Introduction
Climate change is real! Various indicators in the atmosphere like rise in sea level and extreme weather changes which prove it time and again. Global warming caused by greenhouse gasses (GHGs) is a major reason behind this climate change. This prioritizes efforts aimed at reducing greenhouse gas emissions.
Before diving into initiatives to reduce GHG emissions, it's essential to grasp the nature of these gases.
In this blog, we will delve deeper into concepts like as follows:
The science of GHGs,
The identification and classification of GHGs,
The significance of metrics like GWP and ODP
What are Greenhouse gasses?
Greenhouse gasses (GHGs) are atmospheric gasses that traps heat when sunlight passes through them and do not reflect it back. These gasses result in the phenomenon called the GHG effect.
The phenomena of GHG effect with GHG molecules
How to identify the GHGs?
Although GHGs are predefined now as 6 major gasses under the Kyoto Protocol. Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and the so-called Fluorine-gases (hydrofluorocarbons and perfluorocarbons) and sulfur hexafluoride (SF6).
But how did we identify Greenhouse gasses back then?
1. The scientific approach
The scientific approach to identifying GHG emissions is to use their unique physical and chemical property.
Physical property of GHGs - Based on the principle that GHGs absorb infrared radiation at specific wavelengths. An infrared spectrometer can be used to measure the absorption of the infrared radiation by the sample gas and identify it as per the wavelengths or infrared radiation that are absorbed.
Chemical property of GHGs - Based on the structure of the molecule, there are some chemical properties like dipole moment (μ).Only if an atom has the ability to exhibit dipole moment will it absorb the infrared radiation.
2. The practical everyday approach
After conducting science experiments we simplify it for the next time making a list of gasses, so for theoretical identification of GHGs we refer to the already made list from these scientific experiments.
Apart from the six major GHGs, many other gasses create the greenhouse effect. Some greenhouse gasses also deplete the ozone layer and therefore have both Ozone depletion potential (ODP) and Global warming potential (GWP)
This official page of EPA Ozone-Depleting Substances | US EPA can be referred to for a detailed overview for getting the ozone-depleting values (ODP) and (GWP) along with chemical name, chemical formula and Chemistry Abstract Service (CAS) registry numbers.
Classification of gasses: GHGs and ODS
Greenhouse Gases (GHGs)
Greenhouse gases are compounds that trap heat in the atmosphere, contributing to global warming and climate change. The primary GHGs include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases. These gases absorb infrared radiation and prevent heat from escaping the Earth's surface, creating a "greenhouse effect."
Ozone Depleting Substances (ODS)
Ozone depleting substances are compounds that contribute to the thinning of the Earth's ozone layer, which protects life from harmful ultraviolet (UV) radiation. Common ODS include chlorofluorocarbons (CFCs), halons, and other related chemicals.While there is a prepared list of gasses with both its ODP and GWP. A trend is seen that the majority of ozone-depleting substances are GHGs. These gasses are categorized into classes and subgroups in accordance with the Clean Act Air.
The ODS are split into two classes under the Clean Air Act:
1. Class I - ozone depleting substances (ODS)
Class I ODS consists of substances that have a high ODP, causing significant damage to the ozone layer such as chlorofluorocarbons (CFCs).
Class I has 8 subgroups as follows:
Group I: CFCs like CFC-11, CFC-12.
Group II: Halons like Halon-1211, Halon-1301.
Group III: Other halogenated CFCs.
Group IV: Carbon tetrachloride.
Group V: Methyl chloroform.
Group VI: HBFCs (Hydrobromofluorocarbons).
Group VII: Methyl bromide.
Group VIII: Miscellaneous halogenated compounds
2. Class II - ozone depleting substances (ODS)
Measuring Greenhouse gas potential
What cannot be measured, cannot be reduced" highlights the need to accurately measure the GHG and ODS and its ability to harm the environment. This capacity of GHG is known as global warming potential and that of ozone-depleting substances is known as ozone-depleting potential (ODP).
What is Global warming potential (GWP) ?
The concept of global warming potential was developed to perform comparison or to draw relative estimate as to which gas has the most potential to degrade the environment
According to the EPA, it is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO2). Here carbon dioxide is used as a reference and has GWP of 1.
Global warming potentials of other greenhouse gases for 100-Year Time Horizon
Greenhouse gases | Formula | Fourth assessment report | Fifth assessment report |
Carbon dioxide | CO2 | 1 | 1 |
Methane | CH4 | 25 | 28 |
Nitrous oxide | N2O | 298 | 265 |
Sulphur hexafluoride | SF6 | 22800 | 23500 |
Nitrogen trifluoride | NF3 | 17200 | 16100 |
Methane GWP Changes in the Fifth Assessment Report
The Intergovernmental Panel on Climate Change (IPCC) in its Fifth Assessment Report highlighted that the Global Warming Potential (GWP) of methane has been revised from 25 to 28 over a 100-year period. This change underscores the increasing impact of methane on climate change. Read the Fifth Assessment Report.
With each new IPCC assessment report arrives a question of recalculation, should the report be re-calculated each time there is a new report and whether to adopt a 100-year or 20-year GWPs is another question.The answer is not as simple as you might think and depends on regulation in your region and the purpose of your report. However, in the absence of any bespoke requirements, the best practice is to adopt the new AR6 100-year GWPs.
Global warming potential for other greenhouse gases can be referred to the official page Global Warming Potential Values .
Conclusion
In this part we have understood the basics of GHGs, its scientific background and common terminologies. In the next part, we continue delving deep into how ESG professionals can account for GHGs and help businesses in their GHG reporting journey.
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