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Background on Impacts,
Emission Pathways,
Mitigation Options and
Costs
The 2°C target
Information Reference Document
S UB 1
Information Reference Document
Prepared and adopted by EU Climate Change Expert Group ‘EG Science’
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Final Version, Version 9.1, 9 July 2008, 16:15
With contributions to earlier drafts from: Terry Barker, Outi Bergall, Svante Bodin, Martin
Cassel-Gintz, Steve Cornelius, Eric De Brabante, Ursula Fuentes, Hans-Martin Füssel, Marc
Gillet, Benno Hain, William Hare, Ger Klaasen, Brigitte Knopf, Katrine Krogh Andersen, Gunnar
Luderer, Ben Matthews, Frank McGovern, Malte Meinshausen (Ed.), Pauline Midgley, Klaus
Radunsky, Jože Rakovec, Stefan Rösner, Tom van Ierland, David Warrilow, Martin Weiss.
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Summary
This paper outlines the scientific background for the EU climate
protection target - the 2oC limit - established by the EU Governments in
1996 and reaffirmed since then by the Environment Council 2003, and
European Council, 2005, 2007. The paper also identifies how this target
may be achieved through global action.
The Fourth Assessment Report of the Intergovernmental Panel on
Climate Change (IPCC AR4) indicates that the global mean temperature
increase 1 provides an important common metric for analysis of many
climate change impacts associated with global warming. In highly
vulnerable areas, such as parts of Africa, Asia and small island states in
the Pacific and the Caribbean, serious regional impacts are already
occurring. Significant global impacts on ecosystems and water resources
are likely at global temperature rises of between 1 and 2°C, and the risks
of net negative impacts on global food production occur at temperature
increases upwards from 2-2.5°C, compared to pre-industrial levels.
Analysis of current atmospheric greenhouse gas (GHG) concentrations
indicates that only a narrow window of opportunity exists to ensure that
these serious negative effects can be avoided. Within the next 10 to 15
years, global GHG emissions need to be shifted to a pathway consistent
with the 2°C target. This can be achieved with technologies that already
exist or are being developed, provided the appropriate incentives are
given. However, the necessary departure of emissions from the present
business-as-usual trends implies, on a global scale, immediate and
substantial investment in these low-carbon technologies.
The IPCC AR4 indicates that, up to 2050, substantial global emission
reductions by at least 50% below 1990 levels are needed with additional
global emission reductions beyond 2050 towards a zero carbon economy
by the end of the century. Recent work on mitigation costs indicates that
meeting the 2°C target could be achieved with GDP losses of at most
2.5% by 2050 (reducing annual growth by at most 0.05%/year), and with
lower costs for earlier years. When taking into account co-benefits in
terms of air pollution reduction, net costs could be significantly lower. The
costs of actions to mitigate climate change are small when compared to
the relative costs of impacts due to inaction.
1
A global mean temperature rise implies higher warming over land than over oceans, with the
tropical regions warming least and the northern polar region warming the most.
3
Key Messages
4
•
Negative effects of climate change are already observed at the
current global mean temperature increase of 0.8°C above preindustrial levels.
•
Global mean temperature increases of up to 2°C (relative to preindustrial levels) are likely to allow adaptation to climate change
for many human systems at globally acceptable economic, social
and environmental costs. However, the ability of many natural
ecosystems to adapt to rapid climate change is limited and may
be exceeded before a 2°C temperature increase is reached.
•
A global mean temperature increase greater than 2°C will result
in increasingly costly adaptation and considerable impacts that
exceed the adaptive capacity of many systems and an increasing
and unacceptably high risk of large scale irreversible effects.
•
In order to have a 50% chance of keeping the global mean
temperature rise below 2°C relative to pre-industrial levels,
atmospheric GHG concentrations must stabilise below 450ppm
CO2 equivalence. Stabilisation below 400ppm will increase the
probability to roughly 66% to 90%.
•
Current atmospheric GHG concentrations and trends in GHG
emissions mean that these concentration levels may be
exceeded. The 2°C target can still be achieved if this overshoot
of concentrations is only temporary and reversed quickly. Thus,
to avoid a warming in excess of 2°C, global GHG emissions
should peak by 2020 at the latest and then be more than halved
by 2050 relative to 1990.
•
Deep emission reductions can be achieved by employing a broad
range of currently available technologies and technologies that
are expected to be commercialised in coming decades.
•
Deployment requires clear, consistent and effective policies and
incentives.
•
Action needs to be taken very urgently as inertia in both the
climate and socio-economic systems means that mitigation
actions and low-carbon investment decisions are needed now in
order to avoid lock in of carbon-intensive technologies.
•
The costs of climate change impacts are directly related to their
magnitude which increases with global temperature and may be
between 5 and 20% of GDP or even higher in the long-term.
•
The costs of actions to mitigate climate change are small when
compared to the relative costs of impacts due to inaction.
•
Some of the costs of impacts can be reduced through investment
in adaptation.
•
According to recent studies, mitigation needed to meet the 2°C
target is projected to cost at most 2.5% of global GDP in 2050
(reducing annual growth by at most 0.05%/year) if policies are
designed in a cost-effective way. These costs are reduced
significantly when co-benefits (i.e. reduction in air pollution health
damage, air pollution control costs and energy security) are
included.
•
Such mitigation, via a portfolio of coordinated policies including a
long-term carbon price and the recycling of tax/auction revenues
to promote low-carbon technologies and to improve market
efficiencies, could even lead to global GDP gains (above those
due to avoided climate impacts).
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Table of Contents
SUMMARY
3
KEY MESSAGES
4
TABLE OF CONTENTS
6
IMPACTS AND VULNERABILITIES
12
EMISSION PATHWAYS
26
MITIGATION OPTIONS
38
ECONOMICS OF CLIMATE CHANGE
44
CONCLUSIONS
51
APPENDIX 1 (REFERENCES)
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APPENDIX 2
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The ultimate objective of the UN Framework Convention on Climate
Change (UNFCCC) as stated in Article 2 is to stabilise atmospheric
greenhouse gas (GHG) concentrations at a level that would prevent
dangerous interference with the climate system. Such a level should be
achieved within a time frame sufficient to allow ecosystems to adapt
naturally to climate change, to ensure that food production is not
threatened and to enable economic development to proceed in a
sustainable manner. The EU considers that this objective would be
achieved by limiting GHG concentrations to levels that would keep the
increase of global mean temperature below 2oC relative to pre-industrial
temperatures 2 .
This view is based on the assessment of the impacts and risks expected
to occur, or to which the world would be committed as the global mean
temperature approaches 2oC above pre-industrial temperatures, as well
as those that are expected to occur if the global temperature increases
beyond this level.
The EU’s global temperature target of 2°C above pre-industrial was first
established in 1996 during preparations for the Kyoto negotiations, and
has been reaffirmed subsequently in various Environment Council and
European Council conclusions. This limit was deduced in 1996 from the
evidence available at the time, mostly from impacts studies that were
assessed in the Second Assessment Report of the Intergovernmental
Panel on Climate Change (IPCC SAR, 1996a,b,c). However, such
studies tended to look only at the impact of doubling CO2 from preindustrial levels to 550ppm. A further consideration in setting a limit was
the concern that rates of change needed to be limited to less than 0.1°C
per decade in order to allow ecosystems time to adapt.
Since then, the information provided in the IPCC’s Third Assessment
Report (IPCC TAR, 2001a,b,c,d), and developments in the scientific
literature and in peer reviewed publications such as “Avoiding Dangerous
Climate Change” (Schellnhuber et al., 2005) supported and advanced
the scientific basis for the assessment of impacts and risks that underpin
the adoption of the 2oC target and confirms our view that 2oC is an
appropriate target.
The IPCC’s Fourth Assessment Report (hereafter: IPCC AR4), the Stern
Review Report on the Economics of Climate Change (Stern, 2006) and
the European Commission communication “Limiting Global Climate
Change to 2 degree Celsius” (European Commission, 2007a) provide
further and improved scientific, technical and socio-economic analyses.
The comprehensive analyses and new findings in these reports are the
main sources for the information contained in this paper.
2
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Pre-industrial being defined as 1850-1899 average global mean surface temperatures.
The 2oC limit cannot be considered to be entirely ’safe’, as severe
impacts are likely to occur increasingly as the global mean temperature
rise approaches 2°C above pre-industrial levels. Changes in extremes
such as heat waves, droughts and extreme precipitation events will
largely shape future climate impacts. In particular, significant impacts are
expected for species, ecosystems and water resources, low latitude
agriculture, and small island states. The latter will be increasingly
impacted by the direct and indirect effects of sea-level rise. Impacts are
already being observed which are consistent with or which can be
attributed to warming to date.
This document provides an overview of the EU’s assessment of the
climate change impacts underpinning the 2°C target (Chapter 2 “Impacts
& Vulnerabilities”) and the implications for global emissions (Chapter 3
“Emission Pathways”). Achievement of the 2°C target implies ambitious
global GHG emissions reductions and a rapid reversal of current trends
of rising emissions. The wide technology portfolio available for reducing
emissions is presented (Chapter 4 “Mitigation Options”). The necessary
deep cuts in global emissions will likely have to draw on the widest
possible range of reduction options. Finally, the most recent literature on
the economics of mitigation are summarised (Chapter 5 “Economics of
Climate Change”), highlighting once more that the costs of inaction are
likely to far outweigh the costs of climate change mitigation.
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10
• Negative effects of climate change are already observed
at the current global mean temperature increase of
0.8°C above pre-industrial levels.
• Global mean temperature increases of up to 2°C
(relative to pre-industrial levels) are likely to allow
adaptation to climate change for many human systems
at globally acceptable economic, social and
environmental costs. However, the ability of many
natural ecosystems to adapt to rapid climate change is
limited and may be exceeded before a 2°C temperature
increase is reached.
