World Climate And Climate Change

Koeppen’s Scheme Of Classification Of Climate

Wladimir Köppen developed a widely used system for classifying climates based on average monthly and annual values of temperature and precipitation. His scheme divides the world into five main climate groups (A, B, C, D, E), each identified by a letter. Within these main groups, there are various sub-types based on seasonal precipitation patterns and temperature variations.

Group A : Tropical Humid Climates

Characteristics: Found within 23.5° latitude of the equator. All months have an average temperature of 18°C (64.4°F) or higher. High annual precipitation, with no significant dry season.

• Tropical Wet Climate (Af):

  Location: Equatorial regions (e.g., Amazon Basin, Congo Basin, Indonesia).

  Characteristics: High temperatures and heavy rainfall throughout the year. Little seasonal variation in temperature. Abundant convectional rainfall.

• Tropical Monsoon Climate (Am):

  Location: South and Southeast Asia, West Africa, parts of South America.

  Characteristics: Similar to Af, but with a short, dry season, often coinciding with the period when the ITCZ is farthest from the region. Rainfall is concentrated during the monsoon season, often brought by monsoon winds.

• Tropical Wet and Dry Climate (Aw):

  Location: Found north and south of the Af and Am regions (e.g., India, Brazil, parts of Africa).

  Characteristics: High temperatures year-round, but with a distinct dry season and a distinct wet season. Rainfall is largely convectional and occurs during the summer months when the ITCZ is overhead.

Dry Climates : B

Characteristics: Found in regions where evaporation exceeds precipitation. Characterized by low annual rainfall and large temperature fluctuations. Precipitation is generally less than 50 cm (20 inches) annually.

• Subtropical Steppe (BSh) and Subtropical Desert (BWh) Climates:

  Location: Located poleward of the tropical wet and dry climates (e.g., Sahara, Arabian Desert, Thar Desert, parts of Australia, southwestern US).

  Characteristics: Hot summers and mild to cool winters. Very low rainfall, with deserts (BWh) being drier than steppes (BSh). Large diurnal (daily) temperature ranges are common.

• Other Dry Climates (Not detailed here but part of Köppen's B group): Mid-latitude Steppe (BSk) and Mid-latitude Desert (BWk) are found in cooler, inland regions.

Warm Temperate (Mid-Latitude) Climates-C

Characteristics: Found roughly between 23.5° and 60° latitude. Have mild winters, with average temperatures in the coldest month between 18°C (64.4°F) and -3°C (26.6°F).

• Humid Subtropical Climate (Cwa):

  Location: Eastern sides of continents in the subtropics (e.g., Southeastern China, Southeastern US).

  Characteristics: Hot, humid summers with convectional rainfall. Mild winters with rainfall often brought by mid-latitude cyclones. Can have a distinct dry winter.

• Mediterranean Climate (Cs):

  Location: Western sides of continents in the subtropics (e.g., Mediterranean Basin, California, Chile, southwestern Australia).

  Characteristics: Hot, dry summers and mild, wet winters. This pattern is due to the seasonal shift of subtropical high-pressure systems (causing dry summers) and westerly winds (bringing rain in winter).

• Humid Subtropical (Cfa) Climate: (Note: Cfa is also a Humid Subtropical climate, often distinguished from Cwa by having no distinct dry season or a dry season in winter).

  Location: Southeastern coasts of continents (e.g., Southeastern US, Eastern China, Southeast Brazil).

  Characteristics: Hot, humid summers with abundant rainfall. Mild winters with precipitation from cyclonic storms.

• Marine West Coast Climate (Cfb):

  Location: Western coasts of continents in the mid-latitudes (e.g., Pacific Northwest of North America, Western Europe).

  Characteristics: Mild summers and mild winters with precipitation distributed relatively evenly throughout the year. Influenced by maritime air masses and prevailing westerly winds.

Cold Snow Forest Climates (D)

Characteristics: Found in the interior of continents in high latitudes of the Northern Hemisphere (roughly 40° to 70° latitude). Have cold winters, with average temperatures in the coldest month below -3°C (26.6°F), and warm to cool summers.

