MadSci Network: Earth Sciences

Re: Why is Antarctica not considered the largest desert in the world?

Date: Wed Oct 17 17:36:49 2001
Posted By: David Scarboro, Faculty, Earth Sciences, The Open University
Area of science: Earth Sciences
ID: 1001896997.Es

Question: Why is Antarctica not considered the largest desert in the 
world? From: john Grade: 4-6 City: Liberty Township, State/Prov.: OH 
Country: USA Area: Earth Sciences Message ID Number: 1001896997.Es We are 
studying about biomes in science. By definition Antarctica is classsified 
a desert because of its low percipation. It is much larger than the Sahare 
Desert. I asked my science teacher this question and he did not know the 
answer. I have been trying to find out why also, but no where have Ihave 
been unalbe to find where it explains the the Sahara desert being the 
largest "hot desert" and Antarctica being really the largest desert. Can 
you explain this to me? 

Dear John,

You are quite correct to point out that Antarctica is a desert.  It is 
what is known as a cold desert, which is probably why you find that it is 
not classified along with hot deserts like the Sahara.  A hot desert is 
defined by geographers as a region where the rate of evaporation exceeds 
precipitation, and where precipitation is below 254 mm per year.  In a 
cold desert, by contrast, there is little evaporation, so low 
precipitation alone determines its status as a desert.

In Antarctica precipitation is less in the interior of the continent than 
along the coasts.  The reason is that coastal areas are more open to the 
influence of cyclones.  In the interior of Antarctica precipitation is as 
low as 50 mm per year, while in coastal regions it can be as high as 250 
mm per year.  Thus even coastal precipitation is usually within the range 
that we would consider to be a desert.  The entire continent is, 
therefore, a vast cold desert.  It is, as you rightly say, larger than the 
Sahara (Antarctica is about 14.2 million square kilometres in size, and 
the Sahara is just over 9 million square kilometres).  

As you rightly point out, Antarctica is clearly the largest desert on 
Earth.  The reason you do not often see it listed along with hot deserts 
is mainly, I suspect, just that people think of deserts as hot.

Best wishes,

David Scarboro

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