• A global mean temperature increase greater than 2°C
will result in increasingly costly adaptation and
considerable impacts that exceed the adaptive capacity
of many systems and an increasing and unacceptably
high risk of large scale irreversible effects.
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Impacts and Vulnerabilities
Anthropogenic emissions of greenhouse gases perturb the global climate
system, resulting in an increase of global mean temperature, changes in
weather and precipitation patterns and increased climate variability
resulting in a higher frequency of extreme events.
There is significant regional variation in climate change and its impacts.
In general, warming will be stronger over land areas than over the
oceans, and some continents and regions will be subject to larger
changes than others. In many regions, current differences in the
distribution of precipitation tend to be amplified, i.e. wet regions generally
will become wetter and dry regions will become drier.
In addition to the impacts mediated via the climate system, increased
atmospheric CO2 concentration results in ocean acidification, which will
have significant negative consequences for marine biology (WBGU,
2006).
Global mean temperature is an important indicator for communication of
the causes and consequences of climate change and provides a
common metric for the assessment of impacts of global warming.
However, the global average temperature does not capture the details of
spatial variability and the large variety of effects that occur at regional
and local levels.
The global mean temperature has risen by approximately 0.8°C above
pre-industrial levels 3 (IPCC AR4 WGI SPM). Unless otherwise stated, all
temperatures given in this paper refer to changes of global mean
temperature relative to pre-industrial levels. Many climate change related
impacts, such as coral reef bleaching, glacier retreat and changes in the
frequency of extreme weather events are already evident (IPCC AR4
WGII). These impacts are expected to intensify and become more
widespread in the future.
The intensity of climate change impacts will accelerate as temperatures
increase (IPCC AR4 WGII) (see Fig. 2.1 and 2.2). Moreover, the
uncertainty of climate change impacts increases substantially with
increasing levels of global warming.
3
Here defined as temperature change since 1850-1899 (beginning of instrumental temperature
records). At that time the anthropogenic influence was small compared to natural variation;
th
temperatures in the late 19 century are in good agreement (order of 0.1°C) with conditions
before the onset of industrialisation in 1750.
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Fig 2.1: Examples of global impacts in various sectors associated with
different levels of climate change based on published studies. Boxes
indicate the range of temperature levels to which the impact relates.
Arrows indicate increasing impacts with increasing warming.
Adaptation to climate change is not considered in this overview. The
black dashed line indicates the EU objective of a 2°C temperature
change relative to pre-industrial. Source and explanation of superscript
references: please consult IPCC AR4 WGII, Fig. TS.3.
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Fig 2.2 (previous page): Examples of global impacts in various world
regions associated with different levels of climate change based on
published studies. Boxes indicate the range of temperature levels to
which the impact relates. Arrows indicate increasing impacts with
increasing warming. Adaptation to climate change is not considered in
this overview. The black dashed line indicates the EU objective of 2°C
temperature change relative to pre-industrial. Source and explanation
of superscript references: please consult IPCC AR4 WGII, Fig. TS.4.
2.1 Projected climate change: impacts in various
sectors and reasons for concern
The Fourth Assessment Report of the IPCC’s Working Group II (WGII),
indicates that climate change will affect a wide variety of natural and
anthropogenic systems in all regions (Fig 2.1 and 2.2). The IPCC AR4
strengthens and advances the risk assessments provided by the Third
Assessment Report (IPCC TAR, 2001b). For a number of areas of
concern, the assessed risks are higher in the AR4 compared to the TAR
assessment, particularly at lower temperatures.
If global warming is limited, many impacts of climate change can be
addressed through effective adaptation. With increasing levels of climate
change, however, there are fewer options for successful adaptation.
There is very limited knowledge on the limits and costs of adaptation.
Significant reductions in emissions to meet long-term mitigation goals
substantially decrease the level of adaptation required.
Ecosystems and species
Increasing levels of climate change are associated with increasing
pressure on ecosystems. Many ecosystems will not be able to adapt to
the projected rates of change. Particularly vulnerable ecosystems include
coral reefs, Arctic ecosystems, Alpine ecosystems and tropical forests,
which are likely to be severely impacted at levels of global warming
approaching 2°C.
A global mean temperature increase exceeding 2-3°C would increase the
risk of extinction for about 20-30% of species and have widespread
adverse effects on biodiversity and ecosystems. Increases significantly
above this range are projected to lead to significant extinctions of species
and, at just above this level, widespread mortality for coral reefs. Global
losses are irreversible; therefore the impacts on biodiversity are of key
relevance. There is a still poorly understood risk that temperature
increases above 2-3°C could cause major and irreversible damage to the
Amazonian rainforest and its biodiversity and, as a consequence, exert a
strong positive feedback on the climate system by turning Amazonia into
a large carbon source.
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Polar regions
The world’s polar regions are particularly vulnerable to climate change.
Decreasing snow and ice cover in the northern hemisphere has reduced
the reflection of sunlight back to space, amplifying climate change effects
in northern high latitude regions (IPCC AR4 WGI). A mean global
temperature increase of 3°C by the end of the 21st century corresponds
to an increase in annual mean temperature of 5-7°C in the central Arctic
Ocean (IPCC AR4 WGI, Ch. 11.8.1). Winter Arctic temperature increases
are projected to be four times higher than the global mean increase. The
extent and depth of Arctic sea ice in the summer time is presently
observed to be reducing rapidly, with 2007 producing record losses.
Some of the IPCC AR4 generation of climate models projected summer
ice to disappear almost completely by the end of the 21st century if the
global temperature increases beyond 3°C (IPCC AR4 WGI, Box 10.1,
Ch. 10.3.3.1). The likelihood of abrupt changes in Arctic sea ice
increases significantly with increasing anthropogenic GHG emissions
(IPCC AR4 WGI, Ch. 10.3.3).
Observed sea ice losses significantly exceed the rate of ice loss
projected by the coupled ocean atmosphere models (AOGCMs)
participating in the IPCC AR4 assessment for the period 1953-2006 and
there is increasing concern that summer sea ice may be substantially
eliminated well before the end of the 21st century (Stroeve et al. 2007).
The loss of Arctic sea ice is likely to strongly perturb atmospheric and
oceanic circulation patterns, to threaten the existence of sea icedependent ecosystems and species, and to change the marine food
chain as well as the living space of about two hundred thousand
indigenous people. Based on the projected loss of sea ice in the AR4,
the polar bear (Ursus maritimus) has been assessed as facing a high risk
of extinction with warming of 2.8°C above pre-industrial (range 2.53.0°C) (IPCC AR4 WGII, Box 4.3, Table 4.1). Earlier loss of ice at lower
temperatures would lower this temperature threshold.
Water
Already at current levels of global warming, significant changes in water
resources are evident, and impacts in the water sector will become
increasingly severe as both precipitation and evaporation will continue to
be altered as a consequence of climate change. The numbers of
additional people at risk of water stress are projected to increase
substantially with increasing temperature from 0.4-1.1 billion for 1-1.5°C
warming above pre-industrial levels to 1.1-3.2 billion for ca 3-4°C
warming. Areas affected by drought will probably increase, and flood risk
will increase due to the higher likelihood of extreme precipitation events
(IPCC AR4 WGII, Box TS.5). Regions already suffering from water
scarcity, such as southern Africa, north-eastern Brazil, southern and
eastern Australia, the Mediterranean basin, and western USA, are
projected to experience further reductions in water availability (IPCC AR4
WGII, Ch. 3). Sea level rise will lead to salinisation of groundwater,
affecting water supplies in coastal regions.
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More than one sixth of the world’s population live in snowmelt- and
glacier-fed river basins and depend on these systems for water
resources. These basins are subject to increased river runoff during the
peak spring and summer melt time, causing structural damage and
flooding. Whilst water flows increase at first with glacial melting, as
glacier mass declines, melt and runoff will substantially decrease. This
will result in substantially increased water stress in such regions, e.g. the
Ganges basin which is home to about half a billion people. The timing of
this decrease depends on the individual region and on the rate of
warming and varies from one decade (Andes) to many decades
(Himalaya).
High mountainous/Alpine regions
High altitude, mountainous and Alpine regions are undergoing major
changes. Most mountain glaciers are receding rapidly. Many small
glaciers are projected to disappear during the 21st century, while large
glaciers will suffer a substantial reduction in volume. The duration and
depth of snow cover is projected to change with global warming. As
outlined above, changes in glaciers and snow cover will have a strong
impact on the water sector in many regions. Melting permafrost due to
rising temperatures will destabilise mountain walls and increase rock fall.
Endemic Alpine biota are highly vulnerable to climate change, and their
adaptive capacity is limited. There is a disproportionately high risk of
extinction in various mountain ecosystems.
Agriculture and food security
Risks to food production and security are projected to differ greatly by
region. Above a global temperature rise of 1.5 to 2°C there is an
increasing risk of a decline in global food production. Even below this
level, at lower latitudes, especially in the seasonally dry tropics,
agriculture will be negatively affected by climate change with negative
impacts on the yield of major cereal crops. Food security and agricultural
incomes are likely to be under threat in many regions of Africa, Asia and
Latin America. In mid- to high latitude regions, increases in local
temperature of 1-3ºC are projected to lead to small increases in yield
which are reversed for higher temperatures (IPCC AR4 WGII, Ch. 5.4,
5.6).
Health
Human health will be strongly affected by climate change. Severe heat
stress has already caused loss of life in Europe (cf. Section 2.2) and
other regions of the world. Even a moderate temperature increase well
below 2°C is likely to result in negative impacts in the health sector such
as increased burden from malnutrition, increased incidence of diarrhoeal
diseases and many vector-, food-, and water-borne infectious diseases.
In particular, it will lead to a net increase in the geographic range of
malaria and dengue fever. At higher levels of global warming, the
negative impacts in the health sector are projected to become more
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severe. Adverse health impacts will be greatest in low-income countries
(IPCC AR4 WGII, Ch.13.4.1).
