Annex A
COMMENT ON THE GLOBAL COMMONS INSTITUTE'S
CONTRACTION AND CONVERGENCE MODEL CC OPTIONS
SUMMARY
Amongst the emission reduction regimes requiring
all nations to set targets, Contraction and Convergence (C&C),
as promoted by the Global Commons Institute (GCI) (Meyer, 2000),
has become the most popularly discussed, both academically and
politically. The Tyndall Centre for Climate Change Research (North)
has assessed GCI's C&C model CCOptions as part of research
on the implications of C&C for UK aviation. This memorandum
sets out our assessment to date. We find the model helpful for
investigating the implications of C&C for economic sectors
and nations and recommend the model for policy use, particularly
for investigating the upper limits of national carbon dioxide
emissions under a C&C regime. These (generally contracting)
limits would need to be applied in any emissions trading system
consistent with C&C. The revised version of the model, incorporating
feedbacks from soil, vegetation and ocean, suggests that stabilisation
of global atmospheric carbon at 550ppmv will require the UK to
reduce emissions by nearer to 70% than the 60% target of the Energy
White Paper. We do note, however, that there is not yet consensus
on the size of these feedbacks.
INTRODUCTION
The GCI, with its "focus on the protection
of the global commons of the global climate system", has,
since 1996, encouraged awareness of the contraction and convergence
concept as the policy interpretation of their belief that every
adult on the planet has an equal right to emit greenhouse gases.
Contraction and convergence is an international
framework for sharing the arrest of global greenhouse gas emissions.
To reduce emissions, the world's nations would work together to
set and achieve an overall yearly emissions target—contraction.
Furthermore, nations converge towards equal per capita emissions
by a certain year—convergence. By simultaneously contracting
and converging, such a policy requires all nations to impose targets
from the outset (Cameron, 2003). Industrialised nations cannot
escape from the fact that they are the main emitters, and will
be required to make substantial cuts under any regime if the world
is to stabilise carbon dioxide concentrations at a level that
avoids global temperature increases of more than two degrees,
(IPCC, 2001). Although it can be argued that some countries should
be permitted to emit more than others, depending on their natural
resources or particular circumstances, the GCI fear that any allowance
made for such differences will further delay negotiations. As
stabilising the carbon dioxide concentration at 450-550[28]
ppmv demands a reduction strategy that is initiated as a matter
of urgency, the GCI consider that the simplicity of their idea
gives it an important practical appeal.
In light of the growing support for C&C,
the GCI have produced a spreadsheet model—CCOptions—to
facilitate the investigation of the impact of varying the contraction
year, the convergence year and the target carbon dioxide stabilisation
level. We have analysed the strengths and weaknesses of the CCOptions
model with the aim of both aiding future users assess the relevance
of CCOoptions to their particular research, and raising awareness
of its strengths and weaknesses.
STRENGTHS AND
WEAKNESSES OF
THE CCOPTIONS
MODEL
The analysis of the CCOptions model has highlighted
a number of key strengths and weaknesses. All of the workings
and calculations are visible within the Excel worksheet, enabling
the user to make modifications to the model and thereby offering
a welcome degree of flexibility. Whilst data used within the model
is taken from a reliable source, (the Carbon Dioxide Information
Analysis Centre—CDIAC), it is currently based on year 1999
figures. It would therefore be desirable and provide more realistic
results if the carbon dioxide and population data for 2003 were
included.
Within the model, the cumulative 110-year carbon
emissions value is inputted by the user, to enable the contraction
profile to be calculated. Its value is crucial to achieving a
desired stabilisation concentration level, and therefore choosing
a suitable value has, in the past, required some guidance. In
the original versions of the model, the version used in the early
stages of our own project, a range of cumulative 110-year carbon
values related to an atmospheric carbon dioxide concentration
of between 330 and 750 ppmv were provided for the user. The range
given was taken from data published in IPCC (1996). Our more recent
analysis of CCOptions shows that the GCI no longer consider that
such recommended values are appropriate, as their model now includes
the addition of a second, and probably more accurate, relationship
between the carbon dioxide concentration and carbon emissions
(based on the latest Hadley Centre data (Hadley, 2002)). The inclusion
of this data, which takes into account some additional feedback
mechanisms that were previously ignored when calculating appropriate
carbon dioxide stabilisation targets, encourages the user to choose
their own 110-year cumulative carbon emission value, depending
on whether or not they wish to meet the feedback or non-feedback
carbon dioxide concentration profile. However, it needs to be
noted that there is not yet widespread acceptance of the size
of the vegetation feedback in the Hadley work, and thus that there
is particular scientific uncertainty in this aspect of the model.
This uncertainty notwithstanding, according
to the Hadley model (Hadley, 2002), the quantity of cumulative
carbon dioxide emitted into the atmosphere that is likely to lead
to stabilisation at 550ppmv is likely to be nearer to 680 GTC
than the 870 to 990 GTC range published in IPCC (1996). The difference
between the results is primarily due to the use of the more sophisticated
carbon-cycle model to calculate the stabilisation concentration-emission
relationship. [29]Within
the latest version of the CCOptions model, the new relationship
between carbon emissions and carbon dioxide concentration established
by the Hadley Centre is used to calculate the contracted emissions.
