperature for the warmest month (January) is about - 20 degrees F. On July 21, 1983, a temperature of -129 F (officially 128.6 F) was recorded at Vostok, in east Antarctica! This isn't a wind chill temperature, but the actual temperature of the air. In fact, if the wind is blowing, the temperatures will often rise on the polar plateau. When the wind blows, while it makes us feel colder, it also breaks up the deep inversions that occur during the winter months, and the turbulent motion of the air keeps the temperature from falling further.

The poles are so cold because they lose more energy than they receive -- a negative radiation balance. An additional factor keeping Antarctic brutally cold is that, with the exception of some coastal areas, it's permanently ice covered. Ice and snow are among the brightest natural surfaces (high albedo) and are exceptionally efficient at reflecting shortwave solar radiation (visible wavelengths) back into space. This reflected energy is therefore unavailable to heat the air and melt the snow and ice. During much of the polar winter, Antarctic is bereft of sunlight, and in order for temperatures to drop to extreme readings, prolonged darkness is required. Temperatures can rapidly fall in the absence of sunlight (and clouds) because snow and ice covered surfaces are particularly efficient at emitting longwave (infrared) radiation into space -- heat readily escapes the surface.

At the equinoxes, there's roughly the same amount of day and night everywhere on Earth. Both polar regions, as well as the Equator, are currently experiencing about 12 hours of daylight and 12 hours of darkness. However, in late June and early July, most of the Arctic revels in continuous sunlight, while at the opposite end of the globe, the light has been extinguished, and Antarctica is cloaked in darkness. This situation is reversed 6 months later. In a nutshell, the South Pole receives the same amount of light as the North Pole, which during the course of a year (discounting the effects of cloudiness), receives the same amount of light as everywhere else on Earth! Actually, though, because Antarctica is so dry, compared to other lands it's cloud cover is generally less pervasive, and because its landscape is so reflective, an argument can be made that it's the brightest continent.

So while the Emperor Penguins indeed have an awful lot to deal with, including breeding at the darkest time of the year, they're not breeding on the darkest continent.

For more about this see the following links:

http://wip.warnerbros.com/marchofthepenguins/
March of the Penguins

http://www.eliasdesigns.com/penguins/large.htm
More About Emperor Penguins

This week's question comes from Dr. James Foster. Dr. Foster originated this series and did it as a solo project for the GSFC website for SEVEN YEARS! Two years ago, Dr. Foster decided to share the enthusiasm he has for this project with other Goddard scientists and will be posing questions on a semi-regular basis.