The 5 Most Abundant Greenhouse Gases and Where They Come From

There’s more to the greenhouse effect than carbon dioxide.

The greenhouse effect is an important part of the reason why our planet is fit for human habitation. However, releasing gases which promote it through human activity into the atmosphere is leading to a warming effect; this is essentially upsetting the Earth’s natural systems. Without pulling any punches, it’s fair to say that humans release a lot of crap into the atmosphere. Though which gases amplify the greenhouse effect, and where do they come from?

1: Carbon Dioxide

The most famous greenhouse gas is without a doubt carbon dioxide. In fact, when measuring the global warming potential (GWP) of a gas, carbon dioxide is the standard to which all other gases are measured. Ergo, it has a GWP of one. 

Carbon dioxide is primarily produced in nature through animal and plant respiration, decomposition of organic matter, ocean and atmosphere exchange, as well as volcanic eruptions. The concentration of the gas has been increasing in the atmosphere mainly due to the burning of fossil fuels and deforestation. It is responsible for roughly three quarters of the warming associated with human greenhouse gas emissions. 

2: Water Vapour

Perhaps one which is not immediately clear is water vapour. It is one of the most powerful greenhouse gases, being responsible for roughly half of the total present-day greenhouse effect (including the natural effect). However, its GWP remains undefined. The vast majority of water vapour in the atmosphere comes from the ocean, and human emissions pale in comparison. Regardless, the main points of emission are irrigation, flying and power plant cooling. 

As the maximum amount of water vapour present in the atmosphere is fixed for a particular temperature and pressure, the real issue comes when other gases are emitted which heat the atmosphere. This in turn increases the amount of water vapour in the atmosphere, thereby creating further heating. This is known as a positive feedback loop. 

3: Methane

Behind carbon dioxide, we have methane, which constitutes 16%, or roughly one sixth of manmade gas emissions. In comparison to carbon dioxide, methane has a GWP of 28 over a 100 year period. This means pound for pound, it contributes more to the greenhouse effect.

Methane is predominantly released due to human activity via paddy rice fields, biomass burning, the anaerobic decomposition of organic material in landfills (including paper) and emissions due to the use of fossil fuels. Perhaps the most famous point of emission is through the use of livestock, and in particular cow farts. Methane is also emitted naturally from wetlands. 

4: Nitrous Oxide

The next gas we have on our list is nitrous oxide. While at 6% this gas is a small part of our global emissions, the GWP is 265 over a 100 year period. This makes it almost 10 times as potent as methane and 265 times as potent as carbon dioxide; that’s right, the gas that dentists use to soothe their patients – and teenagers so gleefully inhale from a balloon – is in fact a very potent greenhouse gas. 

The main sources of nitrous oxide are the agricultural industry – particularly through the use of fertilisers – in addition to wastewater management and the burning of fossil fuels. The gas is also produced naturally as part of the nitrogen cycle. In addition to acting as a greenhouse gas, nitrous oxide is considered one of the more potent ozone destroying gases which we still emit today.

5: Fluorinated Gases

As opposed to a singular one as was the case with those above, for our final entry we have a group of gases: fluorinated gases. These are gases which have a fluorine atom as part of their structure. Being responsible for around 2% of our emissions, these gases include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride. 

The GWP is difficult to pinpoint exactly as they are a group of gases. However, one study suggests the GWPs range from 140 to 23,900. In particular, sulphur hexafluoride has a GWP of 23,500 making it incredibly more potent than any of the gases previously mentioned. These gases can also persist in the atmosphere for thousands of years.

Fluorinated gases are predominantly used as a replacement for ozone depleting gases. Usually they are used in refrigerants, aerosols, blowing agents, solvents or even as insulating gases. 

*This piece was originally posted on the platform Delta-S. Delta-S is a science communication blog aimed at those outside of the scientific community. It takes an evidence based approach and has three main focus points: science, sustainability and society. The goal is to encourage more people to engage with science and to provide them with the tools & knowledge to fight against misinformation.