Climate science

What are the greenhouse gases and why they matter

Published on
September 8, 2021

You’ve heard about carbon dioxide, carbon neutral and carbon negative. The list of buzzwords goes on and on. But is it all about carbon dioxide (CO2) ?
The short answer: NO.

CO2 is our biggest problem given it makes up about 75% of all greenhouse gas emissions (ghgs). Because of this, CO2 is the reference gas for all greenhouse gases. That’s why you’ll hear everyone talking about CO2 and carbon neutrality.

Formally, the impact of all ghgs is converted into a CO2 equivalent notated as ‘CO2e’ and the amounts are usually in tonnes. I.e. tCO2e. Not all ghgs were created equal, however. Here we quickly explain what they are and why they matter. This gets a bit technical and wordy but it’s only a 5-minute read to build your awareness.

"Carbon dioxide is constantly being exchanged in the natural environment. In fact, the UK’s forests, soils and general land acted as a net carbon sink, sequestering 10.3m tCO2e in 2018. Unfortunately, this is only 2% of emissions."

Carbon Dioxide, CO2.

Chemical Formula: O = C = O (1 carbon atom and 2 oxygen atoms make up CO2)
Lifetime in atmosphere: Upto thousands of years
Global Warming Potential (100 years): 1

Our most abundant greenhouse gas (74.4%). A critical component of the biological carbon cycle and essential for all life. The anthropogenic release of carbon dioxide comes from burning fossil fuels and industrial processes like cement production.

When we burn fossil fuels like coal and natural gas, carbon dioxide is formed when the (primarily) carbon and hydrogen found in the fuels react with oxygen in an exothermic reaction (creating heat). CO2 is considered a byproduct of these reactions.

In Industrial processes, like cement production, CO2 is released through burning fossil fuels to drive the process and from the breakdown of the materials used such as limestone. These materials are made of carbon, hydrogen, oxygen etc which release CO2 when heated.

The main causes of CO2 are burning fossil fuels for transportation, electricity and from industrial processes.

Carbon dioxide is constantly being exchanged in the natural environment. In fact, the UK’s forests, soils and general land acted as a net carbon sink, sequestering 10.3m tCO2e in 2018. Unfortunately, this is only 2% of emissions.

The amount of CO2 we release is growing every year although it has slowed in recent years. Many countries are doing better, with peak emissions already reached. The challenge is CO2 quickly becomes globally distributed and impacts us all.

Methane Emissions, CH4.

Methane - Chemical Formula
Chemical Formula of Methane

Lifetime in Atmosphere: 12 years
Global Warming Potential (100-year): 25

Probably the second most talked about ghg. It is 25 times more damaging over a 100 year period than CO2 even though on average it only lasts 12 years in our atmosphere.
Approximately, 17% of global emissions are Methane. Anthropogenic release of Methane is largely through leaks in natural gas systems and livestock. Here’s 3 breakdowns:

  • Our Energy systems release Methane into the atmosphere through production, processing, storage, transmission, and distribution of natural gas and the production, refinement, transportation, and storage of crude oil. Coal mining is also a source of CH4 emissions. Of note, Methane is the primary component of natural gas which we burn as a fuel for heating and other uses. When we burn natural gas, CO2 is released.
  • Methane is released as a byproduct of fermentation in livestock as they eat and
  • Finally, decomposing waste in landfill releases methane as it is broken down by bacteria in the absence of air.

Methane is also released from the natural world, particularly wetlands. As of today, humans are responsible for 50-65% of all methane emissions.

Globally, Methane emissions have increased over the past 30 years but appear to be levelling off as energy systems improve and landfills produce less. As demand for agricultural products grows, upwards pressure remains.

Nitrous Oxide, N2O.

Chemical Formula: N = N = O
Lifetime in Atmosphere: 114 years
Global Warming Potential (100-year): 298

40% of Nitrous Oxide emissions are caused by humans. N2O is 300 times more damaging than CO2 and lasts 114 years in our atmosphere on average. Approximately, 6% of global emissions are from N2O. The main sources of N2O are agriculture and industry, fuel combustion and waste.

The dominant cause is the production and usage of fertilisers for agriculture accounting for about 75% of the emissions. N2O is a byproduct of burning fossil fuels but this depends on the fuel used. Finally, the treatment of wastewater releases N2O.

N2O emissions have been relatively flat over the last 30 years with improvements in cleaner cars offsetting the increased fertiliser usage.

Fluorinated Gases.

Chemical Formulas: HFCs, PFCs, NF3, SF6
Lifetime in Atmosphere: HFCs - up to 270 years; PFCs - 2,600–50,000 years; NF3 - 740 years; SF6 - 3,200 years
Global Warming Potential (100-year): HFCs - up to 14,800; PFCs - up to 12,200; NF3 - 17,200; SF6 - 22,800

Fluorinated gases have no natural sources. These highly damaging gases are released through our activities alone across manufacturing, building use and energy systems. They are incredibly damaging and many countries are attempting to reduce usage. They currently make up approximately 2% of global emissions. Due to their massive global warming potential, a small release can have a disproportionate impact on global emissions impact.

There are four main categories of fluorinated gases—hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3).

HFCs are primarily used as a replacement for the even more damaging substances: chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons which deplete the ozone layer. HFCs have many uses, primarily as a refrigerant and therefore for air conditioning in cars and buildings but also in aerosols and fire retardants.

PFCs are primarily created in manufacturing like aluminium production and semiconductor manufacturing.

SF6 is used as an insulating gas in electrical transmission equipment, including circuit breakers. It’s global warming potential is 22,800, making it the most potent greenhouse gas that the Intergovernmental Panel on Climate Change has evaluated.

The overall trend for these gases is up, largely driven by HFCs usage. In positive news, the emissions from manufacturing and energy systems have decreased over the last 30 years due to mitigation steps.

Sources for reference.

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