GHG ranking: Who's the 'most evil' of them all?

 

Ever wonder why carbon dioxide (CO2) receives more media attention than other greenhouse gases (GHGs)?

Some say it is because CO2 is the biggest contributor to global warming. Not quite right! Other GHGs such as methane (CH4) and nitrous oxide (N2O) are equally potent.

In fact, the global warming potential (GWP) for CO2 is just one, whereas GWP for CH4 and N2O are 28 and 265, respectively.

Meanwhile, naturally occurring GHG such as from water vapour, which is abundant in the atmosphere, is rarely studied due to its unknown concentration.

In layman’s terms, GWP looks at the atmospheric lifetime and heat-trapping potential of each greenhouse gas. The higher the GWP, the more a given gas heats the Earth compared to CO2 over a given time period, usually 100 years.

The GWP values are updated frequently, with the latest being published in Fifth Assessment Report released by the Intergovernmental Panel on Climate Change (IPCC).

Emissions are usually expressed as million metric tonnes of carbon dioxide equivalents (CO2e.). It is derived by multiplying a given gas in tonnes with the associated GWP value.

The only difference is that both CH4 and N2O do not stick around the atmosphere for as long as CO2. For instance, CH4 stays in the atmosphere for only around 12 years, while CO2 can remain for millennia.

‘Firstborn Analogy’

I prefer to use the ‘‘Firstborn Analogy’’ to explain this further. A firstborn is always the centre of attention in a family. He or she will be showered with love and care not experienced by kids who come later into the family.

This is all because the first child offers the first experience to parents as mother and father. It is a new hope to the family, so the firstborn is usually entitled to extra privileges as compared to others.

The same goes for CO2. It was first discovered by Scottish chemist Joseph Black using man-made instruments in the late 18th century.

Then, Swedish chemist Svante Arrhenius recognised in a study that CO2 and other greenhouse gases could potentially warm the Earth’s surface by trapping heat in the atmosphere.

However, the earlier studies only focused on CO2 as a major contributor to global warming. In fact, the first measurement of CO2 levels in the atmosphere was made in the 1950s by Charles David Keeling, who found that atmospheric CO2 was showing a steady increase over time.

This explains why CO2 is the most discussed GHG. It has been in the atmosphere for a long time since it was first discovered by scientists. It has left a long trail of footprints over the years, and no other GHGs can steal the limelight from CO2.

However, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride (SF6) are becoming increasingly known as GHGs that are several thousand times more powerful than CO2 in driving climate change.

These GHGs are ozone-depleting and are usually emitted in the refrigeration, air-conditioning and motor vehicle AC sectors, with emissions occurring in the manufacturing process and due to leakage from pipelines.

According to the United States Environment Protection Agency (US EPA), HFCs, PFCs and SF6 enter the atmosphere as many leakages happen when fridges and air conditioning units are not disposed of properly.

Although these lesser-known GHGs are at lower atmospheric levels compared to CO2, they are just as harmful.

As the temperatures get warmer, air-conditioning is now seen as essential, as well as fridges which extend the food shelf life, both have become a symbol of modernity and comfort. The amount of these GHGs in the atmosphere will surely shoot up over the years, overtaking CO2.

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On the other hand, CH4 and N2O constitute nearly half and two-thirds of GHG emissions respectively from agricultural activities worldwide. The growing demand for food production to meet population growth has led to extensive cattle farming, rice cultivation and fertiliser use.

Interestingly, the agriculture sector contributed to only about three percent of Malaysia’s total GHG emissions in 2019, as shown by our Fourth Biennial Update Report (BUR4) submitted to the United Nations Framework Convention on Climate Change (UNFCCC).

It is the lowest amongst all other sectors reported i.e. Energy, Industrial Processes and Product Use (IPPU), Waste, Land Use Land Use Change and Forestry (LULUCF).

Only time will tell which GHG is the “most evil” of them all. The ranking may change from time to time as one GHG races against another to “conquer” the atmosphere!

One thing is for sure, the IPCC report insisted that global GHG emissions would have to peak before 2025, and be reduced by 43 percent by 2030 for us to limit global warming to around 1.5C! - Mkini

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CHONG YEN MEE is a technical analyst for the Natural Resources and Environmental Sustainability Ministry and enjoys writing doomsday stories that make people act.

The views expressed here are those of the author/contributor and do not necessarily represent the views of MMKtT.