Discover the World climates — classification (Koeppen), greenhouse effect, global warming and climatic changes

World climates — classification (Koeppen)

• The world climate can be studied by organizing and synthesizing information on temperature, precipitation, and vegetation into manageable categories. This process helps to better understand and analyze climate patterns. Three main approaches to classifying climate are used:
  • Empirical: Relies on observed data, particularly temperature and precipitation.
  • Genetic: Attempts to categorize climates based on their causes.
  • Applied: Serves specific purposes.
• Koeppen’s Scheme of Classification of Climate

  

  • The most widely used climate classification system is V. Koeppen’s empirical scheme, developed in 1918. Koeppen identified a close relationship between climate and vegetation distribution, using specific values of temperature and precipitation to define climates. His system divides climates into five major groups:
    • A, C, D, E: Humid climates
    • B: Dry climates
    Each group is further subdivided using small letters based on seasonality and severity of temperature or dryness.
  • Group A: Tropical Humid Climates

    

    • Found between the Tropics of Cancer and Capricorn, with high annual rainfall and a low temperature range. This group has three types:
      • Af: Tropical Wet Climate - Consistent rainfall throughout the year.
      • Am: Tropical Monsoon Climate - High summer rainfall but dry winters.
      • Aw: Tropical Wet and Dry Climate - Distinct dry and wet seasons.
  • Group B: Dry Climates

    

    • Characterized by low rainfall insufficient for plant growth, covering large parts of the planet. Divided into:
      • BS: Steppe (semi-arid)
      • BW: Desert
  • Group C: Warm Temperate (Mid-Latitude) Climates

    

    • Extending from 30° to 50° latitude, mostly along coasts, with four types:
      • Cwa: Humid Subtropical Climate (dry winters, hot summers)
      • Cs: Mediterranean Climate (hot, dry summers, mild winters)
      • Cfa: Humid Subtropical Climate (no dry season)
      • Cfb: Marine West Coast Climate (mild temperatures, year-round rainfall)
  • Group D: Cold Snow Forest Climates

    

    • Occur in the northern hemisphere between 40° and 70° latitude:
      • Df: Cold climate with humid winters
      • Dw: Cold climate with dry winters
  • Group E: Polar Climates
    • Occur beyond 70° latitude:
      • ET: Tundra Climate - Permafrost and low-growing vegetation.
      • EF: Ice Cap Climate - Year-round freezing temperatures.

      

  • Group H: Highland Climates
    • Determined by topography, with large temperature variations over short distances and varying precipitation levels depending on elevation.

Greenhouse effect, global warming and climatic change

• Climate Change
  • Natural Climate Variability
    • The climate we experience today has prevailed for about the last 10,000 years with minor and occasional wide fluctuations.
    • Geological records reveal changes between glacial and inter-glacial periods.
    • Evidence of climate variability includes:
      • Geomorphological features in high altitudes and latitudes showing glacier advances and retreats.
      • Sediment deposits in glacial lakes indicating warm and cold periods.
      • Tree rings providing insights into wet and dry periods.
      • Historical records of climate variability.
    • In India, alternating wet and dry periods were observed:
      • Rajasthan experienced a wet and cool climate around 8000 B.C.
      • The period from 3000-1700 B.C. had higher rainfall.
      • Dry conditions intensified after 1700 B.C., coinciding with the Harappan civilization.

      

    • Climate during the geological past:
      • The Earth was warm between 500-300 million years ago during the Cambrian, Ordovician, and Silurian periods.
      • During the Pleistocene epoch, glacial and inter-glacial periods occurred, with the last major glacial peak about 18,000 years ago.
      • The present inter-glacial period began 10,000 years ago.
  • Climate in Recent Times

    

    • Variability in climate is a constant phenomenon.
    • Significant events in recent history:
      • The 1990s witnessed extreme weather events, including the warmest temperatures of the century and severe floods globally.
      • Severe droughts in the Sahel region (1967-1977) and the Dust Bowl in the U.S. Great Plains during the 1930s.
      • Europe experienced the "Little Ice Age" from 1550 to 1850.
      • Global temperature trends:
        • 1885-1940: Upward temperature trend.
        • 1940 onwards: Slower rate of temperature increase.
        • 1998 was the warmest year of the 20th century and likely the millennium.

  

  • Causes of Climate Change
    • Astronomical Causes
      • Sunspot activity affecting weather patterns:
        • Increased sunspots linked to cooler, wetter weather and greater storminess.
        • Decreased sunspots linked to warmer, drier conditions.
      • Milankovitch oscillations:
        • Variations in Earth's orbital characteristics.
        • Wobbling of Earth and changes in axial tilt altering insolation.
    • Terrestrial Causes
      • Volcanism releasing aerosols that reduce solar radiation, causing short-term cooling (e.g., Pinatubo eruption).
      • Human activities increasing greenhouse gas concentrations, leading to global warming.
  • Global Warming
    • The atmosphere behaves like a greenhouse due to the presence of greenhouse gases (GHGs).
    • Greenhouse Effect:
      • Incoming solar radiation passes through, but long-wave radiation is absorbed, trapping heat.
      • Analogy: Similar to the heat retention inside a greenhouse or a closed vehicle in summer.

    

    • Greenhouse Gases (GHGs):
      • Major GHGs:
        • Carbon dioxide (CO2)
        • Methane (CH4)
        • Chlorofluorocarbons (CFCs)
        • Nitrous oxide (N2O)
        • Ozone (O3)
      • CO2 is the most abundant, primarily emitted from fossil fuel combustion.
      • Deforestation exacerbates CO2 levels by reducing carbon sinks.
      • CFCs damage the ozone layer, leading to the ozone hole over Antarctica.
    • International Efforts:
      • The Kyoto Protocol (1997) aims to reduce GHG emissions, with targets for industrialized nations.
  • Effects and Concerns
    • Global warming may cause:
      • Sea level rise due to glacier melting and thermal expansion.
      • Inundation of coastal areas and islands, leading to social challenges.
    • Efforts are needed to reduce GHG emissions and adopt sustainable lifestyles.
  • Temperature Trends
    • The global near-surface air temperature averages 14°C.
    • Significant warming trends in the 20th century during:
      • 1901-1944
      • 1977-1999
    • The last decade of the 20th century recorded the seven warmest years since 1856.