The results show that a much lower cumulative carbon dioxide amount
can be released into the atmosphere if a stabilisation level of
550ppmv is to be achieved and if the feedback carbon dioxide profile
is the target.
Within this new version of CCOptions, the emphasis
has moved from ensuring that the user inputs a recommended 110-year
cumulative carbon value (as suggested by the IPCC), and instead
focuses on the concentration curves, encouraging the user to find
suitable cumulative carbon values, depending on the stabilisation
level required. The difference between the 110-year cumulative
emissions required within the new version of the model for a non-feedback
carbon dioxide concentration profile, and one that incorporates
the feedbacks is as much as 460GTC for a stabilisation level of
550ppmv. This has a significant effect on any calculations carried
out using CCOptions regarding the percentage cuts that individual
nations may have to meet if they are to achieve a given stabilisation
level.
It should be noted that in all cases, the actual
relationship between carbon dioxide concentrations and emissions
is far more complicated than is suggested in the CCOptions model,
which reproduces these relationships using simple regression formulae.
The CCOptions model is attempting to reproduce model data that
incorporates many more variables than are available within its
own structure. Equations within CCOptions are simply good estimates
of the sophisticated climate model data, and only suitable for
indicating the level of stabilisation required for particular
emission paths.
The CCOptions model is further limited by its
exclusion of any of the other greenhouse gases. Other simplifications
in the model include the treatment of deforestation and bunker
fuels which are both assumed to be world overheads; currently
no data on bunker fuels is provided within the model.
EXPERIMENTS WITH
CCOPTIONS
Having established the suitability of the model
for our own investigation of the aviation sector, the second research
phase produced a series of model runs, with differing carbon dioxide
stabilisation targets, to apportion global carbon emissions between
nations. One of these model runs replicated the RCEP's (RCEP,
2000), and subsequently the energy white paper's claim that the
UK would have to cut its emissions by 60% by 2050 to stabilise
carbon dioxide concentrations at 550ppmv. The 60% target was essentially
derived from an earlier version of CCOptions with the relationship
between the carbon dioxide concentration and global carbon emissions
based on the Met Office's 2D modelling data, incorporating only
basic carbon-cycle feedbacks.
More recently, we conducted model runs designed
to reach the 550ppmv stabilisation target, using the latest version
of CCOptions, which includes all the carbon-cycle feedback effects
mentioned in the previous section. Using similar parameters to
the original RCEP work, the results indicate a cut in carbon emission
of nearer to 70% will be required to stabilise emissions at 550ppmv.
This indicates that less than 50MtC will be available for all
sectors of the UK economy by 2050. If however, a stabilisation
level of 450ppmv were to be chosen, the cut in emissions would
need to increase to 84%, leaving just 25MtC for all of the sectors.
CONCLUSIONS
In short, CCOptions is a simple and useful tool
for policymakers investigating the upper national limits of an
emissions trading scheme, but it is a tool that needs to be used
with a knowledge of its workings and assumptions (as with all
models). Not only is it written using a familiar software package—Microsoft
Excel, but its results are presented in a plain and relatively
unambiguous manner allowing the user to make a quick evaluation
of their thought-experiments and scenarios, without involved data
manipulation. Experiments are easily set up and modified and the
model successfully predicts sensible emissions profiles for different
nations between today and 2200 based on a contraction and convergence
regime. The model generally avoids making over complicated assumptions,
but rather attempts to show the most basic apportionment of emissions
between nations, thereby minimising the need for policymakers
to go into more detailed, lengthy and possibly fruitless debates
in setting carbon emission targets. Discussion between researchers
at Tyndall (North) and the model designer is on-going and it is
likely that the model equations will continue to evolve as climate
science itself progresses.
28 Reaching 450 or 550ppmv requires there to be a
strict limit on the amount of carbon emissions released over the
next 100 years. The long life-time of carbon in the atmosphere
mean that any action taken today, will need to continue for at
least 100 years. Back
29
The atmospheric concentration of carbon dioxide depends not only
on the quantity of carbon dioxide emitted into the atmosphere
(natural and anthropogenic), but also on changes in land use and
the strength of carbon sinks, such as the ocean and biosphere.
As the atmospheric concentration of carbon dioxide increases (at
least within reasonable bounds), so there is a net increase in
the take-up of carbon dioxide from the atmosphere by vegetation
(carbon fertilisation). Changes in temperature and rainfall induced
by increased carbon dioxide affect the absorptive capacity of
natural sinks. Climate change alters the geographical distribution
of vegetation and hence its ability to store carbon dioxide. Changes
in ocean circulation and mixing brought on by climate change also
alter its ability to take up carbon dioxide from the atmosphere
and a warmer ocean absorbs less carbon dioxide. To incorporate
all of these feedbacks, the Hadley Centre used a simple climate
carbon-cycle model which includes the feedbacks from vegetation,
soils and the ocean (Cox, 2002). Back
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