WJEC GCSE Geography Theme 5

Climate Change during the Quaternary Period

• Definitions of Weather and Climate

  • Weather: The atmospheric conditions at a particular place and time, including measurements of temperature, precipitation, wind, and sunshine.

  • Climate: The average weather conditions measured over a long period of time (typically at least $30$ years).

  • Climate Change: A large-scale, long-term shift in the Earth's weather patterns, especially in average temperatures.

• Historical Context of the Quaternary

  • Climate change is a natural phenomenon. Over the last $11,000$ years, the Earth's surface temperature has fluctuated significantly.

  • Medieval Warm Period: A period of warmer temperatures that allowed the Vikings to colonize Greenland due to ice-free seas.

  • Little Ice Age: A notably colder period in northern Europe where temperatures were, on average, $1$ to $1.5\,^\circ\text{C}$ colder than modern levels.

  • Glacials and Interglacials: Over the past $400,000$ years, the Earth has experienced natural cycles. Glacials are periods of cool temperatures below $15\,^\circ\text{C}$ (global average), while interglacials are periods of relative warmth represented by narrow peaks in temperature records.

Evidence for Climate Change

• Historical and Archaeological Evidence

  • Fossils: Discovery of plant and animal remains in locations where they would be unable to survive in current conditions.

  • Glaciation Findings: Evidence of past glacial activity in regions that are now entirely free of ice.

  • Historical Records: Sources include diary extracts, crop yield records, and paintings. For instance, paintings documenting "ice fairs" on the River Thames provide evidence of the Little Ice Age.

• Scientific and Quantitative Evidence

  • Ice Cores: Samples from the Antarctic show that atmospheric concentrations of carbon dioxide ($CO_2$) and methane have fluctuated over the past $420,000$ years.

  • Dendrochronology (Tree Rings): The study of tree ring growth patterns reveals that growing seasons have varied in length throughout history.

  • Keeling Curve: Scientists have measured $CO_2$ levels accurately since $1958$ in Hawaii (selected due to low atmospheric pollution). Measurements show an increase from approximately $315\,\text{ppm}$ in $1960$ to nearly $380\,\text{ppm}$ by $2000$.

  • Met Office Measurements: Global average temperatures have increased by $0.6\,^\circ\text{C}$ over the past $100$ years.

  • Arctic Sea Ice: Records from $1979$ to $2016$ show a decline in March sea ice extent from approximately $16.5\,\text{million}\ km^2$ to roughly $14.5\,\text{million}\ km^2$.

  • Glacial Retreat: The Pasterze Glacier in Austria has retreated by approximately $8\,km$ in the last $160$ years.

  • Biological Shifting: Shifting seasons have altered the migration patterns of birds and insects.

Causes of Climate Change

• The Carbon Cycle

  • Carbon Stores: In the short term, carbon is stored in the atmosphere, oceans, and biosphere. Long-term storage occurs in fossil fuels (coal, gas, and oil).

  • Carbon Flows: Movement between stores occurs through processes like photosynthesis (plants absorbing $CO_2$ to create glucose), respiration (plants and animals releasing $CO_2$), and decomposition (bacteria/fungi returning carbon to the atmosphere).

  • Human Impact: Atmospheric $CO_2$ levels are approximately $30\,\%$ higher today than they were $150$ years ago due to human interference in the cycle.

• The Greenhouse Effect

  • Natural Greenhouse Effect: A vital natural process where naturally occurring greenhouse gases (primarily carbon dioxide) absorb long-wave heat radiation from the Earth's surface, preventing it from escaping into space.

  • Enhanced Greenhouse Effect (Global Warming): Human activities increase the concentration of these gases, leading to excessive warming. Sources include:

    • Burning Fossil Fuels: Releases stored carbon as $CO_2$.

    • Deforestation: Reduces the number of trees available to absorb $CO_2$ via photosynthesis.

    • Landfill Sites: Decomposition of waste produces methane ($CH_4$).

    • Farming: Livestock, such as cattle, release methane as a byproduct of digestion.

• Natural Causes and Milankovitch Cycles

  • Solar Radiation: Variations in the output of energy from the Sun.

  • Milankovitch Cycles: Explained by Milutin Milankovitch, these involve long-term shifts in Earth's orbit and rotation:

    • Orbit (Eccentricity): The Earth's orbit shifts from circular to elliptical every $100,000$ years.

