Climate on an Earth the Size of a Football Field

By: John A. Lanier

This week's Ecocentricity is a repost of something I wrote for the Drawdown Georgia blog several weeks back. Since it has relevance beyond Georgia, I wanted to post it here as well. As you'll see, when you imagine the earth at a smaller scale, it's remarkable just how sensitive our climate is to relatively minor changes in our atmosphere.

The earth is so big, it can be hard to imagine how sensitive our climate is to the greenhouse gas emissions we produce. The ground under our feet seems to extend out forever, as does the sky over our head. It can be difficult to intuitively grasp how impactful humans can be on our environment when the earth and our atmosphere seems so endless. Yet really sound scientific inquiry has shown us that we are that impactful, and frequently to ill effect. There is no issue where this is more true than our changing climate.

A Climate Change Thought Experiment

So in an effort to demonstrate just how sensitive the earth’s climate is to relatively small changes in our atmosphere, I wanted to lead you through a thought experiment. Imagine if we shrunk our planet down to a more manageable size - that of a football field.

To be more precise, imagine that the earth’s diameter, instead of being 7,926 miles at the equator, was exactly 100 yards. You could start at one goal line, say the city of Quito, Ecuador, and start walking through the earth’s crust. At the midfield, you’re in the very center of the planet’s core, and when you reach the other goal line, you pop back out at Singapore. Get the idea?

Climate Change and the Atmosphere

Now, to be clear, I’m just talking about our planet’s landmass. We also have an atmosphere, that seemingly endless sky I mentioned above, which extends out into the endzones of the football field. You might think that it extends quite a ways into the endzone, maybe a few yards at least, but you would think wrong. At this scale, the earth’s atmosphere (measured out to a demarcation point called the “Kármán line”) would only stick out 0.784 yards into each endzone, which is about two feet and four inches.

So essentially, all of the air on our planet fits within that less-than-a-yard band of atmosphere when you think of the earth at this scale. Shockingly thin, isn’t it?

Earth's Atmosphere and Climate Change

When it comes to climate though, most of the earth’s air has no impact at all. Due to their molecular structure, gasses like nitrogen, oxygen, and argon do not trap any of the sun’s energy and keep it held against the planet’s surface (the so-called greenhouse effect). Heat energy passes right through them, unlike greenhouse gases like carbon dioxide, methane, and nitrous oxide. 

So what if we unmixed the gasses in our dry atmosphere (in other words, excluding the water vapor that is constantly moving through the water cycle) and took them out?

Well, nitrogen is about 78% of the dry atmosphere, so there goes 1.83 feet of what was sticking out into the endzones. Oxygen is another roughly 21%, taking up another 0.49 feet. Argon is only about 0.93% of the atmosphere, so it takes up 0.26 inches. But if you’re following along, that’s more than 99% of all of our atmosphere.

Carbon Dioxide: The Greenhouse Gas Effect Culprit

Every bit of the greenhouse effect is caused by the remaining 0.07% of our atmosphere. If we didn’t have it, the earth would be about as hospitable to life as the moon is.

On our football field, that corresponds to 0.02 inches, or about half of a millimeter. It’s tiny! Of that amount, carbon dioxide makes up the clear majority. As of the end of March 2022, carbon dioxide makes up 0.0420% of the dry atmosphere (in other words, 420 ppm, or parts per million). That’s about 0.3 millimeters on our football field.

I want to say it again, so you get the main point in all of this math that I’ve thrown at you. If the earth were the width of a football field, then the gases that keep our planet warm enough to live on would be less than half a millimeter wide!

The Sensitivity of the Planet's Thermostat

Yet we know, because climate scientists have shown us, that the climate on earth has always changed. So how thick would that atmospheric blanket have been back in the ice ages of the previous million years? The National Oceanic and Atmospheric Administration has a good graphic showing us, and back in the ice ages, carbon dioxide would dip down to lows of about 180 ppm. On my football field, that equates to 0.13 millimeters.
 
So at 0.13 millimeters of carbon dioxide, my football-field-earth is in an ice age. At 0.3 millimeters of carbon dioxide, it is quite warm and rapidly losing ice coverage at its poles. That is the width of just a few human hairs.
 
As I hope you can see, our planet’s thermostat is incredibly sensitive. Even slight changes to the composition of the atmosphere can cause rapid shifts in our climate, which we are seeing play out in real time today. Because of the greenhouse gases we have put into the atmosphere, our climate has tipped out of its delicate balance. This is why it’s so urgent that we achieve Drawdown as soon as possible.
 

Tracking Greenhouse Gas Emissions in Georgia

Ready to learn more about emissions in our state? Take a deep dive into local climate data with the Drawdown Georgia GHG Emissions Tracker, a first-of-its-kind resource to track emissions data at a state and county level.

 

 

Comments