Most of us know what a greenhouse gas is: it’s a gas which traps heat in the earth’s atmosphere. These gases let sunlight pass into the earth’s atmosphere, but don’t let the heat brought with the sunlight leave. This is more commonly known as the greenhouse effect. Greenhouse gases are necessary because they make the earth habitable for all life we see on it today. However, in excess greenhouse gases can be extremely harmful to that very same ecosystem.
But what are the 5 main greenhouse gases? The most common greenhouse gases are carbon dioxide (CO2), water vapour (H2O), nitrous oxide (N2O), methane (CH4), and chlorofluorocarbons (CFCs). The most infamous of the 5 is carbon dioxide. Most people learn from a young age about its harm to the environment. However, people are often less aware of the other four greenhouse gases. In this article, we will ask what makes them different to carbon dioxide, and are they more or less harmful to our environment?
How can we compare the impact of different gases?
All the greenhouse gases behave in a different manner, and so it can be difficult to compare their effect on the environment. However, we can assign each gas a “Global Warming Potential (GWP)”. The GWP of a gas gives their heating effects on the environment compared to carbon dioxide. Carbon dioxide has a GWP of 1. We can calculate GWP using two factors:
- How much heat the gas absorbs and emits back to earth
- How long it takes the gas to decay in the atmosphere
If a gas emits more heat towards earth and takes longer to decay in the atmosphere, it will have a higher GWP. If you want to learn more about the GWP of different gases, and how it is calculated; check out this article.
We often see carbon footprints written as CO2e (carbon dioxide and equivalent). This means that your carbon footprint is calculated by considering all the greenhouse gases emitted. However, if you emit a greenhouse gas with a higher GWP, it will contribute more to your carbon footprint. If a gas had a GWP of 2, 10kg of that gas would be the same as 20kg of carbon dioxide.
Water vapour is by far the most abundant greenhouse gas in our atmosphere, therefore meaning it traps the most heat. In fact, 1 out of every 200 air molecules is an H2O, which is enough to trap half of the heat radiated off the earth. As scary as that may seem, water vapour is perhaps the least harmful of all the greenhouse gases. This is because there is a limit to how much water the atmosphere can hold. If this threshold is surpassed, the atmosphere releases the water vapour through rain.
That being said, if the volume of another greenhouse gas in the atmosphere were to increase, more water vapour could be soaked up. This would cause even more trapping of heat. Water does not cause global warming. However, as a result of this feedback loop, water is able to speed it up.
Methane is another relatively abundant greenhouse gas in our atmosphere, after water vapour and carbon dioxide. Despite this, methane is around 84 times more potent than carbon dioxide over a 20-year period. Not only is methane a key ingredient of natural gas, but it one of the most common atmospheric gases. Cattle burps and farts as well as decaying waste in landfills are huge emitters of methane. One in every 600,000 air molecules is methane. This means it is one of the greenhouse gases which is heating the earth up the most.
Nitrous oxide (N2O) comes in fourth after methane as one of the most abundant greenhouse gases in the atmosphere; one in around every 3 million air molecules is a nitrous oxide molecule. While that may not seem like a lot, nitrous oxide is actually 300 times the potency of carbon dioxide. Nitrous oxide actually damages the ozone layer as it breaks down higher in the atmosphere, which allows more radiation into the earth’s atmosphere.
Furthermore, while limiting carbon and methane emissions seems to be a relatively straightforward goal, limiting nitrous oxide emissions is comparatively much harder. The thing is, with the nitrous oxide issue, it all boils down to agricultural soil management. In lieu of the green revolution, the use of fertilisers has drastically increased, leading to an increase in nitrous oxide emissions. This is because the manure used in fertilisers can convert into nitrous oxide if lacking in oxygen. Not only that, but only around half the fertiliser is used up by crops, meaning the other half can wash away into nearby water sources, leading to eutrophication. Therefore, we can see that nitrous oxide has many more indirect environmental and economic implications than the other greenhouse gases.
Chlorofluorocarbons (CFCs), another greenhouse gas, seemingly takes up a minuscule percentage of the greenhouse gases in the atmosphere. However, a single CFC molecule can actually hold 11,000 times the heat of carbon dioxide, making it an extremely potent gas. CFCs are emitted by aerosols, old refrigerators, and air conditioners; these molecules travel towards the stratosphere, breaking down into chlorine molecules by UV radiation, which can damage the ozone layer. A small percentage of these harmful chlorofluorocarbons can have a huge impact on the temperature of the earth, as the depletion of the ozone layer means more UV radiation on the earth’s surface.
So which is the worst?
So, how do these four greenhouse gases compare to carbon dioxide? While it is blatantly obvious that they seem to do much more damage due to their potency, carbon dioxide actually still takes the crown on environmental damage. Despite the other gases’ ability to heat things up much more effectively, there’s just simply too much carbon dioxide in the air, and humans just keep rapidly adding more. Since the industrial revolution, carbon dioxide levels have gone from being one out of every 3,600 air molecules to one out of every 2,400 air molecules. This extra carbon dioxide has caused around 70% of the warming over the last 250 years.
It is clear that, even though carbon dioxide is the weakest in terms of its heat-trapping mechanism, its sheer volume in the atmosphere means it is by far the most lethal of the greenhouse gases.