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
Technological Potential for Mitigation
Nebojsa Nakicenovic
International Institute for Applied Systems Analysis
Laxenburg, Austria
Mitigation options are discussed primarily in the Working Group II IPCC assessment, in the chapters that deal with the energy sector (including transport) and the other consuming sectors. It is important to recognize that the energy system involves more than just the energy sector. One typical energy chain goes from crude oil to gasoline and through the consuming sectors to the energy services provided (distance traveled, illumination, heat, etc.). There was a high degree of agreement among the authors of these chapters that one cannot look at the energy sector in isolation, but must instead look at the whole energy system and its major driving forces, namely higher quality of final energy and energy services delivered.
Currently, the world requires about 9 gigatonnes of primary energy, used at an overall efficiency of about 70 percent which leaves 6.4 gigatonnes of final energy delivered. The carbon flows from this part of the system are about 2.3 gigatonnes of carbon released in the conversion from fossil fuels to final energy, with an additional 3.7 gigatonnes released in the conversion from final energy to useful energy and energy services. The mitigation potential, from the technological point of view, involves structural change in the future as we go to cleaner and higher quality fuels, so the share of emissions from the energy sector is likely to increase; therefore the importance of mitigation in this sector may be amplified.
More efficient
conversion of fossil fuels is one of the greatest areas of mitigation
potential. About 30 percent efficiency gains are possible in the
short run, and up to 60 percent in the long run, at relatively low or
even zero cost.
Technical mitigation potentials were classified into the following groups:
1. More efficient conversion of fossil fuels
This one of the greatest areas of mitigation potential. About 30 percent efficiency gains are possible in the short run, and up to 60 percent in the long run, at relatively low or even zero cost, if one allows sufficient time for technological development. There was very broad consensus on this point.
2. Switch to lower carbon fuels
Typically, this involves a shift from coal to natural gas (a 40 percent lower carbon fuel which can also be more efficiently converted) which results in about a 50 percent mitigation. That there is large mitigation potential in this area was also a non -controversial point.
3. Decarbonization of fossil fuels
Technologies to remove CO2 from power plant flue gases include amine absorption, membrane separation, and centrifugal separation (which is very expensive and not yet feasible). Today, all of the decarbonization technologies are very costly, about $100 per ton of carbon removed. Taking carbon out of flue gases also reduces the efficiency of the power plant and raises the cost of electricity by approximately 50 percent. Also discussed were technologies for removing or reducing carbon from the fuels themselves. These include gasifying coal and steam reforming natural gas. These technologies are quite expensive, in the range of $200 to $400 per ton with current economics. And once carbon is separated it must be stored. One project in Norway involves injecting CO2 into underwater aquifers in the North Sea, which is cost effective given Norway's carbon tax. There are also projects which use CO2 for enhanced oil recovery or deposit it into depleted natural gas fields. One more controversial option is to deposit CO2 into the deep ocean; there are great concerns about the environmental impacts and costs of this. Sequestering carbon, particularly by biomass was also discussed by the group and there was agreement that it is probably better to use biomass to produce energy than to sequester carbon.
4. Switching to zero-carbon options such as nuclear and renewable sources
The general perception in the literature was that the costs of nuclear power can be expected to increase in time due to many problems. The conclusions was that, at least in the short term, the potential for mitigation from nuclear power is not very large. With regard to renewables, there was a very high variation of costs, in the $50-$500 range, making these sources very attractive in some parts of world and very expensive in others.
Today, all of
the decarbonization technologies are very costly, about $100 per ton
of carbon removed. Taking carbon out of flue gases also reduces the
efficiency of the power plant and raises the cost of electricity by
approximately 50 percent.
Energy Efficiency
The potential for increases in energy efficiency is enormous, since the current end use technologies are very inefficient, in the range of 10-20 percent efficiency. The main issues are the timing, cost development of new technologies, and consumers' behavior. A surprising result of the research was that Eastern Europe used to have higher energy efficiency due to structural components, such as more people traveling by bus and using large scale systems such as district heating. The shift from collective to individual transport, etc., has brought energy efficiency down.
Over what time scale could we expect a doubling of energy efficiency? Historical data of U. S. energy intensity reveals that it took about 70 years to double the energy efficiency of the economy. As far as carbon intensity, OECD economies evolved such that it took 40 to 50 years to halve carbon intensity. There is a learning curve; the more we emit, the better we know how to emit less, Nakicenovic says. We won't run out of potential; the question is how fast we can achieve part of the potential.
Flagging the carbon intensity of primary energy in several countries, France halved its carbon intensity from 1960 to 1990 through its increased reliance on nuclear power and Japan reduced its carbon intensity by using more methane. The rapidly growing, extremely carbon -intensive economies of the large developing countries, China and India, are cause for great concern. There was a consensus that a shift away from fossil fuels will not happen due to resource constraints. There is plenty of inexpensive fossil fuel. The shift must occur for other reasons.
A shift away
from fossil fuels will not happen due to resource constraints. There
is plenty of inexpensive fossil fuel. The shift must occur for other
reasons.
Renewables
There was a fair amount of controversy over the potential contribution of renewable energy sources, but it appears that renewables could contribute about half of the today's total global energy use by 2025, and in the long run, gigantic potential was identified. The issue is not so much absolute potentials but rather the transition times and dynamics. The large diversity in opinions made it impossible to state specifically which technologies offered what potentials to achieve carbon reductions. The best the group could do was come up with a statement that carbon emissions could be reduced by 2 gigatonnes per year by 2100 through the use of renewable energy.
Regarding the dynamics of the energy system, Nakicenovic points out that the entire system is very interrelated. For example, we need not only a process to produce hydrogen but also the whole system that supports it. In addition, the typical lifetimes of energy system components are in the range of 30-50 years. Thus, in the 50- to 100 -year time frame of this assessment, most of the energy system infrastructure would be replaced twice. This demonstrates that some mitigation would be achieved through natural technological evolution. If we want a much lower emission world, then stronger policies also come into play. For example, there is a strong relationship between a sustained increase in price and a decrease in energy intensity. Incidentally, the time frame for such structural changes, coming about by around 2050, is the same as the time frame predicted for major changes in the climate system.
A final point was that research, development and demonstration of new, lower-carbon technologies is needed. Though up-front costs will increase, this will offer long term benefits and diffusion potential. Immediate investments in research and development are needed if these technologies are to reach usefulness in 50 years.
The typical
lifetimes of energy system components are in the range of 30-50
years. Thus, in the 50- to 100 -year time frame of this assessment,
most of the energy system infrastructure would be replaced twice.