The core of the global warming problem: energy

Transcription

1 354 Int. J. Global Energy Issues, Vol. 23, No. 4, 2005 The core of the global warming problem: energy Eric Hu School of Engineering and Technology Deakin University, Geelong Vic Australia Fax: erichu@deakin.edu.au Abstract: From the thermodynamic point of view, the global warming problem is an energy balance problem. The heat (energy) accumulation in the earth and its atmosphere is the cause of the global warming. This accumulation is mainly due to the imbalance of (solar) energy reaching and the energy leaving the earth, caused by greenhouse effect in which the CO 2 and other greenhouse gases play a critical role; so that balance of the energy entering and leaving the earth should be the key to solve the problem. Currently in the battle of tackling the global warming, we mainly focus on the development of CO 2 -related measures, i.e., emission reduction, CO 2 sequestration, and CO 2 recycle technologies. It is right in technical aspect, because they are attempting thinner the CO 2 blanket around the earth. However, Energy that is the core of the problem has been overlooked, at least in management/policy aspect. This paper is proposing an Energy Credit i.e., the energy measure concept as an alternative to the CO 2 credit that is currently in place in the proposed emission trading scheme. The proposed energy credit concept has the advantages such as covering broad activities related to the global warming and not just direct emissions. Three examples are given in the paper to demonstrate the concept of the energy measure and its advantages over the CO 2 credit concept. Keywords: global warming; energy measure; CO 2 credit; emission trading. Reference to this paper should be made as follows: Hu, E. (2005) The core of the global warming problem: energy, Int. J. Global Energy Issues, Vol. 23, No. 4, pp Biographical notes: Dr. Eric Hu has been working in R&D of renewable energy, energy efficiency and energy system modelling areas for over 15 years in Australian universities. He has published over 100 papers in the related areas, especially on the topics of solar thermal refrigeration technologies, CO 2 reduction for coal-fired power stations and vehicle air conditioning system and emission control. 1 Introduction The Kyoto Protocol endorsed the free market approach to the greenhouse gas issue: the international emissions trading, i.e., countries are allowed to obtain credits toward their (CO 2 reduction) targets through project-based emission reductions/offsets in other countries. The CO 2 is proposed to be used directly as the currency in the trading, although its political (and technical) acceptance is still in doubt (Boom, 2001). Generally speaking, the so-called CO 2 credit states that if a company or a country wants to emit Copyright 2005 Inderscience Enterprises Ltd.

2 The core of the global warming problem: energy 355 extra CO 2, it needs to take some measures (e.g., planting trees or buying credit forest somewhere else in the world) to reduce or offset/absorb CO 2 emission somewhere else. From the thermodynamic point of view, the cause of global warming is the heat (energy) accumulation in the earth and its atmosphere. This accumulation is mainly due to the imbalance of (solar) energy reaching the earth (in the form of short wavelength thermal radiation) and the energy leaving the earth (in the form of long wavelength), which is caused by greenhouse effect in which the CO 2 and other greenhouse gases play a critical role. In other words, the global warming problem is an energy balance problem. In addition, the current direct CO 2 measure is not able to cover some human activities (e.g., road constructions) that may have contributed to the global warming (i.e., the unbalance of the energy) but did not emit CO 2 directly; so that an energy measure i.e., energy credit concept is proposed in this paper, which is basically to use energy rather than CO 2 as a measure in the emission trading between parties. The energy credit proposed in lay language is defined as follows: to emit extra CO 2 or to conduct any other activities contributing to global warming, you need send the energy out of the earth s atmosphere, which equals the energy trapped due to the extra CO 2 you emitted. 2 Advantages of adoption of energy credit concept The parties that do not agree the CO 2 credit idea have the argument that the CO 2 credits obtained especially by carbon sinks i.e., planting trees are temporary (it is not a real credit) and any benefit may be countered by reducing surface albedo (Betts, 2000). The carbon sink (forest) may become a CO 2 generator when the forest is matured or in case of bushfire. Technically, only CO 2 sequestration may be possible to gain genuine CO 2 credits. There is even argument that the CO 2 level/concentration increasing in the atmosphere has a positive effect on the life on the earth because CO 2 is the food for plants. The global warming ultimately is an energy (balance) problem. The greenhouse gases or CO 2 play an important role in it. Thus, using energy as the currency directly in the emission trading is more reasonable. The concept of energy credits can be defined as the credit to offset the extra energy trapped/absorbed in the earth (and its atmosphere) due to the extra man-made (anthropogenic) emission (or other activities) by a country or company. The energy credit can only obtained through the anthropogenic process or activities. In other words, any country or company that wants to emit additional greenhouse gas or to conduct any other activities which would trap an extra amount of (solar) energy in the earth, needs to get the same amount of energy which would be otherwise trapped in the earth naturally, out of the earth by some means. The energy measure is thought to have the following advantages: Energy credit concept is able to measure and guide other human activities which contribute to increasing radiative forcing (and thus contributing to global warming). Some human activities like big construction projects and agricultures which are not emitting CO 2 directly but do have some effects on the energy balance on earth by decreasing the earth s surface albedo should be treated as emissions. These activities may not be a concern now, but may be a problem in future when we are facing more direct and serious results of global warming.

