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Earthonfre
Clim
atechangeromaphilosophicaland
ethicalpersp
ective
Mickey Gjerris,Christian Gamborg,
Jrgen E. Olesen
Jakob Wolf (Eds.)
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Earth on fire
Climate change from a philosophical and ethical perspective
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Earth on Fire climate change from a philosophical and ethical perspective is an electronic open
access version of the bookJorden brnder klimaforandringerne i videnskabsteoretisk og
etisk perspektiv published by ALFA 2009. ALFA has kindly given their permission to this
translation under the conditions that the English text is in no way used for commercial
purposes. The printed Danish version of the book can be bought in book stores or
at the publishers web-site: http://www.forlagetalfa.dk/alfa_detail.asp?ID=2859
The English translation has been published with economic support from
Theme Cluster 1 and The Institute of Food and Resource Economics, both
from the University of Copenhagen and from the University of Aarhus.
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Earth on fire
Climate change
from a philosophical andethical perspective
Edited byMickey Gjerris,
Christian Gamborg,Jrgen E. Olesen &
Jakob Wolf
2009
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Earth on fire
Climate change from a philosophical and ethical perspective
Edited by Mickey Gjerris, Christian Gamborg, Jrgen E. Olesen, Jakob Wolf
The authors and The Institute of Food and Resource Economics,
The Faculty of Life Sciences, University of Copenhagen
Cover: @ Arne Naevra (Norway); Polar meltdown
Translation: Overstterhuset A/S
Layout and typesetting: Narayana Press
Cover: Religionspdagogisk Center, Bjarne Jensen
Printed by: Narayana Press
ISBN: 978-87-993282-0-8
The publishers have been unable to contact the legal copyright holders
of some of the pictures in this book. Any violation of their copyrights
etc. has been unintentional. Legal obligations arising will, of course,
be honoured as if permission had been granted in advance.
The Danish edition was published with funding from Torben & Alice Frimodts Fond,
Direktr Einar Hansen og hustru fru Vera Hansens Fond, the Institute of Food and
Resource Economics at the University of Copenhagen, the Faculty of Life Sciences at the
University of Copenhagen and the Faculty of Agricultural Sciences at Aarhus University.
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7Content
Content
Foreword to the English edition
Mickey Gjerris 9
Introduction
Mickey Gjerris 11
The climate is changing but why?
Jrgen E Olesen 17
What will happen?Scenarios of the future
Jrgen E Olesen 37
Climate science how did it come about?
Matthias Heymann 55
What is climate science all about?Philosophical perspectives
Matthias Heymann, Peter Sande & Hanne Andersen 69
The price of responsibility ethical perspectives
Christian Gamborg & Mickey Gjerris 89
A religious perspective on climate change
Jakob Wolf 115
The climate debates debating climatePolarisation of the public debate on climate change
Gitte Meyer and Anker Brink Lund 135
Case 1 Biofuels
Biofuels Crops for food and energy
Claus Felby 163
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8 Content
Biofuels: Hunger, subsidies and lack of effect on CO2 emissions
Christian Friis Bach 169
Study questions 173
Case 2 Genetically modified organismsGMOs: A solution to changed climate conditions
Preben Bach Holm 175
GMOs: The right way of taking responsibility?
Rikke Bagger Jrgensen 182
Study questions 189
Case 3 Trading in CO2 quotasCO2 trading. A cost-efficient tool to achieve political goals?
Alex Dubgaard 191
CO2 trading. Should you be able to buy your way outof the problems?
Peder Agger 200
Study questions 207
Further reading 209
About the authors 215
Index 2 1 9
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9Foreword to the english edition
Foreword to the English editionMiCkey gjerris
This book is about climate change and what it does to us and our planet.
But even more it is about the philosophical and ethical challenges that arise
from the changing weathers. The book was originally written for Danish
students by Danish researchers, but just as global warming is a global phe-
nomenon so is the questions that are put forth here. The book has therefore
been translated into English so as to make it available for a wider audience
The English online version is free for all to use. All we ask you is that youshare the existence of the book with your colleagues and fellow students so
that as many as possible might benefit from it.
Should you have any comments or ideas for improvements to the next
edition, please mail Mickey Gjerris [email protected].
The editors would like to thank Forlaget ALFA and our editor Jeanne Dal-
gaard for their generous permission to translate the original text and their
good cooperation throughout the process. Furthermore we would like to
thank Overstterhuset A/S for their efficient work with the translation and
Annette Larsen for her help. Finally we would like to thank Theme Cluster
1 and The Institute of Food and Resource Economics from the University
of Copenhagen and the University of Aarhus for their economic support to
this translation.
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11introduCtion
IntroductionMiCkey gjerris
The Earth is on fire. Our world is getting warmer, and the climate is chang-
ing. There is a lot to suggest that this is due to how we are using the Earths
resources. Also, it is a matter of urgency if we want to be able to exercise
just a modicum of control over what the future will bring. So, in a manner
of speaking, the Earth is getting too hot under our feet. We need to find out
what is behind the climate change, but we also need to find a solution fast.
At least that is how things stand at the moment. Just a few years ago,however, many scientists, politicians and laymen still questioned whether
the climate was in fact changing, let alone whether human activities had
any role to play. How could it be that all this doubt evaporated, and that
everyone suddenly started talking about the climate and marketing them-
selves on low CO2 emissions? A significant shift has occurred. Today, very
few people question that climate change is happening and that it is largely
due to human activity. Have we arrived at a new scientific certainty, or is it
the result of a less transparent process where ethical values and political
considerations have come to influence the scientific agenda? How definite
actually are the climate models on which we are basing our actions, and
how much of the discussion about them is science and how much relates
to the ethical and philosophical considerations which have shaped them?
It is not absolutely clear what will happen with the climate in the coming
years, but there is general agreement that the world will change. And man
has started to prepare for these changes. This gives rise to important ethi-
cal questions. What must we do, who must we consider, and what does the
natural world mean in an ethical sense? Should we save endangered speciesfor their own sakes or for ours? Should we help the people who will benefit
most from our help or those that most need the help and do we in fact
have a duty to help anybody apart from ourselves? Major changes threaten
and the solutions risk being rushed through without careful consideration.
Thats what happens when the Earth suddenly gets too hot under ones feet.
This book is about climate change, one which will contribute to our
understanding of what is happening and why it is happening. The objective
is to show how climate change raises not only a number of questions to do
with natural science, but also many questions of a more universal nature
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12 MiCkey gjerris
that are based on philosophical, political, ethical and religious assumptions
about how the world is and how itshould be. We hope that this book willencourage critical reflection and ethical consideration of what is happen-
ing, why it is happening and what we ought to do. Because something is
happening:James A. Hansen, as head of NASAs Goddard Institute for Space Stud-
ies and one of the worlds leading climate researchers, is one of those who
repeatedly points out that the situation is far more serious than we are
willing to acknowledge. According to him, the targets for CO2 reductions
which have been set in the international agreements which applied for 2008
already exceed what is necessary to stabilise the situation. According to
Hansen we must act far more effectively and radically and we must take
action now. In a speech given to The National Press Club in Washington DC
on 23 June 2008, he said:
Changes needed to preserve creation, the planet on which civilisation de-
veloped, are clear. But the changes have been blocked by special interests,
focused on short-term profits, who hold sway in Washington and other
capitals. I argue that a path yielding energy independence and a healthier
environment is, barely, still possible. It requires a transformative change of
direction in Washington in the next year.
