Download The Science of Climate Change

The Science of Climate Change:
Informing your decision making
Version: March 2012
Carbon Dioxide
Now
389ppm
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CO Concentration (PPM)
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1700
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Air Temperature
A document prepared by the
Australian Institute of Physics (Victorian Branch)
Education Committee
The Science of Climate Change:
Informing your decision making
1.
2.
3.
4.
5.
6.
7.
8.
9.
The Earth’s atmosphere
Electromagnetic radiation
Greenhouse Effect
Climate Models
What do climate models predict?
Interpreting data
Climate change impacts
Cause for concern
Expressing concern
Overview
The Earth's climate is remarkably suited to the development and sustenance of life.
Neither of our neighbours in space has produced life. Venus is too hot. It has a runaway
greenhouse effect which keeps it at around 4600 C. Mars has a very thin atmosphere
which hardly traps any heat and so its temperature ranges between a frozen -1400 and
+20°C. While their distance from the Sun is significant, it is the atmospheres of these
three planets that make all the difference.
It is our atmosphere, along with the moderating effect of the oceans, that have provided
the Earth with the stable climate which has enabled life to develop and thrive. The
'greenhouse effect' is a crucial part of this climate system, but it is this which we are
modifying by our use of fossil fuels. The essential ingredient of coal, oil and gas is
carbon. When burnt, this combines with air to produce carbon dioxide, a key
'greenhouse gas'. We have already increased the amount of carbon dioxide in the air by
35% and it is still rising. To imagine that this will have no effect on our climate would
seem foolish in the extreme.
For this reason, over the last few decades, climate scientists have been working to
understand the role of carbon dioxide and other human produced greenhouse gases in
the complex climate system upon which we are so dependent. What they have
discovered has given cause for alarm.
Action to reduce the amount of greenhouse gas we are putting into the atmosphere will
require global cooperation on a scale never before seen in human history. Despite
widespread agreement in the scientific community that strong action is needed, so far
little action of any real significance has come from the political sphere and global
emissions continue to increase. Only when there is widespread understanding of the
real nature of the issue are politicians likely to find the will needed to take the steps
necessary to produce the global cooperation required to avoid what is probably the
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greatest threat that human civilisation has ever faced. Hence this attempt to increase
public understanding of the issue.
The earth's temperature is determined by the balance between the incoming energy
radiated from the Sun and that re-radiated back into space from the Earth's surface. The
atmosphere plays a crucial role in this process. In order to appreciate the effect of
human added greenhouse gases we need to understand the nature of the radiation from
the Sun and that re-emitted by the Earth, and the interaction between that radiation and
the atmosphere.
Our brief journey of understanding starts with a description of the evolution of the
Earth's climate and the factors that have affected it in the past. We then look at the
nature of the incoming and outgoing energy radiation and the way the Earth's
temperature is determined by the interaction between these factors. While the serious
physics and chemistry of the climate is very complex, it is quite possible for all of us to
appreciate the way in which climate scientists have been able to come to grips with it
and then to use this understanding to determine the probable consequences of the 35%
increase in carbon dioxide since humans began using fossil fuels.
This document was prepared by a group of current and former science teachers. They
are also parents and grandparents who believe by building greater understanding of the
science of climate change that this will empower the community to force governments
to take stronger and more urgent action.
Useful Resources
Internet:
The page, www.vicphysics.org/teachingclimate.html , on the Education Committee’s
website contains an annotated list of links to resources from Intergovernmental Panel
on Climate Change (IPCC), The Australian Academy of Sciences, the Bureau of
Meteorology, The Royal Society, the Joint Science Academies of the G8 nations, etc.
The page also lists links to teaching resources and to Ideas on ‘What I can do to help’.
Texts:
The Hot Topic: How to tackle global warming and still keep the lights on, by Gabrielle
Walker and Sir David King, Bloomsbury Publishing. 2008.
Australian Institute of Physics (Victorian Branch) Education Committee
PO Box 304, Glen Waverley, VIC 3150. www.vicphysics.org
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1.
The earth’s atmosphere
For many thousands of years the earth has been surrounded by a finely balanced
atmosphere that protects it from high-energy radiation and also absorbs enough heat to
provide a moderate climate to support life. If we upset this balance, then our life
support system will be at risk. However the early atmosphere was not always so.