Extreme events
Increases in global mean temperatures will result in significant changes
in the intensity, frequency and location of extreme events such as heat
waves, flooding, wildfire and tropical cyclones, even below 2°C rises in
temperature. Greater warming is projected to further substantially
increase the risk, frequency and intensity of many extreme events.
Extended heat waves are projected to become more intense and
frequent, adversely affecting human health, natural ecosystems,
agriculture, and the power industry (IPCC AR4 WGII, Ch. 12.6.1). Heat
and drought will also strongly increase the risk and severity of wildfires.
Tropical cyclone intensity (peak wind speeds and precipitation) is
projected to increase with increasing tropical sea surface temperatures,
and hence with increasing levels of global warming (IPCC AR4 WGI, Ch.
3.8.3 and Box 3.5; WBGU, 2006, Ch. 3.1.2). Above a global warming of
2-3°C, a greater increase in winter rainfall in combination with a loss of
winter snow storage will increase flooding in many regions. High levels of
global warming also imply a strongly increased risk of dam bursts in
glacial mountain lakes.
Coastal zones, small islands, sea-level rise
In the long term, an increase in sea level rise is likely to be one of the
most severe and important consequences of global warming. The IPCC
AR4 report projects a sea-level rise of 0.18–0.59 m until 2100. This
range does not account for possible rapid changes in ice sheet flow due
to processes not presently included in the ice sheet models that were
used in the AR4 assessment, which would result in significant additional
sea level rise. Semi-empirical projections of sea level rise based on
observed rates of temperature and sea level change over recent
decades indicate that there is a risk that the IPCC AR4 sea level
estimates are biased on the low side. These projections give a sea level
rise of 0.4-1.4 m by 2100 (Rahmstorf, 2007).
Even if the global temperature is stabilised, sea level would continue to
rise for many centuries to millennia due to the enormous thermal inertia
of the oceans and the slow melting of major ice sheets. Higher levels of
global warming will result in a larger rise in sea level. Sustained global
warming greater than 1.5-2.5°C is a threshold beyond which there is
likely to be a commitment to at least partial deglaciation of the Greenland
ice sheet, and possibly of the West Antarctic ice sheet, causing sea level
rise of 4-6 m over centuries to millennia. For global warming of 3°C,
WBGU (2006, Ch. 3.1.1.4 and Table 3.1-1) projects the global sea level
to rise by as much as 2.5-5.1 m by 2300.
Coastal zones are home to about one fifth of the world’s population and
population growth rates in these areas are very high. Sea level rise,
possibly in combination with changing atmospheric circulation patterns,
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will increase the risk of storm surges. Sea level rise also increases
coastal erosion and has impacts on groundwater levels and ecosystems
in coastal zones. Small islands are especially vulnerable to an increase
in sea level.
Distribution of impacts
The impacts of climate change are not evenly distributed across regions
and sectors. At global warming levels below 2°C, a few sectors in certain
regions might benefit from climate change (e.g., agriculture and tourism
in high latitude regions), while in most other regions and sectors effects
are likely to be negative, and sometimes even severely so. For many
countries, a 2°C warming limit may not be wholly safe. Generally, less
developed areas are at greatest risk due to both higher sensitivity (e.g.,
small islands) and lower adaptive capacity (IPCC AR4 WGII, Ch. 19.3.7).
Climate change is identified as a major obstacle to poverty reduction
objectives and achievement of the Millennium Development Goals (IPCC
AR4 WGII, 2007; Stern, 2006).
In developed countries, the poorest also tend to be the most vulnerable
to climate change (Stern, 2006). Climate change tends to increase
differences in economic wealth both between regions of the world and
within individual countries. Given that industrialised countries are
responsible for a large amount of the GHG emissions and that emissions
are strongly related to consumption, this raises issues of international
and social equity. As temperature increases in excess of 3°C, there will
be net negative impacts in developed countries and also even more
severe net negative impacts in many developing countries (IPCC AR4
WGII, Ch. 19.3.7).
Security and migration
Climate change could, within a few decades, become a major threat to
international security (WBGU, 2008). Climate change will add an
additional burden to already existing pressures in relation to food security
and water availability in many unstable regions, particularly in the
developing world. Moreover, climate change is likely to increase storm
and flood disasters. The population in already politically unstable states
with poorly performing governments and institutions will be most
affected, since climate change will overwhelm local capacities to adapt
(WBGU, 2008). Climate change is likely to induce additional migration
both within national borders and internationally. Europe and North
America are likely to have to face substantially increasing migratory
pressure, and this migration will likely become an additional source of
destabilisation on national, regional and international scales.
Economic impacts
Many economic sectors and activities will be adversely affected by
climate change (Stern, 2006). Current studies estimate that, for a global
mean temperature of up to 2 to 3°C above pre-industrial levels, positive
market impacts (such as increasing crop yields in higher latitude regions)
19
almost balance the negative market impacts of climate change, giving
rise to aggregate impacts of plus or minus a few percent of global gross
domestic product. However, positive impacts are not likely to be evenly
distributed and most people, particularly in developing countries, would
be negatively affected (IPCC AR4 WGII, Ch. 19.3.7). With further
increases in global temperature, the net damages are likely to increase
at a disproportionate rate (Stern, 2006). Cost estimates increase if nonmarket impacts are considered (Stern, 2006; IPCC AR4 WGII, Ch.
19.3.7). A more detailed discussion on the costs of climate change is
provided in Section 5.
2.2 Projected effects for Europe
The European Environment Agency (EEA), IPCC and other regional and
national analyses have provided extensive analyses on the impacts of
climate change for Europe (EEA, 2004; IPCC AR4 WGII, Ch. 12). The
magnitude of impacts is expected to increase as global temperatures
rise. Europe, however, may have the capacity to substantially reduce the
adverse impacts outlined here by undertaking adaptation measures
(European Commission, 2007b).
Heat waves
In 2003, large parts of Europe were affected by an extended heat wave.
This resulted in about 35,000 heat-related excess deaths (IPCC AR4
WGII, Ch. 12.6.1). A similar but less intense heat wave occurred in the
summer of 2006. Increased evaporation and lack of precipitation during
these heat wave events threatened water resources, causing adverse
impacts in many economic sectors. Crop losses, heat-stress on livestock
and widespread forest fires resulted in losses in the agriculture and
forestry sectors. Extremely low river flow rates resulted in disruption of
inland navigation. In combination with high water temperatures, the low
water levels in rivers also forced a reduction of electricity generation in
thermal power plants which utilise water cooling. The frequency of such
extremely dry summer conditions will increase at a disproportionate rate
(IPCC AR4 WGII, Ch. 12.6.1). Such heat wave events will become much
more severe and frequent even with a 2°C temperature increase. The
conditions experienced in 2003 could become the norm for the latter part
of the 21st century under a non-mitigation scenario (IPCC AR4 WGII, Ch.
12.6.1).
Water sector
Many climate change impacts are related to the water cycle. Climate
change is projected to result in a significant perturbation of precipitation
patterns in Europe, with the sharpest decreases projected for summer
precipitation in southern Europe. In contrary, northern Europe is likely to
experience a substantial increase in winter precipitation (IPCC AR4
WGII, Ch. 12.3.1.1). Whereas the models agree well on the spatial and
seasonal patterns of precipitation change, large uncertainty remains
20
about its magnitude. For large parts of the Mediterranean, a decrease in
summer precipitation of up to 30-45% (in some parts up to 70%) is
projected for the end of the 21st century for a scenario corresponding to a
global warming of 3-3.5°C. For Scandinavia, an increase in winter
precipitation of 15-30% is projected (IPCC AR4 WGII, 12.3.1.1). Such a
precipitation change would exacerbate existing water stress in southern
and south-eastern Europe and increase the frequency of drought. In
these regions, agriculture already relies heavily on irrigation, and
irrigation requirements are thus projected to increase. Changing
precipitation patterns and larger climate variability are likely to increase
the risk of floods in northern, central and eastern Europe (IPCC AR4
WGII, Ch. 12.4.1). An increase in the frequency of intense short-duration
precipitation events will likely increase the risk of flash-floods in most of
Europe.
Coastal zones
Europe has many low-lying coastal areas, many of which are densely
populated and therefore vulnerable to sea level rise. The coastal strips of
the North Sea running through eastern England, Belgium, the
Netherlands, north-western Germany and Denmark as well as the Po
delta in northern Italy are Europe’s most threatened coasts (WBGU,
2006). Regional influences may result in sea level rise in Europe
exceeding the global mean increase by 50% (IPCC AR4 WGII).
Maintaining the 2°C target is important for limiting the risk of
destabilisation of polar ice sheets, which would contribute substantially to
long-term sea level rise (cf. Section 2.3).
Mountain regions
Mountain regions are amongst the most vulnerable natural systems in
Europe and climate change adds to other environmental stresses.
Glaciers in the Alps are retreating at a rapid pace; for each degree of
local warming, the snow line moves upward by about 150 m (EEA,
2004). Thawing of Alpine permafrost causes destabilisation of mountain
walls and increases the frequency of rock falls. Fragile Alpine
ecosystems are forced to move uphill and will eventually disappear.
Recent findings indicate that impacts on biodiversity will be
disproportionately severe in the European mountain regions, where the
species loss by 2080 is projected to be as high as 60% for a high
emissions scenario (IPCC AR4 WGII, Ch. 4.4.7). Climate change may
also severely affect the tourism sector in mountain regions. In the
Austrian Alps, for instance, an increase of 1°C may lead to some 70
fewer skiing days per year, depending on altitude (IPCC AR4 WGII,
12.4.9).
Economic impacts
Currently, research activities are being undertaken to quantify the
economic impacts of climate change in various sectors such as coastal
systems, energy demand, human health, agriculture, tourism and floods.
