The tropical wet & dry climate of Africa
In the tropical regions of Africa, there is a distinct seasonal variation in temperature and particularly precipitation. Tropical wet and dry aka tropical continental climate (generally lies within 5 and 15 degrees N+S of the equator).
(Look in pack page 3 for map)
Location of countries with a tropical wet and dry climate:
- South America: Brazil, Ecuador, Venezuela, Mexico
- Africa: Angola, Zambia, Kenya, Tanzania
- South Asia: Thailand, India
- Northern Australia
In Africa the tropical wet and dry is sandwiches between the equatorial and arid climate
(Look in pack page 4 for map)
Climate graph for Kano in Nigeria
Look in pack pg 5 for climate graph
- hot all year round
- small temp range (10 degrees. 22-32)
- temp dips slightly in wet season from 30 to 22 at the lowest
- dry season has lowest temp of 20 degrees
- wet season is mainly March-October
- Jan, Feb, Nov, Dec = 0mm rainfall
- 50% of annual rainfall in Jul & Aug
Insolation - incoming solar radiation
We receive heat energy from the Sun in the form of UV radiation (aka short wave radiation). It reaches the Earth's surface as insolation. (Look at pg 5)
Why is there a net surplus of energy at the equator? (MORE insolation/heat energy)
- Sun is overhead so insolation stronger
- The more vertical the Sun's rays, the stronger they are, this is because these rays heat up a smaller area on the Earth's surface
- They also have a shorter journey to travel through space (lose less energy)
Why is there a net deficit of energy at the poles? (LESS insolation/heat energy)
- The Sun's rays were more angled (oblique) so are weaker
- This is because these rays eat up a larger area on the Earth's surface
- They also have a longer journey to travel through space
- Daylight hours are shorter in winter
Wind (in the atmosphere) and currents (in the ocean) redistribute this heat from the equatorial regions to the poles. As a result, 3 circulation cells are generated in each hemisphere, and this is shown by the tricellular model.
3 circulation cells are: the hadley cell, the ferrel cell, the polar cell
(Look at page 7 for diagram)
(page 7 for diagram)
In order to explain the climate belts in Africa, it's necessary to take a closer look at the Hadley Cell. The Hadley Cell refers to the circulation of heat taking place either side of the equator.
What the climate is like over the equator and why:
Hot and wet. The insolation is stronger, it's concentrated over a smaller area and has less space to travel through so it's hot. It's wet due to ground heating, resulting in warm air which rises, cools and condenses to give convectional rainfall occuring in equatorial areas.
What the climate is like at 30 degrees South/North and why:
Cold and dry. Air sinks, and sinks back to surface. It warms up. Desert has arid climate and it's hot and dry. Cold dry air sinks, and warms up, no condensation (As it's already rained so lost its water vapour) so clear sky and insolation still shining in tropical region.
30 deg North: Sahara Desert
30 deg South: Kalahara Desert
- At the ITCZ, the Sun heats the moist tropical air causing it to rise (as warm air is less dense)
- The rising air experiences adiabatic cooling, which causes water vapour to condense into rain and fall back to Earth
- The condensation of water vapour produces latent heat release. This causes the air to expand and rise farther up into the atmosphere
- The warm, rising air displaces the cooler, drier air above it to the North and South
- The cool, dry air sinks and experiences adiabatic heating. It reaches the Earth's surface as warm, dry air, and then flows back towards the equator
Terms and defintions
ITCZ (Inter-tropical convergence zone) - This is the meeting point of the two Hadley Cells and is the zone of CONVERGENCE of the NE and SE trade winds. It also marks the point where the Sun is directly overhead. The Sun heats the ground leading to air rising (convectional uplift) causing cloud and convectional rain.
Sub-Tropical Anticyclones (High Pressure) - The descending limb of the Hadley Cell leads to High Pressure and very dry conditions as the air is stable.
Insolation - This is the heat energy from the Sun and so represents the incoming solar radiation.
Trade winds - These are the prevailing winds which blow in from the high pressure areas of 30N and 30S towards the low pressure areas at the ITCZ.
Adiabatic heating - As cool air high in the atmosphere is dense, it sinks. The pressure from the weight of the sinking air above it, pushes air molecules closer together, causing them to heat up. As a result, the air temperature rises, even though no heat has been added.
Adiabatic cooling - As air is heated it expands becoming less dense. It will rise upwards and as it does so, this air continues to expand. This allows the air molecules to spread out more. As a result the temperature of these air molecules drops leading to cooling.
Coriolis Effect - The Earth's rotation means that moving objects like the wind experience an apparent force. This deflects the direction of the wind to the right in the Northern hemisphere and to the left in the Southern hemisphere.
(look at pg 9) rising air= unstable.
However, the explanation for the tropical wet and dry climate is a little more complicated than shown in the previous task. The position of the overhead sun changes throughout the year due to the earth’s tilt. This causes seasonal movements of the “thermal equator”, ITCZ and pressure belts of the Hadley Cell. This movement of the Hadley cell helps to explain the distinctive wet and dry seasons experienced in the tropical regions of Africa.
(Look on page 10 for diagram)
Orbit - the Earth's tilt
KEY INFO - NEED TO KNOW.
The Sun is overhead at:
- The equator on 21st March
- The Tropic of Cancer (23 1/2 degrees North) on 21st June (Summer in UK. - North - Cancer)
- The equator on 21st September
- The Tropic of Capricorn (23 1/2 degrees South) on 21st December (Winter in UK. - South - Capricorn)
Explaining Africa's tropical wet & dry climate
The equator on 21st March (Start of wet season):
- Sun is directly overhead at the equator (Kano is close to the equator at 12N) so temps are rising
- Kano is positioned at the edge of the ITCZ. The higher temps result in convection (rising, unstable air) and convectional rainfall. This is the start of the wet season.
The Tropic of Cancer (23 1/2 deg North) on 21st June:
- The Sun is overhead at the Tropic of Cancer. The ITCZ moves northward following the overhead Sun. Temps are not as hot as March due to cloud cover which will stop some insolation from reaching surface.
- Kano is in the ITCZ causing rising unstable air and low pressure. This produces heavy convectional rainfall. Moist air is drawn in from over the Atlantic Ocean.
The equator on 21st September:
- The Sun is now overhead at the equator so the ITCZ has moved Southwards. Temps are peaking because there is less cloud cover. The NE trade winds also blow over the Sahara Desert - they are warm, dry winds. The winds are locally known as the "Harmattaan".
- Kano is at the edge of the ITCZ and so low pressure belt. This means theres some convection (rising, unstable air) and some rainfall.
The Tropic of Capricorn (23 1/2 deg South) on 21st December:
- The Sun is overhead at the Tropic of Capricorn, and so temps are lower as Kano is furthest from the Sun.
- The dry season in Kano is due to the Sun moving to its most southerly extent 23.5S - The Tropic of Capricorn. This causes the ITCZ to also move southwards. This leaves Kano in the subtropical high pressure belt. Descending air is adiabatically warming to give clear skies. Kano is affected by strong NE trade winds. The trade winds are warm and dry as they blow over the Sahara Desert.
Explaining the climate of Kano
Wet season begins in March because:
- As Kano is on the edge of the ITCZ, at the edge of the low pressure belt.
- Uplift of unstable air leads to some convectional rainfall.
- As air rises it adiabatically cools and rises and condenses.
Temps rise sharply in March and peak in April because:
- The Sun passes over Kano as it moves Northwards. This brings the thermal equator with it.
- Sun's rays are most concentrated on Kano at this time and have travelled through less atmosphere so remain strong.
Precipitation increases in June and July, reaching its peak in August because:
- The Sun is North of the equator (overhead at Tropic of Cancer).
- This brings the thermal equator, ITCZ and low pressure belt Northwards.
- Uplift of air and heavy convectional rainfall.
Temps fall from April to August because:
- Cloud cover with convectional rain lowers insolation and temp.
Second peak in temps in October because:
- The Sun is moving South of the equator towards the Tropic of Capricorn.
- Kano is on the edge of the low pressure belt, so there is less cloud coverage and stronger insolation, raising temp by a few degrees.
Dry season from November to February because:
- Kano is in the subtropical anticyclone belt.
- Air is descending and adiabiatically warming.
- Clear skies so no rainfall. (air is dry as lost moisture in ITCZ so is dry)
- (ITCZ follows Sun)
Temps at their lowest in Decemeber and January because:
- The Sun is South of the equator and so furthest from Kano.
- Insolation is waker so temps are lower.
Suptropical anticyclone is high pressure because there's more air at surface which was due to it sinking
The climate graph of Kano clearly shows that there is a delay between the movement of the Sun and the temp/pressure belts. This is because it takes time for the ground to heat up for convectional rainfall.
Sub tropical anticylone is hot and dry. Desert conditions, descending air adiabatically warming to the high pressure
ITCZ , convectional rainfall and Low pressure and trade winds meet
Dodoma in Tanzania also has a tropical wet and dry climate, but the climate graph differs to that of Kano's in Nigeria.
Tanzania location: 6 degrees South of the equator. Eastern side of Central Africa.
