Weather and Climate: Comprehensive Study Guide

1. Concept of Weather and Climate

To understand our atmospheric environment, we must distinguish between weather and climate. Though closely related, they differ primarily in the dimension of time.

• Weather refers to the atmospheric condition of a specific place at a particular point in time. It is highly variable and can change from hour to hour, day to day, or even minute to minute. For example, a rainy morning can turn into a hot, sunny afternoon.
• Climate is the average weather conditions of a large area recorded over a long period, typically 30 to 35 years (according to the World Meteorological Organization). Climate provides a generalized picture of the atmospheric expectations of a region.

2. Elements of Weather and Climate

The physical properties of the atmosphere that define both weather and climate include:

• Temperature: The degree of hotness or coldness of the atmosphere. Measured in Celsius (°C) or Fahrenheit (°F).
• Atmospheric Pressure: The force exerted by the weight of the air above the Earth's surface. Measured in millibars (mb) or hectopascals (hPa).
• Wind: Air in motion, characterized by its speed and direction.
• Humidity: The amount of water vapor present in the atmosphere. It can be expressed as absolute humidity or relative humidity (percentage).
• Precipitation: Any form of moisture falling from the atmosphere to the Earth's surface (rain, snow, sleet, hail).
• Cloud Cover: The fraction of the sky covered by clouds, measured in oktas (eighths).
• Sunshine: The duration and intensity of solar radiation reaching the surface.

3. Measuring and Recording Weather Parameters

Meteorological stations use specialized instruments to accurately record weather elements. These instruments must be kept in standard conditions, often inside or near a Stevenson Screen (a white wooden box with louvered sides designed to protect thermometers from direct solar radiation while allowing air to circulate freely).

4. Factors Controlling Weather and Climate

Several global and local factors control how elements of weather and climate vary across the Earth:

• Latitude (Solar Radiation): The primary control of temperature. Equatorial regions receive direct vertical rays, making them hot, while polar regions receive oblique rays, making them cold.
• Altitude (Elevation): Temperature decreases with altitude at the Normal Lapse Rate of approximately 6.5°C per 1000 meters (or 1°C per 160 meters) because the atmosphere is heated from below by terrestrial radiation.
• Continentality (Distance from the Sea): Land heats up and cools down faster than water. Coastal areas experience moderate climates (maritime), while inland regions experience extreme temperatures (continental).
• Ocean Currents: Warm currents (e.g., Gulf Stream) raise temperatures of coastal areas, while cold currents (e.g., Benguela, Canary) lower temperatures and can lead to the formation of coastal deserts.
• Winds and Air Masses: Large bodies of air (air masses) carry the characteristics of their source regions. For instance, the Tropical Continental (cT) air mass brings hot, dry, and dusty conditions (Harmattan) to West Africa, while the Tropical Maritime (mT) air mass brings warm, moist conditions and rain.
• Local Relief/Aspect: Windward sides of mountains receive heavy orographic rainfall, while leeward sides (rain shadow areas) remain dry. Also, slopes facing the equator receive more solar radiation than those facing away.

5. Climatic Classification: Greek and Köppen Systems

A. The Greek (Classical) System

Based entirely on latitude and temperature, the ancient Greeks divided the world into three zones:

• Torrid (Tropical) Zone: Located between the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S). Extremely hot all year round.
• Temperate Zone: Located between the Tropics and the Polar circles (23.5° to 66.5° North and South). Mild, with distinct seasons.
• Frigid (Polar) Zone: Located beyond the Arctic and Antarctic circles (66.5° to 90° North and South). Permanently cold and frozen.
• Limitation: It is too simplistic and ignores critical factors like precipitation, vegetation, and local geography.

B. The Köppen Climatic Classification System

Developed by Wladimir Köppen in 1884, this quantitative and empirical system is based on the close relationship between climate, temperature, precipitation, and vegetation distribution. He used uppercase letters (A, B, C, D, E, H) for major groups:

• A: Tropical Rainy Climates (Average temperature of coldest month is above 18°C. High precipitation).
• B: Dry (Arid and Semiarid) Climates (Evaporation exceeds precipitation).
• C: Warm Temperate Rainy (Mesothermal) Climates (Mild winters).
• D: Cold Snowy Forest (Microthermal) Climates (Severe winters).
• E: Polar Climates (Warmest month is below 10°C).
• H: Highland Climates (Dominated by altitude; added later).

These groups are further subdivided using lowercase letters based on the seasonality of precipitation:

• f: Wet all year (no dry season)
• m: Monsoon climate (short dry season, heavy rainfall)
• w: Winter dry season
• s: Summer dry season
• S: Steppe (semi-arid)
• W: Desert (arid)

Summary of Major Köppen Climatic Subtypes

• Af (Equatorial Climate): Found in the Amazon Basin, Congo Basin, and coastal West Africa. High temperature (27°C average) and heavy, convectional rainfall throughout the year. Dense tropical rainforests.
• Am (Tropical Monsoon): Found in parts of India, Southeast Asia, and coastal West Africa. Characterized by seasonal wind reversals and heavy monsoon rains.
• Aw (Tropical Wet and Dry / Savanna): Surrounds equatorial regions. Has a distinct dry winter season. Supports savanna grassland vegetation.
• BWh (Hot Desert Climate): Found on the western coasts of continents between latitudes 15° and 30° N/S (e.g., Sahara, Kalahari, Mojave). Very high daytime temperatures and extremely low precipitation.
• Cs (Mediterranean Climate): Found on western coasts in mid-latitudes (30°-45° N/S). Characterized by hot, dry summers and mild, wet winters.

6. The Basic Science of Climate Change

A. Definition

Climate change refers to significant, long-term shifts in global or regional climate patterns, particularly changes in temperature, precipitation, wind patterns, and ocean currents over several decades or longer.

B. Causes of Climate Change

Climate change is driven by both natural and human (anthropogenic) factors:

• Natural Causes: Volcanic eruptions (releasing dust and aerosols), solar radiation output variations, and changes in the Earth's orbit (Milankovitch cycles).
• Anthropogenic (Human) Causes: These are the primary drivers of modern global warming. They include:
  • Greenhouse Gas (GHG) Emissions: Burning of fossil fuels (coal, oil, natural gas) releases Carbon Dioxide (CO2), Methane (CH4), Nitrous Oxide (N2O), and Chlorofluorocarbons (CFCs) into the atmosphere. These gases trap heat (the Greenhouse Effect).
  • Deforestation: Cutting down forests reduces the Earth's capacity to absorb CO2 through photosynthesis.
  • Industrialization and Agriculture: Industrial processes and livestock farming (producing methane) significantly increase atmospheric warming.

C. Effects of Climate Change

• Rising Sea Levels: Caused by the thermal expansion of seawater and the melting of polar ice caps and glaciers, leading to coastal flooding.
• Extreme Weather Events: Increased frequency and severity of hurricanes, droughts, heatwaves, and intense floods.
• Desertification: Encroachment of desert-like conditions into formerly fertile lands (especially in regions like the African Sahel).
• Loss of Biodiversity: Disruption of ecosystems and habitats leading to the extinction of vulnerable plant and animal species.

D. Remedies and Mitigation Strategies

• Afforestation and Reforestation: Planting new trees and restoring depleted forests to act as carbon sinks.
• Adoption of Renewable Energy: Transitioning away from fossil fuels to wind, solar, hydro, and geothermal energy.
• Reduction of Carbon Footprint: Improving energy efficiency, using public transit, and supporting eco-friendly practices.
• International Agreements: Global compliance with treaties like the Paris Agreement and the Kyoto Protocol to limit global warming below 1.5°C.