(Hansen, 2008)
Research published in winter 2008 by the Canadian geophysicist David
Barber suggests that, by 2015, the Arctic will be ice-free during the sum-
mer. Whether this happens in 2015, 2025 or 2035 is, in this context, fairly
irrelevant. What is important is that the temperature increases on the planet
seem to be having quite an impact and that things are developing at a pace
which, time and again, takes the scientists by surprise. The climate and the
factors which have a bearing on it are complex. Often, individual scientists
only see part of the picture, but when the various factors start reinforcingeach other, the whole picture suddenly changes. In the past eight to ten
years, the possible climate changes have led to worried minds and interna-
tional agreements which have not really put the big players under any sort
of obligation and to the setting of national targets which have basically been
ignored in practical politics. The general consensus is that we can no longer
afford such procrastination. Things are hotting up now really hotting up.
So we need to both act fast and think carefully about what we are doing.
This book is primarily intended as a textbook in ethics and science theory
at university level, where it can be used on all study programmes to provide
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13introduCtion
recurrent case material. The more technical chapters can be used depending
on the field of study. The book can also be used as a source of background
information for upper-secondary school teachers and other teachers in the
educational system and as a study book by reading groups, or simply by
readers who want to understand what the climate debate is all about. Thebook is the result of scientists from many different fields and institutions
collaborating together, which is evident from the author presentations at
the back of the book. The breadth of expertise clearly reflects the radical
significance of climate change for the future. Climate change literally cuts
across all boundaries. It is the hope of the editors that this broad approach
will contribute to understanding the complexity of the problems and a
healthy level of scepticism towards any over-simplified messages in the
climate debate.
The book consists of seven chapters which show how the climate changesare rooted in our scientific, philosophical, political, ethical and religious
understanding of the world. Chapters 1 and 2 are written by the climate
scientist and member of the UN climate panel Professor Jrgen E. Olesen
from Aarhus University. The first chapter describes the changes which the
climate is undergoing, which physical, chemical and biological mechanisms
are interacting to cause climate change, and what is driving the changes.
The second chapter looks at the consequences of climate change for life on
Earth both generally and specifically for a number of areas such as agricul-
ture, infrastructure and urban planning. The books third chapter is written
by the science historian Matthias Heymann from Aarhus University. This
chapter puts the present discussion about climate research into a historical
perspective and shows how climate research has always been embedded in
philosophical and political discussions.
Matthias Heymann has also been involved in Chapter 4, this time with
the philosopher Peter Sande from the University of Copenhagen and the
science theorist Hanne Andersen from Aarhus University. Together they
describe the science-theoretical challenges raised by the use of computermodels in climate research, and seek to show how scientific uncertainty also
becomes a political issue. Chapter 5 is written by the ethicist Mickey Gjerris
and the natural resource ethics researcher Christian Gamborg, both from
the University of Copenhagen. The chapter focuses on the ethical dilemmas
presented by climate change as far as mankind is concerned as well as in
relation to the natural world in general. In Chapter 6, the theologian Jakob
Wolf, also from the University of Copenhagen, looks at climate change from
a religious perspective, and offers his views on how religion, broadly speak-
ing, can help to fight climate change. Finally, in Chapter 7, senior lecturer
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14 MiCkey gjerris
and journalist Gitte Meyer from the University of Copenhagen and professor
in media management Anker Brink Lund from Copenhagen Business School
write about the political discussion about the climate which has dominated
the media over the past twenty years, and put this discussion into a broader
context concerning the role of science in the current debate.The seven chapters can be read independently of each other, but as they
each have something to offer, reading them all will provide a solid founda-
tion from which to relate to climate change. The chapters are written as
textbook chapters, and thus provide a general introduction to the issues
from what is hopefully a neutral perspective. Nonetheless, it is important
to note that the chapters are written by different researchers, each of whom
possesses expertise within their particular field. The various chapters are
therefore, unavoidably, coloured by their respective views. This basic condi-
tion for all communication should make the reader take a critical approachto the chapters and not be seduced by what is presented as obvious conclu-
sions. These chapters are not the final answer to anything, but invite the
reader to participate in a broader discussion about climate change.
At the end of the book, three actual cases from the climate debate are
discussed: CO2 trading, GM crops and biofuels. These cases are addressed
by experts who have played a prominent role in the public debate of these
topics. What all three cases have in common is that they describe contro-
versial solutions to problems resulting from climate change. The purpose
of these cases is partly to present some of the more controversial strategies
for countering climate change to the reader, and partly to show how the
ethical and philosophical issues on which the seven main chapters centre
can be used as keys to understanding the disagreements that arise when
discussing some of the most important issues currently faced by mankind.
Each case is preceded by various working questions which can be used as a
starting point for a discussion of the case and as a way of focusing on the
ordinary problems that lie behind the specific differences of opinion.
Each chapter is followed by a list of the references which have been usedas background material. These can be used as inspiration for further read-
ing. There is also a list at the back of the book of commented suggestions
for further reading, organised by chapter. The intention is that students and
others will easily be able to find further literature for project work, studies
etc.
The editors would like to thank all the contributors for their time, Jeanne
Dalgaard from the publishers Alfa for her good and thorough editing, and
a number of Danish financial contributors who have made the publication
of this book possible: 1: Torben & Alice Frimodts Fond 2: Direktr Einar
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15introduCtion
Hansen og hustru fru Vera Hansens Fond 3: Institute of Food and Resource
Economics, University of Copenhagen 4: Faculty of Life Sciences, University
of Copenhagen 5: Faculty of Agricultural Sciences, Aarhus University.
The changes we face are both alarming and far-reaching. They will have
a major impact on our lives. In order to meet this challenge, it is necessarythat we understand both the scientific details and the broader contexts of
the different problems. Technical solutions detached from the social reality
into which they must be incorporated cannot solve these problems, just as
theoretical musings on background, causes and values are of no use in the
present situation. However, if we gather the threads and endeavour to tackle
the task based on a high level of expertise and sound knowledge about the
context of the problems, we believe there is every possibility that the huge
challenges we face can be resolved. We hope that this book will make a
small contribution to this task.
ReferencesHansen JA: Global Warming Twenty Years Later: Tipping Points Near (2008).http://www.
columbia.edu/~jeh1/2008/TwentyYearsLater_20080623.pdf
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17the CliMate is Changing but why?
The climate is changing but why? jrgen e. olesen
1. Introduction
The mean temperature at the Earths surface is increasing, and at the same
time the patterns of precipitation are changing towards more intense rainfall
and longer periods of drought. These changes are controlled by physical
as well as biological processes. Even though there are natural processes
which can lead to global temperature increases, research shows that human(anthropogenic) activities especially CO2 emissions are most likely to
be the main reason for the increasing temperatures on Earth over the past
30 years. Model calculations show that global temperatures will probably
increase by 1.8-4.0 C during the twenty-first century depending on emis-
sions of greenhouse gases.
Following the Fourth Assessment Report (AR4) of the UNs Intergov-
ernmental Panel on Climate Change (IPCC) and Al Gores documentary An
Inconvenient Truth as well as the Nobel Peace Prize which was awarded to
the IPCC and Al Gore in 2007, there has been an unparalleled level of atten-
tion on man-made climate change. This is largely due to the fact that the
IPCC now concludes that: Most of the observed increase in global average
temperatures since the mid-20th century is very likely due to the observed
increase in anthropogenic GHG concentrations. However, in the media this
is still being debated although most researchers support this conclusion.
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18 jrgen e. olesen
IPCC the UNs climate panel Box 1
The UNs climate panel is called the IPCC, which stands for Intergovernmental
Panel on Climate Change. It was set up in 1988 as a follow-up to the Brundtland
Report Our Common Future. Based on its reviews of scientific literature,about every five years the panel publishes a summary and an assessment of
research and knowledge on climate change and the effects of these changes.
The scientific reviews are conducted by recognised scientists within the various
fields. The scientists are appointed by the UNs member countries. The assess-
ment consists of a report from each of the three main working groups:
Working group I: Describes the scientific aspects of the climate system and
climate changes.
