Global Warming Guide

Transcription

GLOBAL WARMING
A guide to its origins and effects
GLOBAL WARMING a guide to its origins and effects
Acknowledgements:
Research for this report was conducted by
David Zekria under the direction of Dr Ian Mays and
Stephen Balint of Renewable Energy Systems Ltd
(RES) ([email protected]).
With thanks to Crispin Aubrey for editorial advice.
Additional editing by Anna Stanford. Design and
production by Inmarc Associates. The authors would
also like to express their thanks to those organisations
and individuals who contributed illustrations, the
sources of which are referenced in the text.
Disclaimer:
This Guide (the ‘Report’) has been prepared by
Renewable Energy Systems Ltd (‘RES’) by reference
to internal and published materials. RES has
endeavoured in preparing this Report to ensure that it
is accurate and objective, its purpose being to inform a
wider audience of the current status of research on
climate change, its origins and effects. As a company
whose business is derived from wind energy and other
renewable resources, RES has its own perspective on
the subject matter of this Report. Nonetheless, it has
tried to ensure that the Report is accurate and
balanced.
It is hoped that readers of this Report will find it helpful
and informative, but it is not RES’s intention that it
may be relied upon by others, and anyone utilising the
Report for any reason does so at their own risk.
Accordingly, RES shall not be deemed to make any
representation regarding the accuracy, completeness,
methodology, reliability or current status of any
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of its affiliated companies or employees assume any
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referred to or contained in the Report.
This Report is subject to copyright protection. This
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copyright status of the material is made evident in so
doing.
© Renewable Energy Systems Limited 2007.
CONTENTS
FOREWORD ................................................................................................................................2
EXECUTIVE SUMMARY..............................................................................................................3
PART ONE:
THE BACKGROUND TO GLOBAL WARMING..........................................................................5
PART TWO:
WHY THE EARTH IS GETTING WARMER ................................................................................6
1 Irradiance ........................................................................................................................6
2 The Greenhouse effect ..................................................................................................6
PART THREE:
THE FUTURE DEVELOPMENT OF GLOBAL WARMING .........................................................9
1 Future emissions and atmospheric levels of CO2 ......................................................9
2 Future global temperature...........................................................................................10
3 Feedback mechanisms ................................................................................................11
PART FOUR:
THE CONSEQUENCES OF GLOBAL WARMING....................................................................14
1 Direct effects of heat and cold ...................................................................................14
2 Disease ..........................................................................................................................14
3 Agriculture and nutrition .............................................................................................15
4 Drought and water resources ....................................................................................15
5 Sea level rises and flooding........................................................................................16
6 El Niño ...........................................................................................................................16
7 Storms ...........................................................................................................................17
8 Ecosystems and biodiversity......................................................................................17
9 Economic consequences ............................................................................................18
PART FIVE:
SOLUTIONS...............................................................................................................................19
PART SIX:
CONCLUSIONS .........................................................................................................................20
REFERENCES ...........................................................................................................................21
1
GLOBAL WARMING
a guide to its origins and effects
Foreword
Global warming has become the most prominent
environmental issue of our times. Growing public
awareness of the effects of elevated global
temperatures has been driven by clear signs around
the world that climate change is already happening.
Climate change is now one of two key drivers for
sustainable energy investment, the other being energy
security and the availability of future fuel resources.
We therefore recommend that this report is read in
conjunction with ‘Plugging the Gap: A Survey of World
Fuel Resources and their Impact on the Development
of Wind Energy’, published by RES and the Global
Wind Energy Council. We hope that together they will
demonstrate that quickening our pace along the clean
energy path can bring social, environmental and
economic benefits to us all.
Dr Ian Mays, CEO, RES Group
©Greenpeace/Beltrá/Archivo Museo Salesiano/De Agostini
From the UK Stern Review in 2006 to the latest
Intergovernmental Panel on Climate Change (IPCC)
report published in February 2007, stark warnings are
coming from scientific and economic experts that
climate change is a reality and that the consequences
to our society will be significant. Governments around
the world are taking action in the form of legislation,
such as the UK’s Climate Change Bill and the
European Union’s 2007 target of a 20% reduction in
emissions by 2020. Individual countries, regions and
states, such as California, have ambitious plans for
action. But how can these challenging obligations be
achieved? Mechanisms such as emissions trading
schemes have an important role to play. However,
renewable energy technologies have huge potential to
assist in meeting reduction targets. Making greater
use of wind and solar power, geothermal energy,
biomass and marine technologies such as tidal and
wave power, represents one of our best strategies for
meeting the climate change challenge, whilst also
helping to secure the availability and security of future
energy supplies.
Our aim in publishing this report is to provide an
accessible and up-to-date overview of current scientific
thinking on global warming, its origins and effects, that
will be of use to all those with an interest in the
subject. The report has been written and published by
Renewable Energy Systems Ltd (RES) following a
comprehensive survey of scientific and technical
sources including leading international and national
bodies such as the IPCC, NASA, the World Health
Organisation (WHO), and published papers in
scientific and technical journals. A full list of references
is given at the end. It is intended that this report can
be used freely as a resource to help inform policy and
activities in the field of climate change and sustainable
energy.
The decline of glaciers, such as the Upsala Glacer in Patagonia, seen here in
1928 (top) and 2004 (bottom), could be one sign of rising global temperatures.
2
Executive Summary
Global mean temperatures are currently at their
highest level since direct measurements were first
made. Over the last 100 years, the world’s
temperature increased by 0.74°C, faster than at any
time in recent human history. The warmest year on
record was 20051, with eleven of the last twelve years
(1995 – 2006) ranking among the twelve warmest
years on record. Temperatures before the mid-19th
century, when worldwide measurements became
widespread, can be estimated from indirect sources
such as tree rings. This data suggests that
temperatures are now higher than at any time over the
last 2,000 years. 2007 is expected to break the global
record again2.
The temperature of the earth has fluctuated over the
4.65 billion years of its history. What is important for
our society in the 21st century is how the current trend
of rising temperatures compares to long-term patterns,
what the underlying causes driving this increase might
be and how we can avoid the potentially devastating
impacts of a warming world.
It is now accepted that the increase in the atmospheric
concentration of carbon dioxide, the principal so-called
‘greenhouse gas’, caused by the combustion of fossil
fuels, is a significant driver behind growing global
temperatures. The most recent report from the IPCC,
the Fourth Assessment Report published in 2007, is
firmer than ever before in its conclusion that
humankind is having a significant input into global
warming: ‘Most of the observed increase in globally
averaged temperatures since the mid-20th century is
very likely due to the observed increase in
anthropogenic greenhouse gas concentrations3.
Many other factors also interplay to determine the
global heat budget, and identifying the exact extent to
which global warming is anthropogenic (humanrelated) is still contentious. However, measurements of
past atmospheric carbon dioxide concentrations and
global temperatures indicate a clear correlation
between the two. Anthropogenic sources of other
gases, such as methane, nitrous oxide, ozone and
CFCs, as well as black carbon and sulphates, also
influence global temperatures.
Predicting future temperatures is complicated because
it is difficult to be precise about ‘climate sensitivity’ – to
what extent temperature depends on atmospheric
carbon dioxide levels – and because future levels of
CO2 are uncertain. This uncertainty has been dealt
with by considering a number of different scenarios,
outlined by the IPCC, spanning the range of the most
likely courses of events. This enables us to see the
boundaries within which future carbon dioxide levels
are likely to fall, even if we are unable to accurately
determine actual values. Climate sensitivity has been
defined as an increase of 2.0 – 4.5°C, with a best
estimate of 3.0°C, for a doubling of carbon dioxide
concentrations, a level anticipated around the year
2100.
The latest research suggests that we should therefore
expect a warming of about 0.2°C per decade for the
next two decades. By the final decade of the 21st
century global temperatures are expected to have
risen by 1.8–4.0°C compared with the end of the 20th
century. This estimate, however, does not take
feedback mechanisms into account, which could
amplify the warming process.