Differences between Dodoma's (in Tanzania) climate and Kano's (in Nigeria):
- Highest rainfall and also highest temp in March, there's no dip like in Kano
- Smaller temp range of 5 degrees (10 in Kano)
- Dry season in Tanzania when it's wet season in Kano
- Wet season and most rain: Jan - May
- Less rain overall (570mm) but Kano has 812mm
- Lower temps but still high
- Highest rainfall in January, in Kano it's August.
Closer to arid region = less rainfall
Closer in tropical wet and dry to equator = more rain because ITCZ is stronger
Reasons for differences:
- When Kano in wet season, Dodoma in dry season because overhead Sun is moving to North and ITCZ is there so subtropical anticyclone and no rainfall in Dodoma
- Kano has more rain because gets moist air from sea and so more rain in Western Africa from Atlantic Ocean.
- Altitude differences (1,120m Dodoma & 500m Kano). Higher altitude = lower pressure so temp is cooler (higher up=cooler). So longer for ground heating,less warm air rising so less rainfall. Altitude=height above sea level
Climate changes progressively as you move from the high pressure centres over the tropics, through the Savannah (tropical wet/dry climate) to the equatorial climate. This causes a change in vegetation from desert to semi-arid scrub to savannah to trpical rainforest. Such a gradual change is called an ECOCLINE. (Look in pack page 15 & 16)
Tropical revolving storms
Definition of tropical revolving storms (also known as tropical cyclones):
An intense low pressure weather system with wind speeds in excess of 74 mph. They develop over tropical seas and occur between 5 and 20 degrees North and South.
Conditions needed for development of Tropical revolving storm (TRS):
- Oceanic location with sea temps above 27 degrees - provides a continous source of heat to maintain rising air
- Ocean depth of at least 70m - this moisture provides latent heat, rising air causes the moisture to be released by condensation and the continuation of this process drives the system
- A location at least 5 degrees North or South of the equator - in order that the coriolis effect can bring about the maximum rotation of air (coriolis effect is weak at the equator and will stop a circular flow from developing)
- Low level convergence of air in the lower atmospheric circulation system - winds have to come together near centre of low pressure zone
- Rapid outflow of air in the atmospheric circulation - this pushes away the warm air, which has risen close to the centre of the storm
Why is a TRS a hazardous event for coastal regions
- WINDS - exceeding 155 mph causing structural damage include damaged bridges, power lines and collapsed buildings.
- HEAVY RAIN (+100mm/day) - causes severe flooding and landslides (if in moutainous areas)
- STORM SURGES - causes coastal flooding in low lying, unprotected areas. Waves are 'piled up' by strong winds and the ocean rises under the low air pressure of the cyclone.
Measures used to MANAGE the hazard
- Satellites predict the size of the TRS and can follow track. (GOES & POES)*
- National Hurricane Centre in Miami, Florida monitor TRS in Atlantic Ocean. Will give evacuation orders to coastal zone in advance
- Hurricane Hunters fly into TRS to collect data
- Use hard engineering (e.g. flood walls, sea walls etc) or soft engineering (e.g. coastal forestation, leand use planning)
- Cloud seeding - drop silver iodide into clouds by flying over them. This forces TRS to rain and weakens the storm. It's not used however as it could alter global distribution of air.
*GOES: Geostationary operational environmental satellites - sit in stationary orbit above equator. Scan the globe and produce images every 30 mins, can see scale of hurricane.
The global distribution of TRS
Describe the latitudinal distribution of TRS:
- 5 - 20 degrees N/S - In ITCZ and important as low level convergence of air in low pressure area. Sea temp (27degreees) for warm moist air to rise. Minimum 5 degrees N+S for sufficient coriolis effect.
Tropical revolving storms have different names in different parts of the world.
- HURRICANES - what USA call them. Develop in Carribean sea/Gulf of Mexico (11% of TRS)
- CYCLONES - In Indian Ocean. Arabian sea/Bay of Bengal area. (8% of TRS) E.g. India, Bangladesh, Sri Lanka, Madgascar.
- TYPHOONS - In Pacific. Off South East Asia (main area with 1/3 of TRS)
- Willy Willies (North Western Australia) South West Pacific and North Western Australia (20%)
TRS season occurs in late Summer, going into Autumn. This is because this is when sea temps are favourables (27 degrees)
Global Sea surface temperatures (N. Hemisphere Summer)
TRS are slow-moving systems of extreme low pressure which help to move excess heat from the equatorial regions towards higher latitudes.
They tend to track from East to West (Westwards) across the oceans, then NORTH (in the Northern hemisphere) (or South in the Southern hemisphere)
Track of storms is always initially westwards due to trade winds and then turn North in the Northern hemisphere and South in the Southern hemisphere due to coriolis efffect. Don't get TRS at British Isles as sea temps not warm enough (not enough evaporation) and too far North, so TRS would lose energy anyway.
Life cycle of TRS (formation & development)
TRS's go through a 3 stage life cycle. They begin as a tropical disturbance which may develop into a tropical depression and in time, may continue to enlarge into a tropical storm which may intensity further into a tropical revolving storm.
TROPICAL DISTURBANCE: A disorganised area of thunder storms in the tropics that exist for over 24 hours.
TROPICAL DEPRESSION: A circulating mass of defined clouds and thunder storms with sustained wind speeds of up to 38mph
TROPICAL STORM: A circulating system of strong thunder storms with sustained wind speeds of up to 73 mph
TROPICAL REVOLVING STORM (or tropical cyclone): A spinning mass of towering clouds producing torrential rain and strong winds over 74mph. The eye is visible.
Causes of a TRS
Conditions and mechanisms necessary for a tropical disturbance to grow and intensity into a TRS:
- Water is warmed by the overhead sun in Summer and so by Autumn sea temps are warm, so water evaporates and water vapour rises from the surface as the air is unstable (wants to rise).
- Hurricane development firstly requires an ocean temp of over 26 degrees and heated to a depth of 50-70 metres
- Ocean temp of this heat is usually found in areas between latitudes 5 and 20 degrees N and S
- Rising moist air cools, condenses and spirals outwards
- The Coriolis effect/force is greatest at this latitude. The rotation of the Earth aids the rotation of the storm. Also at this latitude, the trade winds converge to intensify the low pressure and allow more unstable air to rise.
- The rising air causes low pressure at the surface
- More air is drawn in and the updraft of air continues until a huge cumulonimbus clouds are formed (Cb clouds)
- As the air rises it releases latenet heat
- Wind direction and wind speed must be equal at all altitudes (if not the storm will be broken)
TRS eventually loses power as the more in land it gets, it's losing moisture and heat which provides energy to the storm and also friction.
Characteristics of TRS
(1) The eye. (2) Eye Wall. (3) Spiral rainbands = 3 key areas of TRS.
Typical width: 500km. Typical height: 12km.
The Eye wall:
- Completely or partially (at least 50%) surrounds the eye of a mature hurricane and is an area where winds may gust to more than 200mph.
- Consists of a ring of tall thunderstorms that produce heavy rains and very strong winds.
- Has the most destructive section of the storm on the side where the wind blows in the same direction as the storms forward motion.
- Located at the hurricanes centre and can measure 20-30 miles wide.
- An eye will usually develop when the maximum sustained speeds go above 78 mph.
- A cloud free area of sinking air and light winds that usually doesn't exceed 15mph
- The calmest part of the storm
- Generally shrinks in size when the storm strengthens
- Curved bands of clouds that trail away from the eye wall in a spiral fashion.
- Capable of producing heavy burses of rain and wind perhaps 1/2 or 2/3 the strength of those associated with the eye wall.
- Many cause a hurricanes diameter to extend outwards up to 34 miles.
In Southern hemisphere:
- Rotate clockwise
- Increased windspeed + increased destruction are on left of eye wall
- Track South West/Westwards
In Northern hemisphere:
- Rotate anticlockwise
- Increased windspeed and increased destruction are on the right of the eye wall
- Track North West
Measuring the magnitude of a TRS:
The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the tropical revolving storm’s present intensity. This is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall. Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf in the landfall region. 1 = lowest mag storm (least damaging) 5 = highest
In a mature tropical cyclone, warm, moist air rises. This in turn draws in winds along the surface to replace the air that has risen. As they track North West across the ocean, more air continues to converge and then to rise. The Coriolis effect/force causes the rising air to spin around the centre of the low pressure, creating a vortex of warm air.
The centre of a mature tropical cyclone is known as the eye, and is typically 20-30 miles wide (20-50km). Air sinks in the eye to fill the low pressure (vacuum) created by the rising air in the eye wall. The lowest air pressure is in the eye at about 960 mb. As the air descends, it compresses and warms. This is known as adiabatic warming. As a result, temps are highest in the eye and can be as high as 32 degrees. Humidity is reduced due to evaporation, so the eye remains cloudless. Winds are also calm.
Immediately surrounding the eye is a wall of Cumulonimbus (Cb) cloud which can be as high as 12km. This forms the eye wall. Here, warm, moist air is rising and cooling. Condensation occurs, and this releases latent heat which means that the air continues to rise. The air rises faster and faster, and in the upper atmosphere flows outwards away from the centre. This in turn, helps to draw in more warm, moist air from the surrounding ocean to fill in the low surface pressure. Spiral rain releases more latent heat, which causes air to continue to rise and flow outwards from the system at high altitude.