Working group II: Describes vulnerabilities in the socio-economic and
natural systems in the face of climate change, impacts as well as the
possibilities for adaptation. Working group III: Describes how to reduce emissions ofgreenhouse gases
and other ways of preventing climate change.
In addition to these assessment reports, the IPCC also publishes a number of
special reports on specific subjects, for example emission scenarios, technolo-
gies for reducing emissions or methods for calculating greenhouse gas emis-
sions. The latest assessment report (the fourth) was published in 2007. The
IPCC does not conduct independent research itself on climate changes or their
impacts, but is charged with drawing conclusions from the available scientific
literature on the subject.
2. Climate changes whats happening?
Worldwide, the temperature has increased by 0.7-0.8 C since the end of the
nineteenth century. By far the largest share of this increase (0.55 C) has oc-
curred within the past 30 years. However, it is not just the temperature which
has increased. Other aspects of the climate systems have also changed: Sea levels worldwide have risen, and the rate of increase is growing,
such that sea levels are now rising by 3-4 mm per year.
In many places, ice caps and glaciers are melting, contributing to rising
sea levels.
Snow cover in the northern hemisphere has decreased by about 5 per
cent since 1966.
The area covered by permafrost has decreased by 10 per cent in the
northern hemisphere.
The extent of Arctic sea ice has decreased by 20 per cent since 1978.
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19the CliMate is Changing but why?
Precipitation has increased at high latitudes in both the northern and
southern hemispheres.
There are more periods of drought. This increase in droughts has mostly
been observed in the already dry areas of the world, i.e. the dry tropics
and subtropics. The frequency of heavy precipitation has increased, even in areas with
reductions in total rainfall.
There is no change in the number of tropical hurricanes, but they tend
to be stronger and to last longer.
Over a longer time-scale, climate on Earth has varied considerably more
than what we have seen in recent decades. However, we only have reliable
measurements of temperature and precipitation for the past 150 years or so.
To look at the climate over longer periods of time, we must resort to indirectmeasurements. Here, measurements of e.g. oxygen isotopes in ice cores and
sediment layers play an important role in describing the climate (Box 2).
However, there are considerable uncertainties associated with translating
these observations into a global average temperature. Using such measure-
ments, the IPCC assesses that the global average temperature during the
past 50 years has not been as high for the past 1,300 years.
3. The Earths radiation balance
As mentioned above, in the course of the Earths long history the climate
has varied considerably more than what has been observed within the past
100 years. Basically, the climate is determined by the balance between the
energy which is supplied by sunlight, and the energy which is lost through
longwave heat radiation from Earth (Figure 1). Two factors in particular af-
fect the radiation balance: 1) The amount of sunlight intercepted by Earth,
and 2) the strength of the greenhouse effect.
Incoming solar radiation corresponds to an average of about 342 W/m2on the entire Earths surface, day and night, 365 days a year. However, 31
per cent of this radiation is reflected by clouds, atmospheric particles and
the Earths surface. This is called the planetary albedo. It is the remaining
69 per cent (or 236 W/m2) which heats the Earth and the atmosphere.
Earth loses heat by emitting longwave infrared radiation. The amount
of longwave radiation is proportional to the absolute temperature to the
fourth power (Stefan-Boltzmans law). Over a long period of time, the
outgoing radiation will be the same as the incoming radiation (236 W/m2).
Using Stefan-Boltzmans law, this gives a mean temperature for the globe
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Measuring temperature Box 2
Traditionally, air temperature is measured by placing a thermometer in what
is termed a Stevenson screen, which provides shade and ventilation, ensuring
that it is the air temperature that is measured and not the effect of solar radi-ation on the thermometer. Such measurements have been conducted worldwide
since the mid-nineteenth century. Temperature measurements are affected lo-
cally by urban development (the urbanisation effect), and it is being discussed
whether such effects have affected the global temperature series so they show
excessive temperature increases. It is well known that the climate in large cities
is significantly warmer than beyond the city limits, but by far the most weather
stations are situated in the countryside, far away from urbanised areas. More-
over, temperature measurements from towns and cities are corrected to take
account of the urbanisation effect. A number of recent studies show that, at
most, urbanisation produces a small uncertainty (0.06 C over 100 years), whichis far less than the observed increases in temperature.
In recent decades, measurements using satellites have provided new ways of
measuring the Earths temperature. However, such measurements provide in-
formation in particular about changes in temperature distribution at various
heights in the atmosphere. Here, observations show that the temperature in
the uppermost part of the atmosphere has been falling, which ties in with the
greater greenhouse effect leading to reduced outgoing radiation from the lowest
part of the atmosphere. Reconstructing the temperature over longer time-scales
calls for other indirect methods. Geological deposits provide information
about the fauna and flora in the past, and the composition of these organismsprovides information about climatic and temperature conditions at the time
when these organisms were living. Similar information can be obtained by
studying the thickness of tree rings.
Studies of longer time-scales are concentrated on ice cores in Greenland and
on the Antarctic as it is possible to indirectly read the variations in temperature
several hundred thousand years ago. One of the most important methods of re-
constructing the temperature back in time is to measure the amount of different
forms of oxygen (oxygen isotopes), both the ordinary oxygen isotope 16O and the
heavier and rarer18O. Oxygen is the heaviest constituent of a water molecule
(H2O), and as it is easier for the lighter16O to evaporate than the heavier18O, in
colder periods there will be less 18O present in the atmosphere than in warmer
periods. The relative content of the two isotopes in the ice caps can therefore
tell us about the temperature of the atmosphere at the time when the snow fell.
In cold periods there will be less 18O present in the atmosphere than in warmer
periods. The relative content of the two isotopes in the ice caps therefore tell us
about the atmospheres temperature at the time when the snow fell.
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21the CliMate is Changing but why?
of 254 Kelvin (approx. -19 C). This is about 34 C lower than the mean
temperature of 15 C which has been measured. Another mechanism (the
greenhouse effect) must therefore be influencing climate on Earth.
A number of gases in the atmosphere (for example water vapour, car-
bon dioxide and methane) are, like the clouds, able to absorb some of the
outgoing longwave infrared radiation. The absorbed radiation warms theair and is emitted again as longwave radiation, just at a lower temperature
than at the Earths surface as the atmospheric temperature declines with
height. Seen from space, the heat is not emitted from the Earths surface
but from greenhouse gases and clouds some way up in the atmosphere. On
average, it is at the level where the effective outgoing radiation temperature
is 254 Kelvin (at a height of just over 5 km).
With a greater concentration of greenhouse gases in the atmosphere, the
radiation effectively takes place higher up in the atmosphere and for a period
at a lower temperature, so that heat builds up in the climatic system until
Figure 1: The Earths radiation balance consists of the balance between incoming solar radiation(shortwave radiation) and solar radiation reflected by clouds and the surface of the sea and theEarth as well as longwave heat radiation from the surface, sea, clouds and atmosphere (Taken
with permission from H Meltofte (ed.) (2008): Klimandringerne: Menneskehedens hidtil strsteudfordring. The Environmetal Library. Hovedland Publishers)
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22 jrgen e. olesen
Box 3: Feedback mechanisms
The Earths climate system consists of a
closely interconnected system involving the
atmosphere, land, ice, soil and vegetation.If the temperature changes, it will lead to
changes in the other components, which in
turn may affect the temperature. These feed-
back mechanisms can both enhance and
weaken temperature changes. Here are a few
examples of feedback mechanisms:
Water vapour
Water vapour is a greenhouse gas, but the
maximum amount of water vapour that the
atmosphere can contain greatly dependson temperature (almost 7 per cent increase
for every 1 C increase in temperature). The
warmer it is, the more water vapour the
atmosphere can hold, and the greater the
warming effect from the water vapour (posi-
tive feedback).