There are numerous examples of ‘feedback effects’
which could have a climatic influence. Melting of white
polar ice, for instance, reduces the reflectivity of the
land, causing more sunlight to be absorbed and thus
greater heating of the environment, leading to further
melting of ice. Stagnant sea-surface waters could
become saturated with carbon dioxide, thereby losing
their ability to absorb CO2 from the atmosphere.
Carbon dioxide-absorbing phytoplankton, which
depends on nutrients drawn from the ocean floor by
the circulation, could also dwindle. Rising
temperatures may cause greenhouse gases frozen in
polar ice, permafrost and sea floors to be released,
further strengthening the greenhouse effect. These,
and other potentially unrecognised mechanisms, are
likely to play a role in the evolution of the climate, and
may even lead us beyond a point where temperatures
can be restored to their original state.
Global warming is important because of its many
influences on our lives. The anticipated rise in sea
levels threatens to flood and submerge low-lying land
masses. Sea levels have already risen by 17cm during
the last century. Higher temperatures will influence the
transmission and range of diseases such as malaria,
the quality and productivity of agriculture, the
availability of fresh water and the frequency and
intensity of weather events such as storms. We can
expect hundreds of millions of ‘climate refugees’ and
significant impacts on the global economy.
Whilst global warming-related climate change may
benefit some sectors, the effects will on balance be
negative. If we are to limit the detrimental
consequences of global warming, we must take steps
to counter its root cause and do so without delay. This
3
means cutting our emissions of greenhouse gases by
reducing our dependence on fossil fuels and replacing
them with clean, renewable energy. The potential for
low-carbon technologies such as wind, biomass,
geothermal, solar and marine power is enormous and
increasing investment in these as soon as possible
makes economic, social and environmental sense.
AT A GLANCE
4
●
Global temperatures now higher than at any time in the last 2,000 years
●
Eleven of the last twelve years have been amongst the warmest twelve years on record
●
Latest IPCC report (2007) concludes that global warming is ‘very likely’ caused by
greenhouse gas emissions from human activity
●
Measurements of past CO2 concentrations and global temperatures (eg in ice core data
and tree rings) shows a correlation between the two
●
Before the industrial era, atmospheric concentrations of CO2 were relatively stable for
several thousand years at around 280 parts per million (ppm). Over the past 650,000
years, the range of concentration has never been above 300ppm
●
In 2005 atmospheric CO2 concentration stood at 379 ppm, a 35% increase on preindustrial era levels
●
Other greenhouse gas emissions, such as methane and nitrous oxide, are having an
additional heating effect on the earth
●
CO2 concentrations are predicted to rise by the end of the 21st century under three
emissions scenarios used by the IPCC
●
The last 100 years registered a warming of about 0.74°C and an increase of 17cm in sea
levels
●
During the last interglacial period, when temperatures were 4°C higher than at present,
sea levels were 6 metres higher
●
By the year 2100, it is estimated that global average temperatures will have risen by
between 1.8 and 4.0°C over present values
●
This may be even greater if feedback mechanisms kick in and could lead to runaway
climate change
●
Global warming will have significant impacts on human health, the economy and the
biodiversity of the planet
●
While some warming is inevitable and adaptation is important, an immediate shift to a lowcarbon economy and increased investment in sustainable energy can help avoid the most
serious consequences of climate change and bring social and economic benefits
PART ONE:
THE BACKGROUND TO GLOBAL WARMING
The mean surface temperature of the earth has been
steadily rising, particularly over the last 30 years. Over
the last 100 years (1906–2005), the world’s
temperature increased by 0.74°C. The warming trend
over the last 50 years is nearly twice that for the last
100 years4.
0.6
0.5
Temperature Anomaly /ºC
0.4
0.3
0.2
0.1
0
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
-0.1
Natural variations in mean temperature take place on
a wide range of timescales, from yearly fluctuations to
changes over millions of years. The world has been
free of ice over much of its history, but these iceless
periods have been interrupted by several major glacial
epochs. The current epoch began about 3.2 million
years ago. Since then we have had about 15 to 20
major advances and subsequent retreats of the ice
field, the advances being known as ice ages, the
retreats as inter-glacial periods. We are currently in an
inter-glacial period.
Climatic fluctuations may also be localised. Over the
last two millennia, there have been two periods of
anomalous (abnormal) temperatures across Europe,
and possibly further afield. A relatively warm period,
often referred to as the Medieval Climatic Optimum7,
lasted from the 10th to 14th centuries, then a relatively
cold period called the Little Ice Age8 from the mid-15th
century to the beginning of the 19th century.
-0.2
-0.3
-0.4
Year
Annual mean
5-year mean
Figure 1: Global mean surface temperature variation from
1951–1980 mean, from direct measurements since 1880 5.
Before the middle of the nineteenth century,
temperature data was not gathered widely on a global
basis. Direct measurements are therefore not
available. But we can still reconstruct local climatic
conditions from secondary sources such as ice
boreholes and cores, sediment records, tree rings and
corals. From these analyses it is clear that recent
temperatures are not only the highest they have been
over the last century, but probably over the last two
millennia.
0.6
0.5
Most of the warming that has occurred since then has
been in two phases. The first lasted from around 1910
to the early 1940s, the second from around 1975 to
now. Current global mean surface temperatures are
the highest they have been for at least two thousand
years, and are continuing to rise. It is suspected this
anomalous recent trend is a result of human
influences. While natural climatic variations and the
many factors influencing them, underline the difficulty
in establishing the exact extent to which current trends
are anthropogenic (caused by human activity) in
origin, the latest (2007) conclusions from the IPCC are
less equivocal than previously, stating in its Working
Group I report that it is extremely unlikely that the
observed widespread warming of the atmosphere and
ocean in the last century can be due to known natural
causes alone.
This report looks first at the factors which drive global
temperatures, then at the likely future trends, and
finally at the impact of global warming on our planet
and society.
Temperature Anomaly /ºC
0.4
0.3
0.2
0.1
0
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
-0.1
-0.2
-0.3
-0.4
Year
Annual mean
Figure 2: Global mean surface temperature anomaly from proxy
data (years 200–1980) and direct measurement (1981–2005), with
respect to 1951–1980 mean based on direct measurement data 6.
5
PART TWO:
WHY THE EARTH IS GETTING WARMER
1. Irradiance
The source of practically all heat at the surface of the
earth, and in the atmosphere above us, is the sun. Its
brightness is a critical factor determining the earth’s
temperature. The temperature of the earth is normally
at equilibrium – as much energy is absorbed from the
sun’s rays as is radiated back into space. The energy
radiated back depends fundamentally on the
temperature of the earth’s surface and atmosphere
system. If the energy absorbed from the sun’s rays
increases or decreases, the temperature of the earth
will also increase or decrease until a new equilibrium
is reached.
In order to understand global warming, it is therefore
important to know to what extent variability in the sun’s
brightness, measured by its ‘irradiance’, affects the
earth’s surface temperature. The sun’s irradiance at
the distance of the earth from the sun is approximately
1,367 Watts per square metre (W/m2). This quantity is
often referred to as the ‘solar constant’, although it
does in fact vary slightly.
The largest cause of such variations is the existence
of sun spots (dark patches on the surface of the sun),
the number of which tends to follow an 11 year cycle.
Results from satellite observation show that the
variation in irradiance over the sun spot cycle is of the
order of 1 W/m2. This would lead to a small
temperature change at the earth’s surface. It is
therefore clear that sun spots cannot account for the
global temperature changes we have seen over the
last 30 years.