The contrast in pressure between the eye and the outer spiralrain bands results in a steep pressure gradient, and high windspeeds. The most destructive winds occur in the eye wall. The wind speed in a category 1 tropical cyclone is greater than 74mph, but in a category 5, can exceed 155mph. The heaviest precipitation also occurs in the eye wall with totals of about 250mm per day. Bands of cloud spiral into the low pressure, and represent bands of rising and sinking air. In general, the wind speeds and precipitation totals decrease with distance from the eye.
Physical factors influencing impact of TRS on an a
- MAGNITUDE: The higher the magnitude, the more destructive/devastating the impacts. Category 1 is less destructive and category 5 is most destructive.
- SPEED OF MOVEMENT OVER A REGION: Over the sea, slow moving storms will be more destructive as they will have more time to build up energy. Over land slow moving is more devastating as it stays over one area for longer so the area gets more strong wind and rainfall for a long time.
- DISTANCE OF A SETTLEMENT INLAND: The further inland, the less power as more energy is lost, so there is less rainfall and less windspeed. Loses energy as less moist air being drawn up (cut off from power source - heat and water)
- PHYSICAL GEOGRAPHY OF THE AFFECTED REGION (E.G. RELIEF. MOUNTAINOUS/FLAT): Steep, mountainous:less likely to be flooded by storm surges so flat areas hazard is lessened. However,landslides in mountainous areas are hazard. Higher altitude = less likely to flood. Low lying coastal regions are prone to flooding from storm surges.
Management of TRS
Ways in which tropical revolving storms are predictable:
- Location: Most occur between 5 and 20 degrees N or S of the equator. The majority occur on the West sides of Ocean areas.
- Time of the year: Late Summer, early Autumn.
- Track: Westwards. North West or South West.
- Coriolis effect is greatest at this latitude. The rotation of the Earth aids the rotation of the storm. Also trade winds converge to intensify low pressure and allow more air to rise.
- Late Summer, early August as sea is warm/correct temp (27 degrees) so air can rise due to it being warm. 70m depth to maintain rising air.
- All track westwards due to trade winds. Then deflect North in the Northern hemisphere and South in the Southern hemisphere due to Coriolis effect.
Exception to the rule:
- Hurricane Sandy hit New York - October 2012. This was a strange location to occur because it was 40 degrees which is too high altitude
- Hurricane Lily hit the Carribean in 1984. This was unusual because it hit in December (winter)
- Cyclone Nargis hit Burma in 2008. This was an unexpected track as it suddenly changed direction.
evidence that can be used to predict TRS occurance
1) Measurement of sea temperature
Sea temps can be read from thermometers, as well as a network of buoys throughout the oceans. Meteorologists know that TRS can occur where sea temps are at least 27 degrees to a depth of 70m between latitudes 5 N/S and 20 N/S.
2) Measurement of wind speed and Air Pressure
Hurricane Hunter aircraft: Hurricane Hunters fly into a hurricane aiming to take 4 different cuts through the centre of the storm so that they can collect weather data
A dropsonde (aka dropwindsonde) measures: A small tube with weather instreuments and a parachute attached to it, is dropped from the hurrican hunter at several different points (e.g. in eye call and eye). It has a radio transmitter attached to send weather data (e.g. temp, wind speed, pressure etc) back to the aircraft. As instrument falls to ground (water) it records data at a rate of every 30 seconds.
3) Satellite Tracking
GOES (geostationary operational environmental satellites) orbit the equator at a speed matching the earths rotation. This allows them to stay above a fixed spot on the surface and allows for the track of the TRS to be monitored and give indication of its size and scale.
4) Historic tracks of TRS
Meteorologists know that TRS track Westwards and then North in Northern hemisphere & South in Southern hemisphere. They can then attempet to warn coastal zones of an approaching TRS and give evacuation.
Human factors that influence damage-managing
PREPARATION AND EDUCATION: (look at pg 41 in s/g)
- Advanced evacuation - need storm shelters in place already, food etc.
- Educating the population on risks
- Hurricane drills
- Project safeside used in USA
- AID companies can be alerted so they have AID ready (FEMA)
- Warnings need to be accurate as evacuations result in high economic cost
- Poor communication in LEDCs mean that people tend to be poorly prepared causing higher death tolls
POPULATION DENSITY: More people = harder to evacuate as more places needed to evacuate them to, traffic jams etc.
ABILITY TO PREDICT AND WARN PEOPLE ABOUT A HAZARD:
- Warning systems
- Hurricane Hunters
LEVEL OF DEVELOPMENT AND BUILDING QUALITY:
- LEDCs have poorer building quality
- Concrete buildings are best
case studies of TRS from contrasting areas of worl
Hurricane Katrina, USA (Sept 2005) and Typhoon Haiyan , Philippines (Nov 2013).
- Category 5 at landfall
- 400mm rain
- 8th Novemeber 2013
- Category 4-5
- 150mph surface winds for 1 minute and strongest ever recorded at landfall
- Low pressure (895mb) was due to very warm, deep water and low wind shear, allowing vertical development
- Moved quickly across the region
- 5 landfalls
- Worst hit region was low-lying Eastern Visayas with flooding up to 1km inland
- 6021 death toll
- Main evacuation centre - Tacloban City Convection Centre - became a death trap because the storm surge entered the hall where people were sheltering. No clean water, electricity or food
- Mobile phone network was lost and lack of news from survivors exacerbated the stress
- Vehicles over turned and no fuel available, transport difficult
- Storm surge of 5.2m destroyed the terminal building at Tacloban airport and washed large ships ashore
- Fishing industry badly hit
- 95% of boats and equipment were lost to storm surge
- 1000's paddy fields destroyed leaving 10,000 farmers without income
- LEDC so not many prediction methods
- Low level public warning but within 24 hours this was raised to the highest level
Hazard management cont(prediction/prep/protection)
- Nov 6th PAGASA (Phillipines Atmospheric Geophysical and Astronomical Services Administration) issued a low level public storm warning but within 24 hours this was rasied to the highest level, indicating expected winds in excess of 115 mph.
- When Haiyan made 1st landfall, the international charter on space and major disasters was activated.
- Allows relief agencies in times of disaster to have access to satellite data from space agencies to help relief and recovery
- Military deployed planes and helicopters in advance to areas expected to be worst hit
- Community buildings such as convection centres were designated as storm shelters
- Evacuation of whole islands such as Tulong Diyot. 1000 residents left ahead of Haiyan
- Community preparedness and education raised awareness
- Turbulent sides
- Topped 74mph winds
- Counter clockwise direction
- 1st hit FLORIDA - where it was category 1. 80mph wind. eye = 30 miles wide
- 2nd hit GULF OF MEXICO - became category 5. Headed to Louisiana and Mississippi. Category 4, 145mph wind. 6am in morning
IMPACTS of Katrina
- Destruction to buildings
- Severe winds
- Flooded a hotel lobby
- Storm surges
- Collapsed power lines
- Homless people
- 75% of New Orleans underwater
- 100's of people homeless
- More than 13,000 died
- Survivors poor
- Levees breached
- New Orleans was like a war zone (due to violence when food shortages etc)
- Traffic jams
- Crushed coastal towns in Mississippi
- No water or power
- Storm shelters were provided
- Superdome and convention centre. 50,000 people wait for evacuation buses
- Centre has no food and water until 5 days later and there was violence
Hurricane Katrina resulted in a very high death toll despite The USA being one of the richest countries in the world. This case study is therefore interesting as there were many factors which interplayed to increase the vulnerability of the population to the hazard.
1st 48 hours: Strengthened to become a category 1 hurricane. Wind speeds of 75mph. Hit East coast of Florida. -> continued westwards into the Gulf of Mexico , strengthening to become a category 5 hurricane, wind speeds of 175mph and gusts of 215mph -> swerved back round to the north east, weakening in strength but growing in size. Struck the Louisiana coastline as a category 3 storm. -> Huge waves of 10-35 feet built up by the hurricane force winds. Storm surge battered coastal settlements. -> Strong winds = damage to buildings, huge amounts of rainfall fell in a short period of time = widespread flooding -> continued to cause problems as it moved inland, although it finally weakened 240km inland.
Factors which led to a high death toll: (Human and Physical) Human= H. Physical = P
1. Hurricane Katrina was a natural disaster
- Most deadly tropical storm for over 75 years
- Size and scale - Hurrican'e path covered about 500kms. High destructive wind speeds
- Storm surge - Low pressure system contributed to ocean unplif. Surface rose up to a dome which was 8 metres high
- Weather - Gulf of Mexico was extremely warm by normal standards in August (bewtween 30 and 31 deg celcius). Helped to make it to a category 5 hurricane as = more uplift of warm moist air
- High winds - exacerbated the problem. Helped to produce surface waves over 6 metres high on top of the surge
2. Resident poverty led to a higher than normal death toll:
- Although America is one of the wealthiest countries in the World, Hurricane Katrina hit the port of Neew Orleans which is 1 of the poorest cities in the USA. 30% of children in New Orleans live below the poverty line - this figure is more than twice the national average.
- Black Americans make up 67% of the population in New Orleans but account for 88% of the unemployment.
- The poorest districts of New Orleans had the highest death tolls after Hurricane Katrina struck.
