253

A Consideration on Dangerous Level of Global Warming
Hideo HARASAWA
National Institute for Environmental Studies
16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japane-mail: harasawa@nies.go.jp

Abstract
To prevent global warming, as stated in Article 2 of the United Nations Framework Convention on
Climate Change (UNFCCC), stabilization of greenhouse gas concentrations in the atmosphere andlimitation of temperature increases to certain levels are required. Identification of the critical level oftemperature increase (i.e., the level where danger occurs) in order to allow ecosystems to adapt, food tobe produced and economies to develop is a fundamental issue, as is the implementation of reduction
measures to ensure that temperatures do not exceed this level. However, to identify dangerous levels oftemperature increase, we need to examine the factors that influence the target temperature so as toensure it does not exceed the threshold, i.e., the border between danger and safety. For example, theEuropean Union (EU) has accumulated scientific knowledge and decided that 550 ppm should be thestabilization concentration of greenhouse gases, and a temperature rise of 2°C or less should be thelong-range target for preventing global warming. Examination has started of the framework stated in the
Kyoto Protocol for beyond 2013. To set up a specific long-range target, scientific knowledge of related
factors such as stabilization concentrations, level of temperature increase, and effect threshold plays animportant role. On the basis of past impact studies, this paper considers levels of temperature rise andthresholds for the impacts caused by global warming.
Key words: global warming, impact threshold, stabilization, UNFCCC, 2°C temperature rise

1. Introduction
To prevent global warming, as indicated by Article
2 of the UNFCCC, stabilization of greenhouse gas
concentrations in the atmosphere to below certain levels is required. Namely, the ultimate objective of preventing global warming is to stabilize greenhouse gas
concentrations, so that they will not interfere artificially with the climate system, and to achieve a stabilized level within a time frame in which a ecosystems
can adapt naturally and in which both developed anddeveloping countries can progress in a sustainable
manner without threatening food production.
The problem here is the level of effect at whichthese ecosystems can adapt naturally without succumbing to these above-mentioned threats. In considering the “danger level” – because exceeding it leads
to risk – we need to define who is at danger and how
we will comprehensively treat this danger, becausefrom the point of view of effects the danger level isclosely related to the amount of temperature increase,greenhouse gas concentrations in the atmosphere andvolumes of greenhouse gas emissions.
In regard to the danger level, starting with theIntergovernmental Panel on Climate Change (IPCC),
Global Environmental Research
10(2)/2006: 253-259
printed in Japan

there have been a succession of studies based on
scientific knowledge in relation to Article 2 of the
UNFCCC. In 1994, the IPCC held a workshop in
Fortaleza, Brazil, to discuss global warming and stabilization concentrations. The results of the workshop
were summarized and incorporated in the Second andThird Assessment Reports, but the IPCC has not yet
identified the danger level. The reason the IPCC has
not identified the level is that the line of thought has
been that scientists should simply utilize their scientific knowledge to analyze dangerous levels, and thejudgements should be left to the policymakers.
On the other hand, European countries such as the
Netherlands and Germany understand stabilization
concentrations as a long-range objective for preventing global warming. They have furthered analyses of
the relationship between absolute temperature rise andthe rate of rise, and their effects, and the amount of
reduction of greenhouse gas emissions at whichatmospheric temperatures are stable. On the basis ofearly accumulated scientific knowledge, the EU determined a value of 550 ppm as the stabilization concentration for a 2°C temperature rise and set this value as
the long-range objective of global warming measures
such as energy policies.
©2006 AIRIES254

H. HARASAWA

The Kyoto Protocol came into effect on 16 February 2005. Various sorts of provisions securing the effectiveness of the Kyoto Protocol at COP11/
COPMOP1 were laid down in December 2005. Finally,
to fulfill the international treaty to reduce greenhousegas emissions by 5% within the first commitment
period, progress is being made on real preventive
countermeasures. Achieving the objective of the
Kyoto Protocol is most important. However, discussions of the post-Kyoto Protocol now that it has
started, including the availability of goal-setting after
2013 (i.e., Beyond Kyoto or the Beyond 2013 issue),
have been initiated. In these discussions, the stabilization concentration in the atmosphere, as defined in
Article 2 of the UNFCCC, and the time taken toachieve this concentration, are the most important
items to think about.
This paper summarizes the background scientificknowledge on stabilization concentrations and looks
into stabilization with a temperature rise of less than2°C, as proposed by the EU, as the current long-range
objective of global warming prevention.