Some solar
radiation is
reflected by
the earth and
the atmosphere
2. The Greenhouse Effect
The basic principle of the ‘greenhouse effect’ is that
heat is trapped by the atmosphere, thereby providing
a secondary heating effect on the earth in addition to
that from the sun. Short-wavelength sunlight easily
penetrates the earth’s atmosphere to reach the ground
and warm it up, whereas the longer-wavelength light
radiated by the earth is absorbed or trapped within the
atmosphere, rather than escaping into space. This
causes the atmosphere to warm up marginally, which
itself then reradiates long-wavelength light into space,
as well as back towards the ground, providing the
additional warming. The greenhouse effect keeps our
climate at an inhabitable temperature. It is estimated
that without it the earth would be about 33°C cooler.
The constituents of the atmosphere responsible for
trapping this radiation are known as ‘greenhouse
gases’. The most important of these is water vapour.
Other significant greenhouse gases include carbon
dioxide, methane, nitrous oxide, ozone and
halocarbons.
Greenhouse gases: Water vapour
Water vapour is the most abundant greenhouse gas,
and accounts for the largest proportion of the
greenhouse effect, although its concentration is
variable. Generally, warmer air has a greater capacity
for holding water vapour, leading to a feedback
mechanism. The warmer the atmosphere, the higher
its average water vapour content and the higher its
heating effect. However, water vapour has a short life
in the atmosphere, as it is quickly removed through
Some of the infrared radiation
passes through the atmosphere,
and some is absorbed and re-emitted
in all directions by greenhouse gas
molecules. The effect of this is to
warm the earth’s surface and the
lower atmosphere
Solar
radiation
passes
through
the clear
atmosphere
Most radiation is absorbed
by the earth’s surface
and warms it
Figure 3: The Greenhouse Effect mechanism
6
Infrared radiation
is emitted from
the earth’s surface
Greenhouse gases: Carbon dioxide
Carbon dioxide (CO2) is considered the most
significant greenhouse gas because its concentration
in the atmosphere has increased at an exceptional
rate over the last half century. Before the industrial
era, atmospheric concentrations of CO2 were relatively
stable for several thousand years at around 280 parts
per million (ppm). Between 1850 and 2000, however, a
total of 1,620 billion tonnes of carbon dioxide is
estimated to have been released into the atmosphere
from anthropogenic sources. Of this, 560 billion tonnes
originated from changes in land use, 1,030 billion
tonnes from combustion of fossil fuels and 20 billion
tonnes from chemical processes involved in cement
manufacture. Approximately half of this has been
removed by plants and the ocean, the rest remaining
in the atmosphere.
The 2005 value of atmospheric CO2 concentration
stood at 379 ppm10, a 35% increase on pre-industrial
era levels. The average rate of increase since 1980
has been 0.4%/yr11. It has been estimated that the
increase of CO2 between 1750 and 2005 has caused a
global average radiative forcing, or additional heating
effect, of 1.66 W/m2 on the earth10.
Historical atmospheric carbon dioxide levels can be
measured from ice cores. These are formed in polar
regions when layers of snow are gradually
compressed into solid ice under the weight of
successive annual layers. During this compression,
samples of atmospheric air are trapped as tiny
bubbles in the ice. These can be analysed to
determine both the historical atmospheric gas
composition and temperature.
Such measurements were made from ice cores
extracted at the Vostok station in the Antarctic, giving
data spanning over the last 400,000 years and four
glacial/interglacial periods. In November 2005,
Science Magazine12 published new data from the
European Project for Ice Coring in Antarctica (EPICA)
which went even further back to 650,000 years ago
and confirmed the Vostok records. As can be seen on
the graph (Figure 4), atmospheric CO2 content and
Although not completely understood, the 100,000 year
periodicity of these ice ages is believed to result from
small, periodic changes to the position of the Earth as
it orbits around the sun. These changes influence the
irradiance from the sun, increasing it where the Earth
is slightly closer, and decreasing it where it is further
away. The shape of the Earth’s orbit around the sun is
eccentric, meaning that rather than following a
perfectly circular path, it is elongated somewhat into
an ellipse. The shape of this ellipse itself varies, with a
principal periodicity of 413,000 years, and other
periodicities varying between 95,000 and 136,000
years. These loosely combine into an approximately
100,000-year cycle, commensurate with the ice-ages.
Carbon Dioxide and Temperature Records
-320
400
Vostok temperature
Vostok CO 2
Present CO 2 level
-360
EPICA temperature
EPICA CO 2
-340
350
-380
-360
-400
300
-380
-420
-400
-440
4
250
Atmospheric CO2 (ppm)
Nevertheless, much uncertainty exists in defining the
extent and importance of water vapour in the climatic
balance. As vapour levels increase, more of it will
eventually condense into clouds, which are able to
reflect sunlight back into space, and thus allow less
energy to reach the surface of the earth and heat it up.
Greater understanding of the feedbacks related to
water vapour is critical in projecting future climate
change9.
temperature appear to follow a very similar pattern.
Over the last 650,000 years there have been seven
periods of relative coolness, with a frequency of
approximately 100,000 years. These correspond to ice
ages. We are currently in an interglacial stage, and
therefore sit at a relative peak in temperature.
δ²H (permille)
precipitation (rain/snow). As far as global warming is
concerned, therefore, it is more important as a
feedback mechanism than a driver.
-420
-460
6
-440
650
200
-480
600
550
500
450
400
350
300
250
200
150
100
50
0
Thousands of Years Ago
Figure 4: Historic atmospheric carbon dioxide and temperature (by
proxy) data for the last 650,000 years obtained from the Vostok and
EPICA ice core analyses. Source: Science Magazine
It has been estimated that the rise of atmospheric CO2
concentration associated with glacial terminations, i.e.
the ends of the ‘ice ages’, actually lags the local
temperature profile by approximately 800 years13-16,
suggesting that these periods of warming were not
triggered by rises in atmospheric CO2, but rather were
the initial cause of them.
This does not, however, contradict the role of CO2 in
global warming. Although atmospheric CO2 levels may
not have been responsible for the initial rise in
temperature in these periods, the subsequent increase
in CO2 concentration has contributed to the continuing
rise in temperatures in a feedback cycle, causing a
further release of CO2 and consequently greater
warming. The entire warming process, and associated
temperature rise, at the end of a glacial period, takes
place over about 5,000 years.
The results of the ice core analyses show that preindustrial era atmospheric CO2 concentrations were
much lower than present levels and have not
exceeded 300ppm in any of the last eight inter-glacial
7
periods. The present day concentration is 379ppm.
CO2 levels today are therefore 27% higher than their
highest previous level in the last 650,000 years.
Greenhouse gases: Methane
Methane is a significant greenhouse gas because,
although its atmospheric concentrations are much
lower than CO2, it is over 20 times more effective at
trapping heat in the atmosphere. The gas is produced
principally through anaerobic decay of organic matter,
major natural sources being wetlands, oceans,
termites and methane hydrates17. Over half of all
methane emissions are anthropogenic, mainly from
animal husbandry, waste management, fossil fuel
production, rice cultivation and biomass burning.
At present, atmospheric methane concentrations stand
at around 1,774 parts per billion (ppb)18, having more
than doubled since the pre-industrial era. This excess
methane contributes an additional heating of 0.48
W/m2, or about 18% of the greenhouse effect from all
the long-lived greenhouse gases18. Such
concentrations exceed by far the natural range of the
past 650 000 years, as determined by ice cores18.
However, as methane has a relatively short lifetime in
the atmosphere of about 12 years, any reduction in
emissions will be promptly followed by a
corresponding reduction in atmospheric concentration.
Greenhouse gases: Nitrous oxide
Current atmospheric levels of nitrous oxide (N2O)
stand at approximately 319ppb, up about 18% on preindustrial levels18. Approximately one third of current
emissions are estimated to have anthropogenic
origins, principally from the use of fertilisers in
agriculture, nylon and nitric acid production, cars with
catalytic converters and the burning of organic matter.
The oceans, forests and soil are the main natural
sources.
Nitrous oxide is a strong absorber of infrared radiation.
