GS Notes

5. Environment Notes 05

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Elaborate Notes

Biogeochemical Cycles: An Introduction

A biogeochemical cycle is the pathway by which a chemical substance moves through both biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth. The term, coined by Russian scientist Vladimir Vernadsky in his 1926 book The Biosphere, emphasizes the integration of geological and biological processes. These cycles are fundamental to life, facilitating the continuous circulation of essential elements like carbon, nitrogen, sulfur, and oxygen, which are transformed from inorganic to organic forms and back again. The cycles can be broadly categorized based on the primary reservoir or ‘pool’ of the element.

  • Gaseous Cycles: In these cycles, the main reservoir of the element is the atmosphere or the hydrosphere. The elements move relatively quickly through the ecosystem. Examples include the Nitrogen, Carbon, Oxygen, and Water cycles.
  • Sedimentary Cycles: Here, the primary reservoir is the Earth’s crust (lithosphere), typically in rocks and soil. The movement of these elements is significantly slower and less perfect, as elements can get locked in sediments for long geological periods. Examples include the Sulfur and Phosphorus cycles.

Sulfur Cycle

The Sulfur Cycle is a crucial sedimentary cycle, though it has a significant gaseous phase. Sulfur is an essential component of certain amino acids (methionine and cysteine), proteins, and vitamins, making it a vital macronutrient for all living organisms.

  • Reservoirs and Sources:

    • Lithosphere: The largest reservoir of sulfur is in rocks and sediments in the form of sulfate minerals like gypsum (CaSO4·2H2O) and sulfide minerals like pyrite (FeS2, also known as “Fool’s Gold”). Weathering of these rocks is a primary natural process that releases sulfur.
    • Atmosphere: Sulfur enters the atmosphere through both natural and anthropogenic sources.
      • Natural Sources: Volcanic eruptions release large quantities of sulfur dioxide (SO2) and hydrogen sulfide (H2S). The decay of organic matter in anaerobic conditions (e.g., in swamps and wetlands) by microorganisms releases H2S. Forest fires can release compounds like ammonium sulfate.
      • Anthropogenic Sources: The burning of fossil fuels (coal and oil), which contain sulfur impurities, is the dominant source of atmospheric SO2. Industrial processes like oil refining (using the Claus process to recover sulfur) and paper and chemical manufacturing also release significant H2S and SO2.

  • Processes in the Cycle:

    1. Mineralization and Decomposition: When organisms die, decomposers like fungi (e.g., Aspergillus) and bacteria break down the organic matter. This process, known as mineralization, releases sulfur, primarily as hydrogen sulfide (H2S).
    2. Oxidation: In the presence of oxygen, chemosynthetic bacteria like Thiobacillus oxidize H2S into elemental sulfur (S) and then into sulfate ions (SO4^2-). This sulfate is the primary form of sulfur assimilated by plants.
    3. Assimilation: Plants absorb sulfate ions from the soil through their roots. This sulfur is then incorporated into organic molecules. Animals obtain sulfur by consuming plants or other animals.
    4. Reduction: Under anaerobic conditions, sulfate-reducing bacteria like Desulfovibrio (the summary mentions Salmonella as a general example of bacteria involved in reconversion) can convert sulfate ions back into hydrogen sulfide (H2S). This process is common in waterlogged soils and deep-sea sediments.
    5. Atmospheric Reactions and Deposition:
      • In the atmosphere, H2S is rapidly oxidized to form SO2.
      • SO2 can further react with atmospheric oxygen (often catalyzed by pollutants) to form sulfur trioxide (SO3).
      • Wet Deposition: SO2 and SO3 react with water vapor to form sulfurous acid (H2SO3) and sulfuric acid (H2SO4). These acids dissolve in rainwater, fog, or snow, falling to the ground as acid rain.
      • Dry Deposition: Sulfate particles and SO2 gas can also settle directly onto surfaces as dust or aerosols without precipitation.

Nitrogen Cycle

The Nitrogen Cycle is a classic gaseous cycle, as the largest reservoir of nitrogen (about 78%) is the atmosphere in the form of dinitrogen gas (N2). However, this N2 is chemically inert due to a strong triple covalent bond, making it unavailable to most organisms directly. The cycle converts this inert N2 into biologically usable forms. Nitrogen is a critical component of amino acids, proteins, nucleic acids (DNA and RNA), and ATP.