- Spending on flood control in Louisiana was cut from $69 million to $34 million in 2004 and by the evening of Tuesday 30th August 2005, 80% of New Orleans was submerged.
- After Hurricane Betsy in 1956, the levee system was modified to withstand a category 3 hurricane, but little money was spent on protection from a category 4 hurricane like Katrina. If this had been done many lives would have been saved, as it is the poorer members of the population that live on the land that lies below sea level.
- One of the hardest hit areas in New Orleans was the Lower Ninth Ward, also one of the poorest.
- Many residents in this ward were among the 100,000 in the city who lacked a car or any other means of leaving the city which left them at risk from natural disasters.
- The poorest residents of New Orleans would have to depend on an untested emergency public transportation system to evacuate them.
3. govt negligence contributed to a higher death t
- The govt were criticised for mismanagement and poor preparation. They were criticised for the slow response to the flooding of New Orleans. Media coverage intensified the blame towards the govt as reports showed hunger, death and lack of aid.
- FEDERAL Govt: President Bush was on holiday in Texas when the hurricane hit on the Monday but didn't break off his vacation until Wednesday and was seen to not understand the full force of the hurricane. It took Bush 4 days to sign for a $10.5 billion relief package. The slow response was claimed to be due to the poverty in the area. National Guard troops arrived within 1-2 days with food, water and medicine. However the attempt was critcised as many National Guard units were short staffed due to war in Iraq (40% National Guard deployed to Iraq).
- LOCAL/STATE govt: Governor Blanco and state officials delayed the respoinse to the hurricane. Blanco only requested for more National Guard troops a day after the hurricane when much of the city was underwater.
- Mayor Nagin failed to execute the New Orleans disaster plan which involved evacuation using school buses, when the floor hit the buses were destroyed.
- The last scheduled train left Saturday 27th August and had room for several hundred passengers but the city declined.
- The Superdome was used as a refuge and as a result saved many, but it is claimed that food and water were not provided. Although many accept that Mayor Nagin had requested use of Superdome if the New Orleans disaster plan was enforced there would be fewer casulties.
govt negligence cont..
- FEMA: FEMA was accused of deliberately slowing things down; wal-mart trucks loaded with water were turned away and the coast guard delivering 1000 gallons of diesel fuel was also turned away. FEMA were also accused of blocking evacuation efforts saying rescuers were not authorised. FEMA had also asked for school buses not to be used in evacuation as they were not air conditioned, they informed them of more suitable buses they were providing. Howevver these buses were coming from another state and would not be there in time.
- RACE/CLASS issues:2/3rds of the resident are black. New Orleans one of America's poorest - 25$ of residents and 40% of children below poverty line. Many depend on welfare and social security. The hurricane made landfall when many had exhausted their resources, this meant many of them couldn't afford to flee the city.
4. flood engineering failure led to higher death t
- Destruction of communication lines and transport routes - Levees which were damaged, causing 75% of New Orleans to be flooded, could not be fixed to ensure that the flooding in the area did not escalate further.
- Breaking of city's levees - The city is already low-lying and when the levees were damaged and breached due to the volume of water this led to the water not being able to drain away naturally.
- Damage to the wetland areas surrounding the city - Since the 1980's the Louisiana coast has suffered a loss of more than half a million hectares of wetlands. For every 3km of wetlands between the city of the Gulf, this reduces the storm surge by approx. 15cm. Such a dramatic loss of wetlands results in an increased storm surge when hurricanes hit the area.
- Dependence on fuel for the levee system to run efficiently - New Orleans levee system relies on pumps which are fuelled by electricity created by fuel which needs to be transported into the area. The failure of the transport system, electricity supply and access to fuel led to drainage issues in the area.
- Many of the flood defences were simply overwhelmed by the force of hurricane Katrina - In the mid 90's US congress approved a scheme to improve the city's flood defencesl however with budget cuts the scheme never took place. As a result many of the flood defences were designed to withstand a maximum category 3 hurricane. Hurricane Katrina was a category 5 storm meaning that may of current storm defences were damaged.
- There were not efficient flood defences to withstand the dramatic storm surges 0 The low pressure weather system lead to the oceans surface rising up some 8m and the storm surge eventually measured 28miles. There was no prediction that such a massive storm surge could be genersated from a hurricane and as a result the flood defences were not designed to withstand such a massive storm surge.
5. human activity on the Mississippi delta
Hurricane Katrina struck New Orleans on the 29th August 2005,, leaving 1245 people dea and $200 billion of damage. The Mississippi Delta contributed to the huge impact of the hurricane. HUMAN ACTIVITY:
- New Orleans has always been susceptible to flooding as it lies below the level of the Mississippi River. The city should have been protected by floodwalls, levees and the delta itself.
- For every 6.4km of wetlands, the height of the storm surge should be reduced by 0.3m. However, the delta lands surrounding New Oreleans have been disappearing into the sea. This leaves this city in danger and the storm surge will have been very high due to lack of delta to slow it down.
- Due to the new levees and floodwalls, the river is no longer able to deposite new sediment to maintain the delta, and with the current sediment being compressed by its own weights and the weight of urban New Orleans, the ground beings to sink. This left New Orleans in more danger, as it was more susceptible to flooding, and the size of the delta was reduced which would have otherwise reduced the height of the storm surge. Therefore much of New Orleans was underwater by up to 8m, which resulted in a high death toll.
- New Orleans is a busy port, it has therefore been forced to flow through the city and has been lined with concrete walls to make it flow faster. Therefore by not allowing the river to take its own course and silt up its own river bed, the delta ends up being moved far out to sea, where it was no used for protecting New Orleans. This therefore led to an increased death roll, as the delta did not protect the city.
- Oil extraction from the gulf of Mexico has also caused the sea floor to sink and parts of the delta to slip away, which reduced the amount of wetland that could reduce the height of the storm surge, thus resulting in a high death toll.
- Shipping lanes have also reduced the size of the delta.
- By reducing the size of the delta by human acitivity in new orleans the city is less protected from hurricanes and storm surges. the delta would slow down and reduce the size of the storm surge.
Physical factors that made Katrina worse
- Became intense as Gulf of Mexico was very warm (30-31 deg cel.) - category 4 when hit New Orleans, Florida was category 1. Impact on Florida = 11 deaths and New Orleans = 13,000 dead
- Low lying city (New Orleans) between the Mississippi river and Panchatrain, surrounded by water. National Hurricane Centre knew the storm surge would lead to flooding
- It was only a day long. Went through region quickly - so not as bad as slow moving storm
- New Orleans coastal city on Gulf of Mexico = higher chance of flooding
- Levees breached - built to withstand category 3 - not built to withstand higher as they had lack of money as the Iraq war was at the same time
Human factors that made Katrina worse
- Pop density = very high
- Prep and education = not very well prepared. George Bush was in Texas on holiday and didn't call of his holiday. FEMA took aid down as the aid wasn't authorised. FEMA were slow. The evacuation buses didn't make it in time as came from another state, and FEMA said don't use school buses as they were not air conditioned
- People too poor so didn't have own transport to evacuate
- Trains were left half empty when leaving but govt. didn't allow people to get on them
- Some people decided to remain in the city despite evacuation orders as some were poor and were expecting social security cheques at start of the month
- Hadn't experienced TRS of such a high category, they weren't aware of the hazards - lack of education
- Buildings weren't built to withstand high category TRS
- Wetlands destroyed so no natural drainage on Mississippi delta
- Oil platforms in Gulf of Mexico causing sea floor to sink so sea levels rising
- National Guards of army didn't come until Friday as they were short staffed
Physical factors that made Haiyan worse
- Moved quickly over region - also a category 5. This reduced impact on land. Cold water ahead wasn't stirred up, so it always had warm water so didn't lose energy.
- 7000 islands, so lots of water in between and the water was warm.
- Very strong winds (165mph), 155mph surface winds.
- System was very intense and compact so walls around eye weren't replaced so wind speed maintained.
- Around island water shallow so increased height of storm surge so they were higher due to less friction, so lots of flooding
- Configuration of islands increased storm surge as the water was squeezed up between small, narrow islands = lead to increased strength. Fuelled water straight to city of Tacloban.
Human factors that made Haiyan worse
- Lack of flood defences so the Tacloban Convection Centre = death trap
- LEDC = poor quality buildings, poor quality build also. Struggle to recover as poor because the employment were mainly fisherman and the fish industry was destroyed. Or farmers. Primary environment, living off resources of the land. Either rice growers or coconut plantations, small scale subsistence farming, local markets relied on this farming and fishing.
- Farmers given seeds by aid agencies to ensure harvest and try reduce impacts
- No money or insurance
- 20% revenue went to debt
- 16 million in extreme poverty
- Multiple hazard location as suffers from EQ, volcanoes and typhoons. Is on destructive plate boundary (oceanic/oceanic). EQ hit prior to the typhoon. 7.1 on RS, so not much aid and people already homeless.
- People used to the hazards so they were prepared very well.
Why did Typhoon Haiyan not weaken when it made landfall in Philippines: Extreme low pressure (895mb) was due to the ideal conditions, i.e. very warm, deep water and low wind shear allowing vertical development. Lots of islands and water in between the islands so typhoon doesn't lose its energy.