2. Dangerous Levels for Ecosystems andHuman Communities
2.1 Five concerns caused by global warming
In a serious global warming situation, the effects
grow as the temperature rises. Their scopes andmagnitudes vary, depending on the targeted effects
and the area. For example, it is reported that a watertemperature rise of 1°C generates coral reef bleaching,leading to complete extinction of the coral. Figure 1 isa general outline of the effects in the five fields orconcerns cited in the Third Assessment Report summarized by the IPCC (2001) as follows. (1) Vulnerable

systems such as ecosystems, are influenced by a small
temperature rise (1°C or less). (2) Under extreme
meteorological phenomena (extreme events), even in
the early stage of global warming extreme weather/climates influence the environment. (3) In regard to
the distribution of negative effects, although an areawith a temperature rise of around 2°C to 3°C will
receive some gains (e.g., crop cultivation is possible innorthern cold areas), when the temperature increases
by this amount or more the adverse effects will standout. Because developing countries consisting of small
island states or located in coastal areas are affectedenormously by even a small sea level rise, a rise of
2°C should be considered a high relative risk. (4) If
we view the global economy as integrating the effects
in individual fields, then the adverse effects stand out,
whereas favorable effects can be found in the earlystages of global warming in the case of a 2°C to 3°C
rise. If a further temperature rise is found, then (5) therisk of occurrence of catastrophic phenomena may not
be ignored. For example, although the possibility ofoccurrence of extensive phenomena in the 21st
century, such as the cessation of oceanic generalcirculation, has been estimated to be small (IPCC,
2001), according to recent research, fast global
warming increases the probability and risk of thisoccurring (Rapley, 2006). These days we are focusing
on such phenomena with low probabilities ofoccurrence and enormous effects.
In the Third Assessment Report, in considering
positive or negative effects of global warming in addition to those of Fig. 1, the IPCC interpreted a 2°C to
3°C rise as the threshold from the viewpoint of thesocial economy. Subsequently, researchers proceeded
to study the effects of global warming and found that
global warming and its effects (such as melting of sea

Fig. 1 Five reasons for concern due to global warming. (IPCC, 2001)

A Consideration on Dangerous Level of Global Warming

ice in the Arctic or of mountain glaciers in the
Himalayas) were more widespread than scientists
traditionally thought (Schellnfuber et al., 2006).
Furthermore, the damage caused by the heatwave that
hit Europe in 2003 and by Hurricane Katrina, which
struck Louisiana in 2005, awakened people’s interestin global warming and extreme climate events andprovoked a need to review the danger level.

namely, Type 1 and Type 2 (Schneider & Lane, 2006).
(1) Type 1 threshold (critical limit associated withsocioeconomic effects)
This value is defined as that which brings damage
unacceptable to policymakers when it exceeds a certain point. The threshold takes the function form of aline or smooth variation.
For example, the admissible uppermost limit for a
population exposed to risks such as food shortages,
water shortages, health deterioration caused by climate change, and a decreased extent of admissible
biodiversity is included. Such examples are found in
the range of (2), (3) and (4) in Fig. 1. The function
form examples for temperature rise and effect threshold are considered to be (a) and (b) in Fig. 3. In (a),the effects occur in accordance with temperature rise.
This means that exceeding a certain constant temperature (the danger threshold) actualizes the effects.
Another function form actualizes positive effects
when the temperature rise is small, whereas a continuous temperature rise actualizes adverse effects and thethreshold of effects is reached later. For example, people may be able to develop agriculture in places where
they could not have done it before because the temperatures were too low, or ships can run since the sea
ice has melted.

