The Simple Science of a Greenhouse

Every day, there are stories in the media about climate change. Opinions on the subject vary widely. Based on a UN report, Axios wrote “Nothing is happening remotely fast enough to save humanity from facing the self-inflicted disaster of runaway climate change”. Some see it quite differently. The challenge is the subject consists of incredibly complex and interconnected elements. My goal is to write about this starting with the basics and develop an understandable picture which can shed some light on various policy decisions which could affect the situation.

An executive I reported to many years ago at IBM was a believer in making things simple. He was a brilliant scientist. We were working on a presentation for the board of directors. I will never forget him saying the only way to get this across to the board is to assume they are fifth graders. He had a set of rules for how to prepare a board presentation. One of his rules was to never put more than five bullets on a slide. Keep it simple. Lets start with the greenhouse.

A greenhouse is a building with glass walls and a glass roof. (Some greenhouses use polycarbonate instead of glass). The purpose of a greenhouses is to provide a perfect environment for non-stop gardening. In the early part of the year, it is a good time to get a head start with frost-tolerant plants such as broccoli, cabbage, lettuce, and spinach. When spring arrives, it is time for more tender plants such as cucumbers, melons, and squash. When internal and external greenhouse temperature reaches a peak, it is great for heat-loving plants such as eggplant, peppers, and tomatoes. After a warm summer and the beginning of cool weather, gardeners like to begin a second crop of cool-season vegetables like kale, snow peas, and turnips.

A greenhouse maintains a great environment, staying warm inside, even during the winter. The principles which make this possible are really simple. During the daytime, sunlight shines into the greenhouse and warms the air inside and the plants. At night, it gets colder outside, but the temperature in the greenhouse stays pretty warm. The simple reason is the glass walls and roof of the greenhouse trap the heat of the sun and prevent it from escaping.

Fortunately, we have a virtual greenhouse which envelops our planet Earth and keeps the temperature tolerable. Instead of glass walls and ceiling, our planet’s greenhouse consists of a layer of gasses called the atmosphere. Because the atmospheric gasses act like the walls and ceiling of a greenhouse, they are called greenhouse gases and what they do is called the greenhouse effect. The primary¬†greenhouse gases in Earth’s atmosphere are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3).¬†

The greenhouse effect means the gases in the atmosphere trap the sun’s heat just like the glass roof of a greenhouse.¬†During the day, the Sun shines through the atmosphere and warms the Earth’s surface. At night, Earth’s surface cools, releasing some of the heat back into the air, but some of the heat is trapped by the greenhouse gases. The greenhouse effect is a good thing. It keeps our Earth a warm and cozy 59 degrees Fahrenheit (on average). Without the greenhouse effect, Earth’s temperature would be 32 degrees below freezing. We would not be able to live here.

On the other hand, if there is too much gas in the atmosphere, more heat would be trapped, and the greenhouse effect would make the average temperature on Earth go up. NASA has placed satellites in orbit which measure the amount of gases in the atmosphere. I don’t believe there is much debate the amount of gases has increased quite a bit over the years. The scientific consensus is the increase in greenhouse gases is trapping more heat in the atmosphere and raising the temperature on Earth.

There is debate about what has caused the amount of greenhouse gases to increase. Next week, I will drill down on the subject. The deeper one gets into the subject, the more complex it becomes. I will do my best to keep it simple.

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