The Formation of the Earth’s Atmosphere
At the beginning of the solar system when the earth was being formed 4.5 billion years
ago, the leftover atmosphere of Hydrogen and Helium quickly escaped the earth’s
gravitational field or was ‘blown way’ by the Sun’s radiation. The earth was initially
without an atmosphere. With volcanic activity, an atmosphere formed of nearly all
water with about 2% sulfur dioxide (SO2), 1% carbon dioxide (CO2) and traces of
hydrogen sulfide (H2S), hydrochloric acid (HCl) and ammonia (NH3).
The water in the atmosphere condensed to form the oceans. Simple life forms, such as
algae, began to appear. Through the process of photosynthesis, the algae began to use
sunlight to convert water and CO2 into carbohydrates and oxygen (O2), which bubbled
into the atmosphere. (Our fossil fuels are the compacted bodies of these algae). Initially
most of this oxygen reacted with the metals on the surface to produce the various
oxides, e.g. iron ore, that we mine today. As the oxygen accumulated, ultra violet light
from the sun split the oxygen molecules in the upper reaches of the atmosphere,
producing an ozone shield that blocked the ultraviolet radiation (UV), which damages
DNA. Previously the UV had prevented life from forming on the land or in the
shallows. By about two billion years ago, the oxygen concentration was sufficient
(0.2%) life begin to move out of the oceans.
The development of plants continued to reduce the amount of CO2 and increased the
amount of oxygen. It took until about one billion years ago for the oxygen
concentration to level out. In recent millennia human activity has modified the
amounts of carbon dioxide, methane and nitrous oxide in the atmosphere
Today’s Atmosphere
The atmosphere is now made up
of a mixture of over 16 gases, the
main ones and their proportion are
in the table to the right.
Table 1. Composition of dry
atmosphere, by volume
Gas
nitrogen (N2)
oxygen (O2)
argon (Ar)
carbon dioxide (CO2)
neon (Ne)
helium (He)
methane (CH4)
hydrogen (H2)
nitrous oxide (N2O)
water vapour (H2O)
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Dry Volume
78.08%
20.95%
0.93%
0.038%
0.002%
0.0005%
0.0002%
0.00005%
0.00003%
1% - 4%
Climate change in the past: Hothouse Earth  Snowball Earth
In the last few hundred million years the Earth's climate has swung between a 'hothouse
Earth' with global average temperatures well over 20°C and a 'snowball Earth' with
average temperatures below 10°C. Hothouse conditions were associated with sea levels
over 100 metres higher than today's and no polar ice, while in snowball times polar
icecaps extended down into Europe and ocean levels were much lower because so
much water was locked up as ice.
For most of the last few hundred million years the Earth was much hotter than today,
but about two million years ago it cooled and entered an 'Ice Age'. This current ice age
has, however, been characterised by swings between the very cold periods and
relatively warmer 'interglacials' such as we are currently in. Interglacials are roughly
half way between the hothouse and snowball Earth conditions, with average
temperatures around 15°C
Human civilization has developed in the relatively stable conditions of the current
interglacial, which has so far lasted around 10,000 years. Although there have been
small changes during this time - the 'medieval warm period' and 'little ice age' for
example - these changes have been very much smaller than the hothouse - snowball
swings.
Clearly the concern at present is that if we upset the climate energy balance we could
trigger a return toward the hothouse conditions with much higher sea levels and very
different patterns of rainfall and arable regions. The problem is not so much whether
life could survive in those conditions, it is the havoc that would be caused by the
changing conditions - not to mention that most of the world's major cities would be
drowned. For this reason, scientists have studied past climate change carefully and now
understand many of the factors that have caused climate swings. Some of these are
outlined below.
Over the longer time scale, factors such as the changing composition of the atmosphere,
variations in the Sun's output, massive volcanic activity, meteor impacts, shifting
continents and uplifting land masses have been important in triggering changes in the
climate. What is more relevant to our present task, however, is to understand the
changes that have occurred in the last tens of millions of years. Why, for example, did
the Earth suddenly (geologically speaking) plunge into the current ice age? And why,
over the last million years has it cycled between a full ice age and the milder
interglacials?