3 356 E. Hu It is thermodynamically correct. From thermodynamic point of view, CO 2 is not the core of the problem but energy is. Only energy-focused measures (e.g., energy credit) is capable of ultimately limiting (or even solving) the problem. As long as we keep consuming (at current rate if not more) the fossil energy, the CO 2 -focused measure is not a real solution to the global warming problem. How can you compensate the CO 2 released from the fossils that are the result of carbon sink over million years, with any CO 2 mitigation/sink measures in our lifetime? It will neither limit nor retard the development in all countries. Rather, all countries are allowed to develop their carbon-based industry as long as they get sufficient energy credits. In most of cases, direct reduction/limiting of CO 2 emission would retard the development, so that it is not easily accepted politically. The USA and Australia are still not willing to sign the Kyoto Treaty is an evidence. The energy credit concept avoids the reduction or limitation of CO 2 emission directly, but instead provides a compensating way, i.e., releasing extra energy that is the core of the problem, out of earth. It should be easier to obtain the political acceptance, at least theoretically. It provides us a new angle to reassess the real CO 2 benefit of some of the technologies we may be promoting, e.g., some renewable energy projects. The technologies and measures to gain energy credits may include anthropogenic change/increase of the albedo of local earth surface, shading the earth from outer space and cloud control, etc. The feasibility especially the large scale feasibility of these ideas/technologies is beyond the scope of this paper. The following hypothetical examples do not promote any particular measure e.g., change local albedo, nor endorse its feasibility, but they demonstrate the possible practical application of the principle of Energy Credit and compare it with the CO 2 credit. 2.1 Example Question If Australia wants to increase its annual CO 2 emission by 5%, how much energy credit does it need? To gain these energy credits by installing man-made reflector in its central desert areas, how much land area is required? Compare the land requirement for forestation to absorb (sink) the 5% of CO 2? Solution Australia s annual CO 2 emission in mid 1990s is about 0.5 Gt = 114 Million of Metric Tons Carbon Equivalent (MMTCE). Five percent of this is Gt CO 2, (i.e., Australia wants to emit Gt more of CO 2 ). The correlation between the CO 2 concentration in the atmosphere and the energy absorbed can be calculated by the radiative force (at the tropospheric level) (Lupis, 1999): F = 5.35 ln(c/c 0 ) = 5.35 ln(1 + C/C 0 ) W/m 2 C 0 is the base concentration of CO 2 in atmosphere equivalent to ppmv (in 1997) which is in turn equivalent to Gt CO 2 in the atmosphere.

4 The core of the global warming problem: energy 357 If CO 2 concentration is doubled (i.e., C = C 0 ), then F = 3.7 W/m 2 earth surface. This rough estimation agrees with the calculation in (Myhre et al., 1998). Assume that Earth is a round ball, its surface area is about m 2. This means that doubling the CO 2 (i.e., another Gt CO 2 in the atmosphere) will be equivalent to extra heating at the rate of (3.7)( ) = W. Given that per Gt CO 2 in atmosphere would equivalently gain Earth W heat/gt CO 2. This is the energy credits needed to emit an extra Gt of CO 2. So that, in this example, Australia needs W energy credits to emit an additional 5% (= Gt) CO 2. To gain the energy credits by installation of reflector: Assuming 1 m 2 reflector (in central Australia) reflects 300 W/m 2 more solar radiation back to space than its natural red desert surface does and the reflector works effectively eight hours every 24 hours, that gives 1 m 2 reflector has 100 W energy credits (daily average). For Australia to emit 5% more CO 2, it needs to install m 2 reflector working under the above assumed conditions. If trying to absorb the 5% CO 2 by forestation: The production of a hectare ( m 2 ) pine plantation is about 22 m 3 wood (carbon) per year at density of 0.6 T/m 3. This means that every square meter plantation would be able to absorb Tones of CO 2 per year. Namely, to absorb Gt CO 2 needs to plant m 2 pine trees. The land use figures seem big in both cases, but plantation needs 30 times more land than installation of the reflector. If Australia wants to emit additional 5% every year, it needs to install these areas of reflector every year. This example shows that there are other (than plantation) measures existing when a party has to emit additional CO 2 due to the need of the development if the energy measure concept is adopted. 2.2 Example Question A company proposes to construct a road network across Australia. The total length of the road is 14,000 km and width of the road is about 12 m. Assume the road surface will be black colour with absorptivity of 0.9 to solar radiation while the natural land surface has the absorptivity of 0.6. When the road network was built, how much extra solar energy would be absorbed by the road network and this amount of energy trapped would equivalent to how much CO 2 emitted into atmosphere? If the company changed road surface colour to lighter one with the absorptivity of 0.3, how much energy credits could the company gain when the road network was in place? Solution To simplify the question, we assume the total (global) solar radiation on the road network is 1000W/m 2 for eight hours a day. Roads with black surface would then absorb (turn to infrared energy) X amount of additional solar radiation than natural land surface: X = = (14, )(12)(1, 000) W (daily average).

