Download Unit 1 – The World At Risk

Chapter 7
The Issue of Global Warming
Developing the Case of Human Responsibility
Key Points
 Greenhouse gases maintain the temperature on Earth at a level for live.
 Human activities increase the amount of GHGs in the atmosphere.
 Increased GHGs may lead to warming of the atmosphere and climate
change.
 Increased GHGs may alter weather patterns, shift biomes and increase sea
levels.
 Feedback mechanisms are very comples and changes may lead to positive
or negative results.
 Governments & individuals can act to reduce GHG emissions.
 There is still much controversy & varying preceptions about global
warming.
Short Term Objective 1.
 Describe the functioning of the atmospheric system
in terms of the energy balance between solar and
long-wave radiation.
(ν): The number of waves that pass a fixed point per second
Wavelength, Amplitude, Peak & Valley
Peak
Peak
Valley
Valley
What do you know already
Make a list of causes of climatic change.
 Burning fossil fuels
 Volcanic activity & astroid impacts
 Changes in Earth’s orbit
 Progression of the equinoxes
 Milankovitch Cycles
 Sun spot activity
What are the percentages?
Questions????
 The Earth’s atmosphere is an example of an open
system
 What does this mean and why is it important?
 The Greenhouse effect is natural and important to the
earth. Why?
N
Albedo may
affect the energy balanceS between short
and long term radiation
 What is albedo?
 Use figures from the table to describe how the albedo of
the atmosphere can change the amount of solar
radiation arriving at the ground surface.
 Use figures from the table above to describe how the
albedo of the ground surface can change the amount of
long wave radiation emitted by the earth
If the Greenhouse effect is natural then what’s
the problem?
Climate changes all the time but what has happened
recently?
The problem is that the rate of change seems to have risen
rapidly since the Industrial Revolution.
 Hence it is sometimes called the Enhanced Greenhouse Effect.
Why?
The causes of climate change
1. Increasing levels of Greenhouse Gases in the atmosphere
Climate Change is not a new thing!
 The worlds climate has been changing over the last 18,000
years, sometimes getting hotter and sometimes colder as you
can see from the graph below.
Paleoclimate Cycles
During most of Earth history, global temp. was 8-10°C warmer than
today, but there have been a few long periods of sustained globally
cold periods.
ice ages:
2500 Myr,
700 Myr,
300 Myr and
42 Myr
Even over short periods there are fairly large
fluctuations
Proof of Global Warming?
What do you think?
 Does it matter whether the causes of global warming
are natural or human?
 How do the causes of global warming impact the way
we mediate the problem?
How to Change Global Climate
The ways in which global climate may be influenced include:
•changes in Earth’s orbit
•variable solar output
•changes in ocean circulation patterns
•albedo (reflectivity) effects
•greenhouse effect
Is climate change natural or human induced
(anthropogenic)?
There are 3 main natural events that scientists believe
affect the worlds climate:
1. Variation in solar output
2. Variation in the earths orbit
3. Volcanic eruptions and cosmic causes
1: Variations in Solar Output
 The sun’s output is not constant; it also varies. A variety of cycles
have been detected, most are short term. The most obvious is due
to the 11-year sun spot activity cycle.
 The effect of sunspots is to blast more solar radiation towards the
earth
 Some scientists have suggested that around 20% of 20th Century
warming may be because of solar output variation
 However a study in 2006 showed no major increase in solar output
since mid 1970s
Sun Spot Activity: Q & A
What are sunspots?
How are they linked with the amount of solar radiation the earth
receives?
Describe the pattern of sunspot activity.
What is the link between sunspot activity and global temperature
anomalies?
2: Variations in the Earth’s Orbit
 Milankovitch Cycles
 A Serbian physicist working at the beginning of the
20th century.
 He identified 3 variations in the Earth’s orbit around
the Sun
 Link
Milutin Milankovitch 1879 - 1958
Eccentricity of Earth’s orbit
18_2.swf
 Every 100,000 yrs the Earths orbit changes from spherical to
elliptical, changing solar input
Obliquity of the Earth’s Axis
The Earth’s axis is tilted at 23.5o, this changes over a
41,000 yrcycle between 22o & 24.5o, affecting solar
input, especially in higher latitudes.
Wobbly Axis!
The Earth’s axis wobbles, so which way the hemispheres
are facing to the sun when closest to the sun varies over
21,0000 yrs. Affecting solar input.
Milankovitch Cycles
 Many scientists argue that the Milankovitch cycle may have been just
enough to trigger a major global climate change, but that climate
feedback mechanisms are needed to sustain it.
 Feedback effects are those that can amplify a change and make it bigger
(positive) or smaller (negative).
 An e.g. of positive feedback is snow and ice cover. Small increase in
snow and ice raises surface Aledo reflecting more solar energy back into
space. Resulting in further cooling
 An e.g. of negative feedback s cloud cover. As GW occurs, more
evaporation occurs increasing cloud cover, which in turn may reflect
more solar rays back into space diminishing effects of the warming.