Therefore, in spite of its relatively low atmospheric
concentration, the radiative forcing of increased nitrous
oxide since 1750 is estimated18 at 0.16 W/m2. This is
about 6% of the total from all the long-lived
greenhouse gases18.
Other greenhouse gases
There are a number of other greenhouse gases
present in the atmosphere in low concentrations.
These include man-made halocarbons such as
chlorofluorocarbons (CFCs), hydrochlorofluorocarbons
(HCFCs), hydrofluorocarbons (HFCs) and
perfluorocarbons (PFCs), as well as other gases like
trichloroethane (CH3CCl3), carbon tetrachloride (CCl4),
8
and carbon monoxide (CO).
The atmospheric concentrations of some CFCs,
trichloroethane and carbon tetrachloride have been
decreasing in response to reduced emissions, but
HCFC and HFC concentrations are on the increase as
they have been adopted as CFC substitutes.
Halocarbons contribute a radiative forcing of 0.34
W/m2, which equates to 13% of the total from all
greenhouse gases18. However, CFCs have been
responsible for destroying stratospheric ozone,
resulting in a cooling effect.
Ozone
Ozone is an important greenhouse gas, although its
influence on the greenhouse effect is dependent on its
altitude. Some ozone exists in the troposphere, the
lower part of the atmosphere – from ground level up to
about 12km. This gas originates primarily from
photochemical reactions with hydrocarbons and
nitrogen oxides emitted by motor vehicles, fossil fuel
refineries, power plants and other industries. The
global average radiative forcing due to increases in
tropospheric ozone since pre-industrial times is
estimated to have enhanced the anthropogenic gas
forcing by approximately 0.35 W/m2 18. This makes
tropospheric ozone the third most important
greenhouse gas after CO2 and methane.
Other factors affecting temperature
Apart from greenhouse gases, there are other
atmospheric constituents, some natural, some
manmade, which play a role in the global temperature
balance. Most of these are in the form of microscopic
solid particles called aerosols. Natural aerosols include
dust, sea salt, spores and volcanic particles. Their
influence on the climate is complex, as they have
various absorptive and reflective properties, and also
take part in secondary effects related to cloud
formation and cloud quality. The most significant
aerosols of anthropogenic origin are black carbon and
sulphates.
Black carbon is soot produced by incomplete
combustion of carbonaceous material, mainly fossil
fuels and biomass, each of which are estimated to
contribute about half of the total. As soot particles
absorb sunlight, they have the effect of both heating
the air and reducing the sunlight reaching the ground.
Black carbon is also believed to play a significant role
in the loss of ice and permafrost. As black carbon
infiltrates ice and snow, its dark colour acts to reduce
the albedo, or reflectivity. More radiation is thus
absorbed, warming the ice and promoting its melting19.
The total anthropogenic radiative forcing by black
carbon18, including the indirect effects on snow and ice
albedo, is 0.1W/m2.
Sulphate aerosols have their origins in sulphur dioxide
(SO2) released into the atmosphere primarily from
unscrubbed power plants and large scale agricultural
burning, but also from volcanic eruptions. Sulphur
dioxide is transformed in the atmosphere into sulphate
aerosols. These particles largely reflect the sun’s
radiation, and are therefore believed to have a net
cooling effect. However, it has been suggested that
sulphur dioxide leads to the formation of more ice
crystals in the upper atmosphere, some of which move
upwards into the stratosphere, where they increase
the amount of water vapour. This extra humidity
enhances the greenhouse effect, but water vapour
also destroys ozone20, reducing the concentration of
one of the other greenhouse gases.
The overall influence of these various effects is
complex, A number of studies have suggested that
atmospheric pollution, especially aerosol particles, is
responsible for blocking sunlight from reaching the
surface of the earth, sometimes referred to as ‘global
dimming’. However, there is evidence that the effects
of global dimming have declined since 1990 in
response to reduced atmospheric aerosol pollution
following tighter controls on particulate and sulphurous
emissions21,22. The IPCC estimates21 that anthropogenic
contributions to aerosols (including sulphate, organic
carbon, black carbon, nitrate and dust) produce a
cooling effect, with a total direct radiative forcing of
–0.5W/m2.
Concentrations and their changes
Species
CO2
CH4
N2O
2005
379 ± 0.65ppm
1,774 ± 1.8ppb
319 ± 0.12ppb
ppt
CFC-11
251 ± 0.36
CFC-12
538 ± 0.18
CFC-113
79 ± 0.064
HCFC-22
169 ± 1.0
HCFC-141b
18 ± 0.068
HCFC-142b
15 ± 0.13
19 ± 0.477
CH3CCI3
CCI4
93 ± 0.17
3.7 ± 0.10
HFC-125
HFC-134a
35 ± 0.73
3.9 ± 0.11
HFC-152a
HFC-23
18 ± 0.12
5.6 ± 0.038
SF6
74 ± 1.6
CF4(PFC-14)
C2F6(PFC-116)
2.9 ± 0.025
CFCs Total
HCFCs Total
Montreal Gases
Other Kyoto Gases
(HFCs + PFCs + SF6)
Halocarbons
Total LLGHGs
Radiative Forcing
Change
Change
since
since
1998
2005(Wm-2) 1998(%)
+13ppm
+11ppb
+5ppb
ppt
–13
+4
–4
+38
+9
+6
–47
–7
+2.6
+27
+2.4
+4
+1.5
–
+0.5
1.66
0.48
0.16
+13
–
+11
0.063
0.17
0.024
0.033
0.0025
0.0031
0.0011
0.012
0.0009
0.0055
0.0004
0.0033
0.0029
0.0034
0.0008
–5
+1
–5
+29
+93
+57
–72
–7
+234
+349
+151
+29
+36
–
+22
0.268
0.039
0.320
–1
+33
–1
0.017
0.337
2.63
+69
+1
+9
Source IPCC2007
PART THREE:
THE FUTURE DEVELOPMENT
OF GLOBAL WARMING
1. Future emissions and atmospheric
levels of CO2
Forecasting the future pattern of CO2 emissions is
difficult because it depends on a multitude of factors.
For short timescales, past trends can be extrapolated.
For timescales of several decades, however – more
relevant to the long term development of global
warming – unpredictable factors come into play.
Future world population, economics, the availability of
different energy sources, improvements in efficiency,
changes in land use and government regulations on
emissions are some of the human factors which may
influence CO2 production. On the other hand, natural
feedback mechanisms will potentially have a much
greater effect on future atmospheric levels. As our
ability to foresee the effect of human influences is
limited, and our current understanding of feedback
mechanisms is poor, any firm prediction of future CO2
emissions would be unreliable. Instead, the common
practice is to use a set of scenarios which cover a
range of possible courses of events. On the basis of
these, it is possible to run climatic simulations to give
us an idea of the outer boundaries of future global
warming.
The principal scenarios of future CO2 emissions on
which climatologists base their models are those
produced by the IPCC and the World Meteorological
Organisation. The future is considered in terms of
global economic development and three different
energy scenarios given: fossil fuel intensive, a mixture
of fossil and non-fossil fuels, and making an eventual
transition to non-fossil fuels. The projected annual CO2
emissions from each of these have been used to
make estimates of future atmospheric CO2
concentrations.
Other emissions
As with CO2, similar uncertainties exist over future
emissions of other climate influencing gases. Growth
rates of methane emissions have declined since the
early 1990’s, consistent with total emissions being
nearly constant during this period24. The growth rate of
global atmospheric nitrous oxide concentration has
been fairly constant since 198024. Whilst the growth
rates may not be increasing, this nevertheless means
that, in all cases, the atmospheric concentration is
expected to rise25. Sulphur dioxide is projected to
decrease under all scenarios after about 203026.
Figure 5: Long-lived greenhouse gases, their present-day
concentrations and radiative forcing, with changes since 198823
9
2. Future global temperature
Establishing the exact effect of these increasing
atmospheric greenhouse gas and aerosol
concentrations on future global temperatures is still a
matter of controversy. Some argue that the warming
observed so far is unrelated to changes in
atmospheric greenhouse gas levels, whilst others
believe it is the result of anthropogenic emissions.
