Previous Year Question

Global Warming refers to the long-term increase in the Earth's average surface temperature, primarily caused by rising concentrations of Greenhouse Gases in the atmosphere. These gases absorb Infrared Radiation emitted from the Earth's surface and reduce the rate at which heat escapes into space. Major greenhouse gases include Carbon Dioxide (CO₂), Methane (CH₄), Nitrous Oxide (N₂O), Water Vapour (H₂O), and Ozone (O₃). Common pollutant oxides of Sulfur and Nitrogen are not classified among the major direct greenhouse gases.

Among Sulfur Oxides (SOₓ), the principal pollutant is Sulfur Dioxide (SO₂), which is mainly emitted through the combustion of sulfur-containing fuels such as coal and petroleum, along with industrial processes. Atmospheric oxidation of SO₂ can produce Sulfate Aerosols. These fine particles scatter incoming solar radiation and redirect part of it towards space, producing a Cooling Effect on the Earth. Sulfur Dioxide is also a major precursor of Acid Rain because it contributes to the formation of Sulfuric Acid (H₂SO₄) in the atmosphere.

Nitrogen Oxides (NOₓ) mainly include Nitric Oxide (NO) and Nitrogen Dioxide (NO₂). They are emitted from vehicles, Thermal Power Plants, and industrial fuel combustion. These pollutants contribute to the formation of Nitric Acid (HNO₃), Nitrate Aerosols, and Tropospheric Ozone. The climatic influence of NOₓ is complex; it can contribute to warming through ozone formation and to cooling by shortening the atmospheric lifetime of methane and promoting aerosol formation. NOₓ should not be confused with Nitrous Oxide (N₂O), because N₂O is itself a powerful greenhouse gas, whereas NOₓ generally refers to NO and NO₂ in the context of air pollution.

Among the other options, Methane (CH₄) is a powerful greenhouse gas released from livestock farming, rice cultivation, wetlands, and fossil fuel production. Carbon Dioxide (CO₂) is the principal long-term driver of present human-induced global warming, with emissions increasing due to fossil fuel combustion and deforestation. Water Vapour (H₂O) is the most abundant greenhouse gas in the atmosphere and primarily acts as a Climate Feedback. As temperatures rise, the atmosphere can hold more water vapour, which can further intensify the Greenhouse Effect. Therefore, among the given options, common pollutant oxides of Sulfur and Nitrogen are distinct from direct warming greenhouse gases. However, it would be scientifically inaccurate to describe them as having absolutely no influence on climate.