There are several factors contribute to these climate cycles.

The Milankovitch cycles: Variation in the Earth’s motion.
In the 1930's Ivan Milankovitch found that there appeared to be a relationship
between subtle variations in the Earth's orbit around the Sun and the interglacial
climate cycles.
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The earth spins on its axis giving us day and night. This axis is tilted at about 23
degrees which produces the seasons, however this angle of tilt varies between 22
and 24 degrees over a time span of 41,000 years, the larger the angle the greater
the difference between summer and winter. Because the earth is like a spinning
top or a gyroscope, the axis itself also goes around in a circle, this is called
precession. The earth’s axis wobbles like a spinning top once every 22,000 years.
It increases the seasonal difference in one hemisphere and decreases it in the other.
See Figure 1.
The earth orbits around the sun. This path is an ellipse. The other planets slowly
stretch the ellipse, then ‘relax’ it over a cycle of 100,000 years.
The interaction of these cycles is currently thought to be the principal cause of ice
ages. They determine how much of the sun’s energy reaches the earth, and also
how it is distributed across the earth.
Figure 1. The earth’s orbit is an ellipse with the sun at one focus. The earth moves
around its orbit in the direction of the solid arrow, while spinning about its axis in
the direction shown by the thin curved arrows at the North pole. The earth’s spin
axis also ‘wobbles’ or precesses, shown by the thicker curved arrow, about 22,000
years for one rotation.

Changes in greenhouse gases
Greenhouse gases have not been an initiating factor in the emergence from an ice
age, but they have been an amplifying factor. When the cycles described above
cause the earth to begin to warm, the warming oceans release the gases into the
atmosphere. They ‘insulate’ the earth making it warmer. The oceans get warmer,
releasing more gas, etc. This process is called positive feedback. The temperature
continues to rise until the other factors listed here have a negative impact. The
same process is beginning to happen now, but this time the trigger is human
activity. The greenhouse effect is described later.
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
Movement of continents
The oceans are the principal means by which the earth evens out its temperature.
The warm seas at the equator flow towards the cold poles. The continents move
very slowly across the surface of the earth, colliding and creating mountain ranges.
If they block off this movement of the oceans, then the climate would be affected.

Uplift of Tibetan plateau
The formation of the Himalayas when the continents began colliding several
million years ago produced a large ice sheet located near the equator. The white
ice reflected much of the intense sunlight cooling the earth.

Variation in Sun’s output
The energy from the sun varies slightly with an 11 year cycle which is related to
the variation in the number of sunspots. This cycle is too short to be a factor in
causing ice ages, but may contribute to minor variations, such as the coldest part
of the Little Ice Age in the 1800’s.

Volcanoes
Volcanic eruptions on land could have a significant, but temporary cooling effect.
While undersea eruptions could release methane, a greenhouse gas, which could
also have a temporary effect, but this time a warming effect. As with variations in
the Sun’s output, the impact of volcanoes would be limited to decades.
Figure 2: Ice Ages: Temperature and Carbon Dioxide concentration in the
atmosphere over the past 400,000 years (from Vostok ice core)
http://www.global-greenhouse-warming.com/images/VostokTempC02.jpg
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2.
Electromagnetic Radiation
It is radiation from the Sun that is our ultimate energy source, it underpins life on the
planet. It warms the earth. This warmth radiates into the air. The atmosphere
determines how much energy the earth retains and how warm it gets.
Visible light, infra red radiation, ultraviolet radiation, microwaves, radio waves and xrays are different forms of the same thing: electromagnetic radiation. They differ from
each other in the same way as the signal from one radio station differs from that of
another, that is, they differ only in the frequency, and because they are all waves, also
in their wavelength.
It is the ultraviolet that gives us sunburn. It is the infrared from a fevered face that is
detected at an airport terminal as evidence of a raised temperature.
Figure 3: The Electromagnetic Spectrum
Note: This radiation differs from nuclear radiation which is mostly high speed charged
particles from inside atoms.
The earth’s atmosphere protects life from the more dangerous forms of radiation from
the sun, but fortunately has a window that allows through the long wavelength radiation
emitted by the earth. As we shall see, this emitted radiation keeps the Earth’s energy
balance even and its temperature relatively steady.