Quantifying future warming is difficult because firstly,
we are unsure of the primary temperature response in
relation to changes in atmospheric greenhouse gas
levels, and secondly, the potentially greater influence
of feedback effects is not well understood.
However, the most recent report from the IPCC
provides increased confidence in the understanding of
the climate system’s response to radiative forcing27.
The fact that observed changes are consistent with
their climate models and that the rise in temperatures
has only been reproduced in models that include
anthropogenic emissions, provides a stronger link
between human activities and global warming.
The extent to which the global mean surface
temperature responds to changes in atmospheric
greenhouse gas concentrations is called the ‘climate
sensitivity’. The more accurately we know the climate
sensitivity, the better we can estimate climate change
based on projected atmospheric greenhouse gas
levels. The IPCC, in its 2007 report, stated that the
climate sensitivity in relation to a doubling of
equivalent CO2 concentration is likely to be in the
range of 2.0 to 4.5°C, with a best estimate of 3.0°C,
based primarily on climate models28. The range of the
estimate arises from uncertainties in the models and
their internal feedbacks, particularly those involving
cloud feedback and related processes.
Future temperature projections from the
IPCC report are shown in Figure 6 for a
range of scenarios identified by the IPCC
and as discussed above.
Figure 6: Projected future increase in global mean temperature, based on the IPCC scenarios
Figure 7 (left) shows how observed
continental and global surface temperatures
have changed from 1906–2005. The
average temperature changes that have
been observed (black line) more closely
match the predictions from climate models
that include both natural and anthropogenic
forcings (red shaded band), than the
predictions made from models which only
include natural forcings from solar activity
and volcanoes (blue shaded band).
Figure 7: Global and Continental Temperature Change.
Decadal averages of observations are shown for the
period 1906–2005 (black line) plotted against the centre
of the decade and relative to the corresponding average
for 1901–1950. Lines are dashed where spatial coverage
is less than 50%. Blue shaded bands show the 5–95%
range for 19 simulations from 5 climate models using
only the natural forcings due to solar activity and
volcanoes. Red shaded bands show the 5–95% range
for 58 simulations from 14 climate models using both
natural and anthropogenic forcings29.
10
In 2006 a channel large enough to allow a ship to sail
to the North Pole briefly opened up in the Arctic,
according to the European Space Agency, who said
that this could become more common within the next
two decades31.
The Greenland ice sheet is also showing signs of
recession and thinning. This sheet currently covers
about 80% of Greenland’s 2.16 million square
kilometres, is over 2km thick on average and is the
second largest body of ice in the world after the
Antarctic. Though some areas are actually gaining in
thickness as a result of increased precipitation32, the
ice sheet as a whole lost a volume of approximately
220 cubic kilometres through increased ice melt and
glacier flow in 2005 alone33.
Scenario B1
Scenario A1B
Scenario A2
Source: IPCC, 2007
Figure 8: Surface Temperature Projections for 2020–2029 and
2090–2099 under a range of IPCC scenarios.
3. Feedback mechanisms
The path that global warming actually takes in the
future may be largely determined by climatic feedback
mechanisms. These include phenomena related to ice
and snow cover, oceanic circulation patterns, natural
greenhouse gas emissions and cloud formation. They
are important because their behaviour is non-linear. In
other words, the magnitude of their effect will depend
on the stage reached in the warming process. As
global temperatures increase, those that give rise to
an ever greater warming effect constitute positive
feedback mechanisms, and those that cause a greater
cooling effect are negative feedback mechanisms.
Negative feedbacks have a tendency towards stability
in the system, whereas positive feedbacks force the
system to diverge from its steady state. These
possibilities contribute the greatest uncertainty to our
projections of future global temperatures.
Polar ice caps
Evidence shows that climatic warming has already had
an effect on the Arctic ice sheet. This has been
receding over at least the last three decades. Satellite
observations have been used to create a graphic
representation of the northern polar region, revealing a
clear difference in the extent of arctic sea ice cover
between 1979 and 2003 (see Figure 9).
1979
There are numerous consequences of diminishing
polar ice. The most obvious is the resulting increase in
sea levels from the melting of land-based ice sheets
(ie not floating sea ice), such as the Greenland ice
sheet. Such sea level rise threatens to inundate
coastal areas of some low-lying countries, and even
submerge others completely.
A feedback mechanism associated with receding ice
cover could also accelerate its melting. This is related
to the albedo of the earth’s surface – its reflectivity.
Fresh snow can have an albedo of up to 0.9, meaning
that 90% of incident sunlight is reflected back into
space. With a decreasing coverage of ice and snow,
the albedo decreases, resulting in a locally greater
absorption of sunlight. This acts to warm the region up
further, causing greater recession of the ice, and yet
further warming. Moreover, evaporating melt water
could also increase the water vapour content in the
lower atmosphere. As water vapour is a greenhouse
gas, this would contribute further to the overall
feedback mechanism.
Because of this feedback, continued warming could
push the recession across a threshold beyond which
complete melting of the Greenland ice sheet is
inevitable, an event that could contribute to global sea
level rise by up to 7 metres. It has been suggested
that a regional warming of 2.7°C above present levels
may be enough to trigger the melting of the Greenland
ice sheet. As the local response to global warming is
greater at high latitudes, this corresponds to a global
average temperature rise of about 1.5°C34. As the
IPCC’s 2007 report gives a range for global
temperature rises of 1.8–4 degrees by 2100, it can
reasonably be expected that the initiation of long-term
complete melting of the ice sheet will occur by the end
of this century. The melting would occur over a period
of time ranging from centuries to millennia.
2003
Figure 9: Arctic sea ice in 1979 and 200330. The first image shows
the minimum sea ice concentration for 1979 and the second image
shows the minimum sea ice concentration in 2003. Source: NASA.
11
Thermohaline circulation
Arctic melt water could also influence global sea
currents, or ‘thermohaline circulation’. At present,
evaporation from the sea in the north Atlantic region
leads to cooling and greater salinity of the water. This
has the effect of increasing the density of the water,
whereupon it sinks to the bottom of the ocean, causing
warm equatorial waters to flow in and replace it. The
cold salty water slowly migrates down the Atlantic and
eastwards into the Indian and Pacific Oceans. By the
time it reaches these areas, the salinity has
decreased, and the water rises again to the surface.
It then begins its journey back towards the Atlantic,
picking up heat along the way. The overall effect of
this circulation is to transport heat from equatorial
regions towards the north. These currents warm North
Atlantic regions by an average of 5°C, significantly
tempering the winter season in Europe and North
America35.
The sinking of the cold salty water in the north Atlantic
serves as the engine driving this thermohaline
circulation. However, an influx of fresh water into the
surface of the North Atlantic could form a layer
inhibiting heat loss and evaporation of the sea water
below, preventing it from increasing in density. The
fresh water would also dilute the salinity of the North
Atlantic, further reducing the density of these waters.
The force driving the ocean conveyor would weaken
and disappear, and the ensuing cessation of the
thermohaline circulation would quickly impact on the
world’s climate. Ironically, this consequence of global
warming would plunge Northern Europe into a mini-ice
age, since it would no longer be receiving the heat
brought from the tropics via the circulation.
Ocean currents also govern the rate at which deep
sea waters are brought to the surface. Should such
currents weaken, the replacement of surface water will
be hampered, increasing the acidity of the water due
to saturation with carbon dioxide and reducing the
ocean’s ability to further absorb atmospheric CO2. This
constitutes a potential global warming feedback
mechanism. The ocean’s pH has decreased by 0.1
units since 1750 due to the uptake of anthropogenic
carbon.
