Geography C1

At the Equator

• The Earth's surface is warmed by the Sun at the equator. The Earth transfers this heat to the air, which then rises because it is hot. This results in a low-pressure belt with rising air, rain and clouds.
• The rising air cools and moves away from the equator towards 30o north and south.

At 30 degrees north and south

• The Earth's surface is warmed by the Sun at the equator. The Earth transfers this heat to the air, which then rises because it is hot. This results in a low-pressure belt with rising air, rain and clouds.
• The rising air cools and moves away from the equator towards 30o north and south.

60 degree north and south

• The Earth's surface is warmed by the Sun at the equator. The Earth transfers this heat to the air, which then rises because it is hot. This results in a low-pressure belt with rising air, rain and clouds.
• The rising air cools and moves away from the equator towards 30o north and south

At the poles

• At the poles, cool air sinks and forms a high-pressure belt which moves as surface winds back towards the equator.

The climate is always changing. Below is a summary of how the climate has changed during the Quaternary period (2.6 million years ago - present day):

• There have been regular cold glacial periods (lasting about 100,000 years) and warmer interglacial periods (lasting about 10,000 years).
• The most recent glacial period finished about 15,000 years ago, but there is no sign of this interglacial period ending.
• In the last century, global temperatures have risen sharply. This is a form of climate change called global warming.

The Medieval Warm Period happened from 900-1300.

• Harvest records show that people were able to produce large amounts of grapes during this time.

The Little Ice Age happened from 1500-1700.

• 17th-century paintings show an event called the London Frost Fairs that happened when the River Thames was frozen over.
• Historical records also suggest that Arctic ice and Inuits were seen in Scotland during this time.

Volcanic activity

• Major volcanic eruptions change the atmosphere:
• Lots of particles are thrown out, some of which reflect the Sun's rays, meaning that the surface of the Earth cools down.
• Carbon dioxide is also released, but not enough to cause global warming.
• It's thought that volcanoes are only capable of causing short-term climate changes.

Solar output variation

• Solar output changes in short cycles, and maybe longer cycles as well.
• It is possible that when output is low, the Earth's climate could cool.
• Scientists are not convinced that solar output variation is enough to significantly affect the climate

Asteroid collisions

• When asteroids collide with the Earth, huge amounts of dust particles get thrown up into the atmosphere.
• These dust particles reduce the amount of sunlight reaching the Earth's surface. This causes global temperatures to fall.

Orbital changes

• The Earth's orbit around the Sun changes from circular to elliptical and back to circular every 96,000 years.
• The closer the Earth is to the Sun, the more solar radiation it is exposed to and the warmer it gets.

Ice cores

• Ice cores can be obtained by drilling into ice sheets.
• Every year, one layer of ice forms on the top of ice sheets.
• Analysis of the gases in the core allows scientists to determine the temperature for each of the last 400,000 years!

Tree rings

• Every year, a new ring forms in the trunks of trees.
• By taking cores and counting the number of rings, scientists can work out a tree's age.
• Tree rings are thicker in warm, wet conditions.
• Tree rings are a reliable evidence source for the last 10,000 years!

Historical records

• Temperatures have been measured and recorded globally using thermometers since the 1850's.
  • This record is highly reliable but also very short-term.
• Historical records from sources such as newspapers can be used to paint a slightly longer-term picture.

Greenhouse gases cause the greenhouse effect. This helps keep the Earth warm enough for life. But, the greenhouse effect can cause global warming if too strong. The process is:

• The sun emits short wavelength infrared radiation that enters the atmosphere and travels towards the Earth’s surface.
• The Earth absorbs some of this radiation, but long wavelength radiation is reflected back into the atmosphere.
• Greenhouse gases can't absorb the frequency of radiation emitted by the Sun, but they can absorb the longer wavelength reflected radiation.
• The gases re-radiate this energy.
• Temperature at the Earth’s surface rises.

More deaths due to heat

• But, there have also been fewer deaths related to cold weather.

Problems with water availability

• Changing precipitation patterns are making it difficult for some areas to get water to all their residents.
• In these circumstances, political tensions can develop. This is especially true where rivers span multiple countries.

Loss of coastal areas

• Rising sea levels could lead to low-lying coastal areas becoming uninhabitable.
• This might force people to migrate, leading to overcrowded conditions in other places.

Lower crop yields

• The yields of some crops have decreased because of climate change.
• Malnutrition, ill health and death from starvation are all potential consequences of reduced crop yields. This is especially concerning for low-latitude countries.

More extreme weather events

• More extreme weather events not only directly threatens human lives, but also has financial consequences:
• More money must be spent on improving prediction, minimising their effects, and recovering when they devastate regions.

Transport

• Most modern modes of transport run on fossil fuels, which release greenhouse gases when they burn.
• Increasing car ownership in developing countries (e.g. China) means more cars are on the roads. This increases congestion meaning that car engines run for longer and burn fossil fuels for longer.

Energy

• When fossil fuels (e.g. coal, oil, natural gas) are burned, carbon dioxide is released into the atmosphere.