Black body radiation
Hot objects, such as a stove element, give off electromagnetic radiation, which we can
feel. This is infrared radiation. In fact there is a spread of wavelengths from longer than
10,000 nanometres (nm) to around 1,000 nm. One nm is one billionth (10-9) of a metre.
As the object gets hotter the peak of the spread both gets higher and moves towards
higher frequencies and shorter wavelengths. Eventually the object will get so hot that
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the spread will include the red part of the visible spectrum and the object will begin to
glow. In Figure 4, the graph for the cooler object is flat with a peak near the red. For the
hotter objects, the graph is much larger and the peak has shifted to the left to the yellow
section. The Sun is so hot that it looks yellow and its spectrum goes from infra red to
deep ultra violet. Hotter stars in the sky will look white or even blue.
72000C
57000C
42000C
Figure 4: The spread of radiation from various hot objects
Figure 5: The radiation from the Sun at the top and bottom of the atmosphere
org.ntnu.no/.../pics/chap2/Solar_Spectrum.png. wikicompany.org/wiki/images/thumb/Solar_Spect...
The light colour in Figure 5 shows the spread of light from the sun when it reaches the
top of the atmosphere. On the way through the atmosphere, different wavelengths are
absorbed. . The dark colour shows the radiation that reaches the surface. The ultra
violet radiation on the left is absorbed by the ozone in the upper atmosphere. Some
parts of the incoming infrared on the right are absorbed by CO2 and water vapour (H2O).
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Some of the visible light in the middle is scattered by the air; that is why the sky is blue.
The spectrum at ground level is therefore uneven with occasional gaps.
The strength of the solar radiation reaching the Earth is 1360 Watts per square metre,
but averaged out over the whole surface, it is 340 Watts per square metre. 30% of this
radiation is reflected back into space, mostly by ice and light coloured surfaces such as
deserts. The amount of radiation reflected from a surface is termed its “albedo”, and so
the Earth has an albedo of 30% or 0.3. The remaining 70% is absorbed by the earth’s
surface, heating it up.
Like all hot objects, regardless of their temperature, the Earth’s surface will re-radiate
this energy, but because its temperature is low, this energy will be mainly as long
wavelength infrared radiation. The radiation absorbed from the Sun will raise the
temperature of the Earth’s surface to the point where the amount of incoming radiation
is balanced by the amount of outgoing radiation.
The top part of Figure 8 compares the radiation received from the Sun with that emitted
from the Earth. The graphs may looks similar in shape, but notice that the scales are
very different. If the atmosphere contained no greenhouse gases, the average surface
temperature needed to balance the incoming and outgoing radiation would be frozen 18
0
C below zero. With greenhouse gases in the atmosphere, however, some of the
outgoing radiation is ‘reflected’ back down to the surface, warming the earth. As a
result, the surface temperature needs to rise to an average +15°C in order to achieve a
balance. So the natural greenhouse effect is responsible for a 33 degree rise in the
Earth’s temperature. Our concern now is that we are increasing this figure by adding
more greenhouse gases into the atmosphere.
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Figure 6. The global radiation balance at the top of the atmosphere and at the earth's
surface. Part of the total incoming solar energy (340 Watts per square metre) is
absorbed by clouds and atmospheric gases and part is reflected by clouds, atmospheric
gases and the ground (land and water surfaces). Approximately half (170 Watts per
square metre) is absorbed by the ground. Some of this energy is re-radiated upward
and some transferred to the atmosphere by turbulence and convection. The atmosphere
radiates infrared radiation in all directions. When balance is achieved in the
atmosphere, the total (short wave and long wave) upward radiation from the top of the
atmosphere equals the 340 Watts per square metre received from the sun.
Notice that if you add together the numbers on the in-coming arrows at the top, then
add together the numbers on the arrows going out at the top the totals are the same?
Other maths questions:
1. How much of the incoming 340 Watts per square metre of solar energy is
reflected? Express this as a percentage.
2. The amount of energy radiated out into space ( three up arrows on the right)
should balance the energy absorbed by the clouds, the atmosphere and the land
and sea. Show that it does.
Answers
1. 20+68+14 = 102 W/m2, 30%. 2.
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20+88+130 = 238 = 14+54+170
3.