2.2 Effect threshold (critical limit of global warming effects)
Figure 2 indicates that the concentrations of greenhouse gases discharged as a result of human activity
increase in the atmosphere, giving rise to climaticchanges such as temperature rises and changes in rainfall, as well as influencing, and having relevance to,each field and region.
What range of levels is not dangerous to ecosystems and human beings, social economy systems,
etc.? We call this point the “threshold” or “limit
value” of global warming effects. The level that is notdangerous varies around the threshold or limit value,depending on the target (exposure unit), whether it isan ecosystem or a social economy system, andwhether or not it is decided that all the Earth’s systems
will be catastrophically affected. Schneider classifies
the type of threshold or limit value into two categories,

Fig. 2 Emission scenario－climate prediction－impacts/adaptation assessment.

Negative

Impacts(a) Linear(b) Non-linear(c) Non-linear(uncontinuous)

Dangerous
level

Positive

０
Temperature (°C )255

Temperature (°C )Fig. 3 Temperature increase and impact threshold.

Temperature (°C )256

H. HARASAWA(2) Type 2 threshold (threshold associated with catastrophic effects)
To keep the major processes of the climate systemstable and express the geophysical and biological limit
values, this value should not be exceeded. The function form of this threshold shows changes that are
nonlinear or that “jump.”
For example, it includes the cessation of thermohaline circulation, which destabilizes the climate system,
melting the West Antarctic Ice Sheet and theGreenland Ice Sheet and thus causing irreversible sea
level rise. Melting of the permafrost (permanently
frozen ground) causes rapid emission of greenhousegases. Such examples are found in the range of (1),part of (2) and (5) in Fig. 1. Figure 3 (c) is an exampleof the effect threshold in a catastrophe.
2.3 Dangerous level of global warming andapproach to the effect threshold
On the basis of the results of effect studies, we
examine the threshold that actualizes the danger level
and the effects of global warming. Ecosystems(coastal wetlands, animal species and onshore, forestand marine ecosystems), agriculture, water resources,
human health, energy and economics are included.
There have been studies summarizing global warmingin these fields in terms of the danger level (See Table
1).
Smith & Hitz (2003) and Hitz & Smith et al.
(2004) reviewed studies of the effects of temperaturerise according to various fields, thereby proposing thatthe effect threshold for global warming should be 3°C
to 4°C. Parry et al. (2001) studied four main fields –food, flooding, water shortages and malaria – showing
the relationships between temperature rise and popula-tions at risk. Although the relationships between temperature rise and its effects differ according to thetargeted field, for a population at risk of water shortages, when a temperature rise of 1.5°C to 2°C isreached, the risk to the population rapidly increases.
Their assumption was that the temperature range is arough indicator of the threshold. Hare (2003) deviseda system for comparing effects and risks by expressing
them by dark and light colorings (“Burning Embers”
diagram.) Schneider and Lane (2006) indicated thethresholds for various fields in a table (Table 2). On
the basis of recent case studies, they showed effects
ranging from those on ecosystems to large-scale
phenomena.
After reviewing studies of the effects on ecosystems, Leemans and Vliet (2004) pointed out that 2°C,
which the EU set up as the long-range objective toprevent global warming, could not ensure the safety of
ecosystems. They indicated that it should be reduced
to 1.5°C, and they further insisted that the rate of
reduction should be 0.05°C/ decade. Warren (2006)
organized the effects reported at the scientificsymposium entitled “Avoiding Dangerous Climate
Change,” held in the UK in February 2005, as well asother effects. He insisted that a rise of 1°C would
influence the ecosystems of the oceans and Arctic; arise of 1.5°C would cause melting of the Greenland
Ice Sheet; and a rise of 2°C would cause a reduction incrop production, increase in populations with water
shortages and food shortages. It would produce
refugees in coastal areas because of the rise in sea
level, increase the risk of malaria, collapse Arctic
ecosystems and cause the extinction of ecosystems
around the world. Furthermore, a temperature of 3°C