Snow and ice
Warming leads to a melting of snow and
ice on the Earths surface and consequentlya reduction in snow cover and sea ice. This
minimises the amount of reflected sunlight
to space and leads to additional warming
(positive feedback). This is the main reason
why global warming leads to the greatest
temperature increases at high latitudes.
Clouds
Clouds affect the climate system in vary-
ing ways depending on how high they are
in the atmosphere. This is because cloudshave an insulating effect while also reflect-
ing sunlight. High clouds generally have a
warming effect while low clouds are cooling.
The overall effect of clouds is thought to be
cooling, corresponding to about 20 W/m2.
This should be seen in relation to the fact
that man-made changes in the radiation
balance so far are only approximately 1.6
W/m2 (Table 2).
CO2Man-made climate changes are particularly
due to emissions of CO2 from using fossilenergy and from deforestation. Over longer
periods of time, however, CO2 also plays a
role in feedback systems. For example, the
solubility of CO2 in sea water falls with in-
creasing temperature, which reinforces the
role of CO2 as a greenhouse gas. Warming
also increases the temperature in areas with
permafrost where very large quantities of
carbon are fixed in the soil, which is released
at higher temperatures. This too amounts toa positive feedback.
Temperature profile in the atmosphere
The temperature change will be greater
at the effective level of outgoing radiation
higher up the atmosphere than at the
Earths surface. On the surface there will
therefore be smaller temperature changes
(negative feedback).
Heat transportLarge volumes of energy are transported
in the atmosphere and in the oceans. In a
changed climate, these flow patterns can
become altered, which can lead to both posi-
tive and negative feedback.
Vegetation
The Earths vegetation influences how much
sunlight is reflected and how much water
evaporates. As vegetation is also influenced
by changes in temperature and precipita-tion, there is the possibility of many dif-
ferent feedbacks which can be very hard to
predict.
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23the CliMate is Changing but why?
the Earths temperature again corresponds to the loss through outgoing
heat radiation. This leads to warming in the lowest part of the atmosphere.
4. Greenhouse gases
The most important greenhouse gases are water vapour (H2O), carbon
dioxide (CO2), methane (CH4), nitrous oxide (N2O), CFC (chlorofluoro-
carbons) and tropospheric ozone (O3) (Table 1). It is not possible to rank
with any certainty the effect of the individual gases with respect to the total
greenhouse effect. This is, among other things, due to a number of feedback
mechanisms between the greenhouse gases (Box 3). Basically, the ratio
between the most important greenhouse gases water vapour, clouds and
carbon dioxide is estimated at 2-1-1.
Table 1. Estimates of the radiation contributed by a number of factors which influence the overallradiation effect of the greenhouse gases (W/m2) for 2005 compared with pre-industrial levels(Solomon et al. 2007).
Cause Type Factor Radiation effect (W/m2)
Man-made Long-lived greenhouse gases Carbon dioxide (CO2) 166 (149-183)
Methane (CH4) 048 (043-053)
Nitrous oxide (N2O) 016 (014-018)
CFC 034 (031-037)
Ozone Stratospheric -005 (-015-005)
Tropospheric 035 (025-065)
Stratospheric water from CH4 007 (002-012)
Surface albedo Land use -020 (-04-00)
Black dust on snow 010 (00-02)
Aerosols (particles) Direct effect -050 (-09- -01)
Cloud albedo -070 (-18- -03)
Contrails (vapour trails from aircraft) 001 (0003-003)
Natural Solar radiation Direct 012 (006-030)
Total man-made 160 (06-24)
The man-made sources of CO2 are the burning of fossil fuels (coal, oil
and natural gas) as well as changes in land use, particularly deforestation.
Emissions of CO2 have increased greatly since 1960 (see Figure 2), and the
atmospheric content of CO2 now exceeds by far the natural level seen over
the past 650,000 years (140 to 300 ppm). The concentration of methane and
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nitrous oxide has also increased sharply during the past 50 years. Methane
is produced anaerobically, i.e. through the transformation of organic mat-
ter under oxygen-free conditions, for example in the rumens of ruminant
animals, from livestock waste, landfills and in paddy rice fields. Methane
has a global warming potential which is 23 times greater than for CO2. Themethane content of the atmosphere has, compared to pre-industrial levels,
risen by 160 per cent, which is largely due to rapidly increasing numbers of
livestock and growing volumes of waste.
Nitrous oxide is an even more potent greenhouse gas than methane with
a global warming potential which is 298 times greater than for CO2. The
concentration in the atmosphere has increased by 17 per cent compared
to pre-industrial levels; it is also a very long-lasting greenhouse gas with a
lifetime in the atmosphere of 120 years. Nitrous oxide stems in particular
from the microbial transformation of nitrogen in the soil, and the rap-idly growing volumes of nitrogen which are added through agricultural
activities are the main cause of increased emissions of nitrous oxide to
the atmosphere. Emissions of CFC gases from refrigerators, freezers, air-
conditioning systems, fire-extinguishing agents etc. also contribute to the
greenhouse effect, which is being further intensified by ozone in the lower
part of the atmosphere the troposphere. Ozone is formed when sunlight
decomposes mono-nitrogen oxides (NOx) and carbon monoxide (CO), for
example from car and truck exhaust gases. Thus, a large number of differ-
ent sources of pollution contribute to boosting the atmospheric content of
greenhouse gases.
The combustion of coal and oil in particular also results in the emission
of many small particles to the atmosphere, which generally have a cooling
effect, because they increase the amount of sunlight which is reflected (the
albedo). Changes in land use have also increased the albedo, but there
is considerable uncertainty regarding both these effects (See Table 1). In
addition to man-made factors influencing radiation, there have been very
large but relatively brief cooling contributions in connection with volcaniceruptions when many small particles are emitted, increasing the albedo.
Finally, variations in solar radiation have also resulted in a slight increase in
radiation effects in the first half of the twentieth century (Table 1). A hand-
ful of scientists claim that these factors together with other natural causes
can be the main reasons for the observed climate changes rather than the
emission of greenhouse gases (see subsequent chapter on the suns indirect
influence on the climate).
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5. Climate sensitivity
Warming as a result of an increase in the atmospheric content of greenhouse
gases (or of the other parameters in Table 1) is described using the concept
of climate sensitivity. Climate sensitivity states how much the global tem-
perature will rise through a change in additional energy of 1 W/m2. Such a
change in added energy can be due to an increase in the atmospheric contentof greenhouse gases or a change in solar radiation.
The climate sensitivity makes it possible to calculate the temperature
increase from different forcings of the climate system which, directly or
indirectly, influence the energy addition. If we know the change in energy
addition, it is then possible, using climate sensitivity, to immediately esti-
mate the temperature change. Unfortunately, we do not know a lot about
climate sensitivity. If, for example, we only look at what a change in energy
addition should result in based on how dependent the longwave outgoing
radiation is on temperature, we arrive at a sensitivity of 0.269 K/(W/m2).
Figure 2. Development in the atmospheric concentration of carbon dioxide (CO2) following theend of the last ice age measured in air bubbles trapped in ice cores taken from Antarctic ice. Theenlarged section shows the concentration for the period 1750-2005. The full-draw line showsdirect measurements in the atmosphere (Solomon et al. 2007).
Content of CO2
(ppm)
Years before present day
CO2-concentration (PPM)
Years before now
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This produces far too small a climate sensitivity. In reality, a number of
feedback mechanisms reinforce the temperature change (Box 3). One of
the most important feedback mechanisms is the effect of temperature on
the atmospheric content of water vapour. Water vapour is a greenhouse
gas, and as a warm atmosphere can contain more water vapour than a coldatmosphere, warming will lead to an enhanced greenhouse effect due to
the presence of more water vapour in the atmosphere.
