Exam Study Notes

Cloud

• Urban areas experience thicker and up to 10% more frequent cloud cover than rural areas.
• This is attributed to:
  • Convection currents caused by higher temperatures.
  • A greater abundance of condensation nuclei.

Precipitation

• Mean annual precipitation is 5-15% higher in urban areas.
• Days with less than 5 mm of rainfall are 5-15% greater in urban areas.
• Reasons are similar to cloud formation (thermals, condensation nuclei).
• Strong thermals in urban areas increase:
  • Thunder likelihood by 25%.
  • Hail occurrence by up to 400%.
• Higher urban temperatures can change snow to sleet.
• They limit the number of days with snow on the ground by up to 15%.
• Fog frequency, length, and intensity are much greater in urban areas, especially under anticyclonic conditions.
  • Winter fog may be up to 100% more frequent.
  • Summer fog may be up to 25% more frequent.
  • Caused by condensation nuclei concentration.

Atmospheric Composition

• Dust particle concentration may be 3-7 times higher in cities.
• Burning fossil fuels, industrial processes, and car exhausts release impurities.
• Urban areas can have:
  • Up to 200 times more sulphur dioxide.
  • 10 times more nitrogen oxide (acid rain components).
  • 10 times more hydrocarbons.
  • Twice as much carbon dioxide.
• Pollutants increase cloud cover and precipitation.
• They cause smog, higher temperatures, and reduced sunlight.

Forest and Lake Microclimates

• Different land surfaces create distinct local climates.
• Further research is needed to confirm some microclimate characteristics.

Forest Microclimates (Coniferous and Deciduous)

• Incoming Radiation and Albedo:
  • Much radiation is absorbed and trapped.
  • Albedo:
    • Coniferous: 15%.
    • Deciduous: 25% (summer), 35% (winter).
    • Desert scrub: 40%.
• Temperature:
  • Small diurnal range due to canopy's blanket effect.
  • Forest floor is protected from direct sunlight.
  • Some heat lost by evapotranspiration.
• Relative Humidity:
  • Higher during daytime and in summer, especially in deciduous forests.
  • Evapotranspiration depends on day length, leaf surface area, wind speed, etc.
• Precipitation:
  • Heavy rain can be caused by high evapotranspiration rates (e.g., tropical rainforests).
  • 30-35% of rain is intercepted on average; more in deciduous woodland in summer.
• Wind Speed and Direction:
  • Trees reduce wind speeds, particularly at ground level.
  • Trees are often planted as windbreaks.
  • Trees can produce eddies.

Water Surface Microclimates (Lake, River)

• Incoming Radiation and Albedo:
  • Less insolation is absorbed and trapped.
  • Albedo may be over 60%, higher than overseas/oceans, especially on calm days.
• Temperature:
  • Small diurnal range due to water's high specific heat capacity.
  • Cooler summers and milder winters.
  • Lakesides have a longer growing season.
• Relative Humidity:
  • Very high, especially in summer due to high evaporation rates.
  • Air is humid.
• Precipitation:
  • If air rises, it can be unstable, producing cloud and rain.
  • Amounts may not be great due to fewer condensation nuclei.
  • Fogs form in calm weather.
• Wind:
  • Wind may be strong due to reduced friction.
  • Large lakes can create land and sea breezes.

Weather Maps and Forecasting in Britain

• A weather map or synoptic chart shows weather for a specific area at a specific time.
• It results from collecting and collating data at numerous weather stations.
• Data are refined using computers and plotted using international weather symbols.
• Weather maps serve different purposes and scales.

Types of Weather Maps

1. Daily Weather Map
   • Gives a simplified impression of the weather.
2. Synoptic Map
   • Shows selected meteorological characteristics for specific stations.
   • Station model includes:
     • Temperature.
     • Pressure.
     • Cloud cover.
     • Present weather (e.g., precipitation type).
     • Wind direction.
     • Wind speed.
3. Detailed Maps from the Meteorological Office
   • Show finite detail, e.g., cloud amounts at different levels, dew point temperatures, barometric tendency.

• Weather forecasters determine the speed and direction of air masses and fronts.
• They predict the type of weather these movements will bring.
• Satellite images are crucial for short-term weather trend prediction.
• Forecasting uses satellites, radar, and computers to model upper and surface air conditions in 3D.
• Atmospheric complexity and unpredictability can still surprise forecasters.
• Meteorological information is a sample, not a total picture, risking anomalies.