Table 1 Studies of the threshold of global warming effects.
Researcher
Third assessment
report of IPCC
(2001)
Smith & Hitz
(2003),
Hitz & Smith(2004)
Parry et al. (2001)

Hare (2003)
Schneider & Lane(2006)
Leemans &Eickhout (2004)
Warren (2006)

Threshold of effect*
Around the range of a few degree Celsius, the effects are divided into adverse andpositive ones. For example, a temperature rise of a few degree Celsius or lessincreases crop production in some mid-latitude areas. On the other hand, an average
yearly temperature rise of a few degree Celsius or more may decrease crop
production in other areas in the mid-latitudes.
After a review of the studies of effects according to various fields, these authors
comprehensively summarized the function between temperature rise and its effects.
In regard to the effects on the social economy, a temperature rise of 3°C to 4°C
became the threshold.
Focusing on four main fields—food, floods, water shortages and malaria—theseauthors showed the relationship between temperature rise and influence on
populations. In a population at risk of water shortages, when a temperature rise of
1.5°C to 2°C is reached the risk to the population increases rapidly.
Various effects and risks can be compared by expressing them as dark and lightcolors (“Burning Embers” diagram).
Thresholds of various fields are shown in a table. From the effects on ecologicalsystems, large-scale and catastrophic phenomena are organized as study cases.
After reviewing studies on the effects on ecosystems, these authors pointed out thatthe 2°C rise that was set up by the EU as a long-range objective could not ensure
safety and should be reduced to 1.5°C; they further insisted that the rate of
temperature increase should be 0.05°C/10 years.
This author reviewed case studies of the degree of temperature rise caused by global
warming and its effects, and analyzed tabulated data on scientific knowledge of theamount of temperature rise.

Remarks“A few degree
Celsius” isunderstood tobe 2° to 3°C.

* Beginning in 1990, temperatures have risen. The amount of temperature rise since preindustrial years: 0.6°C is required to be reduced.

A Consideration on Dangerous Level of Global Warming

would cause a rapid increase in water shortages, foodshortages, dengue and malaria, and most ecosystems
would not be able to adapt. A temperature rise of 5°C
would cause thermohaline circulation to collapse andthe West Antarctic Ice Sheet to melt. Additionally, thenumber of extreme climatic events was predicted toincrease.
(1) Ecosystems
At the scientific symposium held in the UK, participants summarized the effects on ecological systems,
including the latest scientific knowledge. According to
the report, for example, in coral reefs, a water temperature rise of 1°C would cause bleaching of 82% ofcorals, and 2°C would cause 97% bleaching. Thus,
even a water temperature rise of 1°C would cause serious damage. A rise of 1°C would cause a decrease up
to 47% in the distribution of animal species; 2°C
would cause a 5% to 66% decrease, and 3°C would
cause a 7% to 74% decrease. Another study pointed
out that the danger level of decrease in distribution
range is 20% to 30%.
(2) Food production
The Third Assessment Report by the IPCC stated,in regard to the effects on food production, that crop
production is adequately ensured even if we consider
population increase. However, once the demand andsupply of food are unbalanced, developing countriesof the tropical and subtropical zones will not be able
to conduct agricultural production. Furthermore, since
they will not be able to purchase crops from the market, it is predicted that they will suffer from famine or
starvation. A temperature rise of 2°C to 3°C is predicted to have a positive effect in enabling agricultural
production in some areas. In the case of food production, a temperature rise of 2°C to 3°C globally can beconsidered the danger level. In developing countries,
since this value may have serious effects, the rise
should be limited to 1°C to 2°C.
(3) Water resources
If we take scientific knowledge into consideration
with respect to water resources and their relationshipwith average air temperatures globally, a temperaturerise of 1°C to 1.5°C would influence water resources
and water supply and demand. A rise of 2°C or more