  • Processes in the Cycle:
    1. Nitrogen Fixation: The conversion of atmospheric N2 into ammonia (NH3) or ammonium ions (NH4+).
      • Atmospheric Fixation: The immense energy of lightning breaks the N2 triple bond, allowing nitrogen to combine with oxygen to form nitrogen oxides (NOx). These oxides dissolve in rain to form nitric acid (HNO3), which is carried to the soil as nitrates (NO3-).
      • Biological Nitrogen Fixation (BNF): This accounts for the vast majority of fixation. It is carried out by specialized microorganisms.
        • Symbiotic: Bacteria like Rhizobium live in root nodules of leguminous plants (e.g., peas, beans).
        • Non-symbiotic (Free-living): Bacteria like Azotobacter and Clostridium, and cyanobacteria (blue-green algae) like Nostoc and Anabaena fix nitrogen in the soil and aquatic ecosystems.
      • Industrial Fixation: The Haber-Bosch process, developed by Fritz Haber and Carl Bosch in the early 20th century, synthesizes ammonia from atmospheric nitrogen and hydrogen under high temperature and pressure. This process is the cornerstone of modern nitrogen fertilizer production.
    2. Nitrification: A two-step process of converting ammonia/ammonium into nitrates, which are the primary form of nitrogen assimilated by plants. This is carried out by nitrifying bacteria in aerobic conditions.
      • Step 1: Ammonia (NH3) is oxidized to nitrite (NO2-) by bacteria such as Nitrosomonas and Nitrococcus.
      • Step 2: Nitrite (NO2-) is further oxidized to nitrate (NO3-) by bacteria like Nitrobacter.
    3. Assimilation: Plants absorb nitrates (and to a lesser extent, ammonium) from the soil and incorporate them into organic compounds. Animals get nitrogen by consuming these plants.
    4. Ammonification: When organisms die, decomposers (bacteria and fungi) break down the organic nitrogen back into inorganic ammonium (NH4+). This process returns nitrogen to the soil.
    5. Denitrification: The biological conversion of nitrates (NO3-) back into gaseous nitrogen (N2), which is then released into the atmosphere, thus completing the cycle. This process is carried out by denitrifying bacteria, such as Pseudomonas, under anaerobic conditions (e.g., in waterlogged soils). The sequence is generally: NO3- → NO2- → NO → N2O → N2.

Carbon Cycle

The Carbon Cycle describes the movement of carbon, the fundamental element of life, through Earth’s spheres. It involves two interconnected cycles: the fast (biological) cycle and the slow (geological) cycle. While the atmosphere is a key component, the largest reservoirs are in ocean sediments and the Earth’s crust.

  • Reservoirs and Sources:

    • Oceans: The largest active carbon pool, holding about 50 times more carbon than the atmosphere. Carbon is stored as dissolved CO2, carbonate (CO3^2-), and bicarbonate (HCO3-) ions.
    • Lithosphere: The largest reservoir overall, containing carbon in fossil fuels (coal, oil, natural gas) and sedimentary rocks like limestone (CaCO3).
    • Biosphere: Carbon is stored in living and dead organic matter in terrestrial and aquatic ecosystems.
    • Atmosphere: A relatively small reservoir but crucial for life. The concentration of CO2 has been meticulously tracked at the Mauna Loa Observatory since 1958, producing the famous Keeling Curve, which shows a steady increase due to human activities.

  • Processes in the Cycle:

    1. Photosynthesis: Autotrophs (plants, algae, cyanobacteria) remove CO2 from the atmosphere or water and use solar energy to convert it into organic carbon compounds (e.g., glucose). This is the primary pathway for carbon to enter the biosphere.
    2. Respiration: All living organisms (plants, animals, microbes) respire, breaking down organic compounds to release energy, which returns CO2 to the atmosphere or water.
    3. Decomposition: Decomposers break down dead organic matter, releasing CO2 through respiration. In anaerobic conditions, methane (CH4) may be produced instead.
    4. Ocean-Atmosphere Exchange: CO2 dissolves in and is released from the ocean surface. The “solubility pump” transports carbon to the deep ocean as cold, dense polar waters sink. The “biological pump” transports carbon to the deep ocean as organic matter from phytoplankton sinks.
    5. Geological Processes: Over millions of years, organic matter is buried and converted into fossil fuels. Weathering of silicate rocks removes atmospheric CO2. Volcanic eruptions and the burning of fossil fuels release this long-stored carbon back into the atmosphere, disrupting the cycle’s balance.

