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Geography - Weather Hazards and Climate Change (Atmospheric Circulation…
Geography - Weather Hazards and Climate Change
Atmospheric Circulation
Air moves towards the poles, cools and sinks. Sinks around 30 degrees North and South.
Sinking air – permanent high pressure created and this creates deserts.
Intense heating at the equator means that air rises. As it does so it cools, condenses and it rains either side of the equator – rainforests produced.
Also Ferrel Cells and Polar Cells – see diagram.
The main idea is the Hadley Cells
Air moves from high pressure to low pressure – along the surface of the earth – known as trade winds (key for tropical storm).
Jet Streams
Jet streams – fast moving bands of air in the upper atmosphere.
They can move weather systems around the world.
Ocean Circulation
They move around the world re-distributing heat
Main one for the UK is the North Atlantic Drift – this keeps the UK warmer than places at comparable latitude. E.g. UK is much warmer than parts of Canada in winter at the same latitude.
There are warm and cold ocean currents
Quaternary Period and Natural Causes of Climate Change
3 causes of natural climate change:
Volcanism – Volcanic eruptions emit Sulphur Dioxide – This reacts with water in the atmosphere to form sulphuric acid. This is an aerosol and reflects energy back from the sun. Ash also blocks out sunlight.
Sun spots (solar variation) – These are dark patches on the sun. When there are more of these, then temperatures on earth are higher.
Milankovitch cycles – 3 cycles:
Precession – this is where the earth axis wobbles and this can ‘push’ the earth further away from the sun. When this happens – cooler periods on earth.
Axial tilt – When the earth’s axis is at a larger angle the earth is further away from the sun and colder temperatures found on earth.
Eccentricity – This is where the earth’s orbit varies from circular to elliptical and back again – takes around 100,000 years. Means that when the earth is furthest from the sun – colder temperatures – glacial period.
These have changed climate over the Quaternary period which is the last 1.6 million years.
Evidence of Climate Change in the past
Pollen records – pollen comes from plants – these grow more during interglacial periods when temperature/rainfall is greater.
Tree Rings – width of the tree rings indicates the amount of growth of the tree that year.
Ice cores: taken from polar regions. Tell us about past climates. Ice is in layers – the thickness of the layer provides information on the amount of precipitation that fell in a year. Gas is trapped in bubbles in the ice – the amount of Co2 tells us whether it was a glacial period or interglacial. More CO2 in the ice during a glacial period. Pollen is trapped in the ice – more pollen in ice means temperatures were likely to be warmer/wetter.
Human Causes of Climate Change
Energy Production
Farming activities – these produce more methane e.g. more cows for greater demand for beef. Methane is around 30 times more effective at trapping heat when compared to Co2 and so this is a big issue.
Transport
These have all produced greenhouses gases which add to the enhanced greenhouse effect.
Industry
Important to note enhanced effect as this is occurring naturally – without it world would be around 30 degrees cooler.
Enhanced Greenhouse Effect
Impacts of climate change – rising sea levels, changing patterns of crop production, retreating glaciers
Rising sea levels
Melting of ice which contributes to higher sea levels – melting of ice on Antarctica is significant for this as the ice is not currently taking up any space in the sea.
Thermal expansion which is where the sea is at a higher temperature and so takes up more volume and so sea level rises.
Crop production
Due to higher temperatures some plants may not grow as effectively – may impact food supply.
Photosynthesis is not as effective at higher temperatures.
Glaciers shrinking
Problems of water supply in some regions e.g. Himalayas. Ice melting also adds to sea level rise as the water flows to the sea.
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UK Climate
Variations in temperature and rainfall
Temperature warmer in the South, colder in the North. Due to latitude.
Air masses – 4 air masses influence the UK and these determine the weather that the UK gets.
Variations in rainfall – due to relief rainfall – Mountains on the West of the UK.
Rain shadow on the East of the UK.
Tropical Storm – Characteristics, Hazards and Formation
Around 8-20 degrees north/south (latitude) of the equator. There needs to be sufficient distance from the equator in order for the Coriolis force to have some impact. This provides the spin for a tropical storm.
Above 20 degrees north or south (latitude) – the sea is too cold for a storm to form.
Winds converging at the surface – the trade winds
Low wind shear – winds cannot vary much with height otherwise the storm won’t form.
Sea needs to be 27(degrees Celsius)
Hazards
High winds – can produce flying debris which acts as a further hazard
Intense rainfall – flooding and landslides
Storm surges – Most deadly hazard – wall of water being washed inland due to strong winds.
Only form in certain locations – source areas. They need the following:
Causes of Drought
Dams – Less water available downstream
Deforestation – Less transpiration and so less rainfall
Hydrological – Lower levels of stored water e.g. in reservoirs which is caused by a lack of rainfall. However, this lower level of stored water will mean less water in rivers.
Agriculture – Too much water removed from water sources for irrigation and so less water in rivers.
Meteorological – A lower than average amount of rainfall in an area.
Why is Drought a Hazard?
Fires and dust storms are more likely
People able to produce less food and so famine and malnutrition more common
People are forced to use lower quality water sources which means the spread of water borne disease is more likely
Case Studies - Droughts
Case Study Drought – Developing Country (Page 120) Ethiopia
Impacts
Disease spreading as people use lower quality water
People have to walk miles to collect water – takes children out of school.
Responses
Charities provide food, water and medial care to those most in need
Causes
Rainy season has been getting shorter
Case Study Drought - Developed Country (Page 118) California
Impacts
Wildfires
Loss of jobs in farming – around 10,000 due to lack of water for farming
Responses
Education on reducing water use
Limiting flows during winter months to build water surplus for summer
Causes
Period of very low rainfall
River Colorado supplies California and other states have taken out more water than they should have.
Case Studies - Tropical Storm
Tropical Storm – Developed Country (Page 110) Hurricane Sandy - 29th October 2012
Impacts
150 people killed
US$65 billion in damage
Responses
Government agencies responded – search and rescue etc.
Fires were a major hazard and these were extinguished.
Tropical Storm – Emerging Country (Page 112) Typhoon Haiyan – November 2013
Impacts
6000 people died
Tens of thousands were homeless
Responses
RAF went to help – bringing aid supplies
NGOs such as Save the Children brought shelter, food, water to worst affected areas.