257

would expand the effects on the water supply and demand and on water quality.
(4) Effects on healthThe population that could be affected by diseases
such as malaria and dengue fever was calculated fromthe projected expansion in the potential area of malaria caused by global warming. The lower the temperature rise, the lower the effects, since the size ofthe affected population increases with global temperature. In regard to direct effects such as heat waves andheat stress in the mid-latitudes, certain temperaturesare said to exist at which mortality increases, decreases, or increases further. A threshold of effects on
health can be derived from the relationship between
the effects of heat waves, air temperature, and mortality. For example, in a heat wave in Japan, when thedaily maximum temperature exceeds 30°C, the number of people transported to hospitals with heat stressstarts to increase, and when the temperature exceeds
35°C the numbers of patients rapidly increases.
Because people gradually adapt themselves to heatand can mitigate its effects by using air-conditioners
and other methods of cooling, even if the extreme heat
continues, it is difficult to derive a danger level for
effects on health in terms of global temperature rise
only.
(5) Economic impacts
Economic impacts are calculated mostly by lostamounts of GDP. However, temperature rises work
entirely differently from economic losses (IPCC,
2001). It is thought that an economic loss of 3% to 5%
seriously influences the social economy. However, thecapacity of developed countries is different from thatof developing countries, of course, and there are still
only a small number of case studies on the economic
effects of global warming, because the effects on
ecological systems and damage evaluations are
difficult to comprehend.
(6) Large-scale phenomena
In regard to the threshold for large-scale and irreversible phenomena, such as the cessation of generaloceanic circulation and melting of the West Antarctic
Ice Sheet and the Greenland Ice Sheet, there are few
studies relating to global warming because the level of
uncertainty is still high. However, together with theTable 2 Dangerous anthropogenic interference. (Scheider & Lane, 2006)
Widespread bleaching of coral reefs

Vulnerability>1°C

Broad ecosystem impacts with limited adaptive
capacity (many examples)
Large increase of persons-at-risk of water
shortages in vulnerable regions
Increasingly adverse impacts, most economic
sectors

1°C~2°C

References
Smith et al. (2001),
O’Neill and Oppenheimer (2002)
Leemans & Eickhout (2004),
Hare (2003), Smith et al. (2001)

450~650 ppm

Parry et al. (2001)

Shutdown of thermohaline circulation
Disintegration of West Antarctic Ice Sheet
Disintegration of Greenland Ice Sheet

Gobal mean limit>3°C~4°C

Hitz & Smith (2004)

3°C (100 years), 700 ppm CO2

O’Neil & Oppenheimer (2002), Keller
et al. (2004)
O’Neil & Oppenheimer (2002)
Oppenheimer and Alley (2004, 2005)
Hansen (2004)

2°C, 450 ppm CO2
2°C~4°C, <550 ppm CO2
1°C

258

H. HARASAWA

growing interest in global warming, people are making progress in climate modeling studies and are coming to comprehend such phenomena by examinationof past (geologic) climates. Traditional studies point to
3°C/100 years for cessation of oceanic general circulation and 2°C for melting of the West Antarctic andGreenland Ice Sheets (Table 2).
(7) Scientific knowledge of the rate of temperaturechangeA need has been pointed out to consider the rate ofrise in temperature in addition to the absolute rise intemperature caused by global warming (WBGU,
2003). Table 3 lists studies that consider both theabsolute temperature value and the rate of rise.
The combination of a temperature rise of 1°C to
2°C and a rate of rise of 0.1°C to 0.2°C/ decade has
been reported. Leemans and Vliet (2004) pointed out
that, to retain the soundness of ecological systems, therate should be suppressed to 0.05°C/ decade. Becauseof the lack of scientific data comparing degrees oftemperature rise, the continuous high temperatures
since the 1980s, and the considerably excessive rate ofrise indicated in Table 3, the rate of temperaturechange has not been treated as a long-range objective,
unlike the absolute temperature.
(8) Summary of data on danger level
Scientific data on global-scale effects were collected according to field. On the basis of present dataon the amount of temperature rise, the effects andthresholds can be summarized as follows. These values are rough indications at present. In the future,additional data will be available for conducting
quantitative evaluations of a more definite dangerous
level.
a) Effects on ecosystems
1°C to 1.5°C: Effects on ecosystems
To 1°C: Effects on coral reefsb) Effects on social economic systems
2°C to 3°C: Food production
To 2°C: Effects on food production in developing
countries
To 2°C: Effects on water resourcesc) Effects on global systems
1°C to 2°C: Ice sheets of Antarctica and Greenland
start to melt
3°C or more: Possibility of oceanic general circulation cessation, etc.
The temperature rises shown here use values fromafter the industrial revolution. According to the IPCC