Oxygen Cycle

The Oxygen Cycle is intrinsically linked to the Carbon and Water cycles. The vast majority of Earth’s oxygen is locked in the lithosphere within silicate and oxide minerals. The small fraction in the atmosphere (about 21%) is crucial for aerobic life.

  • Historical Context: Earth’s early atmosphere was anoxic. The Great Oxidation Event, approximately 2.4 billion years ago, marks the point when photosynthetic cyanobacteria began producing oxygen as a waste product, fundamentally changing the planet’s chemistry and paving the way for complex life.
  • Sources of Atmospheric Oxygen:
    • Photosynthesis: This is the primary source. Plants and phytoplankton split water molecules (H2O), releasing O2.
    • Photolysis: In the upper atmosphere, high-energy ultraviolet (UV) radiation from the sun splits water vapor molecules into hydrogen and oxygen. The lighter hydrogen escapes to space, leaving oxygen behind.
  • Sinks (Removal) of Oxygen:
    • Respiration: The most significant sink. Aerobic organisms use oxygen to break down organic matter for energy, producing CO2 and water.
    • Combustion: All burning processes, from forest fires to fossil fuel combustion, consume oxygen.
    • Decomposition: Aerobic decomposers consume oxygen as they break down organic matter.
    • Oxidation (Rusting): Oxygen reacts with exposed minerals, such as iron, in the process of chemical weathering.

Prelims Pointers

  • Gaseous Cycle: Main reservoir is the atmosphere/hydrosphere (e.g., Carbon, Nitrogen, Oxygen).
  • Sedimentary Cycle: Main reservoir is the Earth’s crust/lithosphere (e.g., Sulfur, Phosphorus).
  • Largest reservoir of Sulfur: Rocks and Sediments.
  • Largest active reservoir of Carbon: Oceans.
  • Largest reservoir of Nitrogen: Atmosphere (approx. 78% as N2).
  • Main form of sulfur taken by plants: Sulfate ions (SO4^2-).
  • Main form of nitrogen taken by plants: Nitrate ions (NO3-).
  • Pyrite (FeS2 or Fool’s Gold) is a major sulfur-bearing mineral.
  • Key Bacteria in Nitrogen Cycle:
    1. Nitrogen Fixation: Rhizobium (symbiotic), Azotobacter, Clostridium (free-living).
    2. Nitrification (Ammonia to Nitrite): Nitrosomonas, Nitrococcus.
    3. Nitrification (Nitrite to Nitrate): Nitrobacter.
    4. Denitrification (Nitrate to N2): Pseudomonas.
  • Key Bacteria in Sulfur Cycle:
    • Oxidation (H2S to Sulfate): Thiobacillus.
    • Decomposition: Fungi like Aspergillus.
  • Acid Rain: Caused by atmospheric SO2 and Nitrogen Oxides (NOx) reacting with water to form sulfuric acid (H2SO4) and nitric acid (HNO3).
  • Haber-Bosch Process: Industrial method for producing ammonia from nitrogen and hydrogen for fertilizers.
  • Great Oxidation Event: A period around 2.4 billion years ago when cyanobacteria began producing oxygen, transforming Earth’s atmosphere.
  • Keeling Curve: A graph showing the ongoing increase in the concentration of atmospheric carbon dioxide since 1958.
  • Greenhouse gases associated with these cycles: Carbon Dioxide (CO2), Methane (CH4), Nitrous Oxide (N2O).