The 2003 heat wave resulted in damages of 13 billion € in the agriculture
21
and forestry sectors alone (Stern, 2006 Box II5.4), mostly due to losses
in crop yield, heat-stress on livestock and forest fires. Projections
estimate a more than 10-fold increase in annual flood losses in Europe
by the end of the century for a global warming of 3-4°C, some of which,
however, are driven by economic growth and an increase in physical
assets. Adaptation measures such as strengthening of flood
management have the potential to significantly limit losses (Stern, 2006,
II5.4).
2.3 Positive feedbacks, instabilities, irreversible
changes and tipping points
In assessing the level at which anthropogenic interference with the
climate system must be considered “dangerous”, a particular focus
should be given to instabilities, positive feedbacks and irreversible
changes in the climate system – in risk management language, low
probability, high impact events or processes. Once a certain level of
warming has been reached, self-amplifying processes may result in a
transition of the climate system to another state. Thresholds for such
processes are called “tipping points” in the climate system (IPCC AR4
2007, Box 10.1; Lindsay and Zhang, 2005; Hansen et al., 2007, Lenton
et al., 2008). They include especially the irreversible melting of the
Greenland ice sheet, the risk of disintegration of the marine based West
Antarctic ice sheet, a weakening or even complete shutdown of the
Atlantic Meridional Overturning Circulation (MOC), often termed the
thermohaline circulation (THC), and climate change-induced release of
greenhouse gases from the land biosphere. All these processes have the
potential to trigger large-scale changes, some of them irreversible on the
timescales of centuries to millennia, with dramatic impacts.
Polar ice sheets
The amplified warming of the atmosphere at high latitudes and ocean
warming threaten the Greenland Ice Sheet (GIS) and the West Antarctica
Ice Sheet (WAIS). These account for water masses equivalent to
approximately 7m and 5m of global sea level rise, respectively. Due to
their thickness and the great thermal inertia, complete melting would not
occur abruptly, but would likely take many centuries to complete. Rapid
decay of these ice sheets, or even partial disintegration, leading to multimetre sea level rise over centuries to millennia is likely if warming is large
enough and sustained for long enough. A multi-metre sea level rise
would be a key impact due to the large magnitude of the consequences,
its irreversibility and the likelihood that it would exceed the adaptive
capacity of many regions (IPCC AR4 WGII, Ch. 6 and 19.3.5.2).
22
Above about 2°C warming 4 , there would be, with medium confidence, a
commitment to widespread to near-total deglaciation of the Greenland
ice sheet leading to 2-7m sea level rise over centuries to millennia (IPCC
AR4 WGII, Ch. 19.3.5]. For the West Antarctic Ice sheet 5 , scientific
confidence is lower; however it could be anticipated with low to medium
confidence that for warming of over 2°C there would be a commitment to
partial deglaciation with 1.5-5 m sea level rise over centuries to millennia
(IPCC AR4 WGII, Ch. 19.3.5]. Even a warming of 2°C may commit us to
a sea level rise from melting ice sheets, and this risk greatly increases for
greater warming.
Atlantic Meridional Overturning Circulation (MOC)
The MOC is an important mechanism for the global redistribution of heat.
It is largely responsible for the mild climate in the North Atlantic basin.
According to IPCC AR4, a complete shutdown of the MOC is considered
to be very unlikely to occur during the 21st century. The likelihood of
large-scale MOC responses increases with the extent and rate of
warming. In a risk context, it is to be noted that the likelihood in the 21st
century (<10%) may still be significant given the high consequences of
an abrupt shutdown: these include adverse effects on food production
and terrestrial vegetation, changes in fisheries and effects on oceanic
CO2 uptake and oceanic oxygen concentrations, an increased warming
of southern hemisphere high latitudes and tropical drying. Adaptation to
the impacts of a shutdown of the MOC is very likely to be difficult if the
impacts occur abruptly (IPCC AR4 WGII, Ch. 19.3.5.3). Rapid ice loss
from the Greenland ice sheet or rapid addition of freshwater fluxes from
the Arctic flowing rivers would increase the risk.
Coupled climate models project a decrease in the MOC of up to 50% or
more by the end of the 21st century due to warming of the surface waters
and increased precipitation in the North Atlantic (IPCC AR4 WGI, Ch.
10.3.4). Slowing down of the MOC decreases warming in Europe caused
by the anthropogenic greenhouse effect, a process which is already
embedded in the present generation of coupled ocean atmosphere
models (AOGCMs).
Land biosphere
Currently, the global land biosphere acts as a net sink for CO2. Projected
climate change is likely to add CO2 to the atmosphere and to increase
the fraction of anthropogenic emissions that stay airborne, producing an
additional warming of 0.1 to 1.5°C, which is already included in the AR4
temperature range (1.1-6.4°C). However, additional releases of CO2 and
methane (CH4) are possible from permafrost, peat lands, wetlands, and
4
The model based threshold of global average warming for the onset a net loss of ice from
Greenland is in the range of 1.9 to 4.6°C above pre-industrial levels (IPCC AR4 WGI, Ch.
10.7.4.2).
5
The Antarctic ice sheet as whole contains sufficient ice to raise sea level by 57m (IPCC AR4
WGI, Ch. 4.1). The potential for ice loss for the East Antarctic Ice Sheet is not discussed here
due to scientific uncertainties although it is noted that some parts of the EAIS are presently
losing ice to the oceans (Shepherd and Wingham, 2007)
23
large stores of marine hydrates at high latitudes (IPCC AR4 WGII, Ch.
4.4.6, and 15.4.2). These feedbacks are generally expected to increase
with climate change. Some models indicate a risk that the land biosphere
turns into a net source of CO2 by the 2050s. In these models this is
mostly due to climate-driven decline of vegetation in South America and
the loss of soil carbon due to increased respiration. A number of models
also project an increase in biogenic methane emissions from wetlands
and permafrost associated with a warming climate. Methane is the
second most important contributor to the anthropogenic greenhouse
effect. Several studies indicate that a warming of 2°C would result in ca.
20% growth in methane emissions from wetlands (IPCC AR4 WGI, Ch.
7.4.1.2), and the emissions are likely to further increase at higher
temperatures. Furthermore, methane stored in the form of methane
hydrates on the seafloor and in permafrost soils could become
increasingly unstable with rising temperatures. Even though a
catastrophic, sudden release of large amounts of methane is considered
unlikely to happen on short to medium time scales, ongoing chronic
release of methane as a result of anthropogenic warming could result in
a substantial increase in its atmospheric concentration, thus further
amplifying climate change (IPCC AR4 WGI, Ch. 7.4.1.2).
24
• In order to have a 50% chance of keeping the global
mean temperature rise below 2°C relative to preindustrial levels, atmospheric GHG concentrations
must stabilise below 450ppm CO2 equivalence.
Stabilisation below 400ppm will increase the probability
to roughly 66% to 90%.
• Current atmospheric GHG concentrations and trends in
GHG emissions mean that these concentration levels
may be exceeded. The 2°C target can still be achieved if
this overshoot of concentrations is only temporary and
reversed quickly. Thus, to avoid a warming in excess of
2°C, global GHG emissions should peak by 2020 at the
latest and then be more than halved by 2050 relative to
1990.
25
Emission pathways
The implications of the EU 2°C target for future GHG emissions are
outlined here. If no action is taken to reduce GHG emissions, global
mean surface temperatures are projected to continue to increase, and
will rise by more than 2°C above pre-industrial levels as early as the
middle of this century. The IPCC AR4 indicates that, by the end of this
century, global temperatures may increase to 2.3°C (“likely” range
between 1.6°C and 3.4°C) for the lower and 4.5°C (2.9°C to 6.9°C) for
the higher non-mitigation emission scenarios (see Figure 3.1 below and
IPCC AR4 WGI, Tab.SPM3).
Fig 3.1: Projections of global mean surface temperatures for three
SRES non-mitigation scenarios as presented by IPCC AR4 and the
“Year 2000 constant concentration” experiment. Without mitigation of
emissions, the 2°C target (red dashed line) will be exceeded towards
the middle of the century. “Likely” ranges in average 2090-2099
warming for the six SRES marker scenarios are shown on the right.
Source: Adapted from IPCC AR4 WGI, SPM-5.
26
3.1 Concentration stabilisation levels for keeping
below 2°C
The complexity of the climate system does not allow the temperature
response to GHG emissions to be estimated with absolute certainty. The
IPCC AR4 provides temperature ranges associated with different GHG
stabilisation levels (expressed in CO2 equivalent - CO2eq). For example,
the IPCC estimates that doubling the atmospheric GHG concentration
relative to pre-industrial levels (i.e. to about 550ppm CO2eq), is likely 6 to
increase the global temperature by at least 2°C and up to 4.5°C above
pre-industrial temperatures. The best guess is that this doubling of
concentrations will cause a global temperature increase of 3°C. This
analysis also implies that, at a concentration of 550ppm, CO2eq the
probability of keeping the temperature increase below 2°C is 5-17% (see
Figure 3.2).
In order to meet the 2°C target with at least a 50% probability,
atmospheric CO2eq concentration would need to be stabilised at
approximately 440ppm or lower. Stabilisation at 400ppm CO2eq or lower
would raise the probability of keeping the temperature increase below
2°C to above 66% (see Figure 3.2).
6
In the IPCC AR4, “likely” implies a 66-90% chance of occurrencel.
27
Fig 3.2: The probability of exceeding a 2°C warming at various
stabilisation levels is shown. At stabilisation levels around 400ppm or
below, global mean temperatures are likely to stay below 2°C, and there
is a 50% probability of exceeding a 2°C temperature increase at levels
of around 450ppm CO2eq. The target is unlikely or very unlikely to be
achieved at stabilisation levels above approximately 500ppm CO2 eq.