There are many of these feedback mechanisms, and the climate sensitivity
is influenced by the combined effect of these. To calculate the overall effect,
comprehensive climate models are used which represent all the physical
processes in the atmosphere, the oceans and on land. At the same time, ob-
servations over the past 150 years have been used, as well as reconstructions
of climate changes over the past 500,000 years, to determine the climate
sensitivity. Using these methods, a value of approx. 0.75 K/(W/m2) has beenarrived at. Feedback mechanisms therefore result in almost a tripling of the
sensitivity compared to the effect without feedbacks. This means that the
warming effect of CO2 will be tripled due to feedback mechanisms in the
climate system. However, there is still considerable uncertainty associated
with establishing the climate sensitivity, and the estimates range from ap-
prox. 0.5K/(Wm2) to more than 2K/(Wm2).
Table 1 shows an overall estimated radiative forcing of man-made cli-
mate changes of approx. 1.6 W/m2. A climate sensitivity of 0.75 K/(W/m2)
leads to a temperature increase of 1.2 C. This is considerably more than the
stated temperature increase of approx. 0.75 C, which is due to inertia in
the climate system and which leads to the climate changes continuing for
a period after the radiative forcing has increased. This inertia is particularly
related to the slow warming of the oceans.
6. The suns indirect impact on the climate
In addition to the direct effect of solar radiation on the Earths climate(solar forcing), two specific indirect effects of the suns influence on the
climate have attracted attention in the climate debate. The first effect is due
to the absorption (warming) from ultraviolet radiation in the stratospheres
ozone layer, which is in the uppermost part of the atmosphere (at a height
of 15-30 km). The amount of UV radiation depends on sunspots, producing
greater warming in periods of maximum sunspots. The number of sunspots
varies over an eleven-year cycle. Some studies indicate that the warming can
be transmitted to the lower part of the atmosphere and lead to changes in
the climate systems circulation patterns.
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The second effect has been suggested by Henrik Svensmark, where the
variation in solar activity through changes in the amount of cosmic radiation
can affect the formation of ions in the atmosphere and thereby affect the
formation of the small particles which function as cloud condensation
nuclei for ice and water, and thereby affect cloud formation. Because low-lying clouds in particular have a cooling effect, a change in solar activity
can thereby perhaps indirectly affect the climate. Laboratory experiments
have shown that this type of radiation can promote the formation of cloud
condensation nuclei, but it is unknown whether this mechanism will also
work in the atmosphere.
However, there is nothing to suggest that either of these two indirect solar
effects have been significant for the global warming of the atmosphere over
the past 50 years when there has been no change in the volume of cosmic
radiation hitting Earth. On the other hand, it is possible that changes inthe cosmic radiation and in UV radiation may have been significant for the
warming which occurred in the 1910-1940 period.
7. Ice ages
There has for some time been general consensus among scientists that the
basic cause of the coming and going of the ice ages is due to changes in
the Earths orbit around the sun (see Box 4). This is called the Milankovitch
theory, and states that the ice ages are caused by small, cyclical variations
in the Earths orbit (eccentricity) and axial tilt (obliquity) around the sun.
These variations lead to a complex pattern of changes in the amount and
distribution of solar radiation reaching the Earth, influencing global energy
balances and heat transport and thereby climate.
During the ice ages, large volumes of water are accumulated in glaciers,
causing the sea level to fall. The temperature at the Earths surface is also
lower, resulting in less evaporation of water from the oceans, which in turn
leads to less precipitation. Moreover, as much of the precipitation falls assnow, the ice ages are often accompanied by marked periods of drought in
ice-free areas. This leads to a global climate which is far less favourable for
life on Earth than the present climate. During the ice ages, the climate is
not constantly cold, but there are often considerable global and regional
variations in the temperature which result in the ice sheets advancing and
retreating. The cause of these variations is still poorly understood.
Even though there is general agreement that the Milankovitch theory is
the predominant cause for initiating ice ages, it appears that more is required
to trigger a new ice age. Here, the amounts of dust and greenhouse gases
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in the atmosphere are likely to play a significant role. The geography of theEarth is another factor. Only when the position of the continents hinders an
efficient exchange between cold water at the poles and warm water at the
equator will new ice ages occur. This is actually the case with the Earths
present geography, where there is relatively little exchange between water
in the Arctic ocean and the other oceans. At the same time, the continents
are currently placed so close to the poles that long-lasting ice caps can be
formed.
An ice age typically lasts about 100,000 years, while an interglacial period
lasts 10,000-15,000 years. We are now in an interglacial period which has
Milankovitch and the ice ages Box 4
The shape of the Earths orbit around the sun is not constant but varies accord-
ing to the attractive force of the other planets. Moreover, the Earths axial tilt
(obliquity) and its precession (axial rotation) in space also vary. These variationsaffect the amount of total solar radiation reaching Earth and its distribution,
otherwise known as solar forcing. The Serbian geophysicist Milutin Milankovitch
(1879-1958) was the first person to calculate (by hand) these effects over the past
one million years and thereby demonstrate that these variations are the primary
cause of the switch between ice age and interglacial periods.
Eccentricity
The Earths orbit around the sun changes from being almost circular to slightly
elliptical and back again over a period of approx. 100,000 years. This change in
eccentricity means that the distance between the Earth and the sun changes,
resulting in minor changes in the overall solar radiation reaching the Earth.
Axial tilt
The angle of axis of the Earths rotation in relation to an axis perpendicular to
the Earths orbit around the sun varies between 21 and 24 over a period of ap-
prox. 41,000 years. Changes in the Earths axial tilt affect the distribution of solar
radiation, but not total solar radiation. When the axial tilt is large, the difference
between summer and winter at high latitudes will be greater. Cooler summers
with a low axial tilt are suspected of encouraging the start of a new ice age.
Precession
The direction of the Earths axis of rotation in space changes over a period ofabout 21,000 years. At the moment it is summer in the northern hemisphere
when the Earth is closest to the sun. In about 10,500 years, summer will be in
the southern hemisphere when the Earth is closest to the sun. This does not af-
fect the total amount of solar radiation reaching Earth but rather the seasonal
variation in temperature.
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lasted 11,700 years. However, this does not mean we are on the threshold
of a new ice age. Thus, the IPCC states that it is very unlikely that the Earth
will enter a new ice age within the next 30,000 years as a result of natural
causes. This is because the next major fall in summer radiation to the north-
ern hemisphere will not happen for 30,000 years (see Box 4).
Climate models Box 5
Climate models describe the atmosphere as a physical system based on physi-
cal laws which can be expressed mathematically. As the oceans are also an
important factor for the climate, climate models often include models of the
heat transport and heat exchange taking place within the oceans. In the global
climate models (GCM), the atmosphere is described using a number of boxes
distributed in a spatial network across the entire globe. There are about 200 km
between the grid points, with 30-40 vertical layers in the atmospheric models
and 20-30 layers in the ocean models.
The most important physical laws used in the climate models are:
Equations of motion based on Newtons laws
Mass and energy conservation
Equation of state for ideal gases
Radiation equations, which describe how solar and thermal radiation are
transmitted and deposited in the atmosphere.
Moreover, the models include a number of empirical relations based on obser-
vations. These empirical relations do not necessarily have a reliable theoretical
basis but are necessary to describe processes which occur at temporal and spatial
scales which are not sufficiently resolved in the models. Such empirical relations
often contain a number of parameters which have to be tuned by comparing
model simulations with observations. One example of this is cloud formation,
which often takes place on a much smaller scale than what is represented in
the models.
The empirical relations are necessary, but they also reduce the degree of preci-
sion in the model calculations. This can to some extent be remedied by increas-
ing the models spatial and temporal resolution, but this leads to vastly greater
requirements for computer processing power when running the models. Often
calculations are therefore performed with an increased resolution for a smaller
geographical area with the help of regional climate models (RCM), where a GCM
supplies the boundary conditions for the regional model, i.e. temperature, air
pressure, water vapour at the edge of the geographical extent of the regional
model.