Mains Insights

GS Paper III: Environment & Biodiversity

  1. Anthropogenic Disruption of Biogeochemical Cycles and its Consequences:

    • Cause: Industrial revolution, intensified agriculture (Green Revolution), and reliance on fossil fuels have drastically altered the natural flow of elements.
    • Effect on Carbon Cycle: Burning fossil fuels and deforestation have increased atmospheric CO2 concentrations by nearly 50% since pre-industrial times, leading to global warming, climate change, and ocean acidification (as oceans absorb excess CO2, forming carbonic acid, which harms marine life like corals).
    • Effect on Nitrogen Cycle: The Haber-Bosch process now fixes as much atmospheric N2 as all natural terrestrial processes combined. Excessive use of nitrogen fertilizers leads to:
      • Eutrophication: Runoff of nitrates and phosphates into water bodies causes algal blooms. When these algae die and decompose, they deplete dissolved oxygen, creating hypoxic “dead zones” (e.g., in the Gulf of Mexico), killing aquatic life.
      • Greenhouse Gas Emission: Denitrification and other microbial processes in nitrogen-rich soils release Nitrous Oxide (N2O), a greenhouse gas nearly 300 times more potent than CO2.
      • Soil and Water Contamination: High nitrate levels in drinking water can cause health issues like methemoglobinemia (“blue-baby syndrome”).
    • Effect on Sulfur Cycle: The combustion of sulfur-rich fossil fuels releases massive amounts of SO2, which is the primary cause of acid rain. Acid rain damages forests, acidifies lakes making them unsuitable for fish, corrodes buildings and monuments (e.g., “marble cancer” of the Taj Mahal), and impacts human health.

  2. Interlinkages between Cycles:

    • Carbon-Oxygen Link: Photosynthesis and respiration are two sides of the same coin, directly linking the C and O cycles. Disrupting one inevitably affects the other.
    • Nitrogen-Carbon Link: Increased nitrogen deposition from pollution can act as a fertilizer for forests (N-limitation), temporarily increasing carbon sequestration. However, this effect is complex and can be offset by other negative impacts of pollution.
    • Acid Rain Link: The disruption of both the Sulfur and Nitrogen cycles (emission of SO2 and NOx) is the combined cause of acid rain, demonstrating how multiple human impacts can create a single, severe environmental problem.

GS Paper I: Geography

  • Climate and Biogeochemical Cycles: The carbon cycle is the master control knob for Earth’s climate. The distribution of biomes (e.g., tropical rainforests vs. tundra) is determined by climate, which in turn governs the rates of photosynthesis, decomposition, and nutrient cycling. Climate change, driven by the disrupted carbon cycle, is altering these biomes.
  • Soil Health and Agriculture: Nutrient cycles (N, P, S) are the foundation of soil fertility. Modern agriculture, by breaking these natural cycles (shipping food far from where it’s grown), creates a dependency on synthetic fertilizers, leading to soil degradation and water pollution.

GS Paper IV: Ethics

  • Intergenerational Equity: The current generation’s disruption of these stable, life-supporting cycles imposes significant environmental and economic costs on future generations. This raises ethical questions about our responsibility to maintain planetary health.
  • Climate Justice: The impacts of disrupted cycles (e.g., climate change, sea-level rise) disproportionately affect developing nations and vulnerable communities who have contributed the least to the problem, raising issues of global justice and equity.

Previous Year Questions

Prelims

  1. Which of the following adds/add nitrogen to the soil? (UPSC CSE 2023)

    1. Excretion of urea by animals
    2. Burning of coal by man
    3. Death of vegetation

    Select the correct answer using the code given below: (a) 1 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3

    Answer: (c) 1 and 3 only Explanation: Excretion of urea by animals adds nitrogenous waste to the soil, which is converted to ammonia. Death of vegetation leads to decomposition, which releases nitrogen back into the soil through ammonification. Burning of coal releases oxides of nitrogen (NOx) into the atmosphere, which can then be deposited on land via acid rain, but it is primarily an atmospheric pollutant, not a direct soil enrichment process in this context.

  2. Which of the following can be found as pollutants in the drinking water in some parts of India? (UPSC CSE 2023)

    1. Arsenic
    2. Sorbitol
    3. Fluoride
    4. Formaldehyde
    5. Uranium

    Select the correct answer using the code given below: (a) 1 and 3 only (b) 2, 4 and 5 only (c) 1, 3 and 5 only (d) 1, 2, 3, 4 and 5

    Answer: (c) 1, 3 and 5 only Explanation: While not directly from the summary, this question relates to the broader theme of environmental pollution. Arsenic (from geological sources and industrial pollution), Fluoride (geological), and Uranium (geological) are well-known contaminants in drinking water in various parts of India. Sorbitol is a sugar alcohol and Formaldehyde is a chemical compound not typically found as a widespread natural water pollutant.

