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The Southern most desert in the world is…?

Yep, it’s Antarctica. Counter to what you might think, it doesn’t rain or snow very much there. Deserts are defined by their aridity. Many deserts are also in very warm places but as you now know, not all are! 

I think this begs two questions: First, why? What about the climate of Antarctica makes it so dry? Second, how can there be so much snow then? Okay, let’s dive in.

The Climate of Antarctica: To understand why Antarctica is so dry, I think it’s helpful to compare Antarctica to places we’re more familiar with. Let’s start on the west coast of the US. All along the west coast are very tall mountain ranges. Now let’s compare this to the precipitation (rain and snowfall) along the west coast.

Topography of Western US

What do you notice? West (left) of the mountain ranges precipitation is very high (blue and purple). East of the mountain ranges, it is much much drier (orange and yellow). Why is this? Let’s think about what is happening to the air. The flow of air is predominantly from west to east. The air starts off very moist over the Pacific Ocean and then reaches the west coast. The air is forced up and over the mountains, squeezing the moisture out of the air parcel causing it to rain or snow. By the time the air gets to the other side of the mountains, most of the moisture is gone.

How does this compare to Antarctica? It’s similar, but the air is also a lot colder in Antarctica to begin with. Here, moist air over the ocean must rise up to the top of ice that is miles high (like one big mountain). In the process, most of the moisture is lost so that by the time the air gets to the interior of the continent, it is very dry. Additionally, since it’s a very cold climate, the air can’t hold much water to begin with. Check out the map of Antarctic precipitation (mostly snowfall in this case). Notice the high precipitation along the coast and the much lower precipitation in the interior.

Average precipitation (mostly snowfall) in Antarctica (mm of water equivalent/year)

Thinking about snow accumulation: How is there so much snow in Antarctica if it hardly ever snows? Well it also is very cold so the snow can’t melt. I just did some rough calculations, and if it snows ~50 mm/yr in the middle of Antarctica and the ice is ~4 km (2.5 miles) thick, that means it takes on the order of 78,000 years to build up that much ice! In fact, ice cores that scientists have drilled tell us that there is probably ice that is over 2.7 million years old currently in Antarctica! This is a comparable time scale to that of human evolution. 

In fact, paleoclimate data suggests that glaciation on Antarctica began around 35 million years ago. I think the main point to realize is that the Antarctic climate is very unique and what we see today is the result of millions of years of snowfall and glacial processes.

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