what is the largest desert on earth

The largest desert on earth isn’t exactly what people would think when they think of deserts. When people hear the word “desert,” they usually imagine wide open spaces with sand dunes. That could describe the Sahara desert. But it doesn’t fit the bill for the largest desert. The largest desert on earth is at one of the planets’ poles – Antarctica.

Deserts Defined

Scientists define a desert first and foremost by the amount of precipitation (rain, snow, etc.) an area gets. In order for an area to qualify as a desert, it needs to receive less than 250mm (approximately 10inches) of precipitation per year. Evaporation always outpaces precipitation in a desert, so there will rarely be standing water. While temperature is not the main criteria used to define a desert (it can range from extreme cold to extreme heat), the amount of vegetation will depend on whether the area receives enough precipitation. The United Nations Environment Program (UNEP) and many other organizations consider the minimum requirement for classification as a desert to be precipitation below 250mm annually. Therefore, an area getting 250mm or fewer of precipitation each year would be considered a desert.

Antarctica – A Cold Desert

In spite of the fact that most of Antarctica is comprised of an ice sheet as thick as five km in places, Antarctica qualifies as a desert because of its very small amount of precipitation. This includes the entire 14.2 million km² (5.5 million mi²) surface area of the continent. There are some exceptions along the coastlines of Antarctica where the climate is slightly warmer and there is significantly more moisture available to create clouds and precipitation; however, these areas do not account for a large portion of the total area of Antarctica.

On average, the area inside Antarctica gets far less than 200 mm (approximately eight inches) of precipitation every year. Some areas receive as little as 50 mm (less than two inches) of precipitation annually. These numbers make Antarctica one of the driest areas in the world compared to some of the hottest deserts.

Cold combined with the dryness creates an environment that is inhospitable to almost all forms of life. The frigid temperatures (average -49°C [-56°F] in winter) limit the growth of any plant or animal life that might otherwise exist in such an arid region. Additionally, the extreme cold means that once ice forms in these areas, it remains intact for thousands of years, accumulating slowly through infrequent snowfalls that do not melt during the course of the year.

Dry Valleys – Extremely Arid Environments

One example of extreme desert environments within Antarctica is called the McMurdo Dry Valleys. These valleys are among the driest environments anywhere in the world and are commonly referred to as being similar to the conditions experienced in Mars. The valleys are nearly completely free of ice due to katabatic winds (which occur when cold air sinks downward toward lower elevations) that effectively sublimates (change directly to vapor) any existing ice and snow. This process may take thousands of years.

The Dry Valleys cover approximately 4800km² (1850mi²) and experience almost no precipitation. It has been documented that in some years there is no measurable snow fall in the Dry Valleys. Due to these harsh conditions researchers such as those from the National Science Foundation’s Long Term Ecological Research (LTER) program conduct research here to better understand ecosystems that are capable of supporting life in extreme environments. Specifically, researchers note that despite the extreme conditions, microbial communities continue to live and grow in these environments.

Other Large Deserts Compared to Antarctica

For context regarding how big and cold Antarctica really is, we should examine some other large deserts around the globe.

Arctic Polar Desert

Next largest after Antarctica is the Arctic Polar Desert which spans northern parts of Alaska, Canada, Greenland, Iceland, Norway, Sweden, Finland and Russia and totals an area of approximately 13.9 million km² (5.4 million mi²). Similar to Antarctica, this is defined by minimal precipitation and extremely cold temperatures. However, unlike Antarctica, much of this region consists of frozen sea ice and tundra.

Sahara Desert

While many people incorrectly associate the Sahara Desert with being the largest desert in terms of overall area, it is actually the largest hot desert and covers approximately 9.2 million km² (3.6 million mi²) across Northern Africa. The Sahara is made up of massive expanses of sand dunes, gravel plains and rock plateaus extending from the Atlantic Ocean eastward to the Red Sea. Its extreme aridity stems from its location beneath a high pressure zone near the equator resulting in very few clouds forming and therefore very little rain falling.

Arabian Desert

Another large desert is the Arabian Desert which spans portions of Saudi Arabia, Yemen, Oman, U.A.E., Qatar, etc. and covers an approximate area of 2.33 million km² (900000 mi²). This is one of the largest cold winter deserts globally and contains vast sand seas such as Rub‘ Al Khali (one of the worlds largest contiguous sand bodies).

Gobi Desert

Last but certainly not least is the Gobi Desert located in central Asia and spans parts of Mongolia and China. This is a cold winter desert — experiencing heavy snowfall and extreme cold in winter months followed by warm days in summer. Total area of approximately 1.3 million km² (500000 mi²). Its extreme aridity stems from being on the lee side of mountains creating a rain shadow effect preventing moist air from moving northward from India.

Why Misconceptions Exist

Misconceptions regarding deserts originate from ancient times based upon cultures living near or interacting with hot deserts and relatively recently in human history did humans begin exploring and understanding polar climates in detail. Today we know using current scientific definitions and mapping techniques that Antarctica provides one major exception to these misconceptions due to being a very cold desert and having an incredibly large area.

Is the North Pole a desert?

Yes, in addition to being partially composed of ocean with floating ice and surrounded by land masses; all together this constitutes part of the Arctic Polar Desert and receives only limited precipitation while having extremely low temperatures.

Scientific Definition of Deserts

The definition scientists use for a desert is its aridity; specifically an area receiving less than 250 mm (10 inches) of precipitation annually. Temperature is not the primary descriptor for deserts; therefore both hot and cold deserts exist.

Average Annual Precipitation in the Sahara Desert

Precipitation averages less than 25 mm (about 1 inch) per annum in the driest locations in the Sahara Desert; whereas areas surrounding these are able to receive up to 100 – 250 mm (4 – 10 inches) per annum depending on latitude.

Do Any Plants/Animals Live in Antarctica?

Although large flora exists nowhere in Antarctica, there are simple flora such as mosses, lichens, and algae growing throughout areas of ice-free ground. Animals are abundant along coastlines of Antarctica — especially penguins, seals — and numerous species of birds which feed on abundant marine resources in nearby waters.