  3. In the context of which of the following do some scientists suggest the use of cirrus cloud thinning technique and the injection of sulphate aerosol into the stratosphere? (UPSC CSE 2019) (a) Creating the artificial rains in some regions (b) Reducing the frequency and intensity of tropical cyclones (c) Reducing the adverse effects of solar wind on the Earth (d) Reducing the global warming

    Answer: (d) Reducing the global warming Explanation: This question relates to the application of the Sulfur Cycle. Injecting sulphate aerosols into the stratosphere is a proposed geoengineering technique called Solar Radiation Management (SRM). These aerosols would mimic the cooling effect of large volcanic eruptions (which release SO2) by reflecting sunlight back into space, thereby reducing global warming.

  4. Consider the following: (UPSC CSE 2019)

    1. Carbon monoxide
    2. Methane
    3. Ozone
    4. Sulphur dioxide

    Which of the above are released into atmosphere due to the burning of crop/biomass residue? (a) 1 and 2 only (b) 2, 3 and 4 only (c) 1 and 4 only (d) 1, 2, 3 and 4

    Answer: (d) 1, 2, 3, and 4 Explanation: The incomplete combustion of biomass (like crop residue) releases a variety of pollutants, including carbon monoxide (CO), methane (CH4), volatile organic compounds (which contribute to ground-level ozone formation), and sulfur dioxide (SO2), along with particulate matter and nitrogen oxides.

  5. What is blue carbon? (UPSC CSE 2021) (a) Carbon captured by oceans and coastal ecosystems (b) Carbon sequestered in forest biomass and agricultural soils (c) Carbon contained in petroleum and natural gas (d) Carbon present in the atmosphere

    Answer: (a) Carbon captured by oceans and coastal ecosystems Explanation: This question is directly related to the Carbon Cycle. ‘Blue carbon’ refers to the carbon stored in coastal and marine ecosystems, such as mangroves, tidal marshes, and seagrass meadows. These ecosystems are highly efficient at sequestering and storing carbon in both the plants and the sediment below.

Mains

  1. Discuss global warming and mention its effects on the global climate. Explain the control measures to bring down the level of greenhouse gases which cause global warming, in the light of the Kyoto Protocol, 1997. (UPSC CSE 2022, 250 words)

    Answer: Global warming refers to the long-term heating of Earth’s climate system observed since the pre-industrial period due to human activities, primarily fossil fuel burning, which increases heat-trapping greenhouse gas (GHG) levels in Earth’s atmosphere. This warming is a key aspect of climate change.

    Effects on Global Climate:

    • Rising Temperatures: Increased average global temperatures, leading to more frequent and intense heatwaves.
    • Extreme Weather Events: Higher frequency and intensity of events like hurricanes, droughts, floods, and wildfires.
    • Melting Ice and Sea-Level Rise: Accelerated melting of glaciers and polar ice caps contributes to rising sea levels, threatening coastal communities and ecosystems.
    • Ocean Acidification: Increased absorption of atmospheric CO2 by oceans lowers pH, harming marine life, especially coral reefs and shellfish.
    • Disruption of Ecosystems: Shifts in habitats and seasons affect biodiversity, agriculture, and food security.

    Control Measures under the Kyoto Protocol, 1997: The Kyoto Protocol was an international treaty that committed state parties to reduce GHG emissions, based on the scientific consensus that global warming is occurring and is human-made.

    • Binding Emission Reduction Targets: It set binding targets for 37 industrialized countries and the European community for reducing GHG emissions. These targets amounted to an average of 5% against 1990 levels over the five-year period 2008–2012.
    • Principle of “Common but Differentiated Responsibilities”: It placed a heavier burden on developed nations, recognizing that they are historically responsible for the current high levels of GHGs. Developing nations like India and China were not given binding targets.
    • Flexible Market Mechanisms: To help countries meet their targets cost-effectively, the protocol introduced three mechanisms:
      1. International Emissions Trading: Countries could trade emission units (or ‘carbon credits’).
      2. Clean Development Mechanism (CDM): Allowed a developed country to fund an emission-reduction project in a developing country and earn saleable credits.
      3. Joint Implementation (JI): Allowed a developed country to invest in an emission-reduction project in another developed country.