Change over time: Typhoon Hagupit struck the Philippines in early Dec 2013. There were grace concerns for the region which was still recovering from Haiyan 12 months earlier. But the outcome was different because:
- Persuaded to evacuate people as govt. gives incentives (bags of rice) to ensure lives saved
- Govt looked at risks and decided to evacuate the low lying areas
- In Philippines, one area they did this for a long time -> the community members persuaded to put money in fund to rely on instead of the govt
- Stock piled aid before the storm arrived
Global climate change over the past 20,000 yrs
Evidence of the past climate (palaeoclimate) shows that change has occurred naturally throughout earth’s history. The earth has swung between relatively cooler periods which have generated ice ages (glacial phases) and warmer periods when the ice has retreated (interglacials). Today, however, may scientists argue that climate change is no longer a totally natural process. Evidence suggests that the earth is warming faster than in the past and this is the result of human action.
Global climate change in the last 20,000 years . The British Isles
Evidence that can be used to find out how climate has changed over the last 20,000 yrs (all evidence is inferred)
Observations: changing sea levels; historical records (e.g. paintings at frost fairs); daily wet weather; records from past; global warming - recent evidence
Physical evidence: ice core analysis; sea floor analysis; glacial deposits
Biological evidence: pollen analysis; dendrochronology; colepotra; radiocarbon dating
We know ice sheets up to a mile thick advanced and retreated over Britain many times during the last 2 million years. This era is referred to as the Pleistocene Ice Age and ended around 12000BP. This was accompanied by major environmental changes including a rise in temperature as well as being inhabited by many different kinds of plants and animals.
Pollen analysis shows that the postglacial period can be divided into climatic periods according to patterns of vegetation in the country
main climatic periods in the British Isles in the last 20,000 years. - GALPBASS
- Name of period: Glacial phase in the Pleistocene Ice Age (started 2 million years ago)
- Temperature change: Glacial phase
- Year BP (before present): 20,000BP
- Climate: Glaciated. freezing polar climate. Temperatures in the coldest winter months were probably between -20c and -25c
- Evidence for climate change: Plants and insects found in Southern Britain at that time live only in the high Arctic today (eg lichens and mosses) & sea level at this time was lower than today with water absorbed in the ice sheet
- Name of period: Allerod period (post glacial)
- Temperature change: Increasing warmth
- Year BP: 12,000BP
- Climate: Periglacial but warming. Cool and wet relative to today
- Evidence for climate change: Birch and Scots Pine march North from the continent. and New species of plants appeared in the South then slowly spread to Northern areas
- Name of period: Lock Lomond Stadial (also known as Younger Dryas cold event)
- Temperature change: Cooler period
- Year BP (before present): 11,000BP
- Climate: Periglacial and upland glacial. Arctic conditions. Summer 6 deg celcius/winter sub-zero
- Evidence for climate change: Tundra vegetation. Herbs, mosses and dwarf birch (similar to Iceland today). Beyond the glacial limits there was hardy vegetation such as that found in Iceland e.g. mosses. Analysis of insects found from this time indicates temps were -8 deg celcius.
- Name of period: Pre Boreal
- Temperature change: Increasing warmth
- Year BP (before present): 10,000BP
- Climate: Semi-continental. Started wet but gradually dried.
- Evidence for climate change: Birch forests spread northwards at a rate of 1/4 mile a yeaar. Species of trees and animals spread North to Britain.
- Name of period: Boreal
- Temperature change: Increasing warmth
- Year BP (before present): 9000BP
- Climate: Climate continued to improve. Summers were warmer than today and winters were longer, colder and drier than at present
- Evidence for climate change: Warmer loving tree species, e.g. Elm and Oak trees grew instead of the Birch forest
- Name of period: Atlantic
- Temperature change: Climatic optimum
- Year BP: 7,500BP
- Climate: Rise in temp led to rise in sea levels. Britain had it's climatic optimum - it was warm and wet
- Evidence for climate change: Oak, Elm and Lime dominate. (Lime can't exist in Britain today). Rise in sea level. Mixed decidious forest become established in Southern England.
- Name of period: Sub-Boreal
- Temperature change: Decreasing warmth
- Year BP: 4500BP
- Climate:Became cooler and drier, with a return to a more continental climate
- Evidence for climate change: Lime trees declined and forests mainly of Birch and Oak.
- Name of period: Sub-Atlantic
- Temperature change: Warmer
- Year BP: 900-1200AD. (2500BP to today)
- Climate:The Medieval warm period - warmer than today
- Evidence for climate change: Vineyards were found as far north as York. Warmer and wetter conditions
- Name of period: Sub-Atlantic
- Temperature change: Colder
- Year BP: 1500-1700
- Climate: The Little Ice Age- colder and wetter than today. Not an ice age though-misnomer. Glacial expanision in alpine areas.
- Evidence for climate change: Painting of frost fairs on the river thames.
- Name of period: Sub-Atlantic
- Temperature change: Recent warming
- Year BP: Last 150 years
- Climate: Recent global warming. Global temps have risen by about 0.6-1 degree
- Evidence for climate change: Sea level rise, glacier retreats, extreme weather
Even in the last 12,000 years there have been periods when the temperature was warmer than today. Note down examples: Atlantic period and Medieval warm period
In the last 1000 years, the climate has been much colder than today. When was this: Little Ice Age.
(Look at pg 60 for graph)
Evidence for climatic change
As we have already seen, evidence for climatic change is taken from a variety of sources, which can be used to reconstruct past climates. Most of the evidence is indirect – climatic changes are inferred from changes in indicators that reflect climate, such as vegetation. Only recent changes (last 200 years) have direct evidence in the form of temperature records.
We will look at the following types of evidence in the most detail:-
1. Pollen analysis
Method 1) Pollen analysis
Pollen analysis: We have already seen that pollen analysis has been used to divide the postglacial period into climatic periods according to patterns of vegetation in the country. Temperature and precipitation are primary controls on the distribution of many plant species. Comparison between species' fossil and present-day distributions can be used to estimate past environmental conditions.
Why is pollen a useful indicator of past climates: Different plant species have different climatic requirements
This evidence is normally found: In oxygen free environments, such as peat bogs, they resist decay
The pollen indicates changes over time because: The climatic requirements change. Also changes in the pollen found in different levels of the bod indicate changes in climate overtime.
Once the pollen has been identified, it can be dated using radiocarbon dating. All living things contain carbon e.g. C14 and C12. C12 does not decay, but C14 is radioactive and decays at a steady rate. By measuring the amount of C14 left, & comparing this to C12, it can determine the age of the pollen grain. This method can accurately date organic matter up to 50,000 years old.
Advantage of pollen analysis
Each species has a distinctive pollen grain. As a result, it is possible to tell what kind of trees, shrubs and flowers were around at the time. Several grains trapped in this way are therefore representative of the vegetation growing at that time, which in turn is a reflection of the climate of that time.
One flower from a plant can produce 10,000 – 100,000 pollen grains, so only small samples of sediment are
needed for analysis.
Pollen analysis allows the postglacial period to be divided into phases according to the patterns of plant life e.g. the Atlantic period runs from 7500BP to 4500BP and was dominated by mixed forests of alder, oak and lime
Pollen analysis at a cave in Derbyshire has shown how forest vegetation returned to Britain at the end of the ice age. The study of pollen also shows that new species of plants spread fairly rapidly into Britain with the onset of warmer conditions
Pollen grains are deposited in layers in these sediments. If undisturbed, pollen grains in this sediment core can be dated using radiocarbon dating methods to provide a sequence of climate change over time
Disadvantages of pollen analysis
Different plants produce different amounts of pollen skewing results
Exotic pollen can confuse the sample (such as pollen blown in from distant sites)
Pollen grains do not provide a direct interpretation of climate
Pollen grains may be incorrectly identified - some are even very similar even under a microscope
Some pollen grains are better preserved than others, might be misleading
Taller plants result in a wider dispersal
Method 2) Dendrochronology (analysis of tree rings
Limitations of dendrochronology in indicating climate change:
- Few trees are older than about 4000 years
- Trees respond more to levels of moisture than temperature
Core samples can be taken from living and dead trees to extend dating further back
each year the tree develops a ring
wide tree ring infers warm wet climate
narrow tree ring infers cold and drier climate
methusela (oldest tree = 4600 yrs old) but by using remainence of dead wood also, climate records go back over 8000 yrs.
Bristlecone pine trees are located 11,000 ft up in the white mountains of California. The trees grow very slowly due to the harsh climate (cold temps, high winds, dry soils and short growing season). It takes roughly 100 years for the tree to add an inch to its trunk.
Edmund Schulman, a scientist discovered that the oldest living organism known is a bristlecone pine tree nicknamed "Methuselah" (after Methuselah, the longest-lived person in the Bible). The age of Methuselah was measured by core samples. He counted the number of tree rings. Each tree ring represented one year of life, and so he discovered the tree was 4600 years old. This was more than 1500 years older than any other living tree.
The core samples from Methuselah can be used as a dating instrument (by counting the rings) and climate recorder. The width of the tree rings can be used to reconstruct past climate because tree ring growth is affected by moisture and temperature. For example, Methuselah’s core samples show that there was an extremely cold summer in BC 1628. The tree rings showed obvious cell damage and it is possible that this matches with a volcanic eruption in Santorini, The Aegean sea (7000 miles away). Plumes of ash were released into the atmosphere reducing the amount of sunlight reaching the Earth and causing an increase in cloud cover so that global temperatures dropped.
