L11 Physical Environment and Climate

Physical Environment: Climate vs. Weather

  • Weather

    • Defined as the current state of the atmosphere based on factors such as temperature, humidity, precipitation, wind, and cloud cover.

  • Climate

    • Refers to the long-term (decadal) average patterns of weather in a specific location.

    • Temperature and moisture significantly influence where terrestrial organisms can inhabit.

Solar Radiation

  • Differential across the Planet

    • Variation in solar radiation is not uniform:

    • Temporal Variation

      • The Earth’s revolution around the sun causes changes in solar radiation; the axial tilt additionally affects this differential, creating seasonal variations in climate.

    • Spatial Variation

      • The sun’s rays are most direct at the equator and dispersed over larger areas at the poles.

    • This spatial differential leads to the formation of warm/cold fronts and major storms, essentially driving atmospheric circulation.

Atmospheric Circulation

  • Mechanics

    • The tropics receive the most solar radiation, heating the surface and causing air to rise.

    • As air rises, it cools and decreases its capacity to hold water vapor, leading to condensation and cloud formation.

    • The cooled air then moves towards the poles, eventually sinking back to the surface.

    • This continuous process is termed atmospheric circulation.

Atmospheric Circulation Cells

  • Types of Cells

    • Polar Cells

    • Formed by cold air subsiding at the poles, resulting in higher atmospheric pressure.

    • Ferrell Cells

    • Driven by opposing forces between Hadley and Polar cells, aligning with areas of low and high atmospheric pressure.

    • Hadley Cells

    • Formed by the uplift of warm air at the equator, resulting in lower atmospheric pressure.

Climate Zones

  • Atmospheric circulation cells give rise to three major climate zones:

    1. Tropical Zone

    2. Temperate Zone

    3. Polar Zone

Prevailing Winds

  • Wind patterns flow from regions of high pressure to low pressure and are influenced by Earth’s rotation.

  • The Coriolis Effect induces an apparent deflection of winds:

    • Clockwise in the northern hemisphere.

    • Counterclockwise in the southern hemisphere.

Ocean Circulation

  • Influence of Winds

    • Prevailing winds result in surface currents in the oceans.

    • Deep-water movement also contributes to ocean currents.

  • Key Processes

    • Tropical waters in the Atlantic move towards the poles, cooling and increasing in salinity as they freeze, which leads to higher water density and downward movement (deep ocean currents).

    • Upwellings in the Pacific and Indian Oceans cause nutrient-rich, deep water to rise and warm.

  • The combination of surface and deep ocean currents forms the Great Ocean Conveyor Belt.

Global Temperature Patterns

  • Global temperature is chiefly influenced by:

    • Solar Radiation

    • Oceanic Currents (both surface and deep currents)

    • Terrestrial Topography (affected by air density)

Global Precipitation Patterns

  • Influences on global precipitation include:

    • High and Low Pressure Cells (global circulation cells).

    • Anticipated desert regions near 30° latitude due to climatic conditions.

    • Mountain Ranges lead to forced uplift of air, cooling it and influencing precipitation.

Climate Patterns - Regional Influences

  • Several factors affect climate on a regional scale:

    • Solar Radiation

    • Proximity to Water (oceans or large lakes)

    • Mountain Influence (elevation)

    • Vegetation Types

Proximity to Water

  • Heat Capacity: Water has a higher heat capacity than land; it can absorb more energy without significant temperature changes.

  • Areas closer to water experience less dramatic changes in seasonal climate.

Mountains and Climate Variability

  • Mountains create diverse climates through elevation changes, with increased precipitation at higher altitudes.

  • Rain Shadows

    • Areas on the leeward side of mountains experience lower precipitation, while the windward side receives higher moisture levels.

Thermal Inversions (Heat Bands)

  • Occur when cold air becomes trapped in valley bottoms at night.

  • Compression against hillsides can heat air, creating temperature differentials.

Vegetation's Role in Climate

  • Vegetation impacts local climate through:

    • Surface Energy Exchange

    • Albedo: The degree to which solar radiation is reflected by a surface.

    • Sensible Heat Loss: Energy lost via convection and conduction due to winds.

    • Latent Heat Loss: Energy lost from water vapor during transpiration (water released by leaves).

Chemical Environment - Water

  • 1. Salinity

    • Refers to the concentration of salt in water.

    • Affects organisms' ability to absorb water and can hinder metabolic activities at extreme levels.

  • 2. Acidity and Alkalinity

    • Influences water pH.

    • Organisms display limited tolerance to varying pH levels; shifts in pH can directly affect metabolic processes.

  • 3. Availability of Oxygen

    • Essential for life; absence of oxygen leads to dead zones in water bodies.

    • Hypoxic Conditions: Refers to low oxygen situations that can impact living organisms.

Biomes

  • Definition

    • Biomes are extensive biological communities shaped by both physical and chemical environmental factors.

Terrestrial Biomes

  • Characterized principally by dominant vegetation types.

  • Reflect global precipitation and temperature patterns.

  • Can lead to convergent evolution, where unrelated organisms develop similar adaptations to their environments.

Ocean Zones

  • Cover 71% of Earth’s surface.

  • Organisms are less uniformly distributed compared to terrestrial environments.

  • Ocean zones are categorized based on their physical location in relation to shorelines and the ocean floor.

  • Organism distribution is limited by factors such as temperature, light availability, water depth, and substrate characteristics.