    Although the Kyoto Protocol has been succeeded by the Paris Agreement, its principles laid the groundwork for international climate action by establishing legally binding commitments and innovative market-based mechanisms.

  2. Describe the major outcomes of the 26th session of the Conference of the Parties (COP26) to the United Nations Framework Convention on Climate Change (UNFCCC). What are the commitments made by India in this conference? (UPSC CSE 2021, 250 words)

    Answer: The 26th Conference of the Parties (COP26) held in Glasgow in 2021 was a critical summit aimed at accelerating action towards the goals of the Paris Agreement. Its primary objective was to “keep 1.5°C alive.”

    Major Outcomes of COP26 (The Glasgow Climate Pact):

    • Mitigation: For the first time, the pact explicitly targeted fossil fuels, calling for a “phasedown of unabated coal power and phase-out of inefficient fossil fuel subsidies.” It also urged countries to revisit and strengthen their 2030 climate targets (NDCs) by the end of 2022.
    • Adaptation: Developed countries were urged to at least double their collective provision of climate finance for adaptation to developing countries from 2019 levels by 2025.
    • Climate Finance: While the goal of providing $100 billion per year by 2020 was not met, the pact expressed deep regret and urged developed countries to meet the goal urgently.
    • Rulebook Finalization: COP26 finalized the Paris Agreement Rulebook, particularly Article 6, which establishes a framework for a global carbon market mechanism.
    • Pledges: Several plurilateral deals were announced, including the Global Methane Pledge (to cut methane emissions by 30% by 2030) and a declaration to halt and reverse deforestation.

    India’s Commitments (The ‘Panchamrit’ Declaration): Prime Minister Narendra Modi announced five ambitious targets for India:

    1. Non-fossil energy capacity: To reach 500 GW by 2030.
    2. Renewable energy share: To meet 50 percent of its energy requirements from renewable energy by 2030.
    3. Carbon emissions reduction: To reduce the total projected carbon emissions by one billion tonnes from now onwards till 2030.
    4. Carbon intensity reduction: To reduce the carbon intensity of its economy by less than 45 percent by 2030.
    5. Net-zero target: To achieve the target of Net Zero emissions by 2070.

    These commitments signaled a significant enhancement of India’s climate ambitions and its proactive role in global climate action.

  3. What are the causes and effects of ocean acidification on the marine ecosystem? (UPSC CSE Mains Question - Hypothetical/Based on common themes)

    Answer: Ocean acidification is the ongoing decrease in the pH of the Earth’s oceans, caused by the uptake of anthropogenic carbon dioxide (CO2) from the atmosphere. It is often referred to as the “other CO2 problem” alongside global warming.

    Causes: The primary cause is the absorption of excess CO2 from the atmosphere by the oceans. Since the Industrial Revolution, about 30-40% of the CO2 released by human activities (burning fossil fuels, deforestation) has been absorbed by the oceans. When CO2 dissolves in seawater, it forms carbonic acid (H2CO3). This acid dissociates, releasing hydrogen ions (H+), which increases the acidity (lowers the pH) of the water. These hydrogen ions also readily bond with carbonate ions (CO3^2-), reducing their availability in the water.

    Effects on Marine Ecosystems:

    1. Impact on Calcifying Organisms: The reduced availability of carbonate ions makes it difficult for marine organisms like corals, shellfish (oysters, clams), and some plankton to build and maintain their shells and skeletons, which are made of calcium carbonate. This can lead to weaker shells, slower growth, and increased mortality.
    2. Coral Bleaching and Reef Degradation: Acidification exacerbates the effects of thermal stress that cause coral bleaching. It directly hinders the ability of corals to build their skeletons, threatening the existence of entire reef ecosystems, which are hotspots of marine biodiversity.
    3. Disruption of Food Webs: Plankton, such as pteropods and foraminifera, are at the base of many marine food webs. Their decline due to acidification can have cascading effects, impacting larger species like fish, seabirds, and marine mammals that depend on them for food.
    4. Physiological and Behavioral Changes: Changes in ocean chemistry can affect the metabolism, growth, and reproductive success of various marine species. For example, it can impair the ability of some fish to detect predators through their sense of smell.

    In conclusion, ocean acidification poses a fundamental threat to marine biodiversity, fisheries, and the coastal communities that depend on healthy ocean ecosystems.