The latest research from the IPCC says that it is very
unlikely that there will be a sudden transition this
century. Although the circulation is slowing,
temperatures over the Atlantic and Europe are still
expected to increase due to global warming. The
slowing of the circulation will cause changes to CO2
uptake described above and affect marine
ecosystems36.
12
Figure 10: Illustration of the thermohaline circulation35.
Phytoplankton
Global warming could also affect phytoplankton, the
agent which removes CO2 from water. The oceans
serve as a sink of atmospheric carbon dioxide,
absorbing about 2 billion tons of carbon annually37.
This amounts to about half the total absorption of
carbon dioxide. Phytoplankton absorb carbon dioxide
during the process of photosynthesis, fixing the carbon
and transferring it to the ocean floor as waste. The
plankton, however, rely on nutrients from the bottom of
the ocean being stirred up and brought to the surface.
An increase in global sea surface temperatures
creates more distinct ocean layers, however, and
prevents mixing of deeper nutrient-rich cooler water
with warmer surface water. The lack of rising nutrients
limits growth of phytoplankton, thus reducing the
ocean’s capacity to absorb carbon dioxide38.
Methane hydrates
Gas hydrates are a kind of crystalline compound most
commonly formed by water molecules frozen into a
cubic structure, trapping gas molecules inside them.
Methane occurs most abundantly as a trapped gas in
natural hydrates. If each pocket in the structure is
occupied by a molecule of methane, then the total
volume of methane gas contained within the hydrate
can be up to 170 times that of the hydrate itself39.
Such methane hydrates exist in abundance in nature,
and are therefore a huge potential source of
greenhouse gas emissions.
Methane hydrates are stable only under a range of low
temperature or high pressure conditions, and are
found mainly at high latitudes and along the
continental margins in the oceans40. A temperature
increase of a few degrees could cause these gases to
volatise and be released into the atmosphere. This
would have the knock-on effect of raising global
temperatures further, causing even more release of
hydrate methane, and so on in a feedback cycle.
Once triggered, this cycle could result in catastrophic
runaway global warming, which would continue until all
of the methane has been volatised. Geological
evidence suggests that similar events have taken
place before, one about 55 million years ago and
another 251 million years ago. This came close to
wiping out all life on earth.
Detrital organic
matter 60
Peat 500
Land biota 830
Atmosphere 3.6
Marine biota 3
Gas Hydrates 2900
Dissolved organic
matter 980
Global temperatures would not continue to rise
indefinitely, but would be restricted by the limits of the
system driving them. For example, the decreasing
polar albedo effect would be capped when all ice
cover disappears, or the intensifying greenhouse effect
caused by the release of methane from hydrates
would cease when all of the hydrates have completely
volatised. The climate may be able to return to its preindustrial state, but this is likely to be on a timescale of
many thousands of years, just as the climate of the
earth flipped in the past between glacial and
interglacial periods.
Soil 1400
Fossil fuels 5000
Figure 11: Carbon content of the various carbon stores on earth
(in gigatonnes of carbon). Gas hydrates constitute a significant
proportion.
‘Adaptive Infrared Iris’ effect
All of the feedback mechanisms described so far have
been of the positive variety, threatening to exacerbate
global warming and destabilise the climate. However,
negative feedbacks would have the opposite effect.
It has been suggested that in cloudy regions, a higher
sea surface temperature is strongly linked to fewer
clouds41. A one degree Celsius increase seems to
reduce upper level clouds by 22%. As clouds are
effective at trapping infrared radiation, this reduction in
cloud cover would give rise to an increased cooling
potential, thereby providing a stabilising influence on
sea surface temperatures. This effect is known as the
adaptive iris effect and enables more infra-red cooling.
The magnitude of this effect has not been firmly
established, but some researchers claim that the
widely accepted climate sensitivity of 2.0–4.5 °C would
be diminished to the much lower range of 0.6–1.6 °C if
this feedback mechanism is taken into account.
Runaway global warming
The magnitude of the response to a given increase in
greenhouse gases may be dependent on the state of
the climate at the time, and could be much larger in
the future than it would be now. This means that the
more advanced the stage of global warming, the more
sensitive the climate may be to a further forcing. Of
most significance to the long term development of
global warming is the possibility of ‘tipping points’,
beyond which positive feedbacks become selfperpetuating, causing ‘runaway’ warming regardless of
the quantity of further anthropogenic greenhouse gas
emissions. In this situation, the global climate system
would enter an irreversible state.
13
PART 4:
THE CONSEQUENCES OF GLOBAL
WARMING
Global warming is expected to affect all our lives. For
some of us, the net effects may be beneficial; for
others they could spell disaster. This will depend on
where in the world we live, our ability to respond and
adapt to climatic warming, and its effect on our
environment and livelihood.
In recent years the quantity and quality of studies of
observed trends in the environment and their
relationship to regional climate change has increased
greatly. The IPCC has concluded that many natural
systems are being affected42.
Figure 13: The northern section of the Larsen B ice shelf breaking
away from the Antarctic Peninsular in February and March 2002.
Satellite single and multi-view images. Source: NASA.
This chapter outlines some of the consequences
already identified. Figure 12 shows the changes which
have already been measured in global temperature,
sea level and Northern Hemisphere snow cover,
relative to corresponding averages for the period
1961–1990.
There is a correlation between daily mortality and
weather, in particular extreme temperature events
such as heat waves and cold spells. High
temperatures can lead to heat exhaustion, heat stroke
with possible permanent neurological damage, heart
attacks and death44,45.
1. Direct effects of heat and cold
Hot days, hot nights and heat waves have become
more frequent, and will be both hotter and more
frequent in future46. The expected rise in mean
temperature will result in an increase in the frequency
of extreme warm temperature events. Even a small
warming can cause a relatively large increase. For
example, a rise of 2 to 3°C in average summer
temperatures in temperate climates would
approximately double the number of very hot days47.
August 2003 was the hottest August on record in the
northern hemisphere and caused a large number of
fatalities. France suffered worst, with 14,802 people
dying from causes attributable to the blistering heat48.
7,000 people died in Germany, nearly 4,200 in both
Spain and Italy and over 2,000 in the UK. The World
Meteorological Organisation estimates that the number
of heat-related deaths could double in less than 20
years48.
Figure 12: Observed changes in (a) global mean surface
temperature; (b) global average sea level rise from tide gauge (blue)
and satellite (red) data; and (c) Northern Hemisphere snow cover
for March – April. All changes are relative to corresponding
averages for the period 1961–1990. Smoothed curves represent
decadal averaged values while circles show yearly values. The
shaded areas are the uncertainty intervals estimated from a
comprehensive analysis of known uncertainties (a and b) and from
the time series (c)43
Cold days, cold nights and frost have become less
frequent, and will be both less frequent and less cold
in future46. Exposure to low temperatures can have
direct health effects such as hypothermia, and indirect
effects such as increased rates of pneumonia,
influenza and other respiratory illnesses49. Including
the indirect effects, the overall number of deaths
related to cold exceeds the number related to heat. As
the relationship of mortality to cold is complex, it is
unclear whether the reduction in cold-related deaths
due to environmental warming will exceed50 or be less
than49,51 the expected increase in heat-related deaths45.
2. Disease
Diseases which rely on carriers for transmission, such
as malaria, borne by mosquitoes, also depend on
climatic conditions for their geographical distribution.
14
Malaria has a massive
impact on human health; it
is the world’s second most
prolific killer after
tuberculosis. Up to 500
million clinical episodes of
malaria occur each year,
resulting in over a million
deaths52. The IPCC
concludes that climate
change is likely to expand
the geographical
distribution of several carrier-borne diseases, including
malaria, to higher altitudes and higher latitudes, as
well as extending the transmission seasons in some
locations. For some carrier-borne diseases, such as
tick-borne encephalitis in Europe, climate change may
decrease transmission through reductions in rainfall or
temperatures too high for transmission53.
