1. Introduction The “Kyoto Protocol” under which major industrial countries agreed to reduce their CO2 emissions by 5.2% against 1990 level from 2008 to 2012 (the first commitment period) was passed in December 1997 in Kyoto, Japan. The Protocol allowed these countries to use three types of market mechanisms —joint implementation (JI), clean development (CDM), and emissions trading (ET) — to fulfill their reduction commitments. As a result, quota-based carbon emission trading markets were developed rapidly in these countries, such as EU-ETS. Stern (2008) claimed that trading mechanism for quota-based carbon emission permits should be promoted post-Kyoto. However, the question is whether such a mechanism can ensure global climate protection effectively, efficiently and equally. To answer this question, scholars have carried out quantitative simulation on two aspects: carbon emission quotas allocation and the subsequent trading of carbon emission permits. In the field of carbon emission quotas allocation, Bohm and Larsen’s (1994) study showed that initial quota allocation by net per capita costs of emission reduction is beneficial for short-term equity. However, they also showed that initial quota allocation by the size of population is conducive to the formation of long-term equity. Janssen and Rothmans (1995) introduced calculations for future regional emission quotas by subtracting historical regional emissions from total regional emission quotas within a specified period, and examined the impact of different quota allocation schemes (e.g. population size, GNP and amount of energy usage on regional carbon emission quotas). Cramton and Kerr (2002) analyzed the auction of carbon emission rights, and suggested that auction-style quota allocation schemes are superior to grandfathering (allocating quotas based on historical output or emissions). However, these studies primarily focused on the comparison of different quota allocation principles from the point of view of equity, and lack examination of the impact of limitations on total emission quotas. Most scholars believe that as the first legally binding international emissions reduction agreement, Kyoto Protocol’s effectiveness has been limited(Malakoff, 1997; Najam, 1998). If this is the case then global emission reduction schemes must take into account the specific situation of developing countries, including historic responsibility for emissions, mitigation actions, and assistance provided to the most vulnerable countries or regions etc. (Rajan, 1997; Sagar and Kandlikar, 1997) Relative to the internationally renowned Stern (2008) scheme, Sørensen (2008) scheme, Copenhagen Accord, etc., Chinese scholars such as Ding et al.(2009), Jiang et al. (2009),Wang et al. (2012) also launched multifaceted studies on global carbon emission reduction schemes. In the field of trading carbon emission permits, Nordhaus (1977) pointed out that economically greenhouse gas emissions are externalities and that major solutions to the externalities of greenhouse gases include three key approaches: carbon taxes, carbon trading and emission standards. Zhang (1998) claimed that, with regards to the control of greenhouse gases, carbon trading is superior to carbon taxes, which are in turn better than emission standards. Recent studies of carbon trading models mainly use two types of modeling: computable general equilibrium (CGE) and agent based simulation (ABS). Manne and Rutherford (1994) used a five-region prospective model to analyze the impacts of carbon emissions limits on oil prices, carbon leakage, and carbon trading; Ellerman and Decaux (1998) analyzed CO2emissions trading under the Kyoto Protocol using marginal abatement curves derived from Emissions Prediction and Policy Analysis (EPPA, a CGE model developed by MIT); McKibbin et al. (2000) used a multi-region, multi-sector intertemporal general equilibrium model to analyze carbon trading and capital flows under the Kyoto Protocol; Szabo′et al. (2006) created a global cement industry dynamic simulation model (CEMSIM) to perform simulations on CO2 emissions trading within the EU and Annex B countries. Unfortunately, these dynamic computable general equilibrium trade models are all based on a common assumption that economic growth is always in a steady state of balanced growth. In reality, this steady state of balanced growth assumption is only valid in a single region or an area with no trading, and therefore, this assumption is problematic in multi-regional trade models (Springer, 1999). Compared to CGE, simulation studies using the ABS method are relatively rare. Mizuta and Yamagata (2001) established an international greenhouse gas emissions trading model under an auction mechanism; Chappin (2006) simulated the influence of CO2 trading in the EU on investments in Dutch electricity generation. Bakam and Matthews (2009) built a carbon trading system for agricultural department in Scotland. Based on the ABS method, these studies