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8. Models of the climate system
As described above, the climate is the result of a complex interplay between
many different physical, chemical and biological processes which are si-
multaneously influenced by the geographical distribution of the oceans,land masses, ice caps, lakes and rivers. In order to better understand this
complex system, several mathematical models of the climate system have
been developed (Box 5). These are complex models which demand some of
the worlds fastest computers to simulate the Earths climate.
The most important criterion for assessing whether a climate model is
reliable consists of comparing the model simulations of the present climate
with observations. The climate models are continually being improved, and
at the moment there are about twenty models worldwide which are capable
of producing satisfactory simulations of the climate system. The deviationsbetween the calculated and the observed temperature distribution on Earth
are in most cases just a few degrees, with the biggest deviations being seen
in areas with snow and ice. Generally speaking, the climate models can be
regarded as providing a solid basis for calculating future climate change.
9. Scenario calculations of climate changes
An important question when assessing future climate changes is how society
will develop over the next century and how this will affect the emission of
greenhouse gases to the atmosphere. To assess the uncertainty in this area
and the effect of different social developments, including environmental
awareness and new environmentally friendly technologies, the IPCC has
developed a number of scenarios for the future (Box 6). These scenarios
range from sustainable societies based on the widespread use of renewable
energy and resources to an even more resource-hungry society than that we
know today.
The global increase in temperature up until 2100 is shown in Figure 3for three of these scenarios. In about 2100, the temperature globally will
have increased by 3-4 C if the world develops as shown in the A2 scenario,
but only by 1.3-2.4 C according to the B1 scenario.
Most of the other scenarios show temperature increases which fall within
this interval (see Table 2). It is worth noting that the differences between
the scenarios first become really apparent during the second half of the
twenty-first century. This is partly due to the fact that it takes a long time
to make the very resource-consuming technologies more sustainable and
partly because of inertia in the climate system.
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The IPCCs emissions scenarios Box 6
Future population developments and economic and technological developments
will cause additional anthropogenic emissions of greenhouse gases and thereby
lead to a greater atmospheric concentration and a continued forcing of thegreenhouse effect. At the moment it is difficult to predict how the factors which
determine emissions will develop because different international trends have
an important bearing, including issues such as the development of the global
economy versus a regionalisation of the markets as well as potential changes
in peoples lifestyles. These changes can either lead to less consumption and
thereby relatively small greenhouse gas emissions, or greater consumption of
energy and resources and thereby higher emissions. Another important factor
is the future of the developing countries where high rates of economic growth
and energy consumption on a par with that in the industrialised countries can
become a major source of greenhouse gas emissions. The climate issue is thusclosely integrated with general development issues.
To assess the necessity/effect of possible measures to reduce the emissions of
greenhouse gases, it is necessary to make a number of assumptions about the
future. As mentioned, such assumptions are subject to considerable uncertainty,
and therefore so-called scenarios are presented which describe possible future
global social and technological developments. In 2000, the IPCC carried out
extensive scenario work that shows a number of possible alternative develop-
ment perspectives which are gathered in four groups labelled A1, A2, B1 and B2.
A1. A future world with very fast economic growth. The world population peaksin the middle of the century, and new and more efficient technologies are quickly
introduced. The A1 family comprises three sub-families where fossil fuels are
primarily used (A1FI) or non-fossil energy sources (A1T) as well as a mix of all
energy types (A1B).
A2. A more heterogeneous world with continued population growth and a slower
pace of technological development.
B1. A world which is similar in some respects to A1, but which focuses more on a
service and information-based economy as well as sustainable technologies.
B2. A world which still sees population growth, although at slower rates than
in A2, as well as slower and more diversified technological developmentsthan in A1 and B1.
Together, the scenarios cover the many combinations of world population growth
(approx. 7-15 billion), growth in GDP (approx. 11-26 times), distribution of
energy production on fossil and non-fossil energy sources etc. Even though
some optimistic scenarios predict a reduction in CO2, most show an increase
in CO2 concentration from the present level of 370 ppm to including a level
of uncertainty from under 500 ppm to more than 1000 ppm up until 2100.
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Table 2. Model-calculated projections of global warming and rising sea levels during the twenty-first century (Solomon et al. 2007).
Temperature increase (C) Sea level rise (m)
Scenario Best estimate Likely interval Without accelerated
increase in mel-
ting rate of ice
Constant year 2000 concentration 06 03-09
B1 18 11-29 018-038
A1T 24 14-38 020-045
B2 24 14-38 020-043
A1B 28 17-44 021-048
A2 34 20-54 023-051
A1FI 40 24-64 026-059
The climate systems inertia is illustrated by the lower curve in Figure 2,
which shows the temperature development if the concentration of green-
house gases is maintained at the year 2000 level. Calculations based on the
climate models show that the temperature will increase by 0.4-0.8 C in any
case. This is because the Earths climate and especially the temperature
in the oceans is still out of balance with the present level of greenhouse
gases. The climate will therefore continue to warm, regardless of how the
world and our emissions develop.
10. Regional climate changes
However, what is crucial for the effects of climate changes is not how the
global average temperature develops but how temperature and precipitation
develop regionally. Calculations based on the climate models show large
regional changes occurring basically everywhere around the world. Warming
above land will be higher than above water, and consequently higher than
the global average. The temperature increase over land is usually 50 per centgreater than the global mean value. Moreover, the increase in temperature
is much greater during winter in the Arctic, usually twice the global mean,
which is largely due to the fact that the warming reduces the amount of ice
and snow (see Box 3).
Significant changes will also occur in the distribution of precipitation.
The general picture is that it will become drier in areas which are dry at
present and even wetter where it already rains a lot. In addition, the dry
areas will spread, with increased risk of drought in many places. This is
particularly true in the dry tropics and subtropics, while increases in rainfall
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will be seen at higher latitudes in cooler climates. Where rainfall increases,
there will be a greater risk of flooding.
The changes in the atmospheres circulation will mean that the storm
paths in the middle latitudes will move slightly further towards the poles.
At the same time, calculations suggest that the maximum wind speeds instorms above the sea will increase, leading to a greater frequency of very
intense and destructive hurricanes.
More extreme weather
An enhanced greenhouse effect will not just lead to a generally warmer
climate, it will also result in changes in the frequency, intensity and dura-
tion of extreme weather events. Model calculations show that there will be
more and longer-lasting heat waves, but also heavier precipitation. The
model calculations show increasing precipitation intensity across most ofthe Earth, but also that the number of dry days increases. This accords with
observations of climate changes over the past 50 years, and is linked to the
intensification of the hydrological cycle which stems especially from the
fact that higher temperatures enhance evaporation and the maximum water
vapour content in the atmosphere before clouds form. When evaporation is
limited (e.g. due to dry soils), this leads to less rainfall, whereas it leads to
higher rainfall where evaporation is not limited by water availability.
All in all, this increases the risk of both flooding and drought in many
places worldwide. Again, this is in line with what has been observed over
the past 50 years, where the frequency of flooding has increased throughout
almost all of Europe, while periods of drought have become more extensive,
particularly in southern Europe. Similar changes are seen across the globe.
Rising sea levels
When the temperature increases as a result of anthropogenic emissions of
greenhouse gases, two factors can contribute to rising sea levels worldwide.
On the one hand the water expands as a result of being warmed, and on theother glaciers and ice caps melt in a warmer climate.
The likely range for the increases in sea levels worldwide during the
twenty-first century is reported by IPCC as 15-59 cm depending on the
chosen emissions scenario (see Table 2). The thermal expansion of water
is responsible for 70-75 per cent of this increase. Recent studies suggest
that the ice, especially on Greenland, will melt at a faster rate. However,
these studies are still regarded as being very uncertain and are therefore
not included in the IPCCs estimates in Table 2.