5 358 E. Hu This would equivalent to /( W heat/gt CO 2 ) = Gt CO 2 in the atmosphere in terms of the energy/heat absorption effect. It means if the network was in place, it was equivalent for the company to emit extra Gt CO 2 into the atmosphere. If the road surface was changed to lighter colour, it would gain the company the same amount of energy credits i.e., W or Gt CO 2. It means the light colour road network would gain the company an extra Gt CO 2 emission quota that is about 5% of Australia annual total CO 2 emission, which the company might want to sell to other parties in the emission trading market. In this example, CO 2 credit is not applicable. 2.3 Example Question A 200MW (peak capacity when sun shines at 800W/m 2 ) solar thermal power plant (that uses solar heat to generate electricity) is proposed to be constructed. To make the power plant running, it needs m 2 solar collector areas. Assess the global warming benefit of this plant Solution If the plant was built and worked, to make solar collector work efficiently, its surface should be as black as possible. Assuming the solar collector could absorb 30% more solar radiation (comparing with the bare land), it would then gain earth and atmosphere extra solar energy: m 2 800W/m 2 6 hours/24 hours 30% = 1181 MW (heat). From the Example 1, we know: 1 GT CO 2 in atmosphere would be equivalent to gain earth (and atmosphere) W heating capacity, so that 1181 MW extra heating gained by the collector array would be equivalent to emitting tones CO 2 into atmosphere. In fact, a 200 MW brown coal-fired power unit (in Victoria, Australia) which is not the most efficient coal-fired power station emits about the same amount of CO 2 per year. However, the solar plant only works during the (clear) day time (about six hours per 24 hours), the coal-fired plant runs round the clock. From this point of view, the solar plant emits equivalently the same amount of CO 2 for per unit of electricity generated as a brown coal-fired power station in the first four years. After four years, the equivalent emission from the solar plant becomes nil. So the CO 2 benefit of the solar plant has been deducted by 20%, if the life time of the plant is 20 years, from the nil CO 2 emission (from the plant) that might be thought originally. The above examples were highly hypothetical and had no consideration of any real and side effects. The accuracy of the figures used in the above examples may be arguable and needs to be further explored. The examples simply tried to show the energy measure/concept can be used as an alternative measure to CO 2 measures in emission trading and the assessment of new projects.

6 The core of the global warming problem: energy Conclusion The energy measure proposed is superior to the CO 2 measure (at least theoretically). It is not only able to cover/measure all direct CO 2 -related activities that can be covered by CO 2 measure, but it is also able to cover/measure other activities that may not directly emit CO 2. Although no intensive study on the energy concept has yet been done regarding its fairness and its possibility to succeed, the author believes the concept is able to play a role in the emission trading mechanism because of its wider application potential (than CO 2 only measure). The author is a strong supporter of the reduction of greenhouse gas emissions by all means. The concept of energy measure proposed in the paper is not an objection to the CO 2 -focused measure, but from an alternative angle to look at the global warming problem. Acknowledgment The author wants to thank Mr. Martin Dix at CSIRO Atmospheric Research, Aspendale, Victoria, Australia for his comment and contribution to the paper. References Betts, R. (2000) Offset of potential carbon sink from boreal forestation by decreases in surface albedo, Nature, Vol. 408, pp Boom, J.T. (2001) International emission trading under the Kyoto Protocol: credit trading, Energy Policy, Vol. 29, No. 8, pp Lupis, C. (1999) Greenhouse gases and the metallurgical process industry, Process Metallurgy and Material Processing Science, Vol. 30B, No. 5. Myhre, G., Highwood, E.J., Shine, K.P. and Stordal, F. (1998) New estimates of radiative forcing due to well mixed greenhouse gases, Geophys. Res. Lett., Vol. 25, pp