Industry

• Cement production is an example of an industrial process that releases greenhouse gases:
• Cement is made from limestone, which contains lots of carbon, and so carbon dioxide is released when cement is made.
• Decay of industrial waste in landfill produces methane.

Farming

• The digestive systems of cows produce lots of methane.
• Rice paddies also emit lots of methane.
• Deforestation means there are fewer trees removing carbon dioxide from the atmosphere to use in photosynthesis.

Increased extreme weather events

• Since 1950, heat waves have become more frequent and cold weather extremes less frequent in many areas.
• Between 2010 and 2014, more UK rainfall records were broken than in any other decade on record (and it had only been half a decade!).

Sea level rise and warming oceans

• The causes of the 0.2m sea level rise since 1901 are:
• Eustatic sea level rise - when ice melts on land, it goes back into the oceans.
• Thermal expansion - water expands as it heats up.

Global temperature rise

• Since 1880, global temperatures have increased by about 1oC.
• All of the top 10 warmest recorded years have happened after 2000.

Declining Arctic ice

• The maximum extent of winter Arctic sea ice has decreased by over 3% per decade for the last 35 years.

• Warm air current rise from the ocean. As the warm air rises, more air rushes in to replace it; them it to rises.
• Updraughts of air contain huge volumes of water vapor from the oceans, which condense to form clouds. Condensation releases heat energy stored in water vapor, which powers the cyclone further.
• Coriolis force causes rising currents of air to spiral around the center of the tropical cyclone, so it resembles a whirling cylinder. It rises and cools, and some of it descends to form clear, cloudless, still eye of the storm.
• As the tropical cyclone tracks away from its source, it is fed new heat and moisture from the oceans, enlarging it as it does.
• Once it reaches a landmass, it loses its energy source from the ocean. Air pressure rises as the temperature falls, winds drop, rainfall decreases and it decays to become a mere storm.

Low pressure allows clouds to form and cluster together.

• Coastal flooding
• storm surges
• high winds
• landslides
• intense rainfall

Impacts on people

• Destruction of buildings can leave people homeless.
• People can drown or be injured by flying debris.
• Damage to electricity cables causes supplies to be cut.
• Flooding can lead to sewage overflows and the contamination of water supplies.
• Lack of sanitation increases the spread of disease.
• Damage to transport links makes it difficult for aid to arrive.
• Damage to crops, death of livestock, and blocking of supply lines can all contribute to food shortages.

Impacts on the environment

• Woodland habitats can be destroyed by high winds uprooting trees.
• Coastal habitats can be damaged by storm surges.
• Freshwater environments can be polluted with saltwater by coastal flooding.
• River and lake wildlife can be harmed by the deposition of sediment as a result of landslides.
• Toxic chemicals can be leaked into the environment if industrial buildings are damaged by coastal flooding.

Social vulnerability

• Less wealthy countries are more socially vulnerable as:
• Buildings are less robust and so are damaged more easily.
• Worse healthcare means there can be long delays for treatment.
• Flood defences are poor due to lack of finance.
• Poor infrastructure makes rescue attempts more difficult.

Physical vulnerability

• Low-lying coastlines are more vulnerable to coastal flooding.
• Countries that are located on the typical path of cyclones will be affected more regularly.
• Steep relief of land increases the chance of landslides.

Economic vulnerability

• Less wealthy countries are more economically vulnerable as:
• There is a high dependence on agriculture, which is often heavily affected by cyclones.
• Residents are less likely to have insurance.
• But, the overall economic impact can be greater in wealthier countries because the infrastructure costs much more to build in the first place.

Weather forecasting

• Data from radar, satellites and aircraft can be used to monitor storms.
• This data can be inputted into computer models to work out the predicted paths of storms.
• Accurate prediction of the behaviour of tropical storms allows people to prepare, either by evacuating or protecting their property.

Storm surge defences

• Storm surge defences (e.g. sea walls) can be built along vulnerable coastlines.
• Buildings can be designed to cope with tropical cyclones.
• E.g. they can be erected on stilts to protect them from floodwater.

Evacuation

• Warning strategies alert people of inbound cyclones in advance so that they can evacuate their homes and move to a safer place.
• Emergency services should receive specific disaster training.
• The efficiency of evacuation can be improved if governments plan special evacuation routes.

Core

• The core is in the centre and split into 2 layers:
• Solid inner metallic core.
• Liquid outer core made of iron and nickel.
• The centre of the core is very dense. Further from the very centre, it becomes less dense.
• The core is the hottest part of the Earth, with temperatures ranging from 4,400-6000oC.

Mantle

• The mantle, which surrounds the core, is made of silicon-based rocks.
• The mantle can be thought of as 3 layers with varying rigidity:
• Near to the core, the mantle is quite rigid.
• The layer above this, called the asthenosphere, is less rigid and so is described as semi-molten.
• The furthest layer from the mantle is rigid.
• The mantle's temperature ranges from 1,000-3,700oC.