Temperature variance can also have an indirect
influence on health. Diarrhoeal disease, for example,
has a strong correspondence with temperature,
particularly in developing countries with poor
sanitation. This is because the bacteria responsible
are encouraged by high temperatures. It is estimated
that in such countries there is a 5% increase in
diarrhoea incidence per degree centigrade increase in
temperature54. Deaths from diarrhoeal disease
associated with floods and droughts are expected to
rise in East, South and Southeast Asia55.
3. Agriculture and nutrition
Increased atmospheric carbon dioxide concentrations,
global warming and associated climate change are
expected to have an influence on agriculture. Higher
temperatures will increase crop yields at high and midlatitudes, as the growing season becomes longer, but
decrease them at lower latitudes. More carbon dioxide
will benefit crops, as it is an essential ingredient in the
photosynthesis process. The IPCC reports that with
moderate temperatures, a long-term doubling of
current ambient CO2 will lead to a 30% enhancement
in the seed yield of rice. However, the grain yield will
fall by about 10% for each 1°C rise above 26°C as a
result of a shortening of the growing period and
increased sterility. Similar scenarios have been
reported for soybean and wheat56. Taking Australia and
New Zealand as an example, the IPCC estimates that
by 2030 more drought and wildfire will cause
agriculture and forestry production to decline over
much of southern and eastern Australia and over parts
of eastern New Zealand. However, a longer growing
season, less frost and increased rainfall will bring
initial benefits to western and southern parts of New
Zealand and areas close to major rivers55.
Developed countries are expected to suffer least from
these changes. Most of the developed world lies at
latitudes at which temperature increases are expected
to be of most benefit. With their greater economic
resources and better infrastructure, developed
countries should also find it easier to make the
necessary modifications in agricultural methods57.
Activities at the margin of climatic suitability stand to
lose (or gain) the most from climate change. A
decrease in rainfall or longer droughts could tip the
balance from a meagre livelihood to no livelihood at all
for subsistence farmers under severe water stress in
semi-arid regions of Africa or south Asia. It will also
exacerbate malnutrition in these regions. An increase
in rainfall, on the other hand, could reduce pressure
on marginal areas58,55.
Fisheries could suffer from regional changes in the
distribution and production of particular fish species
due to continued warming. The rising water
temperatures of large lakes is likely to decrease their
fisheries resources59.
The world food trade system may be able to alleviate
the effect of changes in agricultural production on a
global scale, though isolated regions may still face
hardship. Malnutrition will also make people more
susceptible to other risks such as diarrhoea and
malaria.
4. Drought and water resources
Changes in rainfall patterns will undoubtedly affect
water resources. Current global climate models vary
widely in their predictions of the effect of global
warming on precipitation60. It is likely that precipitation
will increase globally, though some regions are likely
to see a reduction in rainfall due to changes in local
meteorological patterns. The area affected by droughts
has increased since the 1970’s and is likely to
increase in future61.
Figure 14: Projected Patterns of Precipitation Changes
Source: IPCC 2007
Climatic and human influences can have a major
impact on the availability of water. Lake Chad in Africa,
for example, covered an area of 25,000 square
kilometres in 1960. As a result of reduced rainfall, and
greatly increased amounts of irrigation water being
drawn from the lake and rivers feeding it, its area has
dropped to less than 1,500 square kilometres. This in
turn has forced people to concentrate around the
shrinking lake edge, leading to conflict or migration,
and adding to social pressures in other areas62. The
dramatic decrease in the size of the lake is evident
from satellite images (see Figure 15).
15
Photo: Getty Images
1973
1987
Figure 15: Lake Chad in 1973 and 1987 (NASA63)
Warmer and drier conditions in the Sahelian region of
Africa has shortened the growing season and in
southern Africa growers are adapting to longer dry
seasons and changes to rainfall patterns64. In Central,
South, East and Southeast Asia, freshwater availability
is expected to decrease65.
Regions that obtain their water as meltwater from
mountain ranges will suffer as water supplies stored in
glaciers and snow cover decline over the course of the
century. More than one-sixth of the world population
lives in such regions66.
5. Sea level rises and flooding
Temperature affects the volume of sea water because
of thermal expansion. The warmer a given mass of
water, the greater its volume. Based on a range of
models, the combined effects of thermal expansion
and melting ice, already described, are expected to
result in a global average sea level rise of between
18 and 59 cm by the last decade of the 21st century,
compared to the last decade of the 20th century67.
However, as the response to climatic change is slow,
sea levels are likely to continue to rise long after that,
even if global warming were to be limited.
16
Higher sea levels threaten to submerge low-lying
lands and coastal areas. Island nations, such as
Tuvalu in the south Pacific, with its highest elevation
of 5 metres, and the Maldives, with a highest natural
ground level of 2.3 metres, are at particular risk. Most
parts of Bangladesh are less than 10 metres above
sea level; about 10% of its land would be flooded if
sea levels rose by 1 metre. Apart from outright
submersion, many low-lying coastal areas will be at
risk of increased flood frequency and severity from
storm surges. Coastal areas will be more susceptible
to erosion, causing retreat of the shore-line. There will
also be intrusion of salt water further inland, affecting
fresh water sources.
The consequences of global warming could be more
serious in the longer term if the melting of the
Greenland and West Antarctic ice sheets is initiated.
As mentioned previously, the complete melting of the
Greenland ice sheet would produce a sea level rise of
7 metres68. Many of the world’s cities would be under
threat of flooding, including London, New York and
Shanghai. Rising sea levels could result in a large
number of environmental refugees and millions
permanently displaced. Historic records support the
link between higher temperatures and sea level rise.
During the last interglacial period (about 125,000
years ago) temperatures were 3–5°C higher than now
and sea level was likely 4–6m higher than during the
20th century69.
6. El Niño
Strong ‘trade’ winds normally blow towards the west
over the Pacific Ocean, driving the surface waters
westwards with them. As a result, cold water from the
ocean depths rises to the surface off the coasts of
North and South America, causing the mean sea
surface temperature in the western Pacific to be as
much as 8°C warmer than in the east. However,
occasionally these winds weaken, causing warm
water to accumulate in the eastern Pacific. This leads
to increased rainfall, storm activity and flooding in the
Americas, and drought in the western Pacific region
covering Australia, Indonesia and the Philippines,
increasing the risk of forest fires. Such events, known
as El Niño, have historically occurred at intervals of
2 to 7 years, with a typical duration of 1 or 2 years.
50
45
40
Percent total hurricanes/category
The strongest El Niño on record was in 1982–83, and
the period from 1990 to 1995 unusually had three
consecutive events, with no real recovery between
them70. Although no conclusive connection between
global warming and the El Niño phenomenon has
been established, it has been suggested that their
apparent increasing frequency will continue until a
permanent El Niño state is established71.
35
30
25
20
15
10
5
7. Storms
0
70/74
Damage caused by storms accounts for almost three
quarters of financial losses from weather-related
catastrophes, amounting to $10–40 billion each year72
and rising sharply. This upward trend can mainly be
attributed to growing, wealthier populations, with
greater assets at risk, but there is evidence to suggest
that the frequency of powerful storms is also on the
rise.
A tropical cyclone is a storm system with a closed
circulation around a central column of rising low
pressure air. Tropical cyclones derive their power from
the latent heat of water vapour. The vapour condenses
in the updrafts, releasing the stored heat and causing
intense precipitation. The source of the storm’s energy
is heat drawn from the warm sea surface and returned
to the cold upper atmosphere73.
Climate change scenarios predict that more intense
cyclones will occur because more energy is available
to the storms from higher sea surface temperatures74.
Although the frequency of cyclones is not anticipated
to change, the frequency of highly destructive storms
is expected to rise75. A look at the number and intensity
of past hurricanes suggests that this effect is already
manifesting itself (see Figure 16).
75/79
1
80/84
85/89
Pentad
90/94
2+3
95/99
00/0 4
4+5
Figure 16: Plot showing frequency of storms categorized by
windspeed per five year period over the last 35 years75.