Measures of Dispersion

• Mean climatic figures are averages over a 30-year timescale.
• The range or degree of variation from the mean is often significant.
• Three statistical techniques measure dispersion:
  • The range.
  • The interquartile range.
  • The standard deviation.
• These techniques apply to geography where the mean alone may be misleading.
• Using quantitative techniques does not guarantee objective interpretation; appropriate methods must be chosen.

Range

• Calculates the difference between the highest and lowest values.
• Example: London's annual temperature range is 14°C (July 18°C, January 4°C).
• Emphasises extreme values and ignores the distribution of the rest.

Interquartile Range

• Consists of the middle 50% of values in a distribution, 25% each side of the median.
• Shows how closely values are grouped around the median.
• Easy to calculate, unaffected by extreme values, useful for comparing similar data sets.

Climatic Change

• Climates constantly change at all scales and timescales.
• There have been surges of change over time.

Evidence of Past Climatic Changes

• Rocks formed under different climatic conditions.
  • Coal formed under hot, wet tropical conditions.
  • Sandstones laid down during arid times.
  • Limestones accumulated in warm seas.
  • Glacial deposits left by retreating ice sheets.
• Fossil landscapes produced by geomorphological processes that no longer operate.
  • Glacially eroded highlands.
  • Granite tors on Dartmoor.
  • Wadis formed during wetter periods in deserts.
• Evidence of changes in sea-level and lake levels.
• Vegetation belts have shifted.

Pollen Analysis

• Shows which plants were dominant at a given time.
• Each plant species has a distinctively shaped pollen grain.
• Grains trapped in peat form a representative vegetation sample, indicating past climatic conditions.

Dendrochronology (Tree-Ring Dating)

• Determines tree age by coring the trunk.
• Tree growth is rapid in spring, slower in autumn, stops in winter.
• Each year's growth is shown by a ring.
• Ring size reflects climatic changes (warm, wet = larger ring).

Chemical Methods

• Study of oxygen and carbon isotopes.
• Isotopes are forms of an element with different atomic weights.
• O-16 vaporizes more readily; O-18 condenses more easily.
• Warm, dry periods leave water enriched with O-18, preserved in polar ice.
• Colder, wetter periods have higher levels of O-16 in ice.

Carbon-14 Dating

• C-14 is a radioactive carbon isotope.
• Plants take in carbon during the carbon cycle.
• C-14 decays at a known rate and is compared with non-decaying C-12.
• Scientists can date organic matter up to 50,000 years old with ± 5 % error.

Historical Records

• Cave paintings of animals in different regions.
• Vine cultivation in southern England between AD 1000 and 1300.
• Changes in grave digging depth in Greenland related to permafrost.
• Fairs held on the frozen River Thames in Tudor times.
• Measurement of alpine glacier and polar sea-ice advances and retreats.

Causes of Climatic Change

• Multiple factors contribute to climatic change over different timescales.

Variations in Solar Energy

• Sunspot activity cycles may affect climate - high temperatures on Earth appear to correlate with maximum sunspot activity.

Astronomical Relationships

• Milankovitch cycles (changes in Earth's orbit, tilt, wobble) cause variations in solar radiation.

Changes in Oceanic Circulation

• Affect heat exchange between oceans and atmosphere.
• Long-term effects: Quaternary ice age current direction changes.
• Short-term effects: El Niño.
• North Atlantic Drift as a conveyor belt; shutdown could dramatically cool climate.

Meteorites

• Meteor impacts can cause extinction events.
• Reduce incoming radiation, deplete ozone, lower global temperatures.

Volcanic Activity

• Lowers world temperatures after large eruptions (Mount Pinatubo, Krakatoa).
• Increased dust particles absorb and scatter incoming radiation.
• May temporarily offset the greenhouse effect.
• Increases precipitation due to hygroscopic nuclei.

Plate Tectonics

• Redistributes land masses and affects climate long-term.
• 'Drifting' land masses enter different latitudes.
• Fold mountains lead to colder climates and act as atmospheric circulation barriers (Tibetan Plateau creating Asian monsoon).