Greenhouse gases
Greenhouse gases are like a blanket keeping you warm on a cold night - too thick and
you overheat.
How do these gases keep energy in?
Because of its temperature, the surface of the earth emits radiation mainly in the long
infra red. This particular radiation can interact with molecules containing three or more
atoms.
All types of electromagnetic radiation can affect substances, but they do it in different
ways.
X-rays and ultraviolet
can break up the bonds joining atoms and create new
chemical species that can damage living tissue.
Visible light
has less energy and can only move electrons around
within the atom producing colour.
Infrared
with even less energy can make molecules bend and
vibrate, but only the flexible molecules with three or
more atoms.
X-ray of hand: https://reich-chemistry.wikispaces.com/file/view/xray.jpg
Prism spectrum: http://www.faculty.virginia.edu/consciousness/images/prism.gif
Figure 7. Infrared radiation can jiggle carbon dioxide and water molecules in many
ways. This means these molecules can absorb many different wavelengths of infrared
radiation.
The two atom molecules such as nitrogen and oxygen which make up most of the
atmosphere are too tightly bound to be affected by infra red radiation. The molecules of
water, CO2 and CH4 have three or more atoms and so are jiggled by infrared radiation.
Figure 7 shows the different ways the molecules can be jiggled. Once they absorb the
infrared radiation coming up from the earth, they then emit it, but in all directions;
some upwards out into space, but some back down to earth to heat up the surface.
The diagrams below show the different wavelengths of infrared radiation that carbon
dioxide and water molecules absorb. These diagrams are called their spectrum.
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ultraviolet
vis
infrared
Figure 8: The absorption characteristics of water and CO2.
The upper portion of the chart shows the spreads of radiation emitted by the Sun and
the Earth. Note the different scales, the left ranges from 0 to 2000, while the right goes
from 0 to 8. The lower panels show the absorption of water (H2O) and (CO2) .
The black sections in the graphs in Figure 8 are the wavelengths that H2O and CO2
absorb. However as these two gases make up such a small percentage (See table 1) of
the atmosphere, much infrared radiation across the full range of wavelengths goes out
into space.
The graphs indicates that water is the most effective of the greenhouse gases, however
the concern about CO2 and methane, CH4, the other strong greenhouse gas, is that,
while water molecules only stay in the atmosphere until the next rain, CO2 and CH4
stay in the atmosphere for over 100 years, so any increase is around for some time, their
emission is almost irreversible.
What should happen if we add more CO2 and CH4 to the atmosphere? The extra gas
‘reflects’ back more infrared radiation. This will make the surface even hotter.
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4.
Climate Models
How does science explain climate?
The patterns of climate on earth can be explained with two sets of information:
Principles: Science of the atmosphere
 the Laws of motion for moving gases and liquids,
 the Gas Laws on temperature and pressure,
 the response of gases in the atmosphere, in particular the greenhouse gases, to
radiation, and
 the various physical, chemical and biological processes that take place, in particular:
- the global energy balance,
- the global water cycle, and
- the global carbon cycle
Data: Initial conditions
 the strength of the radiation from the sun;
 the spherical shape of the earth and the tilt of its axis;
 the composition of the atmosphere;
 the rotation of the earth, and
 the distribution of continents and oceans.
A climate model expresses the principles underlying the science of the atmosphere, as
listed above, in their mathematical form. They are then put in a computer program. This
program uses as its starting point the data from the initial conditions above.
Figure 10 illustrates the extraordinary number of processes that must be included in a
climate model to make it realistic and match observations.
To analyse the climate, the model divides the earth’s atmosphere and oceans into cells.
See Figure 9. Each cell at ground level is about 100km by 100km and 100metres tall.
Cells higher in the atmosphere are taller as the air is thinner. Cells deep in the ocean are
also longer. Most climate models have in excess of 10,000 cells.
Figure 9. The cell structure for a typical climate model. The east-west cross-section in
the left panel is to the grid on the right.
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Figure 10: The components of the global climate system consisting of the atmosphere,
the geosphere (which includes the solid earth, the oceans, rivers and inland water
masses (hydrosphere) and the snow, ice and permafrost (cryosphere)) and the
biosphere (the transition zone between them within which most plant and animal life
exists and most living and dead organic matter (biomass) is to be found). The figure
also shows the physical processes that take place within the climate system and exert
an influence on climate.