Coastal communities and habitats around the world,
in the developed and developing world, are likely to
suffer from an increase in the intensity of tropical
storms.
8. Ecosystems and biodiversity
Ecosystems are vulnerable to a range of climate
change impacts, compounded by land use change,
increased development, pollution and over-exploitation
of resources. A global increase in temperature of
1.5–2.5°C could increase the risk of extinction of
approximately 20–30% of plant and animal species76.
In some areas of Europe, species loss could be as
much as 60% by 2080 under high emission
scenarios77. Impacts on ecosystems and biodiversity
and habitat loss are likely to occur at polar regions,
as a consequence of loss of tropical forest in Latin
America and through increased pests, disease and
wildfire in North American forests. Acidification and
warming of oceans can have negative impacts on
coral reefs and significant loss of biodiversity is
projected at the Great Barrier Reef in Australia by
2020.
17
2–3°C, all regions will experience either declines in net
benefits or increases in net costs and that the
reduction in GDP would be 1–5% for 4°C of warming.
It estimates that projected sea-level rise could cost at
least 5–10% of GDP in adaptation for low-lying coastal
areas with large populations81.
Both conclude that impacts will vary regionally and
that the poorest countries, with high exposure, high
sensitivity and/or low adaptive capacity, will suffer
considerably, losing more than 10% of their output
according to the Stern Review. The IPCC concludes
that their net costs from climate change will be
significantly larger than the global aggregate. The
Stern Review concluded that it would cost just 1% of
GDP each year to stabilise emissions (at 500–550
ppm, a level which he suggests would avoid the worst
impacts of climate change) in the next 20 years and to
reduce them by between 1% and 3% of GDP per year
thereafter. Sir Nicholas Stern’s recommendations for
achieving this include generating 60% of energy from
non-fossil fuel sources by 2050. He also foresees a
continued role for coal but carbon capture and storage
are needed. The most recent report on mitigation
measures from the IPCC says keeping greenhouse
gas concentrations to levels equivalent to between
445 and 535 ppm of CO2 could costs up to 3% of GDP
over two decades82.
Recent anthropogenic warming has already affected
physical and biological systems. Observed changes
include, for example, the earlier arrival of spring and
upward shifts in the range of plant and animal species.
Rising water temperatures also appear to be changing
marine and freshwater biological systems, including
changes to the range and abundance of algae,
plankton and fish and changes to fish migration
patterns78.
The IPCC predicts that by the middle of the 21st
Century, net carbon uptake by terrestrial ecosystems
is likely to peak and could then weaken or even
reverse, causing more climate change79.
9. Economic consequences
The economic impacts of climate change will be
significant and will hit the poorest hardest. Though
varying regionally, rising temperatures and their
impacts are likely to impose additional annual costs.80
In 2006, Sir Nicholas Stern, a former Chief Economist
of the World Bank, compiled a report for the UK
Government on the economic consequences of
climate change80. He reported that a 2–3°C rise in
global average temperatures could reduce global
economic output by 3%. A 5°C rise could reduce
global output by 10%. Extreme weather could reduce
global GDP by up to 1%. The overall cost of not acting
could be as much as 20% of global GDP. The IPCC
estimates that for increases greater than about
18
PART FIVE: SOLUTIONS
The latest IPCC research82 has concluded that there is
substantial economic potential for reducing
greenhouse gas emissions by 2030 and beyond.
This reduction would require measures across a range
of sectors (including the transport, industry, energy
supply, agriculture and forestry, industry and waste
sectors). The IPCC recommends greater energy
efficiency, use of renewable energy, biofuels and
nuclear power, more use of Carbon Capture and
Storage (CCS) technology, along with protection of the
world’s forests and changes in lifestyle patterns. This
is considered technically feasible but incentives are
needed for more investment.
Leading international environmental organisations
support investment in renewable energy, energy
efficiency and cleaner fossil fuel burning technologies
in order to bring about significant cuts in global
emissions. In 2007, WWF83 called on the G8+5 nations
to adopt a technology package that included binding
global energy efficiency standards, a global target of
25% for new renewable sources by 2025, plans for the
development of newer renewable and CCS
technologies, and the fitting of CCS to fossil fuel
plants. Research by Greenpeace and the Global Wind
Energy Council84 has shown that wind power alone
has the potential to supply 34% of the world’s
electricity by 2050 and in so doing save 113 billion
tonnes of CO2 emissions.
Wind power is one of the world’s fastest-growing
energy sources and a vital part of mankind’s response
to the challenge of climate change. It has a leading
role to play in the transition to a low carbon economy.
The installed capacity for wind continues to increase at
a staggering rate of 30% per annum. 2006 saw the
installation of 15,000MW, bringing global wind energy
capacity to over 74GW85.
Decision-makers and investors are recognising the
myriad benefits of a range of renewable heat and
power technologies. The commercial, industrial and
public sectors are increasingly looking to wind,
biomass, ground source heat pumps and solar
collectors as ways to reduce their carbon footprint in a
cost-effective way, whilst having on-site secure and
reliable heat and power generation. Marine renewable
technologies such as tidal and wave energy also have
the potential to make significant contributions to the
provision of secure, renewable and low carbon energy
in meeting the challenge of global warming.
19
PART SIX: CONCLUSIONS
Global mean temperatures have been steadily
increasing over the last 30 years. The 20th century as
a whole registered a warming of 0.74°C. We are
currently experiencing the highest temperatures since
direct measurements began.
At the same time, atmospheric concentrations of the
main greenhouse gases carbon dioxide and methane
have risen sharply since the industrial revolution, and
particularly over the last five or six decades. This is
primarily as a result of anthropogenic emissions
originating from the use of fossil fuels.
Climatic models indicate that global temperatures are
linked to atmospheric greenhouse gas levels. Whilst
other factors influence climate, historical data drawn
from ice cores show that mean temperatures generally
increase with atmospheric carbon dioxide
concentrations. It is thus fairly certain that greenhouse
gases emitted by human activities are contributing to
global warming.
Increased temperatures will have a wide impact on the
climate, influencing such phenomena as precipitation
and cloud cover, affecting industries, economies and
the general welfare of the population. Whilst some
areas may benefit from the effects of global warming,
it is expected that the overall consequences will be
negative.
Mechanisms which threaten to exacerbate global
warming include the effect of positive feedbacks, such
as the warming-melting-warming cycle in polar
20
regions. The more established such cycles become,
the more difficult they are to moderate. There are
believed to be critical points beyond which the effects
are irreversible by human intervention. Existence of
such feedbacks leads to the possibility of ‘runaway’
global warming, which could have catastrophic
consequences.
By the year 2100, it is estimated that global mean
temperatures will have risen by between 1.8 and 4.0°C
over present values. The consequences of such
warming include the direct effects of heat on human
health, on the spread of diseases, agriculture and
nutrition, on drought and water resources, on sea level
rises and flooding, and on storms and other extreme
weather phenomena.
In view of the generally detrimental consequences of
climate change, it is in our best interests to avoid
global warming as far as possible. While adaptation
strategies are essential in order to address the
unavoidable impacts of climate change that we face in
the next few decades, making serious cuts to our
greenhouse gas emissions is the most effective course
of action, however difficult this may seem in a world of
ever-increasing energy demand. Making greater use of
renewable energy sources, such as wind, solar power,
biomass, geothermal and marine technologies,
represents one of our best strategies for meeting this
challenge. We have the technological know-how –
what is needed now is political will, and the earlier we
act, the less we risk damaging our earth.
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Renewable Energy Systems Ltd (RES)
Beaufort Court
Egg Farm Lane
Kings Langley
Herts WD4 8LR
United Kingdom
Tel: +44 (0)1923 299200
Fax: +44 (0)1923 299299
Web: www.res-group.com
Email: [email protected]
Date of publication: May 2007
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Global Warming Guide

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