GLOBAL WARMING

Global warming is an average increase in the temperature of the atmosphere near the Earth’s surface and in the troposphere, which can contribute to changes in global climate patterns. Global warming can occur from a variety of causes, both natural and human-induced.
In common usage, “global warming” often refers to the warming that can occur as a result of increased emissions of greenhouse gases from human activities. Due to this, there are variations in climatic patterns leading to floods, cyclones, storms, water scarcity and desertification. The additional changes are melting of the glaciers, erosion of the soil systems and rise in sea levels etc.

GREENHOUSE EFFECT
The greenhouse effect is a naturally occurring phenomenon that blankets the earth's lower atmosphere and warms it, maintaining the temperature suitable for living things to survive. Just as greenhouses keep the air warm inside, water vapor and greenhouse gases warm the Earth.
Around 75% of the solar energy that reaches the earth is absorbed by the earth’s surface while the rest radiates back to the atmosphere. Some of it is trapped by greenhouse gases, mostly carbon dioxide.
Global warming is likely to reach 1.5°C between 2030 and 2052 if it continues at the current rate.

GREENHOUSE GASES (GHG)
Water vapour: Variable gas; 4% in the tropics, <1% in deserts/poles. Absorbs incoming and outgoing radiation.
Carbon dioxide (CO2): Transparent to incoming radiation, opaque to outgoing terrestrial radiation; major contributor to greenhouse effect.
Ozone (O3): Mostly in stratosphere; absorbs UV radiation. Tropospheric ozone forms from NO2 and VOCs.
Methane (CH4): Produced from decay of organic matter and animal waste. Can be restricted by gobar gas production.
Nitrous Oxide (N2O): NO and NO2 cause cooling by forming OH radicals which destroy methane.
Carbon Monoxide (CO): Short-lived GHG; indirectly increases methane and ozone levels.
Chlorofluorocarbons (CFCs): Phased out under the Montreal Protocol.
Hydrofluorocarbons (HFCs): Used as CFC replacements.
Sulphur hexafluoride: Used in manufacturing and electrical equipment.

IMPORTANCE OF GREENHOUSE EFFECT
A natural process occurring for millions of years. Water vapour + water particles contribute 95% of greenhouse warming.
Maintains average global temperature at +15°C; without it Earth would be –17°C.

MITIGATION MEASURES
Emission norms for thermal power plants:
- Flue Gas Desulphurization (FGD) for SOx
- SNCR and SCR for NOx
- Electrostatic Precipitators (ESPs) for PM
- Cooling towers for water conservation

CARBON SEQUESTRATION
Carbon sequestration is the capture and long-term storage of atmospheric CO2.
Parts: Capture → Transport → Storage (underground/deep ocean)
Types:
- Terrestrial sequestration: Trees, biomass
- Wetlands: Major soil carbon sink
- Oceans: Absorb CO2 due to pressure difference
- Geological storage: Injecting CO2 into depleted reservoirs

Methods:
Natural sequestration: Oceans, forests, soil absorb CO2 naturally.
Artificial sequestration: Capturing CO2 at source (factories) and storing underground.

Potential:
- Faster sequestration
- Higher agricultural yields
- Employment generation

CARBON SINK
Anything absorbing more carbon than it releases. Natural: oceans, forests. Artificial: carbon capture systems. Oceans are the largest sink.

CLEAN COAL TECHNOLOGY (CCT)
Technologies to increase efficiency and reduce emissions during coal use.

Pre-combustion:
- Coal washing/beneficiation
- Low NOx burners

Combustion:
- Fluidized Bed Combustion (FBC)
- Coal Gasification
- Supercritical & Ultra-supercritical plants

Post-combustion:
- Flue Gas Desulphurization
- Electrostatic Precipitators

BHARAT STAGE (BS) EMISSION STANDARDS
Indian emission standards based on Euro norms. Implemented by CPCB. BS-VI compulsory from April 2020.
Importance:
- Reduces pollution, NOx, harmful emissions
- Sulphur reduced to 10 ppm improves air quality

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Subject: Environment

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