Summer is hotter than winter, right? Ever wonder why summer is warmer than winter, and why Phoenix is hotter than Fargo? The answer to both of these questions, of course, has to do with how much heat is coming into the atmosphere, and how much is going out.
The sun’s rays are much more directly overhead in the summer because our side of the Earth is pointed towards the sun and less directly overhead in the winter. Likewise, the sun’s rays in Phoenix are more direct over a longer part of the year, so it is warmer than Fargo.
When the sun’s rays hit the Earth, some of that energy bounces back towards the sun. In order to get to space, the energy travels through gases in our atmosphere. Literally 99% of our atmosphere is made of gases that have only 2 atoms: nitrogen (N2) and oxygen (02). But a few gases, like carbon dioxide (CO2) and water (H2O), have 3 atoms. Because of its 3-atom structure, carbon dioxide is particularly good at trapping heat.
Okay! So the bad luck for us right now is that the fuels we burn – oil, coal, or gasoline, for example – release billions of tons of carbon dioxide into the atmosphere every year. Since we know carbon dioxide is great at storing heat, it makes sense the earth would heat up when there’s more carbon dioxide in the atmosphere. It’s like tossing more blankets on your bed. You get warmer when you get under the covers because less of your body heat is able to escape.
This is how scientists know that the Earth is warming. It’s not because of recent weather trends – we all know weather can be incredibly variable. It’s because when you add heat to anything, and then trap some of that heat with a new layer of insulation, it warms up.
So how much is the Earth warming up? Before the Industrial Revolution, carbon dioxide levels were at about 280 parts per million globally. We are at about 400 parts per million right now.
But what does that mean?
Turns out we know when carbon dioxide doubles in the atmosphere, it adds 4 watts of heat to every square meter of the planet, 24 hours a day. Four watts isn’t a lot by itself. A 4-watt incandescent light bulb is what you might use for a little night light. But when it’s one bulb for every square meter, it adds up. We haven’t quite doubled carbon dioxide levels yet, but if we don’t take any action, it won’t take long.
If we look back into Earth’s history, we see that a few degrees warmer or cooler can make a big difference. We have had ice ages in the past that freeze liquid water and expand dry land, and warmer periods where the ice melts and sea levels rise to cover much more dry land than the ocean does now.
We can’t do anything about how much heat is coming to us from the sun. The good news is that we can control how much carbon dioxide goes into the atmosphere.
In the coming months, we’ll discuss how farmers and ranchers can play an important role in changing these trends, especially by using practices that save cash, burn less carbon, and make their farms and ranches more resilient in the face of severe weather. We’ll also talk about how faith leaders from around the world and across a variety of religions have called on their followers to care for the Earthby addressing climate change.
Special thanks to Dr. Scott Denning, professor of atmospheric science at Colorado State University, from whose talk this article is based. You can learn more and read articles about the science and economics of climate change at www.cfra.org/climate.