• Cold Climate With Humid Winters (Df):

  Location: Northeastern North America, Northern Europe, Northern Asia.

  Characteristics: Warm summers and cold winters with precipitation distributed throughout the year. Snow is common in winter.

• Cold Climate With Dry Winters (Dw):

  Location: Eastern Asia (e.g., Northern China, Siberia).

  Characteristics: Warm summers and very cold winters. Most precipitation occurs in summer, while winters are cold and dry, often influenced by Siberian high pressure.

Polar Climates (E)

Characteristics: Found poleward of 60° latitude. All months have an average temperature below 10°C (50°F).

• Tundra Climate (ET):

  Location: Arctic coastal regions, northern Canada, Siberia.

  Characteristics: Very short, cool summers and long, extremely cold winters. Precipitation is low, mostly as snow. The ground is frozen for most of the year (permafrost).

• Ice Cap Climate (EF):

  Location: Interior of Greenland, Antarctica, high mountain peaks.

  Characteristics: All months have average temperatures below freezing (0°C or 32°F). Permanent ice and snow cover. Extremely low precipitation.

Highland Climates (H)

Characteristics: This category applies to mountainous regions where climate characteristics are primarily determined by altitude, aspect, and exposure, rather than latitude. Temperatures decrease with altitude, and precipitation patterns vary greatly with slope and windward/leeward position.

Example: The Himalayas, Andes, Rocky Mountains.

Climate Change

Climate In The Recent Past

The Earth's climate has naturally varied throughout its history, experiencing periods of warmth (interglacials) and cold (glacials or ice ages). Evidence for past climates comes from various sources:

• Paleoclimatology: The study of past climates using proxy data.
• Proxy Data Sources:
  • Ice Cores: Trapped air bubbles in ice sheets (e.g., from Antarctica and Greenland) provide direct samples of past atmospheric composition (including greenhouse gas concentrations like CO₂ and methane) and isotopic analysis reveals past temperatures.
  • Tree Rings (Dendroclimatology): The width and density of tree rings can indicate past temperature and precipitation patterns.
  • Sediment Cores: Lake and ocean sediments contain fossilized pollen, foraminifera (marine microorganisms), and other indicators that reveal past vegetation, sea levels, and temperatures.
  • Coral Reefs: The isotopic composition and growth patterns of corals can provide information about past sea surface temperatures and salinity.
• Natural Climate Drivers: Past climate changes have been driven by natural factors such as:
  • Milankovitch Cycles: Long-term variations in Earth's orbital parameters (eccentricity, axial tilt, precession) that affect the amount and distribution of solar radiation received by different parts of the Earth.
  • Volcanic Activity: Large volcanic eruptions can inject aerosols into the stratosphere, temporarily cooling the planet.
  • Solar Variability: Fluctuations in solar output, though generally small, can influence climate.
  • Plate Tectonics: Over geological timescales, the movement of continents affects ocean currents and atmospheric circulation patterns.
• Holocene Climate: The current interglacial period, the Holocene (the last ~11,700 years), has been relatively stable compared to glacial cycles, allowing human civilizations to flourish. However, even within the Holocene, there have been notable variations like the Medieval Warm Period and the Little Ice Age.

Causes Of Climate Change

Climate change refers to significant, long-term changes in the global climate. While natural factors have influenced climate in the past, the current rapid warming trend observed since the mid-20th century is overwhelmingly attributed to human activities.

Natural Causes:

• Orbital Variations (Milankovitch Cycles): Drive glacial-interglacial cycles over tens to hundreds of thousands of years.
• Volcanic Activity: Can cause short-term cooling (months to years) due to sulfate aerosols reflecting sunlight.
• Solar Variability: Small fluctuations in solar output can have minor impacts on climate.

Anthropogenic (Human-Caused) Causes: These are the dominant drivers of current climate change.