The initial conditions are first entered for each cell. The climate model program then
uses the scientific principles and their equations to calculate for each cell its new
temperature, pressure, windspeed, rainfall, humidity, etc for an hour later. These values
become the starting data for the next calculation for the next hour, and so on for many
years! With high speed computers these calculations can be done within several hours.
Climate models must be validated against observations. Often the models begin with a
year for which there is comprehensive data, such as 1950. The model is then run and its
‘predicted’ climate is compared with the actual climate for the following decades. If
there is strong agreement then the model can be used to investigate the effect of
possible scenarios into the future.
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Rainfall observations:
1980 - 1999
Average of model
predictions: 1980-99
Figure 12: Comparison of observations with climate model predictions
How good are the climate models?
The models produce graphs showing the variation with time of the various measures of
climate, such as rainfall distribution, temperature variation, formation of poles and
deserts, location and frequency of extreme events, and so on, as well as maps showing
the geographical distribution of these aspects and how they change with time. The
models show such details as seasonal monsoon rains in equatorial regions and the
formation of cyclones off the coast of Queensland.
These calculated measures of climate can be compared to actual climate data. The
climate models show strong agreement and the accuracy of the models is confirmed.
Figure 12 is an example of this, showing model predictions of rainfall compared to
actual observations.
The models can also be used to investigate the impact of the consumption of fossil fuels
since the industrial revolution. The models are run twice, once with the CO2 produced
from fossil fuels and second without the CO2. The two scenarios are compared again
actual observations. This analysis confirms that the greenhouse gases (CO2 and CH4)
generated by humans are having a significant impact on our climate.
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The jagged line in the two graphs in Figure 13 is the variation in global surface
temperature since 1900. The smoother curve in the top graph is the average prediction
of all the climate models taking into account natural climate change factors and human
related factors. The smoother curve in the bottom graph is the average prediction
taking into account only natural climate change factors.
The close fit in the top graph and the increasing gap in the bottom graph is convincing
evidence of the human impact on the climate. The climate models can now be used to
investigate various future emission scenarios, that is, what might happen to global
surface temperature, sea level, rainfall, etc under different energy strategies.
Figur
Figure 13: ‘Most of the observed increase in global average temperatures since the
mid-20th century is very likely (more than 90% certain) due to the observed increase in
anthropogenic greenhouse gas concentrations.’ IPCC (2007)
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5. Emission Scenarios or What do the climate models predict?
Once climate models have been verified against historical data, they can be used to
investigate the likely consequences of various strategies designed to reduce CO2. The
figure below lists the four driving forces and how they combine to generate the four
types of scenarios, for example in A1 there is a more global and technological approach
to solving the problem. The 4 scenarios are:
Figure 14 Categories of Emission Scenarios proposed by the Intergovernmental Panel
on Climate Change (IPCC)
A1 storyline: a future world of very rapid economic growth and rapid introduction of
new and more efficient technologies. Ways of life between regions converge with
extensive social and cultural interactions worldwide.
There are subsets to the A1 family based on their technological emphasis:
A1FI - An emphasis on fossil-fuels.
A1B - A balanced emphasis on all energy sources.
A1T - Emphasis on non-fossil energy sources.
A2 storyline: a very diverse world with economic growth varying across regions.
Technological change and improvements to per capita income also vary across
regions and are slower than in other storylines.
B1 storyline: as in the A1 storyline but with rapid changes toward a service and
information economy, and the introduction of clean and resource-efficient
technologies and an emphasis on global solutions to economic, social and
environmental stability.
B2 storyline: a world in which the emphasis is on local solutions to economic, social,
and environmental sustainability. The economic development will be less rapid
and there will be more fragmented technological change than in A1 and B1.
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Figure 15. Multi-model averages of surface warming (relative to 1980–1999) for the
scenarios A2, A1B and B1. The shading denotes the range of individual model annual
averages. ‘Constant composition commitment’ means CO2 is fixed at 2000 level.
Figure 15 shows the models predict a minimum of about 1.5 degrees of warming this
century on a best case scenario, and at least 3 degrees if international agreement is not
reached on alternative energy sources.
