Chapter Notes

World Climate and Climate Change

To make sense of the Earth's climate, we classify it into smaller, understandable units. There are three main ways to do this:

• Empirical classification: This method is based on observed data, especially temperature and precipitation. It looks at what is happening.
• Genetic classification: This method tries to group climates based on their causes. It asks why a climate is the way it is.
• Applied classification: This is used for a specific purpose, like agriculture or architecture.

Koeppen's Scheme of Classification of Climate

The most widely used system for classifying climate is the empirical scheme developed by V. Koeppen. He noticed a strong link between the type of vegetation in an area and its climate.

Koeppen's system uses mean annual and monthly temperature and precipitation data to define climate boundaries. He created a system of capital and small letters to label different climate groups and types. First developed in 1918, this scheme is still popular today.

Major Climatic Groups: Koeppen identified five major groups. Four are based on temperature, and one is based on precipitation.

• A - Tropical: The average temperature of the coldest month is 18°C or higher.
• B - Dry Climates: Potential evaporation is greater than precipitation. There isn't enough rain for the amount of water that could evaporate.
• C - Warm Temperate: The average temperature of the coldest month is between -3°C and 18°C.
• D - Cold Snow Forest Climates: The average temperature of the coldest month is -3°C or below.
• E - Cold Climates: The average temperature for all months is below 10°C.

Subdivisions and Letter Codes: These major groups are further divided into types using small letters, which describe precipitation patterns and temperature severity.

• Precipitation:
  • f: No dry season
  • m: Monsoon climate
  • w: Winter dry season
  • s: Summer dry season
• Temperature Severity:
  • a, b, c, d: Refer to how severe the temperature is.
• Dry Climates (B) Subdivisions:
  • S: Steppe or semi-arid climate
  • W: Desert or arid climate

Group A : Tropical Humid Climates

Found between the Tropic of Cancer and the Tropic of Capricorn, these climates are hot and humid all year. This is because the sun is directly overhead and the Inter Tropical Convergence Zone (ITCZ) is present. The annual range of temperature is very low, and annual rainfall is high.

There are three types of Tropical Humid Climates:

• Af - Tropical Wet Climate
• Am - Tropical Monsoon Climate
• Aw - Tropical Wet and Dry Climate

Tropical Wet Climate (Af)

• Location: Found near the equator, including the Amazon Basin, western equatorial Africa, and the islands of the East Indies.
• Characteristics: It rains significantly every month, often as afternoon thundershowers. The temperature is uniformly high, with a maximum around 30°C and a minimum around 20°C. The annual temperature range is negligible.
• Vegetation: This climate supports tropical evergreen forests with dense canopies and high biodiversity.

Tropical Monsoon Climate (Am)

• Location: Found in the Indian sub-continent, northeastern South America, and Northern Australia.
• Characteristics: Heavy rainfall occurs mostly in the summer, while the winter is dry.

Tropical Wet and Dry Climate (Aw)

• Location: Occurs north and south of the Af climate regions, such as in Brazil, Bolivia, Paraguay, and Sudan.
• Characteristics: Annual rainfall is much less than in Af and Am climates and is more variable. The wet season is shorter, and the dry season is longer and more severe. Temperatures are high all year, and the daily temperature range is greatest in the dry season.
• Vegetation: This climate supports deciduous forests and tree-shredded grasslands.

Dry Climates : B

Dry climates are defined by very low rainfall, which is not enough to support much plant life. They cover a vast area of the planet, from 15° to 60° latitude.

• Low Latitudes (15°-30°): They are found in areas of subtropical high pressure, where sinking air prevents rainfall.
• Mid-Latitudes (35°-60°): They are found in the interior of continents, far from moist maritime winds, or in areas surrounded by mountains.

Dry climates are divided into two main types:

• Steppe or Semi-arid (BS)
• Desert (BW)

These are further divided based on latitude:

• Subtropical Steppe (BSh) and Subtropical Desert (BWh)
• Mid-latitude Steppe (BSk) and Mid-latitude Desert (BWk)

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

• Location: Found between 15° and 35° latitude.
• Characteristics: The subtropical steppe gets slightly more rain than the desert, just enough for sparse grasslands to grow. Rainfall in both climates is highly variable, which can cause famine in the steppe regions. Rain often falls in short, intense thundershowers.
• Temperature: Summer temperatures are very high. The highest shade temperature ever recorded, 58°C, was in Al Aziziyah, Libya. The annual and daily ranges of temperature are also high.

Warm Temperate (Mid-Latitude) Climates - C

These climates are found between 30° and 50° latitude, mainly on the eastern and western edges of continents. They typically have warm summers and mild winters.

The four types are:

• Cwa - Humid Subtropical: Dry winter, hot summer.
• Cs - Mediterranean: Dry summer.
• Cfa - Humid Subtropical: No dry season, mild winter.
• Cfb - Marine West Coast: No dry season.

Mediterranean Climate (Cs)

• Location: Occurs around the Mediterranean Sea and on the west coasts of continents between 30°-40° latitude (e.g., Central California, Central Chile).
• Characteristics: These areas are influenced by the subtropical high-pressure belt in summer (making it hot and dry) and the westerly winds in winter (making it mild and rainy). Summer temperatures average around 25°C, and winter temperatures are below 10°C.

Humid Subtropical (Cfa) Climate

• Location: Found on the eastern parts of continents in subtropical latitudes (e.g., eastern USA, southern China, southern Japan).
• Characteristics: Unstable air masses cause rainfall throughout the year, with thunderstorms in summer and frontal precipitation in winter. Summer temperatures average around 27°C, while winter temperatures range from 5°C to 12°C. The daily temperature range is small.