    • Tilt (Obliquity): The angle of the axis varies between $22.1^\circ$ and $24.5^\circ$ every $41,000$ years.

    • Wobble (Precession): The Earth wobbles on its axis once every $26,000$ years.

  • Volcanic Activity: Large eruptions eject dust and sulphur dioxide ($SO_2$) into the stratosphere. These form aerosols that scatter sunlight, causing Global Cooling.

  • Case Study: Mount Pinatubo (1991): Erupted on June $15$, $1991$, in the Philippines. It ejected $10\,km^3$ of ash and $15$ million tonnes of $SO_2$. The resulting sulphuric acid droplets caused mean world temperatures to decrease by $0.5\,^\circ\text{C}$.

Global Circulation and Weather Hazards

• Global Circulation System

  • Driven by heat at the Equator: Insolation (solar radiation) heats the air, causing it to rise and create low pressure.

  • Rising air travels north and south at the tropopause, cooling and descending at roughly $30^\circ\text{N}$ and $30^\circ\text{S}$, creating high pressure.

  • Intertropical Convergence Zone (ITCZ): A zone at the equator where trade winds meet and air rises.

• Tropical Storms (Low-Pressure Hazards)

  • Known as hurricanes, typhoons, or cyclones. They develop over tropical seas with temperatures above $27\,^\circ\text{C}$.

  • Mechanism: The Coriolis Effect, caused by Earth's rotation, makes the rising air spiral. Storms move westward, reaching speeds over $120\,km/h$. Heavy rainfall, storm surges (water pushed against a coast by low pressure/winds), and flooding occur.

  • Distribution: $80$–$100$ storms form yearly. Northern hemisphere peak is September; Southern hemisphere season is November–April as the ITCZ migrates.

  • Case Study: Cyclone Idai (March 2019): Hit Beira, Mozambique. It was the deadliest tropical cyclone recorded in the South-West Indian Ocean. Impacts included a $3.5$–$4\,m$ storm surge, $90\,\%$ destruction of Beira, $843$ deaths, $185,000$ homeless, $6,000$ cholera cases, and a cost of over $\$2$ billion.

• Droughts and Heatwaves (High-Pressure Hazards)

  • High Pressure: Descending air leading to dry weather and light winds.

  • Heatwave: At least $4.5\,^\circ\text{C}$ above average temperature for two or more days. European heatwaves are ten times more likely now than before $2000$.

  • Drought: Lack of precipitation over months or years. Severely affected areas include Australia, Brazil, the Sahel, China, India, and the Mediterranean.

  • Case Study: California Drought (2012–2019): High pressure blocked Pacific winter rainfall. Impacts included $\$2$ billion in lost farm production, $17,100$ agricultural job losses, loss of hydroelectric power, and domestic water shortages. Response included compulsory water restrictions ($25\,\%$ reduction) and $\$5$ billion investment in groundwater storage.

Weather and Climate in the UK

• Climate Drivers

  • Temperate Maritime Climate: Characterized by absence of extremes, mild winters ($23.5^\circ$ to $66.5^\circ$ latitude).

  • Factors: Latitude (south is warmer), Altitude ($1\,^\circ\text{C}$ drop per $100\,m$), Aspect (south-facing slopes are warmer), and Ocean Currents (North Atlantic Drift/Gulf Stream).

  • Jet Stream: High-speed winds at $30,000$ feet that drive weather patterns.

• Air Masses Affecting the UK

  • Polar Maritime (North-Westerly): Cool and showery.

  • Tropical Maritime (South-Westerly): Mild and wet.

  • Tropical Continental (South-Easterly): Hot and dry.

  • Polar Continental (Easterly): Hot summer, cold winter.

  • Arctic (Northerly): Cold with snow.

• UK Weather Systems

  • Depressions (Low Pressure): Cause cloudy, rainy, and windy conditions. They feature warm and cold fronts where air masses meet and rise.

  • Anticyclones (High Pressure): Stable conditions with low wind. Summer brings heatwaves; winter brings clear skies, ice, and fog.

Urban Microclimates

• Urban Heat Island Effect: Cities are warmer than rural areas because materials like concrete and tarmac absorb heat by day and release it at night. This can create an anomaly of up to $5\,^\circ\text{C}$.

• Precipitation: Extra urban heat causes air to rise, leading to convectional rainstorms.

• Winds: Buildings can block or channel wind, generally making cities less windy than the countryside.

