Natural

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Natural Anthropogenic sources of climate
variability
Details for Today DATE 7th October
2004 BY Mark Cresswell FOLLOWED
BY Literature Searching

• 69EG3137 Impacts Models of Climate Change

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Lecture Topics

• Introduction
• Natural Milankovitch cycles
• Natural Solar Cycles
• Natural Volcanic activity
• Anthropogenic Fossil fuels
• Anthropogenic Land use change
• Post-lecture tasks today

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INTRODUCTION
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Is this a new phenomenon?
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Introduction 1
It is known that our climate has experienced
warmer and cooler phases throughout the past Sea
levels regarded as rising at an alarming rate
today have been considerably higher in the
past See ARIC website http//www.doc.mmu.ac.uk/a
ric/gccsg/index.html
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Introduction 2

• Proxy reconstructions for the climate of the
  Quaternary Period are considerably more abundant
  and reliable than for earlier periods
• The Quaternary spans the last 2Ma of Earth
  history and is separated into two Epochs, the
  Pleistocene (2Ma to 10Ka) and the Holocene (10Ka
  to present)

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Introduction 3

• Although deglaciation had been taking place for
  at least 4,000 years, a rapid deterioration
  (cooling) in climate occurred at about 10 to 11Ka
• This event is known as the Younger Dryas Cooling.
  The North Atlantic polar front readvanced far
  southward to approximately 45N (only 5 or 10
  north of the glacial maximum position)

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Introduction 4
Holocene thermal maximum 6 to 7 thousand years
ago
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Introduction 5

• Quantitative estimates of mid-Holocene warmth
  suggest that the Earth was perhaps 1 or 2C
  warmer than today
• Most of this warmth may primarily represent
  seasonal (summer) warmth rather than year-round
  warmth

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Introduction 6

• Beginning about 1450 A.D. there was a marked
  return to colder conditions. This interval is
  often called the Little Ice Age, a term used to
  describe an epoch of renewed glacial advance

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Is this a new phenomenon?
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MILANKOVITCH CYCLES
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Milankovitch Cycles 1

• The distance between the Earth and Sun changes
  for a variety of reasons as does the quantity of
  solar energy reaching Earth
• The Earth follows an elliptical orbit around the
  Sun. Orbital stretch/shrink 100,000 yrs

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Milankovitch Cycles 2

• Milutin Milankovitch (a Serbian astrophysicist)
  worked out ways in which the Earth-Sun geometry
  changed as a function of orbital cycles

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Milankovitch Cycles 3
Milankovitch Cycles

1. Variations in the Earth's orbital
   eccentricitythe shape of the orbit around the
   sun.
2. Changes in obliquitychanges in the angle that
   Earth's axis makes with the plane of Earth's
   orbit
3. Precessionthe change in the direction of the
   Earth's axis of rotation, i.e., the axis of
   rotation behaves like the spin axis of a top that
   is winding down hence it traces a circle on the
   celestial sphere over a period of time

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Milankovitch Cycles 4
Illustration of ECCENTRICITY
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Milankovitch Cycles 5
Illustration of OBLIQUITY
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Milankovitch Cycles 6
Illustration of PRECESSION OF THE EQUINOXES
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Milankovitch Cycles 7
Calculated Orbital Variation
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SOLAR CYCLES
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Solar Cycles 1

• There is really no such thing as a solar
  constant
• We already know that orbital effects can change
  the quantity of solar radiation reaching the
  Earth
• The Sun generates variable quantities of energy
  due to its own internal variability
• Solar activity is know to have cycles with a
  periodicity of about 11 years

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• The 11 year solar cycle

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Solar Cycles 2

• The 11 year solar cycle

Historical overview of solar sunspot cycles
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Solar Cycles 3

• The 11 year solar cycle

Historical overview of solar sunspot area from
1870s to 2000
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Solar Cycles 4

• As well as sunspot activity, the Sun can interact
  with our atmosphere by generating solar flares
  leading to a powerful solar storm (enhanced
  solar wind)
• Solar flares can damage satellites, and can also
  affect the Van Allen belts producing Aurora
  (Northern Lights)

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Solar Cycles 5
Coronal Mass Ejections (CMEs) are geomagnetic
disturbances on the Sun surface that generates
the Aurora Borealis.
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VOLCANIC ACTIVITY
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Volcanic Activity 1

• Active volcanoes generate large quantities of
  dust and smoke
• Particulates in the atmosphere block out solar
  radiation, preventing it from penetrating through
  to the ground surface
• The main effects of volcanic eruptions is to cool
  the affected regions (not dissimilar to a
  nuclear winter).

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Volcanic Activity 2

• When Mount Pinatubo erupted in the Philippines
  June 15, 1991, an estimated 20 million tons of
  sulphur dioxide and ash particles blasted more
  than 12 miles (20 km) high into the atmosphere

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Volcanic Activity 3

• A research team ran a general circulation model
  developed at the Max Planck Institute with and
  without Pinatubo aerosols for the two years
  following the Pinatubo eruption
• The climate model calculated a general cooling of
  the global troposphere

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FOSSIL FUELS
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Fossil Fuels 1

• The burning of fossil fuels is believed to be the
  major source of anthropogenic climate forcing
• Burning oil, gas and coal generates a wide
  variety of gases and particulates the most
  important of which is carbon dioxide (C02)
• The natural Greenhouse effect is enhanced by
  extra C02 to create the Enhanced Greenhouse
  Effect. Without the natural greenhouse effect
  global temperatures would be around 253 K (-20ºC)
  but is actually 288 K (15 ºC)

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Fossil Fuels 2

• Other greenhouse trace gases include Methane
  (CH4), Nitrous Oxide (N2O) and water vapour.

Earth System Source C (X 1015 g) Sink C (X 1015 g) FLUX C (X 1015 g)
LAND 100 100 0
OCEANS 100 104 -4
HUMANITY 7 0 7
SUM 3
Contribution of land, oceans and human activity
to carbon flux
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LAND USE CHANGE
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Land Use Change 1

• Human activity can affect the way in which the
  Earth surface responds to solar radiation
• Modifying land surfaces can profoundly affect
  heating and vulnerability to climate change
• The gradual commercial deforestation of the
  tropical rainforest regions in South America have
  removed a valuable carbon sink and released
  carbon as this timber is burned or decays

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Land Use Change 2

• The slash and burn policy attributed to
  subsistence farmers in Africa and South America
  have removed tree species
• Removal of trees can lead to landslips, soil
  erosion and development of dustbowls
• Changes in Sahelian grasslands (removal) may have
  modified the albedo and soil moisture regime
  leading to droughts in the region

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Other Sources of Variability

• Urban heat island
• Ocean circulation
• Geothermal activity
• Tectonic plate movement

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Literature Search Task
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