Marine West Coast Climate (Cfb)

• Location: Found poleward of the Mediterranean climate on the west coasts of continents (e.g., Northwestern Europe, west coast of North America, southern Chile).
• Characteristics: The ocean's influence keeps temperatures moderate. Winters are warmer than other locations at the same latitude. Summer temperatures range from 15-20°C and winter temperatures from 4-10°C. Precipitation occurs all year.

Cold Snow Forest Climates (D)

These climates are found in large continental areas in the Northern Hemisphere, between 40° and 70° north latitude.

There are two types:

• Df - Cold climate with humid winter
• Dw - Cold climate with dry winter

Cold Climate with Humid Winters (Df)

• Location: Found poleward of the marine west coast climate.
• Characteristics: Winters are cold and snowy with a short frost-free season. The annual temperature ranges are large, and weather changes can be abrupt. Winters become more severe further poleward.

Cold Climate with Dry Winters (Dw)

• Location: Occurs mainly over Northeastern Asia.
• Characteristics: A strong winter anti-cyclone creates a monsoon-like reversal of wind. Summer temperatures are lower, and winter temperatures are extremely low, often staying below freezing for up to seven months. Precipitation occurs in the summer and is low overall.

Polar Climates (E)

Polar climates exist poleward of 70° latitude and have two types:

• ET - Tundra
• EF - Ice Cap

Tundra Climate (ET)

• Characteristics: Named after its vegetation of low-growing mosses, lichens, and flowering plants. The subsoil is permanently frozen (permafrost). The short growing season and waterlogged soil only support these low-growing plants. Summers have very long periods of daylight.

Ice Cap Climate (EF)

• Location: Occurs over interior Greenland and Antarctica.
• Characteristics: Even in summer, the temperature is below freezing. The area receives very little precipitation. Snow and ice accumulate, and the mounting pressure causes ice sheets to deform and break off, moving as icebergs in the Arctic and Antarctic waters.

Climate Change

The climate we experience today has been prevalent for about 10,000 years, but Earth's climate has always been changing. This is a natural and continuous process.

Evidence of Past Climate Change:

• Geological records: Show alternating glacial (cold) and inter-glacial (warm) periods.
• Geomorphological features: Traces of glacier advances and retreats are visible in high-altitude regions.
• Sediment deposits: Lake sediments reveal past warm and cold periods.
• Tree rings: Provide clues about past wet and dry periods.
• Historical records: Describe variations in climate and their effects on people.

Examples of Past Climate Change:

• Around 8,000 B.C., the Rajasthan desert in India was wet and cool.
• From 1550 to about 1850, Europe experienced a "Little Ice Age."
• In the 10th and 11th centuries, warm and dry conditions allowed the Vikings to settle in Greenland.

Causes of Climate Change

The causes of climate change can be grouped into astronomical and terrestrial categories.

Astronomical Causes:

• Sunspots: These are dark, cooler patches on the sun that appear in cycles. Some meteorologists believe that an increase in sunspots leads to cooler, wetter weather, while a decrease leads to warmer, drier conditions. However, these findings are not statistically significant.
• Millankovitch Oscillations: This theory refers to long-term cycles in the Earth's orbital characteristics, such as the shape of its orbit, the wobble of its axis, and changes in its axial tilt. These changes alter the amount of solar radiation (insolation) the Earth receives.

Terrestrial Causes:

• Volcanism: Volcanic eruptions throw large amounts of aerosols into the atmosphere. These aerosols can block incoming solar radiation, causing the Earth's average temperature to fall for a few years.
• Greenhouse Gases: The most significant cause of modern climate change is the increasing concentration of greenhouse gases in the atmosphere due to human activity, which leads to global warming.

Global Warming

The Earth's atmosphere acts like a greenhouse. It allows incoming short-wave solar radiation to pass through but absorbs most of the outgoing long-wave radiation emitted by the Earth's surface. This process, known as the greenhouse effect, warms the atmosphere.

Greenhouse Gases (GHGs)

The gases that absorb long-wave radiation are called greenhouse gases. The primary GHGs of concern are:

• Carbon dioxide (CO₂)
• Chlorofluorocarbons (CFCs)
• Methane (CH₄)
• Nitrous oxide (N₂O)
• Ozone (O₃)

Key Greenhouse Gases:

• Carbon Dioxide (CO₂): This is the most abundant GHG. Its main source is the combustion of fossil fuels (oil, gas, coal). Forests and oceans act as "sinks" by absorbing CO₂. Deforestation reduces this absorption capacity and increases atmospheric CO₂.
• Chlorofluorocarbons (CFCs): These are products of human activity. When CFCs drift into the stratosphere, they destroy ozone molecules. This has led to a large depletion of ozone over Antarctica, known as the ozone hole, which allows more harmful ultraviolet rays to reach the surface.

To combat this, international efforts like the Kyoto Protocol (proclaimed in 1997) were initiated to reduce GHG emissions.

Effects of Global Warming:

• Rising Sea Levels: Melting glaciers and ice caps, along with the thermal expansion of seawater, cause sea levels to rise. This threatens to inundate large coastal areas and islands.
• Impact on Life: The adverse effects of global warming will negatively impact life-supporting systems around the world.
• Difficulty to Reverse: Once global warming sets in, it will be very difficult to reverse its effects.