Figure 16: Annual warming for 2080-2099. A1B scenario.
Figure 16 show that the models predict that the warming will not be uniform across the
earth, that even with a ‘balanced emphasis on all energy sources’ the northern latitudes
will experience a massive increase in temperature over 7 degrees. This will have a
significant impact on the frozen tundra.
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6. Interpreting Data
One of the common statements by climate change deniers is that ‘the global surface
temperature has cooled in recent years’. The earth’s atmosphere is a large and complex
system with many diverse and varying factors. The global surface temperature
fluctuates substantially from year to year, however the overall trend is apparent in
Figure 17 below.
A quick glance at the figure reveals numerous time during the last 160 years when the
global surface temperature has declined for several years in a row. Taking the longer
perspective, it is clear that there has been an underlying steady increase in the
temperature since 1900.
1
Temperature Anomaly (Celsius)
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
1850
1870
1890
1910
1930
1950
1970
1990
2010
Year
Figure 17: Global Air Temperature difference since 1850
The other consideration in interpreting this graph is that the Sun not only heats up the
atmosphere, but also the land, but more particularly the oceans as the atmosphere and
the seas easily exchange energy. In fact the massive amount of energy stored in the
oceans means that the variation in temperature due to climate change is smoothed out.
However while satellites enable currently allow the average global sea temperature to
be measured, there is little historical data to provide a view over time.
7. Climate change impacts
Already climate change has had an
environmental impact. Three examples are:
i) The retreat of glaciers means that there is
less water held in the ice and a reduced flow
from the summer melt to feed rivers
downstream. Currently the mountain regions
of South America are being affected, however
of more concern is the Tibetan ice sheet.
Significant retreat here would greatly impact
on the livelihood of both China and India. Of
course the water from the melting glaciers will ultimately lead to sea level rise.
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ii) The decrease of Summer Arctic Sea ice
The graph below shows a steady
reduction in the amount of Arctic
sea ice during the Arctic summer.
Of particular concern is that the
decline is significantly greater
than what the climate models were
predicting. The melting of this
sea ice will not of itself lead to a
rise in the sea level as the ice is
floating, and so, the melted ice
will take up the same volume as
the amount of ice under the
surface.
Figure 19: Extent of summer arctic sea ice:
Graphs of observations and model predictions
However what is of concern is that a surface that was previously white and highly
reflective will be replaced by one that is dark and absorbing. This is an example of
positive feedback, where the melting ice results in warmer water, which leads to more
ice melting.
iii) Changes in acidity and salinity of the oceans.
CO2 is absorbed by the oceans, making them more acidic. This weakens the skeletons
of marine animals. Acidity is measured using the pH scale. A decrease in the pH of
0.1 is equivalent to a 25% increase in the acid concentration.
8.3
8.2
8.1
pH
8
7.9
7.8
10 million 1 million
years ago years ago
1850
Time
1950
1900
2000
Figure 20: pH of the oceans over time
Future predictions are based on
the average of IPCC scenarios.
2050
2100
Figure 21: Salinity in the North Atlantic
This is the largest ocean change measured.
(measured in parts per thousand).
This could impact of the flow of the Gulf
Stream.
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8. Causes for concern
i) Temperature change
Because of the CO2 already in the atmosphere, a two degree rise in temperature above
1990 values by mid century is unavoidable. The temperature rise by 2100 depends on
the energy decisions to be made in the next five - 10 years. A fossil fuel dependent
scenario is expected to result a temperature rise of at least four degrees above 1990
values and possibly more than six degrees. A switch to almost exclusive non-fossil fuel
energy sources would still see the temperature rise, but likely to be only to 2.5 degrees.
It is very likely that heat waves will be more intense, more frequent and longer lasting
in a future warmer climate. Cold episodes are projected to decrease significantly in a
future warmer climate. Almost everywhere, daily minimum temperatures are projected
to increase faster than daily maximum temperatures.
ii) Sea level rise
When materials get hotter they expand, oceans are no different. The warming of the
oceans alone is expected to increase the sea levels. Regardless of the scenario the sea
level is expected to rise by about 3mm per year, which is about 30cm over the century
on average across the globe. The models currently suggest that the Arctic area will
experience the largest increase and the southern hemisphere should experience
marginal sea rise.