report, since calculations of future climate are currently made using climate models based on emission
scenarios starting in 1990 and studies of effects using
the above calculations, there are many possibleamounts of temperature rise. However, the temperature had already increased by 0.6°C during the 100
years of the 20th century. If the starting point is determined to be before the industrial revolution, then we
have to note that the value deducted by 0.6°C from theamount of temperature rise is available with which tocompare. We also have to note that in the mid-latitudearea, including Japan, the degree of temperature risehas been greater than the global average.

3. Conclusion
The Conferences of the Parties to the UNFCCC –COP11 and COP/MOP1 – were held in Montreal,
Canada from 28 November to 9 December 2005 after
the the Kyoto Protocol went into effect. During theseries of conferences, complete rules for administering
the Kyoto Protocol were set out, and developed
countries came to work on achieving the assigned reduction target. Discussion on the framework after the
first committment period (2008 to 2012) has not been
initiated. Although agreements to examine the next
framework were not reached, it was agreed to start a
constructive dialogue on activities for long-range cooperation by all the countries. To examine the next
framework, we will need to quantify a long-range
objective that effectively prevents global warming,
namely, the extent to which greenhouse gases should
be reduced before 2050 or 2100.
At the same time, dangerous levels of temperaturerise and effect thresholds are being discussed. The
UNFCCC has defined the stabilization of greenhousegas concentrations in the atmosphere. Although timelags between the emission of greenhouse gases andtemperature rise have existed from the outset, these
two events are tied closely to each other. Since theconcept of how to value the levels of danger of temperature rise is included in this problem, we can saythat this is not only a scientific issue but also a policy
issue. However, for global warming, the proposal ofscientific data based on scientific knowledge, including professional “risk comprehension,” will be more
important. The author hopes that studies on the effects
of global warming in Japan will yield the fundamental
information we need to set up stabilized concentrations and long-range objectives.

Table 3 Scientific data on dangerous level (temperature rise and rate of rise).
Researcher
Vellinga et al.
Matsuoka et al.
WBGULeemans et al.

Concrete value (Amount of temperature rise and rate of rise)
Temperature rise of 2°C and rate of rise 0.2°C/decade causes
collapse of society and increases risk of global system instability.
Temperature rise of 1°C to 2°C and rate of rise of 0.1°C to
0.2°C/decade.
Temperature rise of 2°C and rate of rise of 0.2°C/decade.
Temperature rise of 1.5°C and rate of rise of 0.05°C/decade.

Document
Vellinga & Swart (1991)
Matsuoka et al. (1996)
WBGU (1995, 1997, 2003)
Leemans & Vliet (2004)