 Also Tundra?? What effect does the tundra have in GW?
3. Volcanoes & Cosmic Collisions
 Major eruptions eject material into stratosphere.
 The sulphur dioxide forms a haze of sulphate aerosols, which
reduces the amount of sunlight received at Earth’s surface
 The eruption of Tambora led to the year without a summer in
1816 as global temperatures dipped by 0.4-0.7 degrees C
 An asteroid smashing into the Yucatan peninsular is thought to
have contributed to extinction of the dinosaurs.
Unprecedented Global warming?
What does this phrase mean?

been seenwidespread
before!
 Never
“The observed
warming of the atmosphere and ocean,
 together
So is Global
warming
unprecedented?
with
ice mass
loss, support the conclusion that it is
unlikelyasthat
global
climate
ofwarming
the past in
50the
yrspast.
 extremely
Not unprecedented
we have
had
periodschange
of global
be explained
external
forcing,
very likely that it is
 can
The IPCC*
sums upwithout
the current
views on
Globaland
warming:
not due to known natural causes alone”
Anthropogenic Causes Seem To Be Confirmed!
Facts
Satellite observations since 1993 suggest an annual rise in sea level
of 3.1mm, and a decline in Arctic sea ice of 2.7% per decade
 The level of CO2 in the atmosphere is far above the ‘natural’ level
and continues to rise.
Temperature rises have been recorded on all continents since 1970
 11 of the 12 warmest years on record occurred between 1995 and
2006
Where do we get the long term evidence
for climate change from?
1. Ice Cores
• Best evidence for climate change comes from Greenland and
Antarctic ice cores
• Ice cores are a frozen record of past climates. Like a time capsule!!
• Within these layers the ice contains air bubbles which contain
carbon dioxide and oxygen isotopes.
• From looking at the graph you can see clearly the periods of low
concentrations of CO2 occur during glacial periods
• High concentrations of CO2 link with warmer periods of time- like the
Holocene interglacial we are going through now!
How accurate and reliable are
these sources of data?
 The sequences of sea level change links very closely with
oxygen and CO2 isotope levels suggesting that this is a very
reliable source!
Where do we get the long term evidence
for climate change from?
2. Pollen Analysis
 Pollen was extracted from
sediment cores in peat bogs and
lake beds.
 Pollen grains are preserved in
waterlogged sediments.
 By analysing pollen we can see
how ecosystems have changed in
response to climate change.
How accurate and reliable are
these sources of data?
2. Pollen Analysis
 Not as reliable - as accurate pollen reconstructions rely on good
preservation of pollen. Long pollen sequences are rare, and
vegetation change may lag behind “climate change”.
Where do we get the medium term evidence for
climate change from?
1. Tree Rings (Dendrochronology)
 Many trees are sensitive to
changes in temp, sunlight
and precipitation
 In warm years trees have
wide rings & vice versa
 Record can go back
10,000years+
How accurate and reliable are these sources of data?
1. Tree Rings (Dendrochronology)
 Good reliability – However, tree records only give localised
records!
Where do we get the medium term evidence for climate
change from?
2. Paintings and written accounts
London Frost Fair 1789
Bruegel Painting 1565
How accurate and reliable are these
sources of data?
Paintings are a good line of evidence
Where do we get the medium term evidence for climate
change from?
The written word
Dickensian Winters
How accurate and reliable are these
sources of data?
 The written word is also good evidence
Where do we get the medium term evidence for climate
change from?
2. Historical records
How accurate and reliable are these
sources of data?
2. Historical records
 Unreliable – These sources did not set out to record climate,
and must be used with care. They are usually local, and
difficult to generalise.
Where do we get the medium term evidence for climate
change from?
3. Glacier Retreat
 Glaciers change in response to climate change.
 We can look at old photos/maps/paintings to measure direct
differences in glacial positions
How accurate and reliable are these
sources of data?
3. Glacier Retreat
 Reliable – Good records stretch back to around 1880, before
this the record is patchy.
Where do we get the short term evidence for climate
change from?
 The last 128yrs of data suggest the Earth is 0.7 – 0.8 oC warmer
 11 of the world’s hottest 12 years occurred in the decade 1995-2006
 Global warming or natural?
How accurate and reliable are these
sources of data?
Good evidence of the
 Link between CO2 & temperature
Three possible effects of climate change.
1. Rise in Global Mean
Temperature
2. Rise in Average Sea Level
3. Decline in Northern
Hemisphere Snow |Cover
Homework
 “An Inconvenient Truth” or
 “The Death of the Oceans”
 Watch it and fill in the sheets ready for discussion
next lesson.
Is the Carbon Anthropogenic (human) or Natural?
Most scientists agree Anthropogenic causes are
producing the enhanced greenhouse effect and
leading to unprecident global warming.