provide a dynamic market trading simulation mechanism in a complex economic and social environment, rather than relying on the assumption of balanced state used in traditional economic theories. To evaluate the effect of quota-based carbon emission permits trading mechanism globally, this article constructs a carbon trading model by using ABS modeling technology, and then develops a global carbon trading system, finally examining the capital flows of carbon trading and its impact on global climate protection. Considering that China and other developing countries have played an increasingly important role in the field of climate change, this article will focus more on these regions. Section 2 will detail the carbon-trading model and research method, Section 3 discusses the results of scenarios simulation and finally section 4 sets out the conclusions. 2. Model and method Focusing on quota-based carbon emission permit trading mechanisms and ABS modeling technology, this article establishes a global carbon emission trading model (CETM) that divides the world into six regions: China (CN), the US (US), the EU (EU), Japan (JP), the former Soviet Union (FSU), and rest of the world (ROW).The CETM is divided into two modules - carbon emission quotas allocation (CEQA) module and carbon emission permits trading (CEPT) module - based upon the reality that carbon emission quota allocation and carbon emission permit trading are the two key functions in a quota-based carbon emission permit trading mechanism. Firstly, the CEQA module computes the global and regional carbon emission quotas, and then the CEPT module simulates the capital flows of carbon emission permits trading and determines the equilibrium price of carbon emission permits. 2.1 CEQA module The goal of the CEQA module is to estimate the carbon emission quotas on both a global and a regional scale. Considering that there is no consensus criterion on global carbon emission quotas allocation, the CEQA module adapts two different methods to calculate the global and regional carbon emission quotas. They are the target control of atmospheric concentration of CO2 (TCACC) and the global carbon emission reduction scheme (GCERS). 2.1.1TCACC method The TCACC method assumes that the CO2 anthropic emissions consist of two major sources: fossil fuel emissions and land-use emissions. It also assumes that a part of the CO2 released into the atmosphere will be absorbed by marine and terrestrial ecosystems (Ding et al., 2009). In this case, given the atmospheric concentrations of CO2 for a target year, the global carbon emission quotas within a specified period can be calculated by the following equation. Q n D f D s *2.12 1 * n (1) where Q n is the n years of global carbon emission quotas; s and f are the initial year and target year, respectively; D s and D f are the atmospheric concentrations of CO2 in the initial year and target year, respectively; n is the number of years from the initial year to the target year; is the absorptivity of CO2 (i.e., the ratio of absorbed CO2 from one unit of CO2 emission by terrestrial and marine ecosystems); and is the annual emissions caused by land-use. According to Canadell et al. (2007), the average absorptivity of CO2 from 2000 to 2006 is 0.54. Here set 0.54 for . Research from The Carbon Dioxide Information Analysis Center (CDIAC) shows little change in CO2 emissions from land-use over the past 50 years, between 1.25-1.70GtC( gigaton carbon) per year (Houghton, 2008). Here set 1.5GtC per year for . The constant 2.12 in formula (1) is the conversion rate from 1ppmv atmospheric concentration of CO2 to the quantity of carbon (Ding et al., 2009). Taking no account of historical carbon emissions from the different regions, global carbon emission quotas can be allocated to each region according to a regional indicator. Depending on different quota allocation principles, the indicator can be GDP, population, carbon emissions etc. In this case, the n years of carbon emission quotas in region i ( Qin ) can be expressed as, xi * Q n Q xi n i (2) where xi is the indicator for region i . Because the n years of carbon emission quotas in region i ( Qin ) are equal to the sum of the annual carbon emission quotas from the initial year s to the target year f Q i ,t Qin (3) t[ s , f ] where Qi ,t is the carbon emission quotas for region i at year t , the subscript t is any year within n years. Assuming that the annual regional carbon emission quotas reductions are evenly distributed after the initial year s to the target year f , and the regional carbon emission quotas are equal to regional carbon emissions at the initial year s , then Qi ,t Ei , s di (t s ) (4) where Ei , s is the carbon emissions in region i at the initial year s , d i is the quantity of annual carbon emission quotas reduction in region i . According to equation (3) and (4), the carbon emission quotas in region i at year t ( Qi ,t ) can be expressed as Qi ,t Ei ,s t s * 2 Ei , s 2Qin / ( f s 1) f s (5) However, because of the large differences in development between developed and developing countries, historical carbon emissions must be considered when allocating the global carbon emission quotas to each region. After comparing and analyzing existing international allocation principles of global carbon emission quotas, Ding et al. (2009) and Wang et al. (2009) highlighted the quota allocation principle using the equal cumulative carbon emissions per capita, meaning that the regional cumulative carbon emissions per capita are equal within a certain period, best reflects the common but differentiated responsibilities and the standards of fairness and justice. In this case, use equation (6) to replace equation (2) cq n cqin ' ' t[ h , s ) Ei ,t popi ,t Q t[ s ,t ] i ,t popi ,t (6) ' where n is the number of years from the historical start year h to the target year ' f , cqin is the cumulative carbon emissions per capita in region i from the historical start year h to the target year f , popi ,t is the population in region i at year t (Population data are obtained fromhttp://databank.worldbank.org/). Here, cq n cqin indicates that the cumulative carbon emissions per capita in every ' ' region are equal. 2.1.2GCERS method Based on the global carbon emission reduction scheme, the GCERS method calculates every regional carbon emission quota according to the percentage of reduction in the target year relative to the reference year. From the point of view of modeling, the GCERS method is relatively easier than the TCACC. Assuming that the regional carbon emission quotas are allocated in each year according to a fixed annual reduction rate, then the carbon emission quotas in region i at year t , Qi ,t can be expressed as Qi ,t Ei , s f t * Ei , s 1 pi * Ei ,r t s 1 (7) where Ei ,r is the carbon emissions in region i at the reference year r , pi is the percentage of carbon emission reductionto the target year in region i . 2.2 CEPT module The CEPT module is responsible for simulating the trading behavior of carbon emission permits in each region. By comparing each regional carbon emission permits with its actual carbon emissions, it calculates each regional carbon emission permits deficit (or surplus) and determines the equilibrium price of carbon emission permits. Calculating the regional carbon emission permits and regional carbon emissions is the premise of the CEPT module. On the one hand, setting the regional carbon emission quotas calculated by the CEQA module as the regional carbon emission permits in the CEPT module. That means Ri ,t Qi ,t (8) where Ri ,t is the carbon emission permits in region i at time t . On the other hand, get regional carbon emissions by estimating regional reduction rates for carbon emissions. By using the abatement cost function proposed by Pizer (1999), the relationship between the regional reduction rate and marginal abatement cost is as follow. MACi ,t ai *bi * bi 1 i ,t *(1 ci *Tt 2 / 9) i ,t (9) where i ,t is the reduction rate of carbon emissions in region i at year t , MACi ,t is the marginal abatement cost of carbon emissions in region i at year t , ai and bi are parameters of the abatement cost function in region i , ci is the damage coefficient of temperature increase on the economies of region i , Tt is the increase of global average temperature since industrialization at time t , and i ,t is the carbon emissions intensity in region i at time t . Given the regional marginal abatement cost, the reduction rate of carbon emissions in region i at time t , i ,t can be expressed as follow. i ,t (b 1) i MACi ,t * i ,t *(1 ci *Tt 2 / 9) ai *bi (10) Then the carbon emissions in region i at time t , Ei ,t would be Ei ,t i ,t *Yi ,t * 1 ui ,t (11) where Yi ,t is the GDP in region i at time t . By subtracting the carbon emissions from the carbon emission permits, the volume of carbon emission trading in region i at time t , Ti ,t would be Ti ,t Ri ,t Ei ,t (12) For all regions, they have T i ,t 0 (13) i The CEPT module assumes that there is only one equilibrium price in carbon permits trading. That means the marginal abatement costs in all regions will be equal when the global carbon emission permits equal to the global carbon emissions. MACt Pt * (14) where Pt * is the equilibrium price of global carbon emission permits at time t . At this time, GDP will be adjusted by the following equation. Yi*,t Yi,t Ti ,t * Pt* (15) where Yi*,t is the GDP adjusted by carbon emission permits trading in region i at time t . It should be noted that this article focuses on the modeling of global carbon trading. The relationship among carbon emissions, economic system and climate system is mainly referenced from the LRICE model established by Wang et al. (2010). The integrated relationship between the CETM and LRICES model is shown in Figure 1. Insert figure 1 here 2.3Agent-based method The description above shows that the process for the CETM module involves an interaction between