Scientists have discovered that taking sample cores from logs, dead trees and wood remnants means that dating records can be taken back even further in time to 8700 years ago. These samples can be studied for matches with samples from the living trees so that when the rings match then there is a continuous record back in time.
Counting the tree rings in a sample core provides an accurate dating instrument, and it has been used to check the accuracy of radio carbon dating. Scientists found that carbon dating was flawed and in some cases was out by as much as 1000 years!
The bristlecone pine trees look as if they could live forever as they are very robust and healthy. Therefore, they could continue to be a dating instrument and climate recorder for many years to come. However, the main threat to these ancient trees is man. For example, following an article by Schulman on the bristlecone pine trees, they have come under threat from tourists who have taken souvenirs off the tree. However Methuselah’s precise location is undisclosed by the U.S. Forest Service to protect the tree from vandalism
In another example, Donald Currey, a Geography student was taking core samples of bristlecones on the crest of a lateral moraine to determine the age of the glacial deposits. He attempted to take core samples from the tree but struggled so the U.S. Forest service granted him permission to cut down the tree. However, when he counted the number of the rings from the core sample, he discovered that he had cut a tree which was even older than Methuselah at 4900 Years old!
why bristlecone pines are useful indicators of cli
- Long and fairly reliable record
- Can survive in harsh environments
- Oldest living organism (4600 yrs)
- The width of the tree can be used to reconstruct past climates because tree ring growth is affected by moisture and temperature
- Counting the tree rings in a sample core provides an accurate dating instrument, and its been used to check the accuracy of radiocarbon dating - allowed flaws in carbon dating to be discovered
- Most straight forward method, but very few trees about
Ice Core Analysis
The use of Oxygen isotopes as indicators of climate change..
2 oxygen isotopes: heavier o18 & lighter o16 (o16 easier to evaporate as requires less energy)
- Their movement is related to the water cycle
- Ocean contains a set amount of both oxygen isotopes
- More o16 compared to o18
- o16 is preferentially evaporated from the ocean compared to o18
- Seawater becomes 'heavier' as more o18 present
- Light o16 isotopes locked in ice during a glaciation due to temperature decrease
- Seatwater becomes isotopically heavy and there is a drop in sea level
- Ice caps will grow
- Any organism (e.g. foraminifera) that uses oxygen from water to form its shell will reflect seawater chemistry therefore the shells are isotopically heavy (less negative) during a glaciation
- If the temp changes due to the change in the amount of solar radiation received by the earth (milankovitch cycle) the ice caps will melt and retreat
- Sea level will rise
- Meltwater or rainwater will be rich in o16
- Adding o18 to seawater makes it isotopically lighter as well as shells of organism that live in the ocean
Advantage of using isotopes on marine sediments: more complete record & get a global picture of continental glaciations
BREADTH to pollen & dendrochronology
Examples of other evidence used to study climate change are:-
The organic remains of beetles (coloeptera) have also been used to reconstruct past climates. Towards the end of the Devensian glacial it heated up as fast as 10 ºC in 50 years and this led to cold living species being replaced by warmer loving species.
By its very nature, historical evidence does not go far back in time. Climate can be inferred from more recent evidence e.g. from paintings of London’s medieval frost fairs & from farm evidence in the Doomsday Book e.g. grape vines were grown in southern England during the medieval warm period. However, since 1873 daily weather reports have been documented and so provide more accurate and detailed evidence of climate change
Ice cores have been drilled from areas like the Greenland ice cap. Air trapped in the ice can be analysed for carbon dioxide content. The greater the amount of carbon dioxide, the warmer the climate.
Relict landscapes in Northern England and Wales show the effects of glaciers on the landscape e.g. corries, arêtes etc. The glacial features can be dated using radiocarbon dating or even pollen analysis to work out when they were formed and so when the area was glaciated.
recent global warming: cause,evidence,effects,miti
As we have already seen, climate change has happened in the past and temperatures have been up and down. However, in the late 20th century there has been a sudden increase in temperatures, and there is a general consensus that the planet is heating up.
Temperature records show:-
- 0.75◦c increase in mean global temperatures in the last 100 years
- The 1990s were the warmest decade since 1873 (2014 claimed as the hottest year since 1910 - Met Office)
- The total number of “cold days” (with sub zero temperatures) has halved in the last 100 years
Although a small minority of people question whether Global Warming is taking place, the vast majority of scientists do now accept its authenticity, although the degree of warming is less certain.
The natural greenhouse effect
Insolation (visible light) in the form of short wave (or ultra-violet) radiation passes through the atmosphere warming the earth’s surface. The earth then emits that heat as long wave (or infrared) radiation. However, greenhouse gases in the atmosphere such as CO2 and water vapour absorb some of this long wave radiation and radiate it back again towards the earth’s surface. This trapping of heat is known as the natural greenhouse effect. Without it, temperatures on earth would be about 33°C colder – too cold to support life on the planet! Provided the amount of greenhouse gases and water vapour in the atmosphere stay the same and the amount of incoming solar radiation is unchanged, then the temperature of the earth remains in balance.
- Solar radiation passes through the atmosphere
- Some energy is reflected by the atmosphere and the earth's surface
- Solar energy warms the earth's surface
- Heat (infrared) energy is emitted by the earth
- The heat is absorbed by greenhouse gases. They re-emit the heat, warming the earth. Some heat also escapes the atmosphere.
The ENHANCED greenhouse effect
However, Since the industrial revolution, the concentration of greenhouse gases has increased in the atmosphere so trapping more infrared radiation. This has produced the Enhanced Greenhouse Effect which has led to Global Warming. Although, Greenhouse gases make up less than 1% of atmospheric gases, they affect long term climate change by heating up the planet. The greenhouse gas which is the biggest contributor to the enhanced greenhouse effect is Carbon Dioxide (CO2). Other greenhouse gases contributing to the enhanced greenhouse effect are Methane (CH4), Nitrous Oxides (NO2) and Chlorflurocarbons(CFCs).
POSSIBLE CAUSES OF GLOBAL WARMING
The Greenhouse effect creates a stable climate. If the earth warms beyond this it is termed the Enhanced Greenhouse Effect.
These can be split into three camps:
A) Natural changes
B) Human Induced changes (known as anthropogenic change)
C) Feedback mechanisms
A) Natural changes
1) Incoming solar radiation (aka solar forcing)
As the vast majority of our heat comes from the sun, the potential for a small shift in solar output having a major impact on our climate seems to be an obvious choice to explain the changes which are occurring. Many scientists have postulated that solar flares (measured as sunspots) are cyclic (11 year cycles) and could link to the changes we are experiencing. Some have even altered the data to make them fit (see The Great Global Warming Swindle for more).
In reality, there appears to be no clear link, and if anything, all measures of solar output have been falling since 1985.
Mini Ice Age 1500-1700 AD coincides with "Maunder Minimum" - period of low sunspot activity so cold temp was due to decreased sunspot activity.
Sunspot = Magnetic storm on the surface of the Sun
Sunspots = more UV released = more warming
11 yr cycle increases and decreases over this period
2)changes in earths orbit around the sun&tilt of e
Earth's orbit gets more eliptical (oval)
Back in the 19th Century, Scottish scientist James Croll discovered a possible link between astronomical cycles of the earth and sun and glacial periods. Today they are known as the Milankovitch Cycles (after the Serbian scientist who finally put the jigsaw pieces together).
Although these can change the earth’s climate, there is no clear evidence that they are causing today’s climate. In fact, most scientists believe that at present they should show a general cooling trend!
3) Volcanic activity and meteorite strikes
Both of these can lead to sudden temperature changes as ash is thrown into the atmosphere leading to a blocking of sunlight and fall in temps. Longer term, they can release CO2 in to the atmosphere causing a gradual rise in global temperatures. Very likely to have caused the mass extinction linked to the Cretaceous-Tertiary (K-T) Boundary (the demise of the dinosaurs).