This figure combines analyses of climate sensitivity reported in IPCC
AR4 WGI. The best estimate of climate sensitivity (the global
temperature increase at 550ppm) is 3°C and the “likely” range is
between 2 and 4.5°C. In addition, current (2005) CO2eq concentration
levels are indicated for GHGs only and the net combined
anthropogenic radiative forcing agents (top left, see text for further
explanation) (IPCC AR4 WGI Tab.2.12). Source: Adapted from IPCC
WGII Fig. 19.1.
28
3.2 How to achieve low GHG stabilisation levels:
Peaking of concentrations a medium-term necessity.
Current atmospheric GHG concentrations and emission trends indicate
that meeting the EU climate protection target is very challenging. The
current atmospheric concentrations of long-lived greenhouse gases i.e.
CO2, CH4, N2O and halocarbons, are equivalent to about 450ppm
CO2eq. However in addition to the warming effect of these GHGs, manmade aerosols have a cooling effect and black carbon a further warming
effect. Although these vary considerably by region, their net global effect,
together with the greenhouse gases, gives a warming effect equivalent to
a best-estimate of about 375ppm CO2eq (IPCC AR4 WGI, Tab.2.12)
(see Figure 3.2). Note that future aerosol emissions, and their regional
net cooling effects on the climate, are assumed to decrease with
increased effectiveness of air pollution control policies around the world.
Because of the inertia of the climate system, the equilibrium temperature
associated with higher GHG concentrations will not be reached if these
concentrations are reduced rapidly enough to a lower stabilisation level,
e.g. if the atmospheric GHG concentrations peak at 475 or 500ppm CO2
equivalence, and are then further reduced to a lower level (see Figure
3.3).
In order to ensure a high degree of probability of staying below 2°C,
urgent action is required to reduce global GHG emissions so that
atmospheric concentrations will peak in the near future and return to a
lower stabilisation level (see IPCC AR4 WGI, FAQ10.3).
29
Fig 3.3: Schematic overview of historic total CO2 emissions (grey),
concentrations (blue) and global mean temperatures (black/red) and
illustrative time-series for a future evolution highlighting the inertia of
the climate system and the different peaking years. If global emissions
peak in the near term, CO2eq concentrations could peak around the
middle of the century before approaching long-term stabilisation levels
consistent with a 2°C target. Owing to the inertia of the climate system,
the peak in concentrations is not necessarily reflected in the global
mean temperature 7 .
7
See Appendix 2 for the assumptions underlying this illustrative figure.
30
3.3 Global emissions have to peak by 2015-2020, and
to decline rapidly until 2050 and beyond
Translating the concentration requirements into emission pathways is
subject to considerable uncertainties, primarily due to uncertainties in the
carbon cycle. The IPCC WGIII analysed a large set of mitigation
scenarios available in the literature and categorised them according to
their maximum 21st century concentrations.
The analysed set of lower mitigation scenarios (category I, see Table
3.1) implies that GHG concentrations will have to peak at or below
500ppm CO2eq (3.14W/m2). This provides a 50% or better chance of
achieving the EU 2°C target, as long as the concentrations are further
reduced after they peak. According to IPCC WGIII, the emission profiles
for these scenarios require near-term infrastructure investments and
early decarbonisation of the energy system, with global GHG emissions
starting to decline before 2015 or 2020 (see Table 3.1 below). Scenarios
in which the GHG concentrations peak later would require larger annual
emissions reduction rates thereafter in order to keep within the 2°C limit.
Global emissions need to be reduced by at least 50% of 1990 levels by
2050 (i.e. from around 40 GtCO2eq/year to ca. 20 GtCO2eq/year). There
is, however, a considerable range within the IPCC scenario classes.
Future emission pathways that aim at (at least) halving global emissions
by 2050, as proposed in the Bali Action Plan, differ slightly depending on
which reference year is chosen. Depending on the reference year and
the emission pathway leading to the 2050 emission levels, the aim of
halving global emissions by 2050 reflects a 50% or better probability of
staying below 2°C (see Figure 3.4). For a current (2005) reference year,
emissions would have to be reduced by about 60% in order to comply
with a 50% reduction using a base year of 1990, since global emissions
increased by approximately 20% between 1990 and 2005.
31
Table 3.1 – Stabilisation scenario classes and their 21st century
characteristics adapted from IPCC AR4 WGIII, SPM 5 and Fig.3.18.
Emission scenarios within category I and the lower end of II are
consistent with a 2°C target, if the probabilities of staying below 2°C shall
be 50% or higher 8 .
Year in which
emissions
decrease below
2000 levels
Cumulative CO2
emissions 20002100
Change in
global
emissions in
2050 (% of
1990
emissions) 9
IPCC
Category
CO2 conc.
CO2eq conc.
Peaking year
for CO2
emissions
WGIII Source
SPM.5
SPM.5
SPM.5
Fig. 3.19
Fig.3.18
SPM.5
ppm
ppm
Year
Year
GtCO2
%
I
350-400
445-490
2000-2015
2000-2030
800-1500
-83.5 to -40
II
400-440
490-535
2000-2020
2000-2040
1000-1800
-56 to -23
8
Note that the CO2eq concentrations listed in Table 3.1 are not directly comparable to the
CO2eq stabilisation levels shown in Figure 3.2. Some of the scenarios envisaged stabilisation at
st
21 century maximum concentrations, not a peak and subsequent decline to lower CO2
stabilisation levels. Thus, the CO2eq concentrations levels were rather comparable to peak
concentrations levels with ultimate stabilisation levels only being determined by post-2050
emission levels.
9
Here the reference year is adjusted to 1990 in accordance with the Kyoto Protocol – taking into
account an approximate 10% increase of global GHG emissions from 1990 to 2000.
32
Fig 3.4: Global GHG emissions under non-mitigation and mitigation
scenarios. Shown in red are non-mitigation SRES scenarios. The blue
lines indicate two mitigation pathways as presented in the Stern
Review (Stern, 2006) and the European Commission (2007a)
communication – leading to peaking concentrations at roughly 500ppm
CO2eq concentrations and a subsequent 450ppm CO2eq stabilisation.
The long-term goals for halving emissions by 2050, as agreed for
serious consideration by G8 in Heiligendamm in 2007, are indicated by
the yellow stars with reference years being 1990 (bottom), 2000
(middle) or 2007 emission levels (top star) 10 . The shaded bands denote
series of different emission pathways ultimately stabilising at 450ppm
CO2eq (orange) and 400ppm CO2eq (green) – with the latter being likely
to stay below 2°C 11 . For comparison, global emissions according to the
EDGAR database (as in IPCC AR4 WGIII, Fig. SPM.1) are shown for the
years 1990, 2000, and 2004 (red circles). Note that current fossil CO2
emission estimates are estimated as being at the upper end of the
SRES range, with additional differences to the EDGAR data points
stemming from different land use-related emission estimates 12 .
10
Reference emission levels for Kyoto-basket greenhouse gas emissions are here derived from
the median across all IPCC SRES scenarios. Actual emissions can differ and might be higher in
recent years.
11
The series of emission pathways were created using the EQW method (Meinshausen, 2006)
and the FAIR-SiMCaP method (den Elzen & Meinshausen, 2006) for the respective stabilisation
levels – using default carbon cycle settings and various assumptions in regard to the shape of
the emission pathway. Individual gas emissions for all scenarios are weighted by their
respective Global Warming Potentials as applied under the UNFCCC and the Kyoto Protocol.
12
See IPCC AR4 WGIII, page 4, footnote 9
33
3.4 From global to regional emission pathways
Emission pathways for different groups of countries are based on
assumptions of global effort sharing. There is usually an assumption that
emissions from developing countries will continue to grow, and that
developed countries implement emissions reductions that will provide
room for such growth and still result in an overall decrease in emissions.
To illustrate what this might mean, Figure 3.5 shows a global emission
pathway that halves global emissions by 50% by 2050. For simplicity and
illustrative purposes, equal per-capita emissions by 2050 are assumed,
which leads to an 85% emission reduction by 2050 in developed
countries’ emissions relative to 1990 levels. 13 . Emissions from
developing countries are then computed from the global and developed
country emission profiles. This shows that, for both sets of countries,
emissions need to stabilise and then be reduced in order to achieve the
2°C target (see Figure 3.5).
13
This assumes median population projections according to: Population Division of the
Department of Economic and Social Affairs of the United Nations Secretariat (UN, 2007).
34
Fig 3.5: Greenhouse gas emissions under an indicative emission
pathway that is consistent with meeting the 2°C target with a medium
likelihood. Global emissions (black line) are assumed to be halved by
2050. Developed country emissions are assumed to decrease by 30%
by 2020 and by 85% by 2050 relative to 1990. Developing country
emissions are assumed to increase up to 2020 with following
reductions determined by the prescribed global emission levels. The
2050 emission shares of developed and developing countries are
illustrative only and represent an assumption of equal per-capita
emissions by 2050. (Source: Adapted from UNDP, 2007)
35
36
• Deep reductions in GHG emissions are necessary in
order to limit the global mean temperature rise to 2°C
above pre-industrial temperatures.
• Deep emission reductions can be achieved by
employing a broad range of currently available
technologies and technologies that are expected to be
commercialised in coming decades.
• Deployment requires clear, consistent and effective
policies and incentives.
• Action needs to be taken very urgently as inertia in the
climate and socio-economic systems means that
mitigation actions and low-carbon investment decisions
are needed now in order to avoid lock in of carbonintensive technologies.
37
Mitigation Options
The IPCC AR4, the Stern Review and the IEA Energy Technology
Perspectives (IEA, 2008) have highlighted the urgent need for deep cuts
in greenhouse gas emissions in order to stabilise atmospheric
concentrations at a level that will avoid dangerous climate change.
Significant GHG abatement potential exists across countries and sectors;
the adoption of a broad portfolio of policies and technologies is required
to realise this potential. However, this requires clear policy signals.
