A warming planet: learning about the greenhouse effect

This is the final blog post about geophysics. We are going to venture into the last domain of the planet we haven't explored, the atmosphere. In particular we are going to talk about the greehouse effect and an experiment I have done about it.

The greenhouse effect is a natural process by which light from the sun goes through the atmosphere as visible light and it warms the surface of the Earth. When the surface cools down, it emits some of this energy back as infrared. This infrared radiation can bounce on some specific gases in the atmosphere, causing the planet to warm up. These gases include carbon dioxide which is the most well-known gas but there are other more potent ones like methane and nitrous oxide.

It is important to note that without the greenhouse effect Earth's average temperature would drop from a comfortable 15°C (59°F) down to a freezing -18°C (-0.4°F), making the planet uninhabitable for most living things.

Surprisingly, carbon dioxide only represents a very small percentage of the gases in the atmosphere as you can see in this graph.

I decided to make the following experiments to prove the greenhouse effect. First, I got two identical jars, drilled a hole, and installed a DHT11 temperature sensor on each of them. One jar contains normal air (the control jar), and the other one has a larger concentration of carbon dioxide than usual (the test jar). Those temperature sensors are connected to a microcontroller.

At the beginning, I tried to read the two temperature sensors with a Micro:bit as usual but I wasn't able to get proper readings. So then I decided to use the Raspberry Pico W. This microcontroller is more advanced, and it's a perfect opportunity to start learning Python.

I was tempted to display those temperature values on a little screen like in previous projects, but thanks to the Raspberry Pico I could try something different to learn new skills. So, this time, I made the microcontroller create a REST API to expose the temperature values, and then an Android app to read them from the REST API. You can see the Python code here.

It was quite a journey as I encountered several issues and had to make several iterations along the way.

An issue was that the DHT11 sensor is quite big, and when the sun heated it directly, it got very hot so it ended up not measuring the temperature of the air inside the jar anymore, but its own temperature up in th high 40's. To overcome this, I covered the jar in white tape, as you can see in the photo below. I also covered the cables as well, just in case because metal is a good conductor.

Initially, I decided to use my own respiration as a way of increasing the concentration of carbon dioxide by breathing into a balloon and breathing the balloon air back several times. This way, the concentration of oxygen decreases and the carbon dioxide diminishes. Unfortunately, I was unable to notice a difference between the test and the control jars. Carbon dioxide is denser and I was hoping it to go to the bottom of the jar, but potentially, the exhaled air from the balloon was warmer and managed to escape the jar before closing it.

To get a larger concentration of carbon dioxide, I decided to use a chemical reaction of white vinegar and sodium bicarbonate. The bubbles this reaction generates are carbon dioxide. I made this reaction inside the jar and covered the jar with a balloon to capture all the carbon dioxide.

In order to make the carbon dioxide gas in the balloon even heavier, I decided to put the balloon in the freezer for a while. This way, the carbon dioxide becomes denser, and in theory, it should stay at the bottom of the jar.

Finally, I attached a straw to the balloon so that I could drop the carbon dioxide at the bottom of the jar, as you can see in the following video. Notice the small size of the ballon as it shrunk inside the freezer.

Unfortunately, as you can see in the Android app screenshot below, I wasn't able to observe a difference, between the control and the test. However, it was a great learning experience, and in fact, the next three blog posts will be about things I learned along the way. If you have any comments or suggestions, leave me a comment.