17. Major source of green house gases are-
    (1) Release of methane
    (2) Burning of fossil fuels
    (3) Respiration
    (4) Depletion of ozone layer

Greenhouse gases (GHGs) are compounds in the atmosphere that trap heat, contributing to global warming and climate change. While several activities and processes release greenhouse gases, one source stands out as the largest and most significant: the burning of fossil fuels. This article explores the major sources of greenhouse gases, explains why fossil fuel combustion is the primary contributor, and clarifies the roles of other sources such as methane release, respiration, and ozone depletion.

What Are Greenhouse Gases?

Greenhouse gases include carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and fluorinated gases. These gases allow sunlight to enter the atmosphere but trap heat that would otherwise escape, creating the greenhouse effect. Without this effect, Earth would be too cold to support life. However, human activities have dramatically increased the concentration of these gases, leading to global warming and climate change.

The Main Sources of Greenhouse Gases

1. Burning of Fossil Fuels

The burning of fossil fuels—coal, oil, and natural gas—for electricity, heat, transportation, and industry is the largest source of greenhouse gas emissions worldwide. When these fuels are burned, they release large amounts of CO₂, the most prevalent greenhouse gas. Fossil fuel combustion accounts for about 89% of global CO₂ emissions, making it the dominant driver of anthropogenic climate change.

• Electricity and Heat Production: Power plants burning coal and natural gas are major sources of CO₂ emissions.

• Transportation: Cars, trucks, ships, trains, and airplanes powered by gasoline and diesel contribute significantly to CO₂ emissions.

• Industry: Manufacturing and industrial processes often rely on fossil fuels for energy, further increasing emissions.

2. Release of Methane

Methane is a potent greenhouse gas, with a much higher heat-trapping ability than CO₂ over a short period. However, it is present in much lower concentrations and comes from different sources:

• Agriculture: Livestock (especially cows) produce methane during digestion (enteric fermentation).

• Waste Management: Landfills and wastewater treatment release methane as organic waste decomposes.

• Fossil Fuel Production: Leaks and venting during the extraction, processing, and distribution of natural gas and oil also release methane.

While methane is a significant contributor to global warming, it is not the largest source of greenhouse gases overall.

3. Respiration

Respiration by humans, animals, and plants releases CO₂ into the atmosphere. However, this is part of the natural carbon cycle and is balanced by photosynthesis, in which plants absorb CO₂. As a result, respiration does not contribute to the net increase in atmospheric CO₂ and is not considered a major source of greenhouse gas emissions in the context of climate change.

4. Depletion of Ozone Layer

Ozone layer depletion refers to the thinning of the ozone layer in the stratosphere, primarily caused by human-made chemicals such as chlorofluorocarbons (CFCs). While CFCs are potent greenhouse gases, their contribution to global warming is much smaller than that of CO₂ and methane. Ozone depletion itself does not directly increase greenhouse gas concentrations, although it does expose the Earth to more harmful ultraviolet radiation.

Comparing the Options

Let’s evaluate each option in the context of greenhouse gas sources:

• Release of methane: Significant, but not the largest source.

• Burning of fossil fuels: The largest and most significant source of greenhouse gases, primarily CO₂.

• Respiration: Part of the natural carbon cycle, not a net source of greenhouse gases.

• Depletion of ozone layer: Not a direct source of greenhouse gases, though some ozone-depleting substances are also greenhouse gases.

Therefore, the correct answer is: Burning of fossil fuels.

The Global Impact of Fossil Fuel Burning

The burning of fossil fuels is responsible for the vast majority of CO₂ emissions, which account for about 74% of all greenhouse gas emissions globally. The increase in atmospheric CO₂ concentration—now more than 50% higher than pre-industrial levels—is the primary driver of current global warming and climate change.

• Electricity and Heat: Power plants burning coal and natural gas are the largest sources of CO₂ emissions, especially in countries with high energy demands.

• Transportation: The transportation sector is a major emitter, with over 90% of its energy coming from petroleum-based fuels.

• Industry: Industrial processes, including cement production and chemical manufacturing, also contribute significantly to CO₂ emissions.

Other Important Greenhouse Gas Sources

While fossil fuel burning is the largest source, other activities also contribute to greenhouse gas emissions:

• Agriculture: Livestock, rice paddies, and fertilizer use release methane and nitrous oxide.

• Waste Management: Landfills and wastewater treatment release methane.

• Industrial Processes: Certain chemicals and refrigerants release fluorinated gases, which are extremely potent but present in much smaller quantities.

The Role of Methane

Methane is the second most important greenhouse gas after CO₂. Although it is present in much lower concentrations, its global warming potential is about 25–30 times greater than CO₂ over a 100-year period. Reducing methane emissions from agriculture, waste, and fossil fuel production is a key strategy for mitigating climate change.

Respiration and the Natural Carbon Cycle

Respiration by living organisms is a natural process that releases CO₂ into the atmosphere. However, this CO₂ is balanced by the CO₂ absorbed by plants during photosynthesis. Therefore, respiration does not contribute to the net increase in atmospheric CO₂ and is not a major source of greenhouse gases in the context of climate change.

Ozone Depletion and Greenhouse Gases

Ozone-depleting substances such as CFCs are also greenhouse gases, but their contribution to global warming is much smaller than that of CO₂ and methane. The primary concern with these chemicals is their impact on the ozone layer, not their role as greenhouse gases.

Key Takeaways

• Burning of fossil fuels is the major source of greenhouse gases, primarily CO₂.

• Methane release is significant but not the largest source.

• Respiration is part of the natural carbon cycle and does not contribute to the net increase in greenhouse gases.

• Depletion of the ozone layer is not a direct source of greenhouse gases, though some ozone-depleting substances are also greenhouse gases.

Summary Table

Conclusion

The major source of greenhouse gases is the burning of fossil fuels, which releases vast amounts of CO₂ into the atmosphere and is the primary driver of global warming and climate change. While methane release, respiration, and certain industrial chemicals also contribute, none match the scale and impact of fossil fuel combustion. Addressing this source is essential for mitigating climate change and protecting the planet for future generations.

In summary, the correct answer is:
(2) Burning of fossil fuels.
Understanding and reducing fossil fuel use is the most effective way to limit greenhouse gas emissions and combat climate change.