Decisions on large investments in energy and transport infrastructure
over the next few years will have a long-term impact on global emissions
levels because of the long lifetimes of capital stock. The choice for our
future is not between growth and non-growth – it is between high-carbon
growth and low-carbon growth. A large shift in investment patterns is
needed as the technology choices we make will play an important role in
achieving the necessary deep cuts in GHG emissions.
In order to achieve the necessary deep cuts in GHG emissions, policies
are required to support the development and deployment of a range of
low-carbon and high-efficiency technologies on an urgent timescale.
Existing and soon-to-be-commercialised technology can provide feasible
mitigation options. The cost of some options is currently high; however it
is expected that costs will decrease with the scale of production,
experience and with investments in research, development and
demonstration (RD&D).
IPCC AR4 suggests that mitigation opportunities with net negative costs
have the potential to reduce emissions by around 6 GtCO2eq/yr in 2030
(for reference, emissions were 43 GtCO2eq/yr in 2000). Realising these
opportunities requires the removal of implementation and behavioural
barriers.
Changes in lifestyle and behaviour patterns can contribute to climate
change mitigation across all sectors. Management practices can also
have a positive role.
4.1 A broad portfolio is needed
A broad portfolio of technologies can be expected to play a role in
managing the risk of climate change. This is because of the scale of
reductions that are required, the large variation in national circumstances
and sectoral differences. The uncertainty about performance of individual
options needs to be included in this assessment as it is not possible to
identify ex ante winners and losers. Results from low stabilisation studies
in line with the 2°C target indicate that a broad portfolio of options is
38
needed and no one “silver bullet” or “quick fix” technology exists.
Technology options across a range of sectors are listed in Table 4.1.
Figure 4.1 gives an example of the options that could reduce global CO2
emissions in line with a medium likelihood of staying below the 2°C
target. On top of energy savings, fossil fuel switches (to natural gas),
renewable energy, increased nuclear power and carbon capture and
sequestration could be part of the mix. Non-CO2 GHGs need to be
reduced as well. Preliminary results of the EU’s ADAM project suggest
that the portfolios depend on the model and on the assumptions made
about the availability and costs of the various technologies. Clearly,
leaving some of the options out, for example, without CCS or with a
restricted supply of renewable energy (e.g. biomass), mitigation costs
would tend to be higher.
45
Energy savings
40
avoided emissions
35
Gt CO2
30
25
Fossil fuel switch
Renewable energies
20
Nuclear energy
15
Carbon sequestration
10
5
0
2000
Emission of reduction case
2010
2020
2030
2040
2050
Fig 4.1: An example portfolio of options needed for deep reductions of
fossil CO2 emissions. Source: IPTS, (Russ et al., 2007)
Key technologies and options include various renewable technologies,
supply and end-use efficiency, CCS, including biomass in combination
with CCS, hydrogen fuel cells and advanced biofuels. In addition, the
assumed development of afforestation and deforestation varies between
the various studies. Stopping (net) deforestation is assumed in some
studies whereas others indicate that increased (forest) sink enhancement
can be part of a cost-effective portfolio to meet stabilisation targets.
39
Sector
Table 4.1: Key mitigation technologies and practices by sector (Source:
IPCC WGIII)
Key mitigation technologies and
Key mitigation technologies and practices
practices projected to be commercialised
currently commercially available
before 2030
Energy supply
Improved supply and distribution efficiency; fuel
switching from coal to gas; nuclear power;
renewable heat and power (hydropower, solar,
wind, geothermal and bioenergy); combined heat
and power; early applications of Carbon Capture
and Storage (CCS, e.g. storage of removed CO2
from natural gas).
CCS for gas, biomass and coal-fired electricity
generating facilities; advanced nuclear power;
advanced renewable energy, including tidal
and waves energy, concentrating solar and
solar PV.
Transport
More fuel efficient vehicles; hybrid vehicles;
cleaner diesel vehicles; biofuels; modal shifts from
road transport to rail and public transport systems;
non-motorised transport (cycling, walking); landuse and transport planning.
Second generation biofuels; higher efficiency
aircraft; advanced electric and hybrid vehicles
with more powerful and reliable batteries.
Buildings
Efficient lighting and daylighting; more efficient
electrical appliances and heating and cooling
devices; improved cook stoves, improved
insulation; passive and active solar design for
heating and cooling; alternative refrigeration fluids,
recovery and recycle of fluorinated gases.
Integrated design of commercial buildings
including technologies such as intelligent
meters that provide feedback and control; solar
PV integrated in buildings.
Industry
More efficient end-use electrical equipment; heat
and power recovery; material recycling and
substitution; control of non-CO2 gas emissions;
and a wide array of process-specific technologies.
Advanced energy efficiency; CCS for cement,
ammonia, and iron manufacture; inert
electrodes for aluminium manufacture.
Agriculture
Improved crop and grazing land management to
increase soil carbon storage; restoration of
cultivated peaty soils and degraded lands;
improved rice cultivation techniques and livestock
and manure management to reduce CH4
emissions; improved nitrogen fertiliser application
techniques to reduce N2O emissions; dedicated
energy crops to replace fossil fuel use; improved
energy efficiency.
Improvements of crop yields.
Forestry/forests
Afforestation; reforestation; forest management;
reduced deforestation; harvested wood product
management; use of forestry products for
bioenergy to replace fossil fuel use.
Tree species improvement to increase
biomass productivity and carbon
sequestration. Improved remote sensing
technologies for analysis of vegetation/ soil
carbon sequestration potential and mapping
land use change.
Waste
management
Landfill methane recovery; waste incineration with
energy recovery; composting of organic waste;
controlled waste water treatment; recycling and
waste minimisation.
Biocovers and biofilters to optimise CH4
oxidation.
40
4.2 The long-term impact of near-term decisions
Investment decisions on energy and transport that will be taken over the
next few years will have a huge long-term impact on emissions pathways
– poor decisions could lock the energy system into a fuel mix and
emissions trajectory that may be difficult and costly to change.
However, new energy infrastructure investments in developing countries,
capital turnover and upgrades to existing energy infrastructure in
industrialised countries create opportunities to achieve significant GHG
emission reductions compared to baseline scenarios.
The IPCC AR4 WGIII estimates that a large shift in investment patterns
in energy infrastructure will be needed by 2030 to achieve a sustainable
emissions pathway. The net additional investment required ranges from
negligible to 5-10% (of 20 trillion US$).
4.3 Investment, cost and RD&D
The pace and cost of any response to climate change depends critically
on the cost, performance and availability of technologies that can lower
future GHG emissions. Currently, many low-carbon technologies are
costly in comparison with the fossil-fuel alternatives. However,
technological costs fall with increased production, scale of use and
experience.
Investments in and world-wide deployment of low-GHG emission
technologies as well as technology improvements through public and
private RD&D are required to achieve stabilisation targets as well as cost
reduction. The lower the stabilisation levels, the greater is the need for
more efficient RD&D efforts and investment in new technologies during
the next few decades. This requires that barriers to development,
deployment and diffusion of technologies are effectively addressed.
Policy frameworks that set the right incentives and remove other barriers
(e.g. market structure, institutional framework, subsidies) as well as
focussed R&D programmes are essential to overcome the technical and
cost barriers facing many new energy technologies.
41
Box 4.1 Legislative Action in the EU
The European contribution to the global effort required
to achieve the 2°C target and to avoid dangerous
climate change is the climate change and energy
package adopted by the European Commission on
10th January 2007 and endorsed by the European
Heads of State and Government (European Council)
on 8-9th March 2007.
The European Council endorsed the following
elements: Developed countries reduce their GHG
emissions by 30% GHG by 2020, compared to 1990
levels, as part of a comprehensive global agreement;
Until a global post-2012 agreement is concluded, EU
decided on a firm independent commitment to achieve
at least a 20% reduction of GHG emissions by 2020
compared to 1990. By 2050 global GHG emissions
must be reduced by at least 50% compared to 1990,
which means reductions in developed countries of 6080% compared to 1990 levels.
Detailed legislative proposals have been adopted by
the European Commission on 23rd January 2008
which were welcomed by the Environment Council on
3rd March 2008. Agreement and adoption of these
proposals as a coherent package is foreseen within
the current legislative term, at the latest early in 2009.
For further information, see:
http://ec.europa.eu/environment/climat/future_action.htm
42
• The costs of climate change impacts are directly related
to their magnitude which increases with global
temperature and may be between 5 and 20% of GDP or
even higher in the long-term.
• The costs of actions to mitigate climate change are
small when compared to the relative costs of impacts
due to inaction.
• Some of the costs of impacts can be reduced through
investment in adaptation.
• According to recent studies, mitigation needed to meet
the 2°C target is projected to cost at most 2.5% of
global GDP in 2050 (reducing annual growth by at most
0.05%/year) if policies are designed in a cost-effective
way. These costs are reduced significantly when cobenefits (i.e. reduction in air pollution health damage,
air pollution control costs and energy security) are
included.
• Such mitigation, via a portfolio of co-ordinated policies
including a long-term carbon price and the recycling of
tax/auction
revenues
to
promote
low-carbon
technologies and to improve market efficiencies, could
even lead to global GDP gains (above those due to
avoided climate impacts).
43
Economics of Climate Change
5.1 Analytical approaches
Standard cost benefit analysis attempts to provide an assessment of the
costs of mitigating greenhouse gases and of the benefits that result from
reducing climate change. However, the widespread environmental, social
and economic impacts of climate change, especially those that are
irreversible, cannot be fully included in standard cost benefit analysis
(IPCC AR4 WGIII]. Therefore more appropriate analytical methodologies
are required.
The EU climate objective is based on a broader risk assessment and
avoidance of large-scale irreversible climate impacts. This integrated
approach, which provides an alternative to cost-benefit analysis, is
considered to provide a more suitable basis for decision-making on
climate change issues.
The Stern Report has also identified methodologies that take account of
the long time horizons that are typical for climate change. They also take
account of equity issues by differentiating the economic impacts in
relation to different levels of regional development.
