Cow vs. G5
... and other thoughts on a hot day
I have a young daughter who loves jets. And by jets, I mean just about anything that can fly. Single engine props, gliders, commercial airliners, and private jets all fall into the category of “jets” by her accounting. That’s my fault; early on I decided it was just an easier word for her to learn than a panoply of terms: airplane, prop plane, turbo prop, and so forth. Regardless of nuance, they all hold a fascination for her, and me, I suppose.
So, on Daddy days, we often ride a bike down to the local private airport to watch the jets come and go. The modest entrance to the airport is a one-and-a-half-lane road. On one side is a fence lined with big fancy jets: G5s, Learjet 60s, and Citations. On the other side is a fence holding back a few hundred cows—brown ones—that’s how much I know about cows. But if cows could spit, they could hit the tail wings.
The juxtaposition of the two is a bit surreal—new world and old world—but not all that unusual for a place like Idaho. The oddity did make me wonder one day: what’s worse for the atmosphere—a G5 or a cow? This idle thought was no doubt spurred by the fiery hell of a summer everyone in the West is suffering through. Somedays it feels like we’re living on the surface of the Sun.
Running the gauntlet between jets and cows that day, I realized I really didn’t have a great grasp on climate change, greenhouse gases, and the overall fate of the world. This was a bit shameful because I was a chemical engineering major in college. However, I figured that if I was a little fuzzy on one of the bigger debates of our lifetime, then chances are others might be, too. I, at least, owed it to my professors—particularly Professor Acrivos who taught me everything I know about heat transfer—to better understand what everyone is getting so hot about.
Planetary scientists like to call Earth the “Goldilocks” planet. As you may or may not remember from the fairy tale, Goldilocks—lurking about in the cabin of the three bears—finds three bowls of porridge: one too hot, one too cold, and one “just right.” Earth, too, is not too hot and not too cold, but just right. Why? Because when the heat coming into our world from the Sun balances with the heat going out to space, we happen to end up at an average equilibrium temperature (59 F) that enables liquid water to exist, without which we wouldn’t exist.
When thinking about this big heat transfer problem, the first thing to realize is that we’re talking about an exchange between only two entities: the Sun is one and the Earth/atmosphere is the second. Our atmosphere and Earth are intimately connected. One might think that the atmosphere is just air that blows around and doesn’t have much to do with us. But because of gravity, our atmosphere is always attached to us. It’s kind of like the cloud of dust that follows Charlie Brown’s buddy, Pigpen, around, only it’s not dust but a bunch of gases all mixed up. Most of it is oxygen and nitrogen (99%), elements also crucial to life for processes like breathing, photosynthesis, DNA, RNA, etc., but not relevant here. Only 0.1% of the atmosphere comprises what we call greenhouse gases: water vapor, carbon dioxide, methane, ozone, nitrous oxide.
So, back to heat transfer (yippee, you say). The Sun bombards us with solar radiation. Some of that energy gets reflected back to space before it gets to us, some is absorbed by the atmosphere on the way in, but most of that energy sails right through the atmosphere and is absorbed by the land and water on Earth. And just like an asphalt parking lot that radiates heat at night when things cool off, so does the Earth as a whole.
But—and this is what the heat transfer test would hinge on if there were one—because the Earth is at a different temperature from the Sun (59 F vs. 9,941 F) the energy returning to space is at a different wavelength from the energy that came in. And because of that subtle fact, a lot of the energy radiated from the Earth is absorbed by greenhouse gases in the atmosphere rather than just sailing unimpeded back to space.
What does absorbed mean? The energy excites the greenhouse gas molecules in the atmosphere. They vibrate and move around faster—kind of like giving a kid a chocolate bar. The average temperature goes up.
This weird wavelength shift causes the atmosphere to work like a one-way filter: the energy comes into our world unimpeded, but not as much is able to get out. Happily, that works out for us because after the energy-in and energy-out balance, the temperature settles at 59 F. If we didn’t have the naturally occurring greenhouse gases up there to prevent some heat from going back to space, the temperature on the Earth would balance out at a much colder and inhospitable 0 F.
So, what’s the problem?
Basically, it comes down to where the carbon is.
Our world—Earth and atmosphere—has always had the same amount of carbon in it, and always will. That carbon is in rocks and fossil fuels underground, in the plants and trees (cellulose), in living organisms (proteins, carbohydrates, fats), and in oceans (living organisms, calcium carbonate, and gases in the water). We are running into trouble because since the Industrial Revolution we have been redistributing that carbon—moving it from the ground (fossil fuels) and plant life and into the atmosphere in its gaseous forms (carbon dioxide and methane, for example). With more of these gases in the atmosphere, more heat is absorbed by them, and so our average temperature here climbs a bit.
Venus is sometimes called our sister planet, mostly because it is our neighbor in the Solar System and has a similar size and density. However, it is not a Goldilocks planet. Its atmosphere is 96% carbon dioxide—a sort of end game scenario for Earth. When your atmosphere has that much carbon dioxide in it, very little of the Sun’s inbound energy escapes from it, and the temperature climbs. The ambient temperature on Venus is about 900 F, which makes this summer look pretty good.
Now back to cow versus G5.
In 2019, the U.S. added a lot of greenhouse gases to the atmosphere, as we do every year. In essence, we took a lot of carbon containing compounds from the ground, plants and trees; used them for one thing or another; and put the end product of all those uses—14.5 trillion pounds of carbon dioxide—back into the sky.
Where do all these emissions come from? By economic sector, it breaks down as shown in the diagram below. The breakdown by type of emissions is shown in the diagram below that. Hidden in these charts are the G5s and the cows.
A G5 burns kerosene at a rate of 400 gallons per hour. At the end of that hour, it has dumped approximately 8,500 pounds of carbon dioxide into the sky.
Now, the lowly cow. You wonder, what could she possibly be doing wrong?
Cows are unusual animals—they are ruminants—which means they have a special stomach that enables them to ferment their food. What’s the byproduct from fermenting all that grass (cellulose/carbon)? Methane, one of the most effective greenhouse gases when it comes to trapping heat. How do cows get rid of all that methane? Not what you think. They burp it out.
Each year, an average cow belches out 220 pounds of methane, which is 28 times more potent than carbon dioxide as far as absorbing heat. Do the math and you get the equivalent of 6,160 pounds of carbon dioxide per year.
A cow left alone might live 20 years, but they aren’t, of course. In reality, a dairy cow is allowed five years of burping, a beef cow two years. So, we’re looking at a maximum of roughly 31,000 pounds of carbon dioxide emitted during the life of that cow, less than four hours in the G5.
Head-to-head, the cow wins the green award.
Unfortunately for the cow, if you lump her together with all her bovine friends they out-belch all the private jets by almost 50-fold.
Doesn’t seem like a fair fight, does it?