Crust

• The crust is a very thin outer shell. This is the layer we live on. It is between 5-100km thick.
• There are 2 types of crust:
• Continental crust is thicker and less dense.
• Oceanic crust is thinner and denser.
• The crust is broken into large pieces called tectonic plates.

• In the Earth's mantle and core, radioactive decay generates heat.
  • This heats up the lower parts of the asthenosphere, making them less dense and causes them to rise.
  • This hot material cools as it rises, becoming more dense and sinking.
• We call these circular movements of semi-molten rock convection currents.
• Because tectonic plates float on the mantle, these convection currents create drag on them and cause them to move.

Conservative

• At conservative plate boundaries, plates slide past each other in opposite directions or in the same direction at different speeds.
• The plates are made of rock that has jagged edges so they catch and snag against one another.
• Friction and pressure between the plates build until the plates can't take the stress.
• They slip past each other and, as a result, the ground may shake (earthquake).

Convergent

• The oceanic plate slides beneath the continental plate. The point at which this happens is called a subduction zone.
• The rocks catch against one another as the plates aren't smooth.
• The pressure between the plates builds until the plates can't take the stress.
• They slip past each other, which can cause both plates to move and, as a result, the ground may shake (earthquake).

Divergent

• At constructive plate boundaries, the plates move apart (diverge).
• The convection currents diverge (push apart) and cause a gap between the plates. Magma (molten rock) rises up to fill this gap.

Convergent plate margins

• At convergent plate margins, the denser oceanic plate is forced under the continental plate.
• The friction and pressure cause cracks (vents) to form in the continental plate. The magma rises up through these cracks.
• This usually creates highly explosive volcanoes (e.g. Mount Vesuvius, Italy) that produce a lot of gas and lava (magma above the surface).

Hotspots

• At hotspots, there is a hot mass of rising heat under a weakness in a plate.
• Magma rises to the surface through this weakness.
• The Hawaiian islands all formed as a result of a mid-Pacific hotspot.

Divergent plate margins

• At divergent plate boundaries, the plates move apart.
• The convection currents in the mantle diverge (move apart) and cause a gap between the plates.
• Magma rises up to fill this gap with a volcano.
• This kind of volcano is common in Iceland.

Shield volcanoes

• Found at divergent plate margins or hotspots.
• Not particularly explosive.
• Consist of only lava.
• Erupt basilica lava, which is runny because it has a low silica content. This means that it flows rapidly over a wide area creating low volcanoes with gently sloping sides.
• Mauna Loa in Hawaii is an example.

Composite volcanoes

• Found at convergent plate boundaries.
• Erupt explosively beginning with ashy explosions. These explosions deposit an ash layer.
• Erupt andesitic lava, which is thick and sticky because it has a high silica content. This means that it doesn't flow far and so composite volcanoes are steep-sided.
• Mount Fuji in Japan is an example.

Lava

• Lava is magma (molten rock) above the surface.

Gases

• Volcanoes emit lots of gases like sulfur.

Ash

• Ash is tiny pieces of burnt rock fragments that are blown into the atmosphere, usually at some force.
• These pieces fall on land and can float in the air to block out the sun.

Pyroclastic flows

• Pyroclastic flows are currents of hot ash, lava and gas that can move downhill at speeds of up to 500km/h during an eruption.
• Pyroclastic flows are impossible to outrun.
• They can reach temperatures of up to 1000C and can cover distances of up to 30km from the volcano.

Can happen at all 3 plate margins

• At divergent margins, pressure can build up from cracks in the plates when they move apart. This can cause earthquakes.
• At convergent margins, a plate can get stuck as it moves under another. This can cause earthquakes.
• At conservative margins, there can be friction between plates because they aren't smooth. This can cause earthquakes.

Caused by plates jerking past each other

• As plates move past each other, pressure builds up from the friction between them.
• When the pressure is sufficient, the plates give way. This causes the plates to jerk past each other and the ground to shake.

Measuring earthquakes

• Earthquakes are measured using the moment magnitude scale.
• The moment magnitude scale measures the magnitude of an earthquake by measuring how much energy is released by the earthquake.

Shock (seismic) waves

• Energy is released from the focus in shock waves (called seismic waves).
• The most damage will occur at the places where the shock waves are strongest (closest to the epicentre).

Epicentre

• The epicentre is the point directly above the centre of the earthquake on the earth’s surface.

Focus

• The focus is where the pressure is released underground and where the energy radiates out from.
• This is the place with the strongest waves that cause the most damage.

Shallow-focus earthquakes

• Shallow-focus earthquakes are those where the focus is 0-70km under the Earth's surface.

Deep-focus earthquakes

• Deep-focus earthquakes are those where the focus is 70-700km under the Earth's surface.
• Deep-focus earthquakes are caused by previously subducted crust moving towards the core, heating up or decomposing.
• Deep-focus earthquakes are generally less damaging than shallow-focus because the shock waves have to travel further and so cause less shaking at the surface.

Underwater earthquakes

• Underwater earthquakes move the seabed, which causes water to get displaced. If enough water is displaced, tsunamis (series of enormous waves) can happen.