AGCI Session II: Characterizing and Communicating Scientific Uncertainty
Session Chairs: Dr. Richard H. Moss and Dr. Stephen H. Schneider
July 31 to August 8, 1996
Emissions Mitigation and Atmospheric CO2
Jae Edmonds
Pacific Northwest National Laboratory
Washington, DC
Edmonds examined implications of alternative actions for atmospheric CO2 concentrations. He discussed a number of proposed strategies and how they relate to the goal of the Framework Convention on Climate Change (FCCC), which is to stabilize concentrations of greenhouse gases (GHGs). The analysis he presented is based on an integrated assessment model known as MiniCAM 2.0 that resides at Pacific Northwest National Laboratory and Tom Wigley's National Center for Atmospheric Research COMMIC models. The analysis is calibrated to the IPCC IS92a scenario except that the period between 1990 and 2010 has been recalibrated to the World Energy Outlook in order to include the events that have transpired since the development of IS92a, particularly in Eastern Europe and the former Soviet Union (which followed the most successful emissions reduction strategy to date: near economic collapse!).
The reason Annex
I has responsibility for taking the lead in mitigation is that these
are the nations which raised the level of atmospheric CO2,
bringing about the climate change problem to begin with.
Annex I refers to the industrialized countries, including those of Western Europe, the U. S., Canada, Japan, Australia, New Zealand, Eastern Europe, and the European part of the former Soviet Union. The rest of the world, essentially the developing countries, are non -Annex I. Three cases were examined by Edmonds: Annex I countries acting alone, Annex I joined by non-Annex I, and atmospheric stabilization by Annex I and non-Annex I countries. Edmonds likened the Annex I countries' non-binding agreement to aspire to the goal of returning CO2 emissions to 1990 levels by the year 2000 to "aspirational pole-vaulting," which differs from the real thing in that you don't actually have to go over the bar. The question is: will the Annex I nations be real pole-vaulters? He points out that the reason Annex I has responsibility for taking the lead in mitigation is that these are the nations which raised the level of atmospheric CO2, bringing about the climate change problem to begin with.
He began by discussing the following possible Annex I actions:
· 0 percent Reduction: stabilizing emissions at 1990 levels by the year 2050
· 5 percent Reduction: stabilizing emissions at 1990 levels by the year 2010 and making 5 percent further reduction thereafter
· 10 percent Reduction: stabilizing emissions at 1990 levels by the year 2010 and making 10 percent further reduction thereafter
· 15 percent and 20 percent Reduction: stabilizing emissions at 1990 levels by the year 2010 and making 15 percent and 20 percent further reduction thereafter
The basic finding is that if Annex I acts alone, the actions can have only modest affects on global CO2 concentrations. In the reference case, CO2 concentrations in the year 2100 would be 689 ppmv. With Annex I following the 0 percent reduction strategy defined above, the CO2 concentration would be 669 ppmv, and if they followed the aggressive 20 percent reduction strategy, the concentration would be 646 ppmv. The bottom line is that no matter which of the above strategies Annex I countries follow, if they act without non-Annex I, CO2 concentrations will still be rising in the year 2100 (see Figure 2.7).
The bottom line
is that no matter which of the strategies Annex I countries follow,
if they act without non-Annex I, CO2 concentrations will still be
rising in the year 2100.
Taking the above scenarios (see Figure 2.7) except that non-Annex I nations begin to reduce their emissions by 10 percent beginning in the year 2010, again we find that there is not a great effect on atmospheric CO2 concentrations and that we do not even come close to stabilizing emissions. So even if the Annex I actions defined above are supplemented by 10 percent non-Annex I reductions in these scenarios, findings estimate CO2 concentrations of 643 ppmv for the 0 percent reduction case and 621 ppmv for the 20 percent reduction case, and again, concentrations are still rising in the year 2100 (See Figure 2.8).
Even if the
Annex I actions defined above are supplemented by 10 percent
non-Annex I reductions in these scenarios, concentrations are still
rising in the year 2100.
Clearly, the strategies discussed thus far do not get us close to the stated goal of the FCCC, which is atmospheric CO2 stabilization. This begs the question, what would we have to do to achieve this goal?