regions. To simulate this interaction effectively, this article adapts an agent-based modeling method. According to functions in the CETM module, it set three types of agents: a global agent, a regional agent, and an observer agent. The interaction and information transmission among the three types of agents are shown in Figure 2. Insert figure 2 here The global agent is the core of the CETM. It has four major functions: to allocate global carbon emission quotas among regions; to iteratively send supply information on global carbon emission permits to the regional agent; to receive feedback on demand information for carbon emission permits from the regional agent; to measure whether the supply and demand of global carbon emission permits is balanced; and search for an equilibrium price for global carbon emission permits. Each region in the CETM will be represented by an independent agent to participate in both the CEQA and CEPT module. Corresponding to regional divisions, the regional agents are divided into the CN agent, US agent, JP agent, EU agent, FSU agent, and ROW agent. They have three fundamental functions: to receive information on the result of quota allocation and the price of global carbon emission permits from the global agent; to make a rational economic decision based on the information received and regional economic development; and to send their decision on permit trading back to the global agent. Here, rational economic decision-making means that the action of trading permits always occurs when the regional marginal abatement cost is greater than the price of global carbon emission permits. Otherwise, the regional agent would prefer to reduce carbon emissions. The observer agent is in responsible for the statistical analysis of data, including economic indicators and trading information for the global and regional agents. In the process of the CETM modeling, the most crucial problem is how to find out the equilibrium price of global carbon emission permits. To solve this problem, this study developed a six step approach: (1) the global agent initializes the price of global carbon emission permits to zero; (2) according to the price of global carbon emission permits, each regional agent calculates its own reduction rate of carbon emissions; (3) according to the regional reduction rate of carbon emissions, each regional agent calculates its own carbon emissions; (4) the global agent adds up all of the regional carbon emissions to obtain global carbon emissions; (5) the global agent compares global carbon emission permits with the level of global carbon emissions, if they are equal, the current price of global carbon emission permits is the equilibrium price; (6) if the global carbon emission permits is less than the global carbon emission permits, the global agent slightly increases the price of global carbon emission permits; otherwise, slightly decreases the price, then returns to step (2). A flow chart for the above is shown in Figure 3. Insert figure 3 here 3. Simulation and discussion Based on the above CETM, this study developed a simulation system (CETS) on global carbon emission trading to compare and predict the effect of carbon emission trading on climate protection under different global carbon emission reduction schemes.To facilitate the study, this article uses the scenario analysis method. 3.1 Scenario set-up Three scenarios are set as follows: Scenario 0: The “business as usual” scenario. Assuming that there is no additional carbon emission reduction scheme for a region, this scenario provides a comparison baseline for other scenarios. Scenario 1: The “equal cumulative carbon emissions per capita” scenario. Considering the differences in historical cumulative carbon emissions among regions, this scenario uses the TCACC method and adapts the principle of equal cumulative carbon emissions per capita to allocate the global carbon emission quotas. According to Ding et al. (2009), this scenario sets 470 ppmv as the ceiling of the global atmospheric CO2 concentrations. To reflect the principle of the common but differentiated responsibilities proposed by the United Nations Framework Convention on Climate Change (UNFCCC), this scenario sets 1990 as the historical start year, 2010 as the initial year and 2050as the target year. It assumes that regional carbon emissions per capita converge by 2050 and remain at their 2050 level after 2050. Scenario 2: The “2°C target” scenario. Based on the GCERS method and the 2°C global carbon emission reduction scheme proposed by Wang et al. (2011), this scenario divides the course of global carbon emission reduction into three phases. In the first phase, from 2010 to 2020, regional carbon emissions are reduced according to the Copenhagen Accord(The reduction scheme of ROW in the first stage refers to CN). In the second phase, from 2021 to 2050, the carbon emissions in developed countries (US, EU, and JP) are reduced by 80 percent, compared to 1990 level. The carbon emissions in FSU are reduced by 50 percent, compared to 1990 level. The carbon emissions in CN and ROW are reduced by 28 percent and 20 percent respectively, compared to 2005 level. In the third phase, from 2051 to 2100, the carbon emissions in all regions remain at their 2050 level. Total emissions reduction will be implemented in CN and ROW at 2025, instead of intensity reduction before that year. It’s worth mentioning that CETM can evaluate global carbon emission trading for all kinds of carbon emission reduction scenarios. But considering that China has become the world’s largest carbon emitter, here this study focuses on two typical scenarios proposed by Chinese scholars as examples. 