  4. How has the emphasis on certain crops brought about changes in cropping patterns in recent past? Elaborate the emphasis on millets in view of climate change. (UPSC CSE 2023, 250 words)

    Answer: The emphasis on certain crops, driven by the Green Revolution, government policies like Minimum Support Price (MSP), and market demand, has significantly altered cropping patterns in India over the recent past.

    Changes in Cropping Patterns:

    • Dominance of Rice and Wheat: The focus on food security led to the widespread cultivation of high-yielding varieties of rice and wheat. This created a cereal-centric monoculture, especially in states like Punjab, Haryana, and Western UP.
    • Decline in Coarse Grains and Pulses: The area under cultivation for traditional crops like millets (jowar, bajra, ragi), pulses, and oilseeds declined as they were less remunerative compared to rice and wheat under the MSP regime.
    • Regional Specialization and Imbalance: Cropping patterns became regionally skewed. For instance, water-intensive paddy cultivation expanded in water-scarce regions of Northwest India, leading to severe groundwater depletion.
    • Shift to Cash Crops: In some regions, there has been a shift towards water-intensive cash crops like sugarcane and cotton, driven by market demand, further stressing water resources and soil health.
    • Impact on Soil and Environment: Monocropping of rice and wheat has led to soil degradation, loss of biodiversity, and increased reliance on chemical fertilizers and pesticides, disrupting nutrient cycles and polluting water bodies.

    Emphasis on Millets in View of Climate Change: In response to the negative consequences of current cropping patterns and the growing threat of climate change, there is a renewed emphasis on millets, culminating in the UN declaring 2023 as the “International Year of Millets.”

    Advantages of Millets:

    1. Climate Resilience: Millets are hardy crops, highly tolerant to drought, high temperatures, and poor soil conditions, making them ideal “climate-smart crops” for a warming world.
    2. Low Input Requirement: They require significantly less water compared to rice and wheat and have a shorter growing season. They can grow in rain-fed areas with minimal need for fertilizers and pesticides.
    3. Nutritional Security: Millets are highly nutritious, rich in protein, dietary fiber, micronutrients (iron, zinc), and calcium. They are gluten-free and have a low glycemic index, helping combat malnutrition and lifestyle diseases.
    4. Environmental Benefits: Cultivating millets enhances agrobiodiversity, improves soil health, and supports sustainable agricultural practices by diversifying cropping systems and breaking pest cycles.

    Promoting millets through policy support (e.g., inclusion in PDS, better MSP), research, and awareness campaigns can help build a more resilient, sustainable, and nutritious food system for India in the face of climate change.

  5. Discuss in detail the photochemical smog. (UPSC CSE 2022, 150 words)

    Answer: Photochemical smog is a type of air pollution characterized by a brown haze, which is prevalent in sunny, warm, and dry urban areas with heavy vehicular traffic. It is a mixture of secondary pollutants formed when primary pollutants react under the influence of sunlight.

    Formation: The formation process is a complex series of chemical reactions:

    1. Primary Pollutants: The main precursors are nitrogen oxides (NOx, primarily NO and NO2) and Volatile Organic Compounds (VOCs). These are released mainly from vehicle exhausts and industrial emissions.
    2. Role of Sunlight: Intense sunlight (UV radiation) acts as a catalyst. It breaks down nitrogen dioxide (NO2) into nitric oxide (NO) and a free oxygen atom (O).
      • NO2 + Sunlight → NO + O
    3. Ozone Formation: The highly reactive oxygen atom (O) combines with an oxygen molecule (O2) to form ground-level ozone (O3), which is a major component of photochemical smog.
      • O + O2 → O3
    4. Formation of other Secondary Pollutants: The VOCs react with nitrogen oxides in the presence of sunlight to form other harmful secondary pollutants like Peroxyacetyl Nitrate (PAN), aldehydes, and other oxidants. PAN is particularly harmful as it is a powerful respiratory and eye irritant.

    Conditions and Effects:

    • Conditions: It typically peaks in the afternoon when sunlight is most intense and is exacerbated by temperature inversions that trap pollutants near the ground.
    • Effects: Photochemical smog causes severe health problems, including breathing difficulties, asthma attacks, eye irritation, and damage to lung tissue. It also damages plants, trees, and materials like rubber and fabrics. The brownish color of the smog is due to the presence of nitrogen dioxide.

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