B) Anthropogenic changes
The list of greenhouse gases, as going down, the quantity of the gas gets lower but it's more potent
how humans are thought to be contributing to the enhanced greenhouse effect (anthropogenic global warming):
- Greenhouse gas: Carbon Dioxide (GREATEST quantity)
- Sources: Burning fossil fuels (e.g. coal); Deforestation and transport; Volcanic eruptions
- Conc. in the atmosphere (PPM - parts per million): 280ppm in 1750 (pre industrial). Around 380ppm today
- Lifetime in atmosphere: 50-200 yrs
- Global warming potential (GWP): X1. Responsible for 60% of the enhanced greenhouse effect
- Greenhouse gas: Methane (CH4)
- Sources: Bacterial decomposition in soil and released into air; cattle farting (1 cow produces 100 litres); landfill sites; rice fields; thawing permafrost - releases CH4 into atmosphere
- Conc. in the atmosphere: Occurs in lower concs than CO2
- Lifetime in the atmosphere: 12 yrs
- GWP: X21 i.e. CH4 is 21 times more effect in causing global warming than CO2 -> only accounts for 20% of enhanced greenhouse effect
- Greenhouse gas: Nitrous oxides (NO2)
- Sources: Increased use of fertilisers
- Conc. in the atmosphere: Makes up a very small amount of the atmosphere. 270 ppb in 1750 (pre industrial) 314ppb today (ppb - parts per billion)
- Lifetime in the atmosphere: 114 years. NO2 has one of the longest atmosphere lifetimes of the greenhouse gases
- GWP: X289 i.e. NO2 is 289 times more effective in causing global warming than CO2
- Greenhouse gas: Chlorflurocarbons (CFC's)
- Sources: Artificially made and were used in fridges and aerosols until mid 1970s; Many of the worlds nations agreed to control the use of CFC's in 1987 when they signed the montreal protocol. Due to the long lifetime they continue to trap heat for centuries to come; the substitute HFC's less damaging to ozone layer, still trap heat in the atmosphere
- Conc. in the atmosphere: Much lower conc than those of the other gases. V. low in 1750 (pre industrial) today it's 553 ppt (parts per trilliob)
- Lifetime in the atmosphere: 1000s of years
- GWP: X7000 i.e. CFC's are 7000 times more effective in causing global warming than CO2
Definition of the Global Warming Potential (GWP)
The global warming potential of a gas refers to the total contribution to global warming resulting from the emission of one unit of that gas compared to one unit of carbon dioxide (which is assigned a value of 1). For example, if methane has a global warming potential of 21, it means that 1 kg of methane causes the same amount of global warming as 21 kg of carbon dioxide.
The negative effects of Greenhouse Gases depends on:
- The concentration (volume) in the atmosphere
- The effectiveness as an infrared absorber (see GWP)
- The lifetime (how long it lasts in the atmosphere)
Water vapour is the biggest contributor to the natural greenhouse effect but does not contribute to the enhanced greenhouse effect. This is because it's not increasing. Even if water vapour did increase it would just lead to more clouds (trap IR radiation) BUT balanced by reflecting more UV.
It should be noted that an increase in temperature will increase the water vapour in the atmosphere and create a “positive feedback mechanism”. However natural process will stabilise this quickly, stopping a “runaway effect” on the climate.
C) feedback mechanisms & global warming
Feedback mechanisms are like a chain reaction, once started, they are self driven.
Positive feedback mechanism could accelerate global warming in the future. Several different examples of positive feedback exist. A positive feedback mechanism is when an effect causes more of itself - so tending to spiral out of control in an unstable way. (So GW causes change to the environment which is further accelerated).
Tipping point - passed a 'tipping point' where global warming and change to natural environment are now non-reversible.
Climate scientists often use the term tipping point in conjunction with feedback mecahinsms. The link between the two: Thawing of permafrost in Siberia due to heat, this melting causes change to natural environment. The melting permafrost releases methane (X21 - potent GH gas). This methane traps IR radiation, leading to more warming and so more permafrost melts and releases more methane and so on... May be past the tipping point now (changes are now irreversible and can't be stopped)
Positive feedback loop:
Loss of snow and ice cover in the Arctic means less sunlight is reflected (darker surface absorbs more UV) so warmings accelerated. The release of methane, a potent GHG from the melting of the permafros, triggering a second feedback loop.
GW -> Less ice (darker surface) due to increase in rocks -> lower albedo effect -> temp increase .. loop starts again
Negative feedback loop:
Every 100,000 years - eliptical orbit -> cold winter -> ice spreads over the surface (lighters surface so more UV reflected - albedo effect) -> even colder ... loop starts again
Evidence of global warming
What does the hockey stick graph show about recent climate change: (pg 77):
Sustained temp for about 1000 yrs and then sharp increase since 1800 - definite proof of human activity causing global warming. The sharp increase coincides with industrial revolution which increased greenhouse gas emissions which causes the enhanced greenhouse effect. Spiralling out of control as it causes changes to natural environment.
- Before 1872 proxy data - temp inferring (this is when temp was fairly stable)
- 1750 pre industrial
- Data from thermometers giving actual data from 1873 daily weather records. (when temps increased)
- Why would the upward trend suggeest recent climate change is predominantly caused by humans? : occured after industrial revolution - factories released GHG so increase in GHGE.
- Some question the validity of the graph as conclusive evidenec as before 1873 the data was only inferred (may not be accurate)
The great climate debate
It is debated as to whether global warming is indeed natural or human induced (anthropogenic).
The Intergovernmental Panel on Climate Change (IPCC) have been at the forefront of global warming research and believe that human activity has contributed to Global Warming. However, global warming sceptics question the validity of this evidence and suggest Global warming is NOT human induced but actually part of a natural cycle of longer term climate change.
Just need to know both sides of argument.
The great climate debate
It is debated as to whether global warming is indeed natural or human induced (anthropogenic).
The Intergovernmental Panel on Climate Change (IPCC) have been at the forefront of global warming research and believe that human activity has contributed to Global Warming. However, global warming sceptics question the validity of this evidence and suggest Global warming is NOT human induced but actually part of a natural cycle of longer term climate change.
Just need to know both sides of argument.
Is the evidence of temp change taken from before 1850 reliable?
Yes: There's a wide range of studies using proxy data which reveal similar patterns when reconstructing temperature patterns
No: Reconstructions of past temperatures are based on proxy data which has its limitations. It also becomes sparser the further back in time so less reliable as evidence for temperature change.
Is the evidence for recent global warming reliable?
Yes: Daily temperature recordings have been taken by the British Meteorological society since 1873. It shows that in the last 100 years the earth has warmed up by 0.8 degrees.
No: Most temperature recordings are from weather stations based in urban areas where temperatures are higher due to the "urban heat island effect". Some regions of the world are also devoid of instruments so have no temperature data. AND the climategate scale at East Anglia University revealed emails which shows climate scientists have carefully selected data that proves global warming is anthroprogenically caused.
Is the change in temperature over the last 100 years definitely human induced?
Yes: The hockey stick graph shows the sharp temperature increase coincides with the industrial revolution and the increased burning of fossil fuels
- Between 1940-1970, global temps went down slightly even after industry boomed and co2 emissions rose.
- Climate change can be explained by natural variability (e.g. changes in the orbit, sunspot activity) etc. For example, there is evidence that the temperature changes with the cycle of sunspot activity. The Little Ice Age coincided with a period of decreased sunspot activity.
- Ice core analysis shows co2 rises AFTER warming by 800 year time lag. The increase in co2 may be as a result of temperature rises.
- There has been a greater conc. of co2 in the atmosphere in the past (e.g. during the Ordovician Ice Age)
The Climate Gate Affair
Impacts of the ClimateGate Affair:
- Began in November 2009 with the hacking of a server at the Climatic Research Unit (CRU) at East Anglia University by an external attacker.
- Emails got intercepted and data leaked to various locations on the Internet.
- Coincided with the copenhagen conference on climate change - all world leaders meeting and supposed to make new targets to reduce greenhouse gas emissions that expired from Kyotot in 1997. No new agreements made due to this leakage.
- Raised the suggestion that scientific evidence can't be fully reliable.
- Data cherry picked - to show global warmining was taking place.
Possible effects of global warming on Britain
As a result of global warming Southern Britain could experience a more Mediterranean climate.
- Summer in South East likely to be drier and hotter - more drought
- Expected to increase between 2-3.5 degreees (highest in S. England)
- Winter rainfall expected to increase especially in West - rainfall could increase by 3.5%
- Summer rainfall expected to decrease - especially in South - rainfall could decreased by 49%
- Expected to increase in North & West. Gales will be 30% more frequent.
d) Sea level rise
- 60% of the sea level rise will be from the expansion of water as it heats=thermal expansion of oceans.
List the effects of sea level rise on the UK:
- Accelerated sea level erosion could cause loss of buildings, rail and road links and resulting economic impact.
- Salinisation of freshwater and agricultural land.
- Increased vulnerability to storm surges.
- Loss of coastal habitats like salt marshes and wetlands, especially those 'hemmed in' by coastal defences.
e) Disease and pests
- Malaria may be re established in UK and diarrhoeal disease is also predicted to increase. Poorest people affected most and increaased heat waves, floods and droughts increases the burden of malnutrition.
f) Plant and animal distribution
- Before 1989 the Little Egret was very rarely seen in the UK. Rising temps have allowed the bird, previously found in wetlands in S. Europe and Africa to move Northwards.
- Soils: higher temp could increase soil moisture deficits, clay soils may shrink endangeing the foundation of buildings, possibly less organic matter in the soil.
In some areas of the UK, global warming could devastate the tourist industry along with the local/ regional economy. 40% of all UK trips are to the coasts, such as Norfolk, but sea level Rise will remove some of the existing coastal resorts and will force others to install unsightly coastal defences, reducing tourist interest. On the other hand, warmer summers and longer spells of hot weather could increase tourism to UK holiday resorts and lengthen the tourist season into late autumn. This will particularly benefit resorts in northern England (e.g. Blackpool and Southport) where cooler weather deters visitors out of season.
+ & - effects global warming might have on UK
- Increased crop productivity due to temperature increasing and longer growing season
- Decline in winter mortality due to higher temps
- Reduction in energy demand for heating
- Expansion of tourist destinations
- Certain fish stock (like Paice) may increase
- Melting of Arctic ice could open new shipping routes, improving trade links with Asia and The Pacific.