Sea levels worldwide during the previous interglacial period (the Eemian
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Interglacial) 125,000 years ago were probably four to six metres higher than
during the twentieth century, probably due to the polar ice caps melting. It
is therefore likely that the melting of the ice caps on Greenland will con-
tribute significantly to rising sea levels in the coming centuries. However,
thousands of years may pass before the Greenland ice sheet has melted awaycompletely. Once so, sea levels would have risen by 7 metres.
Uncertainties
There is no doubt that the Earths climate is changing towards a warmer
and more extreme climate. There is also no doubt that at least the major-
ity of the observed climate change is due to anthropogenic emissions of
greenhouse gases.
However, considerable uncertainty remains on how climate will change
in future. This is not so much due to the obviously chaotic nature of theweather systems or the natural fluctuations in the climate caused by changes
in solar radiation or volcanic eruptions. Rather, the uncertainty is largely at-
tributable to our current lack of understanding of the feedback mechanisms
Figure 3. Model calculations of the global rise in temperature from 1900 to 2100 for three emis-sion scenarios (see Box 3) as well as for the hypothetical situation where the atmospheric contentof greenhouses gases remains constant at 2000 levels. All temperatures are shown relative to the
mean temperature for 1980-1999 (Solomon et al. 2007).
Global temperature increase
A2A1BB1
Year 2000 constantconcentrations20th century
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35the CliMate is Changing but why?
in the climate system. This can make the climate change both larger and
smaller than the present projections.
In terms of how society adapts to climate changes, reliable projections
of temperature and precipitation distribution play a key role at regional
level. In many cases, it is also important to have detailed information aboutchanges in the frequency of extreme weather events such as storms, heavy
rainfall and drought. Here, the climate models have improved markedly in
recent years, but improvements are still badly needed.
For projections towards the end of the twenty-first century, the uncer-
tainties regarding the future emissions of greenhouse gases are far more
important than the uncertainty about the climate sensitivity. This shows
that at we now have a reliable climatic basis for deciding whether we as
a society must take steps to avoid the climate changes. It also shows that
mankind will be forced to adapt to changes in climate some warming isunavoidable.
ReferencesDawson AG (1992): Ice Age Earth. Routledge.Houghton J (2004): Global warming. The complete briefing. Cambridge University Press.Marsh N & Svensmark H (2003): Solar influence on Earths climate. Space Science
Reviews. 107, pp. 317-325.Nakicenovic N, Alcamo J, Davis G, DeVries B, Fenhann J, Gaffin S, Gregory K,
Gruebler A, Jung TY, Kram T, La Rovere EL, Michaelis L, Mori S, Morita T, PepperW, Pitcher H, Price L, Riahi K, Roehrl A, Rogner HH, Sankovski A, Schlesinger M,
Shukla P, Smith S, Swart R, VanRooijen S, Victor N & Dadi Z (2000): Special Reporton Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panelon Climate Change. Cambridge University Press, Cambridge.
Philander SG (2008): Encyclopedia of global warming and climate change. SAGE.Silver J (2008): Global warming & climate change demystified. A self-teaching guide.
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HL (eds.) (2007): Climate Change 2007: The Physical Science Basis. Contribution of
Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on ClimateChange. Cambridge University Press, Cambridge, UK.Svensmark H & Friis-Christensen E (1997): Variation in cosmic ray flux and global
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37what will happen?
What will happen?
Scenarios of the future
jrgen e. olesen
1. Introduction
Climate change is nothing new. In the history of Earth there have been con-siderable climate changes from very warm periods to an almost complete
freezing of the planet (snowball Earth). Over the past half a million years,
the biggest climate changes have happened in connection with the coming
and going of the ice ages. Nevertheless, life on Earth has survived even
though many species have become extinct, especially at the onset of the ice
ages. So, history also shows that life on Earth generally speaking is
pretty robust. However, we should remember that the climate change we
currently face is expected to lead to a warmer climate than the Earth has
experienced for several million years and this will take place over just 100
years! We are therefore on the threshold of a new type of climate change
which will take place at a speed that surpasses what has previously been
seen.
Climate change is undoubtedly one of the biggest challenges faced by
mankind. This is not least because of the huge consequences that climate
change will have for the worlds ecosystems and for our living conditions.
At the same time, climate change poses a colossal political problem where
democracies around the world risk failing to make the right decisions intime.
The political and democratic problem stems from the fact that people
experience only to a very small degree any connection between lifestyle,
greenhouse gas emissions, climate change and the effect of the climate
change on the living standards of individual citizens. This is because there
is both a spatial and a temporal separation between emissions and effects.
The worlds industrial countries, which emit the largest volumes of green-
house gases, are generally less vulnerable to the effects of climate change.
This is because industrial countries have a higher adaptive capacity than
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39what will happen?
change results from greenhouse gas emissions and that these are harmful.
Likewise, the will to act assumes that future harmful effects are deemed
relevant for decisions being made now. It is therefore important to be able
to establish the effects of climate change and their economic consequences.
As climate change in one form or another must be regarded as unavoidable,it is crucial that society adapts in the most appropriate way.
2. The effects are already evident
The effects of climate change do not just belong to the future. Climate
change is already happening as are the effects. The global mean tem-
perature has increased by 0.55 C over the past 30 years. This has led to
documented changes in biological and physical systems across all conti-
nents. Examples include: Increased instability of the ground in areas with permafrost and more
rock slides in alpine areas.
Changes in some Arctic and Antarctic ecosystems, for example for the
polar bears (Box 4).
Increased run-off and earlier spring floods in many rivers which are fed
by glaciers and snow.
Warming of many rivers and lakes with consequences for the food chains
and water quality.
Earlier occurrence of springtime events such as leaf unfolding and bird
migration.
Shift towards the poles in the spread of flora and fauna.
Change in the distribution area of algae, plankton and fish in the oceans
at high latitudes.
Increased occurrence of algae and zooplankton in lakes at high latitudes
(Box 5).
Incipient bleaching of many coral reefs as a result of rising sea tem-
peratures.
A number of changes have been documented in both natural and human
systems, even though it can be difficult to distinguish climate effects from
adaptations to other non-climatic trends:
In northern areas changes are taking place in agricultural and forestry
systems involving earlier sowing and growth in the crops as well as
changes in the occurrence of windfalls, forest fires and pest infestation.
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Changes in health-related risks, for example the occurrence of heat-
related deaths in Europe (see Box 2) and a greater incidence of allergenic
pollens at the mid and high latitudes in the northern hemisphere.
Certain human activities in the Arctic (e.g. hunting and moving across
snow and ice) as well as winter sports in low-lying alpine areas.
There are also indications that climate change is affecting other natural and
human systems. Even though these changes are described in the literature,
they are still not documented trends which can be ascribed to anthropogenic
climate change.
Buildings in mountain areas are subject to an increased risk of flood-
ing from melting glaciers. Governments and other authorities have in
several places initiated the construction of dams and ducts to mitigate
the risk.
Heatwave over Europe in 2003 Box 2
From June to August 2003, many parts of Europe suffered a serious heatwave
with summer temperatures 3-5 C above normal over much of southern and
central Europe. The highest temperatures were recorded at the beginning of
August when the maximum temperature for several days running was 35-40 C.
The average summer temperature was way above normal, which shows that it
was an extremely unusual phenomenon under normal climate conditions. How-ever, the phenomenon is consistent with the combined increase in both mean
temperature and temperature variability that is expected as a result of climate
change. As such, the 2003 heatwave simply represents what can be expected to
be normal for central and southern Europe towards the end of the twenty-first
century. Consequently, the heatwave in 2003 has been taken by many as a sign
of what is to come.
