Greenhouse gases

 The biggest contributors to climate change

Gas emission has always been around. As soon as we could set a fire, gases were set off in the atmosphere. All humans and land-animals produce CO2, just by breathing! And did you know that one cow can actually release up 100 to 120kg of methane gas a year – as farts! Before the Industrial Revolution, human-related activity didn’t produce enough greenhouse gases for it to have an effect on the atmosphere. Nowadays, we emit immense amounts of –invisible– harmful gases.

But what gases are the biggest contributors to the heating of our atmosphere?

back to school – the greenhouse effect

If the Earth did not have an atmosphere, temperatures would be below the freezing point of water. Life, as we know it, would not have been around. The atmosphere – a blanket of gases that consist roughly of 78% nitrogen, 21% oxygen, 0.9% argon and traces of other gases – provides a natural greenhouse effect. Thanks to the atmosphere, the Earth is able to absorb the heat of solar energy and to maintain a habitable temperature.

As early as 1824 Joseph Fourier began to understand that the gases that composed the atmosphere may trap the heat received in the atmosphere from the Sun. In 1859, John Tydall identified gases that are able to trap and hold heat – CO2 and water vapor.

Gasses with the ability to trap heat in the atmosphere, are known as Greenhouse Gases (GHG). Nitrogen and oxygen are considered inert: the majority of the atmosphere does not have this heat-trapping ability.

So, what are the most dangerous gases that contribute to global warming?

 

  • Carbon Dioxide (CO2)

This probably isn’t a big surprise. Carbon dioxide is the most emitted greenhouse gas worldwide: 35.800 millions tons of CO2 in 2013. Carbon is one of the key elements of life. The trees and plants that covered the surface of our planet, 300 million years ago, where also carbon-based. Over the many years, the vegetation withered and got covered by layers and layers of earth. Slowly (like millions of years slow), these layers of dead trees, plants, and animals decomposed into smaller organic molecules called hydrocarbons. The decomposition is facilitated by the combination of microorganisms, the heat of the Earth’s core and pressure from the layers of coverage. Nowadays, fossil fuels –these hydrocarbons– are being burned at a massive rate.

Quick chemistry lesson – CxH+ N(O2) ↔ x(CO2) + y/2(H2O)

The formation of CO2 is always present in the combustion of hydrocarbons! It doesn’t matter which type of hydrocarbon molecule!

  • Methane (CH4)

Methane is the smallest hydrocarbon molecule. But, that doesn’t make it any less dangerous. Methane gas actually has a higher global warming potential (GWP) than carbon dioxide! This means that the molecule is better at trapping infrared-radiation. For example, 1kg of methane can trap 25 times the amount of heat radiation than 1kg of carbon dioxide, in a 100-year timespan.

As you could’ve guessed, methane is a fossil fuel. The widely known usage of natural gas is to generate electricity, heat domestic houses, transport and usage as raw materials in a lot of products. Since methane is a gas, the emission is easy via production, processing, storage, transmission, or distribution.

And didn’t I mentioned that cows also emit methane? Domestic livestock actually produces large amounts of methane gas, as a part of their normal digestive process. The storage of manure in holding tanks and the dumping in lagoons also produces methane. As I calculated in a previous article – the Netherlands alone slaughters about 2.2 million cows a year. The year before the slaughter, each cow has approximetely emitted 100 kg of methane…  220.000.000 kilograms! Only based on numbers generated for the Netherlands…

 

  • Nitrous Oxides (N2O)

The main emission of nitrous oxides is produced by agricultural activities like synthetic or organic fertilizers, the management of the manure of livestock or burning agricultural waste. Unfortunately, N2O has a higher global warming potential than carbon dioxide. The impact of 1kg of N2O on warming the atmosphere is almost 300 times that of 1kg of CO2.

Certain types of bacteria have the ability to absorb nitrous oxide and in time, UV-radiation can destroy the gas.

 

  • Fluorinated Gases

Fluorinated gases have a much higher global warming potential compared to carbon dioxide. Therefore, they are also known as very high potent greenhouse gases. The main difference between fluorinated gases and the previously described gases is that they have NO natural sources. Emission only takes place by human production and there’s no natural cycle to remove them from the atmosphere.

The main usage was as refrigerants — like in air conditioning systems vehicles or buildings. Phasing out is currently taking place, thank the ‘Montreal Protocol’. The complete phasing out should be achieved by 2030. But still, emission also takes place through industrial processes.

There are four categories of fluorinated gases. The following table shows them together with their time in the atmosphere and GWP:

# Name and abbreviation Lifetime in the atmosphere (years) GWP (per 100 years)
1 Hydrofluorocarbons (HFCs) 270 14.800
2 Perfluorocarbons (PFCs) 2.600-50.000 7.390-12.200
3 Sulfur hexafluoride (SF6) 740 17.200
4 Nitrogen trifluoride (NF3) 3.200 22.800

 

Quick conclusion

Take the following example. If the circle in the next image represents 100kg: 76 kg CO2 , 16 kg of methane, 6 kg of nitrous oxide and 2 kg of fluorinated gases would be emitted. By expressing all the gases in CO2  (by multiplying with their GWP), this would result in the following numbers:
16 kg methane x 25 = 400 kg CO2
6 kg nitrous oxide x 300 = 1800 kg CO2
2 kg fluorinated gases x 17.072 (average GWP) = 34.144 kg CO2

greenhouse gas earthlyiris
GHG emission in 2015 – Image via https://www.epa.gov/ghgemissions

Although carbon dioxide is the most emitted gas — approximately 76%, do not forget that the other 24% is way more dangerous! This is a result of the potential to trap the heat better than carbon dioxide. Above that, the natural recycling of many other gases could take forever…


Iris

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