Atmospheric Composition

• Gases change with volcanic eruptions.
• Concern over buildup of CO₂ and other greenhouse gases.
• Use of aerosols and release of CFCs deplete ozone.

Climatic Change in Britain

• Climate has changed in the long, Quaternary, and short terms.
• Following the 'little ice age,' temperatures generally increased to a peak in about 1940.
• After that time, summers became cooler and wetter, springs later, autumns milder, winters unpredictable.
• Since the 1980s, there has been a considerable warming, with eight of the ten warmest years on record in the last decade.
• Increased variations from the norm add evidence to the concept of global warming.

Case Study: Short-term and Long-term Climatic Changes

A. Short-term change: El Niño and La Niña

• Oceans influence world climates due to their heat storage capacity. Ocean temperature changes have large effects on weather patterns of adjacent land masses.
• Interactions between the ocean and atmosphere have become a major area of scientific study.
• El Niño and La Niña events occur periodically in the Pacific Ocean, representing an ocean-atmosphere interrelationship.

Normal Atmospheric Conditions

• Pressure rises over the eastern Pacific Ocean (off the coast of South America) and falls over the western Pacific Ocean (towards Indonesia and the Philippines).
• Descending air over the eastern Pacific gives clear, dry conditions (Atacama Desert in Peru).
• Warm, moist ascending air over the western Pacific gives heavy convectional rainfall.
• Air movement creates the Walker circulation cell.
  • Upper air moves from west to east.
  • Surface air moves from east to west as trade winds.
• Trade winds:
  • Push surface water westward.
  • Sea-level in the Philippines is usually 60 cm higher than in Panama and Colombia.
  • Allow water flowing westward as the equatorial current to remain near the ocean surface, where it gradually heats.
  • The western Pacific has the world's highest ocean temperature, usually above 28°C.
• As warm water is pushed away from South America, it is replaced by an upwelling of colder, nutrient-rich water.
  • Colder water lowers temperatures, sometimes to below 20°C, but provides plankton for Peru's fishing industry.

El Niño

• An El Niño event, scientifically referred to as an El Niño Southern Oscillation (ENSO), occurs on average every three to four years.
• It appears just after Christmas and usually lasts for 12-18 months.
• There is a reversal in the equatorial Pacific region in pressure, precipitation, winds, and ocean currents, contrasting normal conditions.

Changes During El Niño

• Pressure rises over the western Pacific and falls over the eastern Pacific.
• The ITCZ migrates southwards.
• Trade winds weaken or reverse in direction.
• Descending air (now over South-east Asia) gives much drier conditions.
• Air over the eastern Pacific is now rising, giving much wetter conditions.
• Surface water tends to be pushed eastwards, so sea-level in South-east Asia falls while it rises in tropical South America.
• Surface water temperatures in excess of 28°C extend much further eastwards.
• The upwelling of cold water off South America is reduced, allowing sea temperatures to rise by up to 6°C.
• Warmer water in the eastern Pacific lacks oxygen, nutrients, and plankton, which has an adverse effect on Peru's fishing industry.

Global Impacts of El Niño

• Drier conditions in South-east Asia and wetter conditions in South America.
• Severe droughts in the Sahel and southern Africa, as well as across the Indian subcontinent
• Extremely cold winters in central North America, and stormy conditions with floods in California.
• Exceptionally wet, mild, and windy winters in Britain and north-west Europe.

La Niña

• La Niña, or 'little girl,' has climatic conditions that are the reverse of those of El Niño.
• Its occurrence is less frequent and, consequently, effects are harder to predict due to less data.

Changes During La Niña

• Low pressure over the western Pacific becomes even lower, and high pressure over the eastern Pacific becomes even higher, compared to normal conditions.
• Rainfall increases over South-east Asia.
• Drought conditions occur in South America.
• Trade winds strengthen due to the increased pressure difference.
• The stronger trade winds:
  • Push large amounts of water westwards, giving a higher than normal sea-level in Indonesia and the Philippines.
  • Increase the equatorial undercurrent and significantly enhance the upwelling of cold water off the Peruvian coast.

Global Impact of La Niña

• Linked with increased hurricane activity in the Caribbean.
• Can interrupt the jet stream over Britain, resulting in stormier, wetter, and cooler conditions.