The greenhouse effect, as previously mentioned, is the natural warming of the earth due to heat-trapping greenhouse gases (GHGs). The greenhouse effect is what keeps the earth habitable. Too much of the greenhouse effect leads to the earth being too warm simply because too much heat is being trapped in the atmosphere. In short, the more GHGs, the more heat. But how does the greenhouse effect work? When sunlight comes into the earth's atmosphere, it is reflected back into the atmosphere in the form of infrared light, which is a type of invisible light. GHGs then absorb the majority of this infrared light, keeping it from escaping into outer space. 

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Before humans started to burn fossil fuels, emitting GHGs, the concentration of carbon dioxide (the primary GHG that we measure) in the atmosphere was between 200 and 280 parts per million (ppm). This means that for every one million molecules in the atmosphere, 200 to 280 of them were carbon dioxide. However, since the Industrial Revolution, the concentration has increased to 416 ppm as of April 2021. This is the highest level in 800,000 years. That is a much longer timeframe than all of human civilization. What's most significant is that scientists have clear evidence that the greenhouse effect and humans' GHG emissions are the contributors to the warming they've observed. 

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The Greenhouse Gases

The most significant GHGs are carbon dioxide, methane, fluorocarbons, and nitrous oxide. The Environmental Protection Agency (EPA) created the global warming potential (GWP) to compare how much each gas contributes to climate change. The GWP measures how much each gas warms the planet in comparison to carbon dioxide.

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Carbon dioxide is the most significant GHG in regard to climate change. Since GWP is based on carbon dioxide, it has a GWP of 1. Though it is much less powerful than other GHGs, it is most important for two reasons. First, it makes up 76% of global GHGs and 80% of U.S. GHGs. Second, carbon dioxide stays in the atmosphere for a long time. 40% of all carbon dioxide stays in the atmosphere after 100 years, 20% after 1,000 years, and still 10% after 10,000 years. That means the effects of carbon dioxide will still be felt 10,000 years from now.

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Methane is twenty-five times more potent (powerful) than carbon dioxide. That means it has a GWP of 25. Released especially by agricultural and industrial processes, methane is much less abundant than carbon dioxide but still quite dangerous. It can leave lasting damage to the environment even though it's only been around for about 100 years. 

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Fluorocarbons are the most potent GHG. Fluorocarbons are a broad term for GHGs that humans created. They are only emitted by humans and are heavily regulated, leading to them only being 2% of all emissions. However, they are dangerously potent, with GWPs ranging from the 1,000s to the 10,000s. 

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Nitrous oxide is most often emitted by agricultural processes, particularly soil management activities where fertilizers contain nitrogen which is then leaked from the soil into the atmosphere. Nitrous oxide has a GWP of 300 for the first 100 years.