A Consideration on Dangerous Level of Global Warming

Acknowledgment
This paper is based mainly on the results of a study,“Subtitle 1: Studies on dangerous standard and stabilization routes by the integrated assessment model,
Studies on Integrated Evaluation of Influence of
Global Warming for the Determination of Dangerous
Level of Global Warming and Stable Level of Global
Greenhouse Gas, Global Environment Research Fundof Ministry of the Environment (S-4).” The author
would like to cordially acknowledge the people who
participated in this project and cooperated with him in
this study.
References
Hansen, J., (2004) Defusing the global warming time bomb,
Scientific American, 290: 68-77.
Hare, W. (2003) Assessment of knowledge on impacts of climate change – contribution to the specification of Art. 2 of
the UNFCCC.
Hitz, S. and J. Smith (2004) Estimating global impacts fromclimate change. Global Environmental Change, 14: 201-218.
IPCC (2001) Climate Change 2001 Impact, Adaptation and
Vulnerability.
Keller, K., B.M. Bolker and D.F. Bradford (2004) Uncertain
climate thresholds and optimal economic growth. Journal ofEnvironmental Economics and Management, 48: 723-741.
Leemans, R. and A. van Vliet (2004) Extreme Weather does
nature keep up?
Leemans, R. and B. Eickhout (2004) Another reason forconcern: regional and global impacts on ecosystems fordifferent levels of climate change, Global Environmental
Change (Part A), 14: 219-228.
Matsuoka, Y., T. Morita and Y. Kawashima (1996) Background
paper prepared for the Ad Hoc Group on the Berlin Mandate,
Framework Convention on Climate Change, July, 1996
Geneva, 8-19.
O’Neill, B. C. and M. Oppenheimer (2002) Climate change –dangerous climate impacts and the Kyoto protocol, Science,
296: 1971-1972.

259

Oppenheimer, M. and R.B. Alley (2004) The West Antarctic Ice
sheet and Long Term Climate Policy, Climatic Change, 64:
1-10.
Oppenheier, M. and R.B. Alley (2005) Ice Sheets, Global
Warming, and Article 2 of the UNFCCC – An Editorial Essay,
Climatic Change, 68: 257-267.
Parry, M., N. Arnell, T. McMichael, R. Nicholls, P. Martense,
S. Kovatsc, M. Livermorea, C. Rosenzweig, A. Iglesiasg and
G. Fischer (2001) Millions at risk: defining critical climatechange threats and targets. Global Environmental Change,
11: 181-183.
Rapley, C. (2006) The antarctic ice sheet and sea level rise. In:
H.J. Schellnfuber et al. eds., Avoiding Dangerous Climate
Change, Cambridge University Press, 25-27.
Schellnfuber, H.J., W. Cramer, N. Nakicenovic, T. Wigley and
G. Yohe (2006) Avoiding Dangerous Climate Change.
Cambridge University Press.
Schneider, S. and J. Lane (2006) An overview of ‘dangerous’
climate change. In: H.J. Schellnfuber, W. Cramer, N.
Nakicenovic, T. Wigley and G. Yohe, eds., Avoiding Dangerous Climate Change, Cambridge University Press, 17-23.
Smith, J.B., H-J, Schellnhuber and M.M.Q. Mirza (2001)
Vulnerability to Climate Change and Reasons for Concern: A
Synthesis, in Climate Change 2001: Impacts, Adaptation, andVulnerability. In: J.J. McCarthy et al. ed., Cambridge
University Press, Cambridge, 913-967.
Smith, J. and S. Hitz (2003) Background paper: estimating
global impacts from climate change, OECD Workshop on the
Benefits of Climate Policy: Improving Information for Policy
Makers.
Vellinga, P. and R.J. Swart (1991) The Greenhouse marathon: A
proposal for a global strategy, 18: 7-12.
Warren, R. (2006) Impacts of global climate change at difference annual mean global temperature increase. In: H. J.
Schellnfuber et al. eds., Avoiding Dangerous Climate
Change, Cambridge University Press, 93-131.
WBGU (German Advisory Council on Global Change) (1995)
Scenario for the derivation of global CO2 reduction targets
and implementation strategies.
WBGU (German Advisory Council on Global Change) (1997)
Targets for Climate Protection, 1997.
WBGU (German Advisory Council on Global Change) (2003)
Climate Protection Strategies for the 21st Century: Kyoto
and beyond.

(Received 20 August 2006, Accepted 26 September 2006)