Worldwide, the potato is one of the most calorically important food crops along with corn, wheat, and rice. It's the cornerstone of food security for millions of people. Like in 2019 alone, we produced 371 million tons of potatoes worldwide. Which is like 96 pounds of potatoes per person.

Today the top producers of potatoes are China, India, Ukraine, Russia, and the US, but potatoes are still integral to their South American homeland. Somewhere between 2000 and 4000 varieties of potatoes are grown along the length of the Andes mountain chain. 

Different crops need different temperatures, precipitation, and soil conditions to thrive, which brings us to an important distinction we need to get to the root of our potato story: weather and climate are not the same thing.

Weather is what’s going on in the atmosphere at any given time and place. Today it’s dry and sunny but tomorrow it may be cloudy and rainy. Just like my mood can change if I eat fresh, hot french fries or cold, soggy ones, weather happens in the short term and is difficult to predict. 

But climate is a region’s average weather over many years, which is much more predictable and based on trends. So we don’t know what the weather will be like in New York City on January 20th, 2025, but we do know that it's usually chilly, because New York City has a cold winter climate. 

It’s like what former president of the American Meteorological Society Dr. J. Marshall Shepherd famously (probably) said: “Weather is your mood, climate is your personality.” [And my personality is a proud potato fan, even though we've all had disappointing fries before!] Just like there are endless human personalities based on our DNA and how we grow up, all the possible combinations of temperature, precipitation, wind, and ocean currents give us a variety of global climates. And all of those processes begin with patterns of insolation, or incoming solar radiation, across the globe. 

For example, mountains have complex climate patterns, or the somewhat predictable variation in climate.  These mountain climate patterns come from the way insolation and temperature change as we go higher in elevation, or the height of a point on Earth’s surface above a reference, like sea level. In fact, no matter where we are on Earth, for every 1000 meters we go up in elevation, the air temperature decreases by 6.5 degrees Celsius on average, which is the normal lapse rate.

If you’ve ever hiked or driven up from the base of a mountain, you’ve probably felt the air get chilly or brought extra layers to handle the cold temperatures. The normal lapse rate has big implications for Latin America’s physical geography, especially near the equator.  As we climb the Andes mountains from sea level, we can define our major climate zones based on elevation that have dramatic changes in plant life.

At the foot of the mountains is tierra caliente or hot country, a lowland zone of broadleaf evergreen tropical rainforest. The warmth and humidity here allows extensive tall trees and a dense, year-round leaf canopy to develop.   At about 900 m we begin to see mild temperate conditions and deciduous forests in the tierra templada. Then as we continue our climb, at about 1800 m temperate conditions get chillier. Colder temperatures and coniferous forests mark the tierra fria. 

As we move higher each zone gets smaller and at 3,600 m we reach the windswept tierra helada or frost country. In the lower reaches of this zone pine forests transition to alpine meadows and grasslands and mark the treeline, the upper limit of where trees grow.  Further up around 4,600 m we see a shift from grasses to hardy lichens and mosses. And beyond here we encounter the snowline or the elevation where winter snow doesn’t melt in the summer. This is the zone of perpetual snow that make up the snow caps on mountains. The final zone has very little plant or animal life.

Parts of Latin America use this terminology to describe mountain climate patterns, but different vertical zones and geographic terms exist around the world. Each mountain also has unique attributes -- like its slope or total elevation -- which create different ecosystems in these zones. 

The process of paying attention to geographic conditions, like mountain climate patterns, and using them to answer questions like “Why were potatoes domesticated in the Andes mountains and not anywhere else?” is called geo-literacy.  A geo-literate person understands that the world works as a set of physical, biological and social systems, and that processes within these systems connect places to each other. We can use these observations to interact with our environment and create particular outcomes. 

And even though geo-literacy might be a modern term, engaging with the world with a geo-literate lens is something people have been doing for 1000s of years.  Like 7 to 9 thousand years ago Andean farmers observed how a mountain was made of spaces with different climates and ecological niches, which is where certain plants thrive but not others. And they passed down this knowledge over generations, using their geographical understanding to select plots of land. 

Even today, farmers all over the world need to think through all the “ingredients” for weather and climate to plant crops, and we have all sorts of technology to help them track air pressure, precipitation levels, and more. But ancient Andean farmers didn’t have these same tools.

Let’s go to the Thought Bubble.  The Andean foothills and mountains are used to grow lots of crops, like tomatoes, beans, and maize.  But the diversity of potatoes is a source of pride and a cultural symbol of traditional Andean agriculture, food systems, history, community, and identity.  Historically, we think one way time was measured here was by how long it took to cook a pot of potatoes.  Even today potato seeds can be gifted to young couples setting up a household. And farmers in the high Andes measure land based on the area a family needs to grow their supply of potatoes.

