Is Carbon dioxide like glass? Is it plant food?

BUT I LIKE CO2! It’s a plant food after all!

Well, the headline isn’t actually all that accurate. Our metabolism requires oxygen. A plant requires carbon dioxide. To call carbon dioxide a food would be like telling us we could forego pizza. If we’re hungry, just breathe deeply.

Carbon dioxide is just one of several greenhouse gasses (GHG). To understand how they may be responsible for warming the earth, we must understand the mechanism by which they operate. To explain, I’ll use one, very potent, greenhouse gas - water.

First, let’s look at how the earth warms. The earth is warmed, primarily by the sun. The high-energy, short wave infrared energy radiated by the sun can penetrate the gasses in the atmosphere and warm the ground. At night, the heat absorbed by the earth during the day is radiated back out into space. After sunset, have you ever felt the warmth of a brick wall? Like the earth, the wall is radiating stored energy back into space. This re-radiated energy is low-energy, long-wave infrared… and it acts differently than its short-wave cousin.

Ever hear the weatherman tell us that nighttime temperatures won’t drop much because we have a blanket of clouds keeping the heat in? Do you envision a big, fluffy down blanket under which the earth snuggles? Well, it doesn’t work that way. What is a cloud? It’s water vapor… it’s like a fog. Have you ever stepped out into the fog and thought, OH MY, I’m getting warmer! Nope, you get a chill. That’s because water vapor absorbs heat. In this case, it’s YOUR heat. In the case of clouds, it’s the earth’s heat. So, the cloud now absorbs the heat from the earth. It then radiates that heat in all directions… including back down to earth. Does that sound far fetched? If you heat up water, can you not place your hand over the pot and feel the warmth coming from the water? Of course, you can. Does your coffee not retain its heat and radiate it back to the inside of your mouth? Well, clouds work the same way. They effectively prevent some of the earth’s heat from escaping into space. The earth under the water vapor cloud stays warmer. Now, what if the cloud has more water molecules in a given space. The amount of heat they absorb and re-radiate will be greater. So, the more of the greenhouse gas there is, the warmer the earth will stay. Any questions?

Studying sea surface temperature (SST) is a good way to estimate the increase in water vapor in our air. We know the amount of water vapor in the atmosphere has increased. The amount of increase is about 7% per 1.8° of warming (LINK). The trend in SST is found on multiple sites including (LINK) and (LINK2). While the second link may be an interesting read, Figures 8 and 11 are a good place to focus your attention. They show an increase in SST since 1850. The report also tells us that the SST has risen approximately 1° F corresponding to a 4% increase in atmospheric water vapor. Remember, SST determines how much water evaporates into the atmosphere, which causes more clouds, which traps more of the earth’s heat. Now, let’s look at another gas… Carbon Dioxide.

CO2 works the same way water vapor works… it’s just not as potent. It absorbs heat radiated from the earth and in turn, radiates it in all directions… including back to earth. Figure 13 of LINK2 overlays measured carbon dioxide levels onto SST trends. While we’re only to 2020, the author extends the curve based on the current trend in the concentration of CO2 in the atmosphere. So how do we know how much carbon dioxide is in the atmosphere?

In 1953, Charles Keeling began to take hourly measurements of atmospheric CO2 levels. He started at Big Sur, California but eventually set up a station atop Hawaii’s Mauna Loa volcano in 1958. He continued to measure daily CO2 levels until his death in 2005. His son, Ralph Keeling, continues the measurements to this day. From his curve, we can see that, from his first measurements of around 318 ppm, we now have a concentration of over 413 ppm. You can see and track daily levels yourself at this site (LINK). For a nice animation of Keeling’s curve, check out (LINK).

So, now we know how a greenhouse gas absorbs radiated heat and sends it back to earth. We understand that the more of the greenhouse gas we have, the more heat it can absorb and radiate back to earth. We see that there has been about a 4% increase in water vapor since 1850 and an approximately 30% increase in carbon dioxide concentrations since 1958. We see that there is an apparent correlation between the rise in SST and the concentration of carbon dioxide in the atmosphere. Other observations include the shrinkage or disappearance of glaciers (LINK), melting permafrost (LINK) that releases another GHG, methane, into the atmosphere, and a disappearing arctic ice cap (LINK). The last LINK is very disturbing.

So, while there is no “smoking gun” tying all these events to our enjoyment of a nice drive into the country or a raging bonfire, doesn’t it seem odd that they all seem to be happening at the same time?