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Q11(a):
Discuss briefly the following:
(a) Greenhouse gases
Solution :
Step 1: Theoretical Definition and The Core Mechanism
Greenhouse gases (GHGs) are radiatively active gases present in the Earth's atmosphere that are transparent to incoming short-wave solar radiation (primarily visible and ultraviolet light) but are highly opaque to outgoing long-wave terrestrial radiation (infrared radiation).
[Per the principles of atmospheric physics and Wien's Displacement Law], when short-wave solar radiation reaches the Earth, the surface absorbs this energy and warms up. The Earth then re-emits this thermal energy back into space as lower-energy, long-wave infrared radiation. Greenhouse gases absorb these specific infrared wavelengths and radiate the heat back toward the Earth's surface and lower atmosphere. This phenomenon, which traps thermal energy and maintains the Earth's average temperature at approximately $15^\circ C$ (instead of a frigid $-18^\circ C$), is known as the Greenhouse Effect.
Step 2: Identification and Relative Contribution of Major Greenhouse Gases
The total global warming potential of the atmosphere is driven by a mixture of anthropogenic (human-made) and natural gases. The relative contributions of the primary greenhouse gases to the enhanced greenhouse effect are distributed as follows:
- Carbon dioxide ($CO_2$): Accounts for roughly $60\%$ of the total global warming effect.
- Methane ($CH_4$): Contributes approximately $20\%$.
- Chlorofluorocarbons (CFCs): Synthetic compounds contributing about $14\%$.
- Nitrous oxide ($N_2O$): Accounts for $6\%$.
The following geometric SVG accurately models the relative percentage contribution of each gas to the enhanced greenhouse effect:
Step 3: Primary Anthropogenic Sources
The rapid accumulation of these gases over the last century is heavily attributed to industrialization, urbanization, and agricultural practices.
| Greenhouse Gas | Primary Sources |
|---|---|
| Carbon dioxide ($CO_2$) | Combustion of fossil fuels (coal, oil, natural gas) for energy and transportation, and widespread deforestation. |
| Methane ($CH_4$) | Anaerobic decomposition in wetlands, enteric fermentation in ruminant livestock (cattle), paddy (rice) fields, and biomass burning. |
| Chlorofluorocarbons (CFCs) | Industrial refrigerants, aerosol propellants, foaming agents, and air conditioning systems. |
| Nitrous oxide ($N_2O$) | Extensive use of nitrogenous fertilizers in agriculture, combustion of fossil fuels, and industrial chemical production. |
Step 4: Ecological and Climatic Consequences
An unchecked increase in the atmospheric concentration of greenhouse gases enhances the natural greenhouse effect, leading to Global Warming. The cascading environmental impacts include:
- Thermal Expansion and Ice Melt: The gradual heating of the Earth leads to the melting of polar ice caps (e.g., Greenland and Antarctic ice sheets) and Himalayan snowcaps.
- Sea Level Rise: Combined with the thermal expansion of oceanic waters, melting ice severely raises global sea levels, threatening low-lying coastal cities and island nations.
- Climatic Shifts: Disruptions to global weather patterns, leading to extreme weather events (such as the El Niño effect), intense droughts, and erratic rainfall.
Final Solution: Greenhouse gases (primarily $CO_2$, $CH_4$, CFCs, and $N_2O$) are atmospheric constituents that absorb outgoing infrared radiation, retaining heat within the Earth's atmosphere. While essential for sustaining life by keeping the planet warm, their excessive anthropogenic accumulation is the driving force behind contemporary global warming and catastrophic climate change.
More Questions from Class 12 Biology Environmental Issues EXERCISES
- Q1: What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
- Q1: What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
- Q2: List all the wastes that you generate, at home, school or during your trips to other places. Could you very easily reduce the generation of these wastes? Which would be difficult or rather impossible to reduce?
- Q2: List all the wastes that you generate, at home, school or during your trips to other places. Could you very easily reduce the generation of these wastes? Which would be difficult or rather impossible to reduce?
- Q3: Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
- Q3: Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
- Q4: Match the items given in column A and B:
- Q4: Match the items given in column A and B: Column A Column B (a) Catalytic converter (i) Particulate matter (b) Electrostatic precipitator (ii) Carbon monoxide and nitrogen oxides (c) Earmuffs (iii) High noise level (d) Landfills (iv) Solid wastes
- Q5(a): Write critical notes on the following: (a) Eutrophication
- Q5(a): Write critical notes on the following: (a) Eutrophication
- Q5(b): Write critical notes on the following: (b) Biological magnification
- Q5(b): Write critical notes on the following: (b) Biological magnification
- Q5(c): Write critical notes on the following: (c) Groundwater depletion and ways for its replenishment
- Q5(c): Write critical notes on the following: (c) Groundwater depletion and ways for its replenishment
- Q6: Why does ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?
- Q6: Why does ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?
- Q7: Discuss the role of women and communities in protection and conservation of forests.
- Q7: Discuss the role of women and communities in protection and conservation of forests.
- Q8: What measures, as an individual, would you take to reduce environmental pollution?
- Q8: What measures, as an individual, would you take to reduce environmental pollution?
- Q9(a): Discuss briefly the following: (a) Radioactive wastes
- Q9(a): Discuss briefly the following: (a) Radioactive wastes
- Q9(b): Discuss briefly the following: (b) Defunct ships and e-wastes
- Q9(b): Discuss briefly the following: (b) Defunct ships and e-wastes
- Q9(c): Discuss briefly the following: (c) Municipal solid wastes
- Q9(c): Discuss briefly the following: (c) Municipal solid wastes
- Q10: What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
- Q10: What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
- Q11(a): Discuss briefly the following: (a) Greenhouse gases
- Q11(b): Discuss briefly the following: (b) Catalytic converter
- Q11(b): Discuss briefly the following: (b) Catalytic converter
- Q11(c): Discuss briefly the following: (c) Ultraviolet B
- Q11(c): Discuss briefly the following: (c) Ultraviolet B
CBSE Solutions for Class 12 Biology Environmental Issues
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
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