However there is much ice that is on land in Greenland, Antarctica and in many
glaciers around the world. If this ice were to reduce in size and the water to flow to the
sea, then the sea level rise takes on another dimension. The ice in Greenland and the
Antarctic is thick and would take centuries to fully melt, but the various models suggest
that a reliance on fossil fuels would produce a sea level rise by at least double that
caused by thermal expansion of the oceans. Much of this effect would occur after 2100.
The Arctic ice that makes up the North Pole is floating on water. When it melts, the sea
level does not rise because ice is less dense than water, which why it floats. However
the melting of sea ice can have a severe impact. The ice, being white, reflects much of
the sun’s visible radiation back into the atmosphere and out into space. When it melts to
water, it reflects much less, absorbs much more and the water warms, which warms the
atmosphere, which melts more sea ice … . This reinforcing and accelerating process is
called positive feedback. As mentioned in section 2, the capacity of a substance to
reflect light is called its albedo. Ice has an albedo of 35%, while sea water has a value
of 8%. A black surface has a value of 0.
More CO2 in the atmosphere not only increases the temperature of the oceans, it will
also lower their pH, making them more acidic as well as altering their carbon chemistry.
This will weaken the shells and skeletons of sea creatures, affecting their survival and
ultimately ocean ecology.
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i) Best estimate projected rainfall
ii) Observed trend in annual rainfall
change for 2070,
1970-2007
Figure 22: Observed and projected Australian rainfall
iii) Changes in rainfall patterns
For a warmer climate, the models indicate that rainfall will increase in monsoon areas
and the tropical Pacific and decrease in the subtropical and mid-latitude regions. Across
the globe on average there will be more water vapour in the air, (higher humidity),
more evaporation and more rain.
Figure 22 ii) shows for Australia that over the last 37 years there has been a significant
increase in rainfall in the west and while the east has suffered a major decrease. Figure
22 i) indicates that the long term trend is significantly less rainfall across the country.
In mid-latitude regions such as Australia, there would also be longer periods between
larger rainfall events. There is expected to be a tendency for drying of the midcontinental areas during summer, leading to a greater risk of drought.
iv) Changes in crop viability and distribution of pests and diseases
IPCC said in its fourth report that approximately 20-30% of plant and animal species
assessed so far are likely to be at increased risk of extinction if increases in global
average temperature exceed 1.5-2.5oC. With changing weather patterns, the
ecosystems, within which tropical diseases such as malaria occur, are likely to move
north and south away from the equator. There is some evidence that this beginning to
occur. It is also likely that crops will need to planted in other parts of the Earth as
rainfall and temperature change. Climate change significantly affects plant and animal
species.
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9. Expressing concern
At home:
• Retrofit double glazing,
• Lower temperature setting for heating,
• Turn off appliances at the wall,
• Use throw rugs,
• Put up pelmets,
• Install compact fluorescents,
• Use public transport,
• Install solar panels and a solar water heater
With Government:
Write and phone and fax and email and talk to your local representatives (Council,
State and Federal, upper and lower house). Advocate one or more of the following:
• A maximum global CO2 level by 2020 (2050), e.g. 350 parts per million.
• Zero emissions by Australia by, for example, 2050.
• Carbon emissions tax combined with a tax rebate for low income earners.
• Subsidy of alternative fuels, including Geothermal, Solar Thermal, Wind,
Photovoltaic, Nuclear and Biomass, from a carbon emissions tax.
• Feed in tariffs for solar panels.
To find your electorate and federal member go to http://apps.aec.gov.au/esearch/ and
enter your suburb or postcode. To find your federal member’s contact details go to
http://www.aph.gov.au/house/members/memlist.pdf for an alphabetical list of members
with contact details for both their electorate office and the Parliament House office.
A list of senators by state can be found at
http://www.aph.gov.au/Senate/Senators/homepages/index.asp?sort=state Each of their
contact details can be obtained by clicking on their name.
To find the contact details of both your representatives in the Victorian parliament go to
http://www.parliament.vic.gov.au/handbook/menupage.cfm?menuId=2 and enter your
street name and suburb.
To contact your council representative, ring the council.
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