Greenhouse Gas Emissions Basics

What are GHG Emissions?

Greenhouse gases are chemical compounds in the atmosphere that play a crucial role in regulating Earth's temperature. These gases allow sunlight (shortwave radiation) to pass through the atmosphere, warming the land and oceans. As the Earth absorbs this heat, it releases it as infrared light (longwave radiation), which is invisible to the human eye. While some of this infrared light escapes back into space, greenhouse gases absorb a portion of it and radiate the heat back towards the Earth's surface. This process, known as the greenhouse effect, is a natural phenomenon that keeps our planet warm enough to support life. Without the greenhouse effect, Earth's average surface temperature would be about 33°C colder, making our current way of life impossible.

Certain gases in the atmosphere have the ability to absorb heat. These greenhouse gases are generated through both natural processes and human activities. The main ones include:

• Carbon dioxide (CO2) - This gas is a byproduct of the combustion of fossil fuels such as coal, oil, and natural gas. Deforestation and certain industrial processes also contribute to elevated CO2 levels.
  Methane (CH4) - Methane is produced during the decay of organic waste in landfills, livestock digestion, and the extraction and processing of fossil fuels.
  Nitrous oxide (N2O) - This gas is released from agricultural and industrial activities, as well as during the combustion of fossil fuels.
  Fluorinated Gases - This category includes various synthetic gases, such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3), which are released during industrial processes and certain consumer activities.

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• GHG emissions contribute to the enhanced greenhouse effect, leading to an increase in global temperatures and climate change. 
  Water vapour, the most abundant greenhouse gas, plays a crucial role in regulating the climate. Human activities like irrigation and deforestation can influence water vapor levels, directly affecting surface temperatures. However, since human emissions do not significantly alter the overall concentration of water vapour in the atmosphere, it is not included in greenhouse gas inventories.

Why Do Greenhouse Gas Levels Matter?

The levels of greenhouse gases in the atmosphere have become a significant concern, particularly because their concentrations have increased dramatically over the past 200 years, coinciding with large-scale industrialization. The combustion of fossil fuels releases carbon stored deep within the Earth into the atmosphere as carbon dioxide. Similarly, when land is cleared for agriculture, the carbon stored in soils and plants is released as carbon dioxide. While greenhouse gases like carbon dioxide, methane, and nitrous oxide occur naturally and are essential for sustaining life on Earth, human activities have led to a substantial rise in their atmospheric concentrations.

This is crucial because there is a strong scientific consensus among climatologists, atmospheric chemists, and other experts that the increasing levels of greenhouse gases are causing a rise in the Earth’s average global temperature. The Intergovernmental Panel on Climate Change (IPCC) has reported that the Earth’s average global surface temperature has increased by approximately 0.6° to 0.9° C over the past century, and this rise is very likely driven by human activities.

Even though this temperature increase might seem small, it can lead to significant changes at the local level. For instance, some regions, such as the Arctic, are experiencing much more substantial warming than others. These temperature shifts are altering patterns of rainfall, snowfall, droughts, cloudiness, humidity, and the length of growing seasons, all of which can have profound impacts on agriculture and other aspects of human life.

Do All Greenhouse Gases Have the Same Effect?

Not all greenhouse gases have the same impact on global warming; they differ in their ability to absorb heat and remain in the atmosphere. Scientists use two key terms to differentiate the effects of various greenhouse gases:

Global Warming Potential (GWP):
GWP is an index that measures the global warming impact of a greenhouse gas relative to carbon dioxide. It considers both how long the gas stays in the atmosphere and its effectiveness at absorbing outgoing infrared heat. For instance, nitrous oxide has a GWP over 300 times greater than that of carbon dioxide, meaning a single molecule of nitrous oxide has a significantly higher impact on global warming than a molecule of carbon dioxide.

Carbon Dioxide Equivalents (CO2-eq):
CO2-eq is a unit that expresses the impact of a given greenhouse gas on atmospheric warming, based on its GWP. For example, one ton of methane is equivalent to 21 tons of CO2-eq, and one ton of nitrous oxide is equivalent to 310 tons of CO2-eq. This standardized unit simplifies the process of creating greenhouse gas inventories and comparing different strategies to reduce emissions.

Even as the global climate continues to change, there are effective strategies to mitigate climate change by both reducing greenhouse gas emissions and removing carbon dioxide from the atmosphere. Reducing our dependence on fossil fuels, investing in alternative energy sources, and adopting more efficient technologies can significantly decrease greenhouse gas emissions. Additionally, carbon sequestration—removing carbon dioxide from the atmosphere and storing it permanently—offers another important mitigation strategy. This can be achieved through practices such as planting trees or crops that absorb carbon dioxide via photosynthesis and store it in their roots, wood, or soil organic matter.

Note:

As seen from table, the GWP of CH4 witnessed a 33.3% increase in AR5 as compared to AR2, whereas GWP of N2O witnessed a 14.5% reduction. These changes in GWP have resulted in variation in the projected BAU emissions especially for IPPU, Waste and AFOLU sectors where HFCs, CH4 and N2O are the major gages emitted. For BTR (2024), as such a time series correction of the GHG inventory from 2000 to 2016 was carried out using AR5 GWP values. The recalculated emission figures were also used to project the BAU scenario emissions till 2030 using the same Exponential Smoothing technique and maintaining same seasonality values.