The IPCC constructed 10 emissions trajectories which stabilized the atmospheric CO2 concentration. These were defined by 5 different CO2 concentration ceilings, 350, 450, 550, 650, and 750 ppmv, and two timing cases, a more rapid initial mitigation effort and a slower one. Modeling results for these 10 cases reveal that all of these emissions trajectories have three phases: first, increasing emissions, second, emissions stabilization, and third, long-term emissions phase out (see Figure 2.9). All IPCC emissions trajectories exhibit this characteristic pattern for ceilings of 450 ppmv or greater. It is also clear from the results that ceilings below 450 ppmv (close to today's level) require immediate emissions reductions. Immediate and continued reductions in emissions below 1990 levels can, in theory, achieve a ceiling of less than 500 ppmv. But is this the correct policy to pursue?
Edmonds says that by deciding on a policy of immediate and continued reductions, we would be ignoring what the optimum ceiling is. Instead, he says, we could decide what ceiling we wish to achieve and design a policy accordingly, thus working from the ceiling to the policy. However, no consensus yet exists regarding what is the right ceiling. Some argue that a prudent hedging strategy would not exceed a 400 ppmv ceiling until major uncertainties are resolved, thus keeping all options open. Edmonds believes this is an incorrect use of the analysis and could force society to more drastic and immediate action than might be called for. On the other hand, he acknowledges that once we pass a certain level of emissions, it is very difficult to go back; ceilings once reached then become floors.
Immediate and
continued reductions in emissions below 1990 levels can, in theory,
achieve a ceiling of less than 500 ppmv. But is this the correct
policy to pursue?
Edmonds then turned to what must be done and by what dates in order to meet the target ceilings specified in the analysis. The "deflection date" is defined as the year in which emissions are 0.3 PgC/yr or more below IS92a, in other words, the year by which we would have to be significantly departing from that emissions trajectory. For a 450 ppmv ceiling, the deflection date is 2008 and global emissions would peak in 2011 at 9.5 PgC. This would necessitate a major, immediate effort in terms of initiating the institutions and technologies required to achieve this goal, and this would be costly. Edmonds says that there is a great non-linearity between the costs at a ceiling of 450 ppmv and one of 550. With a 550 ppmv ceiling, the deflection date would be 2018, and global emissions would peak in 2031 at 11.2 PgC. He believes this presents a more reasonable approach in terms of getting the entire world on track.
Modeled costs come down dramatically from the 450 ppmv ceiling to the 550 ceiling for a number of reasons, Edmonds explains. There is a premature retirement of capital stock or use of capital stock in ways not originally intended. The model indicates that there is a "carbon cycle dividend" equal to 20 years of emissions at current rates that can be released. There is also the factor of discounting, in which future expenditures are not weighed as heavily as current expenditures. And finally, there is the cost of technology development. A 450 ppmv ceiling would force society to spend large sums developing new technologies rapidly, whereas the 550 ppmv ceiling would allow normal rates of technological development to take care of that, Edmonds says. Due to having less time to build institutions and develop technologies, it would cost four times as much to achieve the 450 ppmv ceiling than the 550 ceiling (nearly 4 trillion dollars compared to less than 1 trillion), model results suggest. An important assumption in the model is that there is total flexibility in where and when emissions reductions are achieved and that they are accomplished in the lowest cost ways possible. It would be far more costly if each country were forced to achieve emissions reductions on its own.
Due to having
less time to build institutions and develop technologies, it would
cost four times as much to achieve the 450 ppmv ceiling than the 550
ceiling (nearly 4 trillion dollars compared to less than 1 trillion),
model results suggest.
There was discussion about these issues, with Nakicenovic saying that in the International Institute for Applied Systems Analysis models, when a learning curve was built in with the up-front investment costs to begin development of new technologies now, results indicated that it was more cost-effective to begin emissions reduction sooner.
Regarding the equity issue, Munasinghe pointed out that there may be a problem with asking the developing countries to start reducing their emissions by 10 percent in the year 2010 when their current levels of emission per capita are still quite small compared to those of the Annex 1 countries.
MacCracken pointed out that if the whole expenditure required to address this problem is well under 1 percent of GDP, why is it generally presented as being such an expensive solution? Why, given the uncertainties and potential for large impacts, would society choose not to make this relatively small expenditure of resources? Others felt that what was required to make this happen was the global political will and an institutional framework.
An important
assumption in the model is that there is total flexibility in where
and when emissions reductions are achieved and that they are
accomplished in the lowest cost ways possible.