5.2 Adaptation lowers costs of climate change
Adaptation can decrease costs substantially (IPCC AR4 WGII). For
example, the PESETA project (Projection of Economic impacts of climate
change in Sectors of the European Union based on bottom-up
analysis) 14 estimated that effective adaptation could reduce the total cost
of the impacts of sea-level rise on the EU by approximately 65% in 2020
and up to 83% by 2080. These estimates include the costs of adaptation
investments.
5.3 Mitigation costs
Mitigation costs have been assessed using bottom-up and top-down
modelling. Bottom-up models estimate mitigation potential based on
detailed sector-by-sector analysis of economically accessible technology
options and behavioural responses. The top-down models are macroeconomic models that consider the economy-wide potential of mitigation
options.
The IPCC AR4 indicates that these approaches provide similar estimates
of aggregate mitigation potentials based on carbon price levels.
14
See http://peseta.jrc.ec.europa.eu/ for further information.
44
However, the sector-based estimates show substantial cost differences
between sectors.
Bottom-up models suggest that mitigation potential can be achieved at
no cost or net benefits/saving in many sectors. This “no regret” potential
amounts to 6 GtCO2eq per year by 2030, or roughly 10% of nonmitigation baseline emissions. However, investment or removal of
barriers (e.g. through policy measures) is required to achieve these
savings.
The IPCC AR4 analysis suggests that mitigation pathways consistent
with stabilisation of atmospheric GHG levels at 550ppm CO2eq, can be
achieved with carbon prices up to 40 €/tCO2 by 2030. Trajectories
consistent with a 450ppm CO2eq stabilisation level will require higher
carbon prices, up to 80 €/tCO2eq by 2030. In order to put these carbon
prices in perspective of the recent rise in oil prices, Table 5.1 highlights
the implied increments on energy prices.
Table 5.1: How does a carbon price of €30, €50 or €80 per tonne of
carbon dioxide affect energy prices? The table indicates the direct
price effect for different fossil fuel energy carriers, for a range of
carbon prices.
Marginal increase of energy price
Electricity
Carbon price
Crude Oil
€30/tCO2eq
+€15/barrel
€50/tCO2eq
+€25/barrel
€80/tCO2eq
+€40/barrel
Gasoline
+€0.07/litre
(+€0.30/gallon)
+€0.12/litre
(+€0.50/gallon)
+€0.19/litre
(+€0.80/gallon)
From coal fired plant
From gas fired plant
+€0.03/kWh
+€0.009/kWh
+€0.05/kWh
+€0.015/kWh
+€0.08/kWh
+€0.024/kWh
15
Adapted from IPCC WGIII Outreach Presentation . Note: No indirect price effects due to
change in demand are considered.
IPCC analysis (AR4 WGIII SPM) indicates that achievement of emission
scenarios consistent with the EU 2°C target are projected to reduce
global GDP by 3% at most by 2030 and by 5.5% at most by 2050,
compared to current growth projections. This high-cost estimate is based
on a single study with relatively high baseline emissions that misses
options to reduce emissions in the transport sector. On the other hand,
recent, provisional results by EU’s ADAM research project 16 indicate that
15
16
Available at www.mnp.nl/ipcc/pages_media/FAR4docs/ IPCC_WGIII_basicpresentation.ppt
See www.adamproject.eu for more information
45
stabilising levels at 450ppm CO2eq would reduce global GDP by 2.0 to
2.2% in 2050 (see Table 5.2, row 1). This implies reductions in annual
GDP growth rates of around 0.05%. The exact costs would depend on a
number of issues: the extent to which optimal policies are implemented,
the availability of technology options and the impact of induced
technological change, how revenues from taxes and/or CO2 permits are
recycled, assumptions on afforestation and deforestation and the full
(life-cycle) impacts of (increased) biomass use. A portfolio of coordinated policies including a long-term carbon price, and the recycling of
tax/auction revenues to promote low-carbon technologies and to improve
market efficiencies, could potentially lead to global GDP gains. Detailed
energy models (POLES and TIMER) indicate that the mitigation costs of
meeting a 450ppm CO2eq target would be around 0.2 to 0.8% of global
GDP in 2050. A broad portfolio of options (including energy efficiency
improvements, renewables (i.e. biomass) and CCS) will need to be
employed to limit the costs.
Table 5.2: Costs of stabilising greenhouse gas concentrations 17
Stabilisation
levels (ppm
CO2eq)
Median GDP reduction
Range of GDP reduction
Reduction of average
growth rates
2030
2050
2030
2050
2030
2050
450 (ADAM)
not available.
2.1
0.7 to 1.7
2.0 to 2.2
not
available
<0.05
445-535 (AR4)
not
available 18 .
not
available
<3.
<5.5
<0.12
0.12
535-590 (AR4)
0.6
1.3
0.2 to 2.5
slightly negative
to-4
<0.1
<0.1
590-710 (AR4)
0.2
0.5
-0.6 to 1.2
-1 to 2
<0.06
<0.05
Source: IPCC AR4 SPM and ADAM project (preliminary results E3MG, MERGE and REMIND)
The European Commission analysis estimates higher mitigation costs for
2030, i.e. equivalent to a reduction of global GDP by 4.6 % (or a
reduction in annual GDP growth rate by 0.19%), implying that global
GDP in 2030 would only be 196% and not 201% of that in 1990. This is
linked to an assumption of a more restrictive global carbon market and
the absence of a well functioning carbon market before 2012. A gradual
development of the carbon market is foreseen to occur only thereafter.
17
It should be noted that all of the above analysis assumed projections of fossil fuel prices
which are much lower than the current level.
18
Although IPCC did not provide a median value, the wide range of estimates is shown in Fig.
3.25 in Chapter 3 of IPCC AR4 WGIII.
46
The Stern Review indicates a lower cost, of about 1% of GDP by 2050
for trajectories consistent with a 500-550ppm CO2eq. The cost estimates
from sectoral analysis range from -1.5% (i.e. net gains) to 3.5% of GDP
for different scenarios. These are sensitive to assumptions on technology
development and the costs of fossil fuels (Stern, Table 9.3). IIASA
estimates suggest global GDP losses of less than 0.5 to 4% in 2100 to
stabilise CO2eq. concentrations at around 450ppm CO2eq (Riahi et al.,
2007).
The Stern Review also estimates that inaction on mitigation will result in
costs equivalent to losing at least 5% of global GDP in 2200, not
including wider market and non-market impacts. This could rise to 20%
of GDP or more, if non-market impacts are included.
Effective mitigation requires a significant shift in investment decisions
towards mitigation technologies. The European Commission estimates
that approximately 0.5% of annual global GDP will need to be invested in
or re-directed towards mitigation measures up to 2030.The Stern Review
suggests that this gross investment should be of the order of 1% of GDP
by 2050.
5.4 Co-benefits
Co-benefits are the ancillary benefits that occur when measures to
mitigate GHG emissions are undertaken. Co-benefits are mostly not
included in modelling exercises to determine the GHG mitigation costs.
Co-benefits include reduced air pollution impacts and decreased
dependency on energy imports.
The IPCC AR4 WGIII concluded that health co-benefits can be
substantial and that these may offset a significant fraction of mitigation
costs. Other co-benefits include increased energy security and reduced
damage to agriculture, materials and ecosystems from improved air
quality and related deposition of nutrifying and acidifying compounds.
Co-benefits depend substantially on the source sector and region in
which the mitigation option is implemented and the technology used. For
example, the replacement of low-quality biomass energy by modern
renewable energy for cooking and heating in developing countries has a
particularly high potential to cut both greenhouse gas emissions and
adverse health effects from pollution. Improving energy efficiency also
results in particularly high co-benefits.
The European Commission’s impact assessment for the Climate and
Energy Package indicated that reducing GHG emissions by 20% in 2020
reduces sulphur dioxide, nitrogen oxides and PM2.5 emissions by 10 to
15% compared to baseline emissions in 2020. This would reduce air
pollution control costs by 8 to 11 billion €/year. That implies that around
10% of the costs for controlling GHG emissions would be saved by
reduced air pollution control costs. In addition, negative impacts on
47
human health (mortality) would be reduced. The reduction in health
damage costs (benefits) was estimated at 12 to 29 billion €. In addition,
damage to materials, crops and ecosystems would be reduced. Taken
together, reductions in air pollution costs and health damage costs in the
EU would offset up to 50 to 75% of the additional costs for controlling
GHGs.
In addition, the European Commission has also identified improved
energy security as a co-benefit. Reducing EU GHG emissions by 36% by
2030 would decrease oil and gas imports by 2030 by a fifth compared to
baseline. This would allow for investment in other areas including wider
investment in global sustainable development.
Lack of a secure or reliable energy supply is a major limiting factor for
economic growth in most newly industrialised countries. Mitigation
options such as renewable energy or energy efficiency therefore often
yield benefits for the economy and the environment.
48
49
50
Conclusions
Global warming of 2ºC above pre-industrial levels cannot be considered
safe. Considerable climate change impacts are already felt today and will
have to be faced in the future – even below 2°C. Beyond this level,
climate change impacts will increase substantially in scale and severity,
including threats to unique ecosystems, risks of multi-metre long-term
sea level rise, and both more frequent droughts and floods across the
globe. If no action is taken, we may exceed 2ºC already by the middle of
this century. To avoid this, global emissions need to peak before 20152020 and to be at least halved by 2050 relative to 1990 levels.
These emission reductions pose a huge challenge. However, the loss of
life, ecosystems and a planet as we know it, would weigh greater than
the efforts needed to reduce emissions. Even in monetary terms, the cost
of inaction is greater than the cost of action. Damage costs could be in
the range of between 5 and 20% of global GDP in the absence of action
on either mitigation or adaptation. On the other hand, avoiding most
damages by following low emission pathways is achievable – both with
existing technologies and enhanced innovation. Mitigation needed to
meet the 2°C target is projected to cost at most 2.5% of global GDP in
2050 (reducing annual growth by at most 0.05%/year), provided that the
right policies and incentives are put in place now. Co-benefits of
mitigation, such as reduced air pollution and energy security, would be
substantial.