• Greenhouse Gas Emissions: The burning of fossil fuels (coal, oil, natural gas) for energy, industry, and transportation releases large amounts of greenhouse gases (GHGs) into the atmosphere. Deforestation also contributes by reducing the Earth's capacity to absorb CO₂.
• Deforestation and Land-Use Change: Trees absorb CO₂. Clearing forests reduces this absorption and can release stored carbon. Changes in land use (e.g., urbanization, agriculture) also alter surface reflectivity (albedo) and evapotranspiration rates.
• Industrial Processes: Certain industrial activities release potent GHGs like hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs).
• Agriculture: Practices like rice cultivation and livestock farming release methane (CH₄) and nitrous oxide (N₂O).

The Enhanced Greenhouse Effect: Human activities are increasing the concentration of GHGs in the atmosphere, enhancing the natural greenhouse effect and leading to global warming.

Global Warming

Definition: Global warming refers to the long-term heating of Earth’s climate system observed since the pre-industrial period (between 1850 and 1900) due to human activities, primarily fossil fuel burning, which increases heat-trapping greenhouse gas levels in Earth’s atmosphere. The term is often used interchangeably with the term climate change, though the latter refers to both human- and naturally-induced changes in Earth’s climate.

Observed Changes:

• Rising Global Temperatures: The average surface temperature of the Earth has increased significantly, with the last few decades being the warmest on record.
• Warming Oceans: Oceans have absorbed a large amount of this increased heat, leading to ocean warming.
• Shrinking Ice Sheets and Glaciers: Ice sheets in Greenland and Antarctica, as well as glaciers worldwide, are melting at accelerated rates.
• Sea Level Rise: Caused by the thermal expansion of warming ocean water and the melting of land ice.
• Changes in Precipitation Patterns: Some regions are experiencing more intense rainfall events, while others face increased drought.
• More Frequent and Intense Heatwaves:
• Ocean Acidification: Oceans absorb excess CO₂, leading to increased acidity, which harms marine life.

Greenhouse Gases (GHGs)

Definition: Greenhouse gases are atmospheric gases that absorb and emit infrared radiation. This process is the fundamental cause of the greenhouse effect. By trapping heat, they maintain Earth's temperature at a habitable level. However, increased concentrations of GHGs due to human activities are causing the planet to warm.

Major Greenhouse Gases and their Sources:

• Water Vapour (H₂O): The most abundant GHG and a potent contributor to the natural greenhouse effect. Its concentration is largely controlled by temperature; as the atmosphere warms, it can hold more water vapour, creating a positive feedback loop.
• Carbon Dioxide (CO₂):
  • Sources: Burning of fossil fuels (coal, oil, natural gas), deforestation, cement production, industrial processes.
  • Significance: The primary long-lived GHG driving current climate change due to its large emissions and long atmospheric lifetime.
• Methane (CH₄):
  • Sources: Natural gas leaks, livestock farming (enteric fermentation), decomposition of organic waste in landfills, rice cultivation, wetlands.
  • Significance: A potent GHG, trapping significantly more heat per molecule than CO₂ over shorter timescales (e.g., 20 years), but it has a shorter atmospheric lifetime.
• Nitrous Oxide (N₂O):
  • Sources: Agricultural and industrial activities, burning of fossil fuels and biomass.
  • Significance: A potent GHG with a long atmospheric lifetime, also involved in stratospheric ozone depletion.
• Ozone (O₃):
  • Stratospheric Ozone: Acts as a protective shield against UV radiation; its depletion is a separate environmental issue (ozone hole).
  • Tropospheric Ozone: Acts as a GHG and a pollutant, contributing to smog and respiratory problems.
• Halocarbons (e.g., CFCs, HFCs, PFCs):
  • Sources: Refrigerants, aerosols, industrial processes.
  • Significance: Very potent GHGs with extremely long atmospheric lifetimes. While CFCs have been phased out due to ozone depletion, their replacements (HFCs) are powerful GHGs.

Radiative Forcing: The difference between the rate at which the Earth receives solar energy and the rate at which it radiates thermal energy. An increase in GHGs increases the net incoming energy, leading to warming. This is known as positive radiative forcing.