Hello everyone! Welcome back to our blog. As we have previously mentioned, this blog post will be dedicated to exploring the different types of greenhouse gases and their anthropogenic sources that has resulted in global warming. However, much like how there are criteria pollutants when considering air quality due to the complex mixture of chemicals in the atmosphere, we will only be covering a few important greenhouse gases.

Greenhouse gases and their source

 

 

Carbon Dioxide (CO₂)

Carbon dioxide is noted to be the biggest contributor of the global greenhouse gas emission taking up 76% of the greenhouse gas emission as noted in the Fifth IPCC Assessment Report (AR5) (Victor et al., 2014). Carbon dioxide is a good starting point for understanding greenhouse gases as it is the benchmark for global warming potential (GWP) scale, which is used to measure the amount of heat trapped in the atmosphere by the greenhouse gas (EPA, n.d.-b). GWP is measured by comparing the amount of energy absorbed by 1 tonne of the greenhouse gas compared to 1 tonne of CO₂, generally over 100 years (EPA, n.d.-b).

Carbon dioxide is mainly emitted due to the process of fossil fuel burning to generate power for industrial processes and vehicles, accounting for 65% of the global greenhouse gas emissions. The remaining 11% of carbon dioxide emission is related to forestry and other land use (Victor et al., 2014). It is important to note that change in land use can emit carbon dioxide as soil is an important carbon dioxide sink, as soil sequester carbon dioxide and are deposited as organic carbon (Lal, 2004).

 

Methane (CH₄)

Methane is the second largest contributor to global greenhouse gas emission at 11%, noted in AR5 (Victor et al., 2014). While the residence time of CH₄ is only about a decade and does not stay in the atmosphere for as long as CO₂, the GWP of CH₄ is 25 over 100 years (Change, 2007). This means that while CH₄ may not be as persistent as CO₂ in our environment, the degradation that CH₄ brings to the environment is still considerable. Additionally, CH₄ can transform into a secondary pollutant of ozone, which is also a greenhouse gas. This is on top of the fact that ground level ozone itself is an air pollutant.

Methane emission ranges from agricultural activities such as rice paddies to waste management such as biomass burning (EPA, n.d.-a). Do note that there are also natural sources of methane such as wetlands (Matthews & Fung, 1987).

 

Nitrous oxide (N₂O)

Nitrous oxide contributed 6% of global greenhouse gas emission (Victor et al., 2014). While N₂O has a lower contribution globally, it has a GWP of ~300 times of CO₂ GWP over 100 years while being persistent, lasting in the environment for over more than 100 years on average, unlike CH₄ (Dalal, Wang, Robertson, & Parton, 2003; EPA, n.d.-b). Similar to CH₄ emissions, N₂O can generally be found in the agriculture sector through fertiliser use as a result of nitrification (Dalal et al., 2003). It is also a secondary pollutant that can contaminate our air and waters.

 

Fluorinated Gases

As covered in our lecture, fluorinated gases are compounds containing halogens, specifically fluorine (F). These are chemicals such as chlorofluorocarbons (CFC), hydrofluorocarbons (HFC) and hydrochlorofluorocarbons (HCFC). Additionally, sulfur hexafluoride (SF₆) is also one such fluorinated compound (Hill, 2010). These gases contribute to only 2% of global greenhouse gas emissions but has the highest GWP compared to the other greenhouse gases (Victor et al., 2014). While CFCs have a GWP of 10900 over 100 years, SF₆ has a GWP of 22800 over 100 years but persists for 3200 years in the atmosphere (Hill, 2010)! This means that SF₆ is capable of trapping much more heat than CO₂ while persisting way longer in the environment.

 

Water Vapour

Water vapour is an interesting point that we would like to raise. While there are debates on whether water vapour is a greenhouse gas as it is not considered under the IPCC, we believe that it is important to talk about its effect on the global warming. While water vapour does not have a GWP, water vapour absorbs infrared radiation (longwave radiation) from the sun which can warm the atmosphere regardless (Hill, 2010). This means that an increase in water vapour concentration in the environment will also result in global warming, resulting in a positive feedback loop as higher temperatures will speed up the process of evaporation.

 

Conclusion

Thank you for sitting through this informative blog post as we break down and identify the different types of greenhouse gases before looking at policies that will tackle the issue of global warming and climate change.

As you can see, the types of greenhouse gases may come from different anthropogenic activities. However, these sources of greenhouse gases are all part of the same continuum based on land use, land cover changes (LULCC). It falls under the same process when (1) we begin deforestation that releases CO₂ –> (2) building of infrastructure or use for agriculture that releases CH₄ and N₂O –> (3) using these infrastructures which releases more CO₂ and other greenhouse gases. This means that we are increasing the greenhouse effect across the total environment regardless.

In our next post, we will be defining climate change and looking at policies concerned with this global issue. See you there!

Ryan

 

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References

Change, I. C. (2007). The physical science basis. In: Cambridge Univ. Press.

Dalal, R. C., Wang, W., Robertson, G. P., & Parton, W. J. (2003). Nitrous oxide emission from Australian agricultural lands and mitigation options: a review. Soil Research, 41(2), 165-195.

EPA. (n.d.-a, 2020). Global Greenhouse Gas Emissions Data. Greenhouse Gas Emissions. Retrieved from https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data

EPA. (n.d.-b, 2020). Understanding Global Warming Potentials. Greenhouse Gas Emissions. Retrieved from https://www.epa.gov/ghgemissions/understanding-global-warming-potentials

Hill, M. K. (2010). Understanding Environmental Pollution: Cambridge University Press.

Lal, R. (2004). Soil carbon sequestration impacts on global climate change and food security. Science, 304(5677), 1623-1627.

Matthews, E., & Fung, I. (1987). Methane emission from natural wetlands: Global distribution, area, and environmental characteristics of sources. Global biogeochemical cycles, 1(1), 61-86.

Victor, D., Zhou, D., Ahmed, E., Dadhich, P. K., Olivier, J., Rogner, H.-H., . . . Yamaguchi, M. (2014). Introductory chapter.