Over the years, farmers realized that when they plant their crops could make the difference between a good harvest and a poor one.  For example, areas in what’s now southern Peru are prone to periods of drought.   As modern geographers, we know that typically there are cold water currents along the Peruvian coast, which help bring rain to the Andean highlands.  But some years, there's a pooling of warm water along the Peruvian coast, which can bring drought until the ocean currents change again. 

Without the aid of satellites or an understanding of ocean currents,  Andean farmers began to notice that if the stars -- especially the Pleiades stars in the Taurus constellation -- were hidden by water vapor in the atmosphere and hard to see around the Winter solstice in late June.  It indicated an El Niño year which is linked to reduced rainfall several months later.   So they’d plant their potatoes earlier to take advantage of whatever rain that fell. If they could see the stars clearly, they knew they’d get enough water to plant the potatoes a little later.  Basically, Andean farmers were geographers who observed the relationship between clouds in the atmosphere and rainfall patterns later in the season, which in turn helped people survive in the Andes for centuries. Thanks, Thought Bubble.

Any way that people observe atmospheric conditions, find patterns, and make decisions based on those patterns is geography in action!  Nowadays, scientists can observe and predict climate phenomena on a global scale, from ocean current patterns like El Niño and the Southern Oscillation to what latitudes different plants (like potatoes) can grow at.

We can categorize climate patterns in a lot of different ways, like using temperature and wind patterns. But those can be hard to see, and something like vegetation growth is much more obvious.  In general, natural vegetation starts with a tropical rainforest at the equator and transitions into ice and snow and sparse vegetation as we get to the poles -- sort of mirroring the mountain climate pattern we talked about before.

This visible connection between vegetation and climate helped climatologist and botanist Wladimir Köppen devise a classification system in the early 1900s called the Köppen system.  It's still widely used today with many improvements by many people and with many terms that reference a type of climate and a type of natural vegetation, like the tundra or the rainforest!

Specifically, the Köppen system divides the world into six major climate categories. Using the visible vegetation as a guide, Koppen came up with precise definitions for each climate region based on average monthly temperature, average monthly precipitation and total annual rainfall.  The first four categories are based on moisture and temperature characteristics, and they're usually labeled with capital letters.

Like (A) represents tropical climates which are known for having high temperatures and receiving a lot of rain. And (E) represents polar climates which tend to be cold and dry.  Then the last two categories are based on moisture and elevation instead of temperature. Like (H) represents the highland climates in the world’s mountainous regions.

Like where our original Andean farmers grew potatoes. Then within each of these big categories there are subcategories marked with additional letters to break climates up into even more precise groups.   So let’s use potatoes as our example. They thrive in cold weather, so if we look at a Köppen climate classification map of South America, it makes sense that they thrive in the Andes.  In the west along the Andes, there are bands of (H) which means highlands and BWk -- which says the area is arid, desert, and cold. The transition out of those desert highlands is a BSk -- which says the area is arid, has a steppe climate, and is cold. Those are some ideal potato growing conditions. 

If we overlay a full Köppen climate classification map with a map of everywhere potatoes are grown, we see that potatoes are really hardy because there’s a lot of overlap with a lot of different climates.  We know that many species of potato were domesticated by Andean farmers, but we also know that plants are adaptable. Those farmers used their geo-literacy to grow more plentiful crops, but also to begin breeding plants to tolerate different temperatures. 

The Andean empires flourished because of food security from crops like potatoes. And thanks to global trade and the hardiness of potato species, today potatoes are grown in over 100 countries -- from India in the tropics to Finland close to the Arctic Circle. 

From hot and cold regions to dry and wet regions, and all climate combinations in between, humans have adapted to the natural environments around us and used our growing geo-literacy to thrive.

But increasingly, the Earth's environments are also impacted by our choices.  In future episodes we'll look at how and why the maps of global climates, vegetation, soils, and ecosystems are changing -- and our response to those changes. And we'll hit the ground running in the next episode, when we discuss how these themes relate to climate change.

Many maps and borders represent modern geopolitical divisions that have often been decided without the consultation, permission, or recognition of the land's original inhabitants. Many geographical place names also don't reflect the Indigenous or Aboriginal peoples languages. So we at Crash Course want to acknowledge these peoples’ traditional and ongoing relationship with that land and all the physical and human geographical elements of it.

We encourage you to learn about the history of the place you call home through resources like native-land.ca and by engaging with your local Indigenous and Aboriginal nations through the websites and resources they provide. Thanks for watching this episode of Crash Course Geography which is filmed at the Team. Sandoval Pierce Studio and was made with the help of all these nice people.

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