The heatwave was accompanied by a significant shortfall in precipitation, and
the resulting drought led to a loss of productivity of 30 per cent for agricultural
and forestry production in large parts of Europe. This obviously reduced agri-
cultural production and increased costs. It has been estimated that total losses
amounted to EUR 11 billion within agriculture and forestry. The warm and dry
conditions also resulted in many very large forest fires, especially in Portugal.
Several large rivers (e.g., the Po, Rhine, Donau and Loire) had record low stream-
flows, affecting river navigation and the use of the river water for cooling and
irrigation. The Alpine glaciers melted at extremely high rates, which helped to
prevent even lower rates of flow in the Rhine and Donau. In large towns and
cities, the heatwave from June to August led to excessive mortality of more than
35,000 people, especially among senior citizens. Many of these large towns and
cities have now introduced emergency plans to prevent a repeat of this in future.
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In the Sahel in Africa, warmer and drier conditions have led to a shorter
growing season with devastating consequences for the crops. In south-
ern Africa, a longer dry season and more uncertain rainfall has led to
changes in patterns of crop cultivation.
Rising sea levels, increased settlement and urban development have ledto a loss of wetlands and mangroves as well as increased damage from
flooding along the coasts in many areas.
Effects depend on the extent of the warming
It probably does not come as any surprise to learn that the greater the extent
of the global warming, the greater the consequences. However, it is only
since the publication of the IPCCs Fourth Assessment Report that an overall
picture has been presented of the consequences across various sectors and
across the worlds continents. Examples of this are given in Figure 1 wherethe expected effects are shown for a number of areas which are deemed to
be relevant for people and the environment.
Figure 1 shows the effects in relation to a rise in the global mean tem-
perature. However, only a few of the most serious consequences of global
warming can solely and directly be ascribed to temperature changes. Most
of the effects are associated with changes in patterns of rainfall or the
increased frequency of extreme weather phenomena such as storms, heat-
waves, droughts and torrential rain. In coastal areas, the rising sea levels
also play a big role.
Figure 1 illustrates what could happen during the present century. Far
more serious effects are likely in the following centuries. These effects will,
in particular, be associated with significant rises in the sea level, leading
to the large-scale displacement of people, economic activities and infra-
structure away from the present coastlines. This will both be extremely
expensive and will pose social, cultural and political challenges of as yet
unseen dimensions. It is expected that parts at least of the Greenland ice
sheet and possibly the ice cap in West Antarctica will melt in the comingcenturies with temperature increases of 1-4 C, leading to sea level rises of
4-6 metres or more. This is on top of the sea level rises resulting from the
fact that water expands when warmed.
3. Water resources
The availability of clean and ample drinking water is regarded as a human
right. At the same time, water is fundamental to agricultural production. Of
total agricultural production, 40 per cent comes from irrigated farming, but
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worldwide agriculture accounts for 80 per cent of total freshwater consump-
tion. In addition, water plays a role in many different contexts which will
be affected by climate change, for example river navigation, hydroelectric
power, cooling of thermal power plants and private and industrial uses.
More than a sixth of the worlds population live on floodplains wheremuch of the water comes from melting glaciers and snow. Here, global
warming will initially lead to increased streamflow in rivers and thereby
greater possibilities for agricultural irrigation. In the long term, the conse-
quences will be smaller volumes of water stored in the glaciers and snow,
resulting in bigger differences between summer and winter streamflow in
the rivers with an increased risk of both flooding and drought.
By the middle of the twenty-first century, the annual run-off in the rivers
and the availability of water is expected to have increased by 10-40 per cent
in the high latitudes and in certain tropical regions. The run-off will cor-
Figure 1. Illustration of how different degrees of global warming during the twenty-first centurywill affect various resources, ecosystems and human health. The solid lines show where the ef-
fects are calculated to take place, and the dashed lines show that the effects continue and arereinforced by increasing temperatures. Adaptation to climate change is not included in theseestimates (Parry et al. 2007).
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43what will happen?
respondingly fall by 10-30 per cent in certain dry areas at medium latitudes
(e.g. southern Europe, South Africa and Australia) as well as in the dry trop-
ics, which are at present among the most water-stressed areas. Increased
drought will often be linked to greatly increased summer temperatures, and
the effect of this can be illustrated by the heatwave over Europe in 2003 (seeBox 2).
The size of the drought-struck area is also likely to grow. At the same
time, the risk of very heavy rainfall increases, increasing the risk of flooding.
The effect of more extensive flooding can be illustrated with the widespread
flooding along the River Elbe in 2002 (see Box 3).
There are a number of options available for adapting to changes to a
rivers water flow, the frequency of flooding and to more frequent drought.
As human society is so dependent on water, most of these methods are
already known by the authorities and private organisations handling water
Major flooding along the River Elbe in 2002 Box 3
On 10 August 2002, a large low-pressure system moved slowly in across central
and eastern Europe. The storm had started several days earlier above the British
Isles and then swung south where it gathered large volumes of humid air from
the warm Mediterranean. While gradually making its way over the central part
of the continent, it released its humidity in the form of sustained and heavy
rain. In some places, almost 250 millimetres of rain fell over a four-day period.
The flooding started in the Czech Republic, where the Vltava River, one of the
main tributaries of the Elbe, caused flooding in the medieval towns of Cesky
Krumlov and Ceske Budejovice. The next victim further downstream was the
low-lying districts in Prague. The flood wave continued into the Elbe and, on 15
August, caused widespread flooding in Dresden. While the flood wave moved
further down the Elbe, the river burst its banks in Wittenberg, Dessau and other
towns in Saxony. The high water levels finally reached the mouth of the Elbe on
24 August. Even though most flooding was seen along the Elbe, the streamflow
increased considerably in the Danube, which led to flooding in many towns inAustria and Slovakia.
When the Elbe and the Danube burst their banks, fertile farmland was flooded
along the rivers, destroying crops which were about to be harvested. The muddy
flood water which swept across low-lying areas forced many businesses along the
river to stop production and trade, and bridges, roads and other infrastructure
was extensively damaged or destroyed. Private homes and other property were
also to a large extent lost in the flooding waters. If the damage from all the
floods in central and eastern Europe is put together, the financial losses from
the floods in August 2002 amount to approximately EUR 15 billion.
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resources in many countries around the world. The possibilities open to us
for managing changes in water supplies basically fall under the following
points:
Political instruments such as regional strategic water plans, which con-
solidate and document the initiatives which the authorities and otherplayers can implement to adapt to climate change.
Technological and structural instruments such as new water reservoirs andimplementing programmes designed to ensure the renewal of ground-
water to safeguard water supplies in the long term as a way of countering
the increasing frequency of droughts.
Risk sharing and spreading in the form of insurance policies against ex-treme climate events and which are made available to poor and vulner-
able societies.
Changes in use, activity and place covers measures for overcoming climatechange, e.g. special zones along rivers to protect the population from
the risk of flooding. This also includes a large number of initiatives to
boost the efficient use of water (especially in farming) and water-saving
methods (in industry and in private and public housing).
Figure 2. Illustration of how the effects of climate change on freshwater resources affect the pos-sibility for sustainable development in various regions (Parry et al. 2007). The background mapshows the estimated difference in annual run-off (in per cent) between the present (1981-2000)and future (2081-2100) climate for the SRES A1B emissions scenario. The blue colours showincreasing run-off, the red declining run-off.
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45what will happen?
4. Ecosystems
Climate change will have serious consequences for the worlds ecosystems.
However, it is important to remember that, globally, ecosystems already
have to contend with considerable impacts of human activities. In the areaswhich are at the moment bearing the brunt of deforestation, agricultural
expansion and pollution, it is expected that these effects and not climate
change will be largely responsible for the loss of biodiversity over the next
50 years. However, climate cha