In summary: Acting on climate change ambitiously and swiftly is the only
rational insurance strategy against the risks of irreversible climate
change damages. This is why the EU believes that the 2 ºC limit can and
should guide global efforts to address climate change.
51
Appendix 1 (References)
For more information on European climate policy, please consult
http://ec.europa.eu/environment/climat/future_action.htm
EEA (2004). Impacts of Europe's changing climate. EEA report 2/2004. Copenhagen,
EEA.http://reports.eea.europa.eu/climate_report_2_2004/en
den Elzen, M. G. J. and M. Meinshausen (2006). Multi-Gas Emission Pathways for
Meeting the EU 2°C Climate Target. Avoiding Dangerous Climate Change. J.
S. Schellnhuber, W. Cramer, N. Nakicenovic, T. M. L. Wigley and G. Yohe.
Cambridge, Cambridge University Press.
European Commission (2007a). Communication from the Commission to the Council,
the European Parliament, the European Economic and Social Committee and
the Committee of the Regions - Limiting global climate change to 2 degrees
Celsius - The way ahead for 2020 and beyond. Brussels, Belgium.http://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:52007DC0002:EN:NOT
European Commission (2007b). Adapting to climate change in Europe – options for
EU action {SEC(2007) 849}; Green Paper from the Commission to the
Council, the European Parliament, the European Economic and Social
Committee and the Committee of the Regions. Brussels, Belgium, EU
Comission.http://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:52007DC0354:EN:NOT
Hansen, J., M. Sato, R. Ruedy, P. Kharecha, A. Lacis, R. Miller, L. Nazarenko, K. Lo,
G. A. Schmidt, G. Russell, I. Aleinov, S. Bauer, E. Baum, B. Cairns, V.
Canuto, M. Chandler, Y. Cheng, A. Cohen, A. Del Genio, G. Faluvegi, E.
Fleming, A. Friend, T. Hall, C. Jackman, J. Jonas, M. Kelley, N. Y. Kiang, D.
Koch, G. Labow, J. Lerner, S. Menon, T. Novakov, V. Oinas, J. Perlwitz, J.
Perlwitz, D. Rind, A. Romanou, R. Schmunk, D. Shindell, P. Stone, S. Sun, D.
Streets, N. Tausnev, D. Thresher, N. Unger, M. Yao and S. Zhang (2007).
"Dangerous human-made interference with climate: a GISS modelE study."
Atmospheric Chemistry and Physics 7(9): 2287-2312.
IEA (2008). Energy Technology Perspectives 2008. Paris, International Energy
Agency.
IPCC SAR (1996a). Climate Change 1995: Economic and Social Dimensions of
Climate Change, Contribution of Working Group III to the Second Assessment
of the Intergovernmental Panel on Climate Change. Cambridge, UK,
Cambridge University Press.
IPCC SAR (1996b). Climate Change 1995: Impacts, Adaptations and Mitigation of
Climate Change: Scientific-Technical Analyses. Contribution of WGII to the
Second Assessment Report of the Intergovernmental Panel on Climate
Change. Cambridge, UK, Cambridge University Press.
IPCC SAR (1996c). Climate Change 1995: The Science of Climate Change.
Contribution of WGI to the Second Assessment Report of the
Intergovernmental Panel on Climate Change. Cambridge, UK, Cambridge
University Press.
IPCC TAR (2001a). Climate Change 2001: The Scientific Basis. Contribution of
Working Group I to the Third Assessment Report of the Intergovernmental
52
Panel on Climate Change. Cambridge, United Kingdom and New York, NY,
USA, Cambridge University Press.
IPCC TAR (2001b). Climate Change 2001: Impacts, Adaptation, and Vulnerability.
Cambridge, UK, Cambridge University Press.
IPCC TAR (2001c). Climate Change 2001: Mitigation: Contribution of Working Group
III to the third assessment report of the Intergovernmental Panel on Climate
Change. Cambridge, UK, Cambridge University Press.
IPCC TAR (2001d). Climate Change 2001: Synthesis Report. Cambridge, UK,
Cambridge University Press.
Lenton, T. M., H. Held, E. Kriegler, J. W. Hall, W. Lucht, S. Rahmstorf and H. J.
Schellnhuber (2008). "Tipping elements in the Earth's climate system."
Proceedings of the National Academy of Sciences of the United States of
America 105(6): 1786-1793.
Lindsay, R. W. and J. Zhang (2005). "Thinning Arctic Sea ice: Have we passed a
tipping point?" Bulletin of the American Meteorological Society 86(3): 325-326.
Meinshausen, M. (2006). What does a 2°C target mean for greenhouse gas
concentrations? - A brief analysis based on multi-gas emission pathways and
several climate sensitivity uncertainty estimates. Avoiding Dangerous Climate
Change. J. S. Schellnhuber, W. Cramer, N. Nakicenovic, T. M. L. Wigley and
G. Yohe. Cambridge, Cambridge University Press.
Rahmstorf, S. (2007). "A semi-empirical approach to projecting future sea-level rise."
Science 315(5810): 368-370.
Riahi, K., A. Gruebler and N. Nakicenovic (2007). "Scenarios of long-term socioeconomic and environmental development under climate stabilization."
Technological Forecasting and Social Change (Special Issue: Greenhouse
Gases - Integrated Assessment) 74(7): 887-935.
Russ, P., T. Wiesenthal, D. van Regemorter and J. C. Ciscar (2007). Global Climate
Policy Scenarios for 2030 and beyond – Analysis of Greenhouse Gas
Emission Reduction Pathway Scenarios with the POLES and GEM-E3
models.
Seville,
European
Commission
Joint
Research
Centre.ftp://ftp.jrc.es/pub/EURdoc/eur23032en.pdf
Schellnhuber, J. S., W. Cramer, N. Nakicenovic, T. M. L. Wigley and G. Yohe, Eds.
(2006). Avoiding Dangerous Climate Change. Cambridge, Cambridge
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Stern, N. (2006). The Economics of Climate Change - The Stern Review. Cambridge,
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53
Appendix 2
Assumptions underlying the illustrative Figure 3.3
The following section briefly highlights the assumptions, data sources
and models employed for deriving the illustrative Figure 3.3. Note that
this figure is intended to be an approximate illustration of the relative
points in time when peaking in emissions is followed by a peak in
concentration and stabilisation in temperatures. The absolute levels
shown are of very limited significance as this schematic diagram neither
takes into account any uncertainties, nor necessarily shows “bestestimate” evolutions. For transparency, the underlying assumptions are
listed here.
Emissions:
The “Kyoto-basket” GHG emissions represent the sum of all greenhouse
gases controlled under the Kyoto Protocol, weighted by their respective
1996 IPCC Global Warming Potential for 100 years in line with the
UNFCCC inventory guidelines. The historic CO2 emissions shown are
total emissions, i.e. the sum of fossil, industrial and land use CO2
inventories. Historic fossil CO2 emissions follow the CDIAC compendium
data by G. Marland, T. A. Boden, and R. J. Andres as available on
http://cdiac.ornl.gov/trends/emis/em_cont.htm. Historic land use CO2
emissions are taken from Houghton and Hackler, as available on CDIAC
at http://cdiac.ornl.gov/trends/landuse/houghton/houghton.html. Future
emissions until 2100 of greenhouse gases, tropospheric ozone
precursors and aerosols follow a harmonised version of an IMAGE
scenario (~500ppm CO2eq peaking / ~450ppm CO2eq stabilisation, see
van Vuuren et al., Climatic Change 81, 119 (2007)). Beyond 2100, CO2
emissions were linearly reduced to zero in 2400 and non-CO2 emissions
were kept constant.
Concentrations:
The CO2 equivalent concentrations express the net anthropogenic
forcing effect, as if the forcing was only caused by elevated CO2
concentrations. Historic concentrations for CO2, CH4, N2O and other
long-lived greenhouse gases are prescribed. Future concentrations are
modelled using emissions as an input for a simple atmospheric chemistry
and carbon cycle model (MAGICC) in line with the IPCC AR4.
Specifically, a medium range carbon cycle model was emulated (BernCC) in order to represent the medium range of the carbon cycle
intercomparison project C4MIP results (P. Friedlingstein et al., Journal of
Climate 19, 3337 (July, 2006)). The CO2 equivalent concentrations
represent the complete net anthropogenic forcing effect on the
atmosphere (including long-lived greenhouse gases, tropospheric ozone,
54
land use albedo, direct and indirect aerosol effects, black carbon on
snow, etc.) according to IPCC AR4 best estimates (see IPCC AR4 WGI,
Table 2.12). Note that the indirect aerosol effect (a forcing with
substantial uncertainty ranges) has been modelled based on SOx, black
carbon, organic carbon and nitrate emissions, matching the IPCC AR4
best estimate for the 2005 forcing (-0.7W/m2).
Temperature:
The temperature evolution is calculated using an updated version of the
simple climate model (MAGICC, see e.g. T.M.L. Wigley, S.C.B. Raper,
Science 293, 451 (Jul 20, 2001)). MAGICC has been used as a simple
climate model in the IPCC AR4 (see e.g. WGI Fig 10.26). The climate
model parameter settings were adjusted to emulate the UKMO-HadCM3
AOGCM, although the climate sensitivity has been reduced from 3.2°C to
3°C in order to represent the “best-estimate” IPCC value. Hence, the
temperature following this 500ppm CO2eq peaking and 450ppm CO2eq
stabilisation scenario is roughly stabilising at 2°C. With higher than 3°C
climate sensitivities, temperatures would exceed 2°C under this particular
illustrative emission scenario.
55