Ecosystem Processes and Biomes

• Biome Distribution and Scale

  • Ecosystem: A community of biotic (living) and abiotic (non-living) components. Large-scale ecosystems are called biomes.

  • Key Factors: Rainfall (deserts receive <25\,cm/year) and Temperature.

  • Rainforest: Found near the equator; hot/wet year-round; continuous growth.

  • Temperate Deciduous Forest: Trees lose leaves in autumn to conserve energy.

  • Coniferous Forest (Taiga): Found at $50^\circ$–$60^\circ\text{N}$; needle-like leaves to survive frost and moisture loss.

• Ecosystem Development and Cycles

  • Succession: Starts with hardy pioneer species colonizing bare ground. Given time, a dominant species (like oak) invades. The final stable state is the Climax Community.

  • Nutrient Cycle: Nutrients move from soil to plants to animals and back. They can be lost via leaching (washing out of soluble nutrients).

  • Food Web: A system of interlocking food chains. Producers (plants) convert sun energy; Consumers (herbivores and carnivores) transfer energy. Energy is lost at each level through respiration and movement.

• Rainforest Ecosystem Case Study

  • Climate: >2000\,mm rain, avg $25\,^\circ\text{C}$.

  • Structure: Five layers (Emergents, Canopy, Undercanopy, Shrub layer, Ground layer).

  • Nutrient Cycle: Rapid decomposition in hot/damp conditions. $80\,\%$ of nutrients stored in biomass, $20\,\%$ in soil.

  • Water Cycle: High rates of transpiration and interception; drives regional rainfall.

  • Carbon Cycle: Tropical forests store more carbon per unit area than any other ecosystem; clearing them releases $30\%$–$60\,\%$ of that carbon.

• Savannah Grassland Case Study

  • Distribution: $5^\circ$–$15^\circ$ N/S of the equator (e.g., Brazil, Tanzania, India).

  • Climate: Marked wet and dry seasons; temperatures $23$–$28\,^\circ\text{C}$.

  • Vegetation: Scattered trees (acacia, baobab); xerophytic (drought-resistant) and pyrophytic (fire-tolerant).

  • Nutrient Cycle: Shorter growing season than rainforest; termites are key recyclers; mounds become nutrient hotspots.

Human Impact and Sustainable Management

• Human Modifications

  • Amazon: Drains $5.5\,\text{million}\ km^2$. In $50$ years, nearly $20\,\%$ has been destroyed for cattle ranching, soy farming, and mining (Carajás iron-ore mine has $7.2$ billion tonnes). Infrastructure like the Tucuruí dam or the $900\,km$ railway to São Luis contributes to loss.

  • Desertification: In the Sahel, rapid population growth ($3\,\%$ annual increase) leads to overgrazing and overcultivation, resulting in soil fertility loss and gully erosion.

• Renewable Energy Case Study: Gwynt y Môr

  • Offshore wind farm $13\,km$ from North Wales coast. Cost $\pounds 2$ billion; features $160$ turbines ($150\,m$ high).

  • Benefits: Supplies $400,000$ households ($30\,\%$ of Welsh homes); prevents $1.7$ million tonnes of $CO_2$ release annually; created $100$ maintenance jobs.

  • Objections: Visual impact on Snowdonia National Park ("visual eyesore"); potential harm to migrating birds.

• Sustainable Management Solutions

  • Agro-forestry: Growing trees and crops together (e.g., in the Amazon or Sahel).

  • Forest Reserves: Protecting core areas (e.g., Alto Maués National Park, Brazil) with buffer zones around them.

  • Great Green Wall: A project to plant a $15\,km$ wide, $8000\,km$ long belt of trees across Africa. In Senegal, $11$ million trees are planted and $15\,\%$ is complete.

  • Selective Logging: Removing only specific trees (FSC certified).

  • Plagioclimax: A plant community resulting from human actions (like introducing rabbits to sand dunes) that prevent a natural climax from being reached.

Sand Dune Ecosystem (Small-Scale Case Study)

• Transect: Ecosystem follows a progression from Embryo dunes (pioneer species) to Fore/Yellow dunes (marram grass) to Fixed/Grey dunes, and finally a Climax Community (birch/oak woodland).

• Human Threats: Recreation (trampling marram grass causes "blow-outs"), Economic grazing (dung enriches soil/decreases diversity), and development for tourism.

• Management: Protective fencing, boardwalks, marram planting, and sand traps.