- Southern England may need to irrigate due to decreased rainfall and drough
- Habitats will change and could lead to species extinction Eg mountain Hare
- Flooding costs would increase from current £1.2 billion a year to £2.1billion - £12billion by 2080
- People hit by storms and floods (Eg those having to leave their homes for extended periods) may suffer mental health problems like depression
- Water shortage could increase
The Big Chill
The “Big Chill” is a programme which shows an alternative perspective on the possible effects of global warming on the UK climate. It shows how Global Warming could cause the warm Gulf Stream (or North Atlantic Conveyor) to be diverted away from the UK, which would then have a very different impact on the UK climate.
a) The Gulf Stream conveyor belt is an example of thermohaline circulation which redistributes heat from the warm equator to the cold poles. What drives the circulation?: It is driven by the differnce in density between the warmer, less dense water at the tropics and the colder, denser salty water that sinks at the poles. The circulation drives currents and modifies the climate and ecosystem in different parts of the world.
b) What impact does the Gulf stream currently have on the UK climate?: Keeps UK warm
c) How might the North Atlantic Conveyor be affected by Global warming? What could be the consequences for the UK? Britain could become bitterly cold. Bursts of extreme rainfall. River flooding more common. Storms. Greenlands water flowing towards the conveyor. The salt would be diluted and it it's diluted too much the conveyor wouldn't sink, this could cause the thermohaline circulation to shut down altogether (parts of it)
Possible effects of GW on the African Savannas wit
The possible effects of global warming on the African Savannas with a tropical wet/dry climate. Tropical wet and dry 5+15deg N&S
- Savanna land likely to experience an increase in temp of some 1.5 degrees by 2050
- Precipiation expected to increase by 15% within Savanna lands close to the equator but might decrease by 10% in areas towards the N & S fringes of the climate zone
- Variability of rainfall will lead to more frequent droughts and flooding in some areas. During wet season 25-50% more rainfall expected to fall. More frequent drought will contribute to desertification
- Arid areas (15 degrees N&S) get drier - leading to more desertification (less under the influence of ITCZ)
- Increased latitude = STA more influential
- 20% reduction in crops (Sub-Saharan Africa)
- Higher rainfall in Savanna lands closer to the equator are likely to lead to increased growth of trees and scrub in what was previously grassland
- A rise in sea level of 25cm is predicted by 2050, so low lying areas along the coast will expeirence in coastal erosion and flooding. Coral reefs in Africa may be lost (In East Coast)
Responses to global warming
International action and cooperation is increasingly seen to be essential if the problems associated with global warming are to be addressed effectively.
Convention: Rio Earth Summit, 1992
Who was involved? What was the international agreement to tackling global warming?: “Think Globally, Act Locally” 160 nations agreed that pollution reduction targets were needed in order to tackle climatic change. The summit also produced Agenda 21 which was a blueprint aimed at a clean up of the global environment and encouraging environmentally sound developments. For example, an area targeted was R&D on non-carbon energy alternatives in order to reduce
Problems encountered: No actual pollution reduction targets were set
From 1992 onwards there was increased awareness about recycling (public transport, recycling etc)
Kyoto Protocol (1997): Signed by 175 countries. Industrialised countries must aim to cut their overall emissions to 5% below 1990 levels by 2012 To achieve this, the UK has set the following targets e.g. To cut CO2 emissions by 60% by 2050. To increase renewable to 10% of energy mix by 2010 and 20% by 2020
Problems encountered: The decision at Kyoto to reach 1990 carbon dioxide levels by 20101 is arbitrary – why 1990 levels. Why not 1980 or even 1950 levels? Co2 has a very long lifetime in the atmosphere of 100 years, so concentrations respond very slowly to any target reductions in emissions.
LEDCs were not included in targets to curb Greenhouse gases The US signed the protocol and then pulled out – damaging to the US economy despite being the being the biggest Greenhouse gas polluter & responsible for a ¼ of GGE countries are expected to monitor their own GGE, there is room for cheating or massaging of figures
UN Copenhagen Conference 2009- NO NEW TARGETS MADE
Target to limit global warming to 2C above pre-industrial temperatures. This means that worldwide carbon emission must start falling in the next 10 years. They met to try and reach agreement on the rules, incentives and targets that would curb GGE. This would involve both MEDCs and LEDCs.
Problems: No quantified targets for emissions reductions were agreed. It was hoped that world leaders would agree to a 50% reductions in emissions by 2050. There are no legally binding commitments on the actions countries have said they will take to curb their GGE. There is no agreement on how the world’s rich countries should help LEDCs to move to low carbon economies and “adapt to climate change” (e.g. tackle droughts, floods and sea level rise). The EU have proposed that LEDCs should be given $100bn in funds annually from MEDCs by 2020. The lack of a consensus at the meeting was partially blamed on the ClimateGate scandal which broke at the same time.
UN climate change conference lima 2014
Involved MEDC'S and rising economies (china, brazil, india)
international agreement to limit globsl temp increase to 2 degrees above preindustrial levels
countries involved have pledged to give new quantified targets to reduce GGE by december 2015 - next UN climate conference in Paris
Decision on new climate change and to LEDCs has been deferred. No agreement reached on how much money MEDCs should help LEDCs cope with the effect of climate change and invest in clean energy.
International response to Global Warming
Stern Report-national response to gw- the eg of th
In October 2006, the UK treasury funded The Stern Report (written by Nicholas Stern) which concluded that the worst impacts of climate change could be avoided if strong action was taken now.
Released on Oct 30th 2006 by Nicholas Stern. Written for the British Govt.
What it's about: The Economics of Climate Change - the economic impacts of climate change (cost of impacts) and the economics of stabilisation greenhouse gases in the atmosphere (cost of responses)
Only 1% of world GDP need to be invested in order to avoid the worst effects of climate change and failure to do this would result in world GDP falling by up to 20%. We face losing 1/5 of the world's wealth from unmitigated climate change. It could trigger a world economic recession.
UK's direct response
- The UK energy mix is heavily dependent on fossil fuels (over 80%) and so results in enormous greenhouse gas emissions.
- The UK Government has now revised the UK targets in cutting carbon dioxide emissions agreed at Kyoto to a more ambitious one: An 80% cut in CO2 emissions by 2050.
UK's direct reponse to tackling climate change:
- The London Array has been given the go ahead to be built. It should the world’s largest offshore wind farm. Construction started in March 2011. It should meet 70% of the government’s renewable energy targets.
- There is great potential to develop marine power off the Orkney islands. Currently there is a site testing out new technology. This location has the potential to be the world’s largest producer of marine energy.
- Lower fuel duty on more environmentally friendly fuels e.g. LPG (liquefied petroleum gas)
- The Govt wants to cut carbon emissions from transport
- The UK government has plans to build 8 new nuclear power stations
Energy mix cont:
- British oil companies are looking into taking CO2 from power stations and piping it to an oil field in the North sea where it would be stored under the seabed (called carbon sequestration)
- The UK has most potential to increase wind farms, biomass (e.g. landfill gas) etc.
- UK government want to increase renewables to 20% of the energy mix by 2020 Plans for 15 new ‘Ecotowns’ which will showcase new energy efficient technologies and promote “greener living”. Aiming for zero carbon standards (in the course of one year, the release of carbon emissions will be balanced by the energy conserved)
- The UK government has increased the no. of gas fired power stations - produces 40% less CO2 emissions compared to coal fired power stations
Energy conservation in the home
Energy conservation in the home:
- The Govt introduced “A Code for Sustainable Homes” in May 2008. New homes must now be built to be energy efficient and will be given a star rating from 1 (least energy efficient) to 6(most energy efficient)
- BEDZED - Built on reclaimed land in South London. An existing housing development with energy efficient technology and a greener lifestyle. Compared to an average household, BEDZED residents have cut electricity consumption by 25%, & car mileage by 65%
- The UK govt has a target of 80% reduction in C02 from 1990 1evels by 2050
Energy conservation in transport
- Improving public transport e.g. Tram system in Manchester will be extended to include Oldham and Rochdale in the North.
- Tesco Lorries run on biogas not petrol. The methane gas (biogas) is made from rotting food, instead of sending it to landfill.
- Road tax is less for cars with lower CO2 emissions, and electric cars are exempt.
- Hybrid cars (run on petrol and electric) are exempt from the London Congestion Charge.
Energy conservation in the workplace
- Tesco lorry drivers are given personal tips on how to reduce energy consumption
- Tesco has a low carbon strategy. They have halved GGE in 6 years
- Tesco have cut the cost of energy efficient products
- Low carbon products offered to consumers. Signs and labels on products – prompts customers to choose the green low carbon products
- The Tesco supermarkets are built so they maximise use of natural light
- Rainwater is used to flush toilets in Tesco
Individuals response to global warming
Change the amount of waste produced: recycle
Change your shopping and eating habits: buy locally produced food; grow fruit & veg yourself; shop less frequently and bigger shops
Change the way you travel: use public transport; car share; cycle; hybrid cars/lower carbon emission cars; walk for shorter journeys; holiday locally
Change amount of energy used in the home: double glazing; switching lights off; energy efficient lightbulbs; A-rated appliances; loft insulation; solar panels