If I can grow enough potatoes, I won’t starve. But how large an area do I need to plant?
It’s a simple question in a complex and desperate situation. In the movie The Martian, an astronaut on a Mars mission is thought to have been killed in an accident and left on the red planet during an emergency evacuation by the rest of the crew. Mark Watney, the unlucky astronaut played by actor Matt Damon, must figure out how to survive. With four years to go before the next scheduled mission will arrive on Mars, but only enough food to last for one, a key part of survival will be avoiding starvation.
In his video log, Watney surmises, “So, I’ve got to figure out a way to grow three years’ worth of food here—on a planet where nothing grows. Luckily, I am a botanist. Mars will come to fear my botany powers.”
In his quest for food, Watney discovers potatoes that were set aside for Thanksgiving dinner. This is the only food that he can attempt to grow to supplement the remaining food rations. He carefully calculates how much area he needs to grow potatoes and ends up with 126 square meters of Martian cropland.
Since potatoes are renewable resources, Watney calculates that harvesting the larger potatoes and re-planting the smaller ones will provide 400 potato plants, enough calories to keep him going until he can be rescued.
Starting to sound familiar? It sure does to us at Global Footprint Network!
When Watney was calculating the rate at which he needed to consume potatoes, he was measuring his personal Ecological Footprint, or in other words, his demand for ecological resources. When he calculated that he would need 126 square meters to grow 400 potatoes, he was calculating the biologically productive area, or biocapacity, needed to meet this demand.
Spoiler alert: if you don’t want more of the movie revealed, we recommend you stop reading here.
Of course, the movie wouldn’t be a Hollywood blockbuster if there wasn’t another disaster. An explosion due to equipment malfunction breaches the pressurized barrier surrounding Watney’s precious potato plants. The sudden drop of pressure ruins Watney’s water supply, and the subzero temperatures kill any bacteria in the soil, shattering his opportunities to re-grow potatoes. Water, soil quality and temperature are among the critical factors that impact biocapacity, but are not directly measured by Ecological Footprint accounting.
It’s a vivid demonstration of how outside forces beyond an individual or population’s control can affect the water supply and then biocapacity. For Watney it was an explosion. For places like California, it’s a drought ultimately forcing farmers to leave millions of acres of land fallow.
In the movie, we also see how Watney’s Footprint almost exceeds biocapacity: He has to tear apart the mission’s artificial habitat to make enough space for the cropland needed to sustain him. On Earth, humanity’s Ecological Footprint has exceeded the planet’s biocapacity. This is largely because on Earth, the Ecological Footprint goes beyond measuring our demand for food. It adds up all the competing demands on our planet’s surface areas, including demand for land for housing and other infrastructure; demand for timber products provided by forests; and demand for carbon sequestration, also provided by forests.
Even though this dramatic story took place on Mars, the situation feels close to home as we face similar challenges of living within our ecological limits here on Earth.