3.2 Analysis of carbon emission quotas allocation Based on the scenarios introduced in Section 3.1, the global and regional carbon emission quotas can be calculated by CETS, see table 1. Insert table 1 here Table 1 shows the global carbon emission quotas in scenario 0 are the largest both during 2010-2050 and during 2051-2100, followed by scenario 1 and scenario 2, and global carbon emission quotas during 2010-2100 in scenario 0 are 1275GtC, more than twice 619GtC in scenario 1 and 457GtC in scenario 2. In other words, scenario 1 or scenario 2 would greatly reduce global carbon emissions relative to scenario 0. Of course, CETM can arrive at other values for global carbon emission quotas by adjusting the control target of global atmospheric CO2 concentration under the TCACC method, for example, 450ppmv for 210GtC during 2010-2050, and by altering the regional carbon emission reduction scheme under the GCERS method, but to help in understanding global carbon emission quotas, this article only discusses those cases outlined in scenario 1 and scenario 2. From a regional point of view, table 1 shows the carbon emission quotas of CN and ROW during 2010-2050 in scenario 1 are larger than those in scenario 2, while the opposite happens with US, EU, JP and FSU. Obviously, scenario 1 favors China and other developing countries (most countries of ROW) more than the developed countries, when compared with scenario 2. It is important to note that quota deficits appear in scenario 1, where the carbon emission quotas of US during 2010-2050 are -10GtC. This suggests that the historical (1990-2009) carbon emissions of US have overdrawn on its future carbon emission quotas. In this case, the principle of equal cumulative carbon emissions per capita would face great difficulty in being accepted by most developed countries in international negotiations on carbon emission reduction. Actually, historical start year plays a critical role in the course of calculating regional carbon emission quotas. For example, if we move the historical start year, 1990 in scenario 1, backward to 1861, the carbon emission quotas of US during 2010-2050 would change from -10GtC to -68GtC. Similarly, we can also move the historical start year forward to 2010, and then we get 15GtC for the carbon emission quotas of the US during 2010-2050. Simulation result shows that the earlier the historical start year we set, more divergent regional carbon emission quotas between the developing countries and the developed countries are obtained. Considering the historical start year involves differentiated responsibilities of regional historical carbon emissions that will not be discussed further in this article. 3.3 Analysis of the trading of carbon emission permits As we know, to date, there is no unified global carbon trading market, so this article assumes global carbon emission permit trading will commence in 2025. To facilitate the simulation of that, this study allocates the regional carbon emission quotas during 2010-2100 to each year with a fixed reduction rate. From the point of view of global average temperature rise, see figure 4, scenario 0 results in a 2.99°C increase by 2100, which exceeds the “2°C threshold “ proposed by the IPCC (2007) by almost 1°C, while scenarios 1 and 2 result in a 2.17°C and 1.98°C increase by 2100, respectively. This coincides with the result of global carbon emission quotas allocation, in which the global carbon emission quotas in scenario 1arelarger than that in scenario 2.In other word, the less the global quotas are, the lower the global average temperature would be. Insert figure 4 here Due to the fact that there are no carbon emission limits in scenario 0, the following analysis on price, and volume of carbon emission trading will focus on scenario 1 and scenario 2. From the point of view of value (see figure 5),the trading prices of carbon emission in scenario 1 and scenario 2 increase from 84$/tC(the unit price of carbon, represent US dollar per ton of carbon, where $ is the constant US dollar in 2000) and 184$/tC by 2025 to 2490$/tC and 3307$/tC by 2100, respectively. There are two factors contributing to increases in trading price. From the perspective of supply, it makes sense that an increase in trading price follows a decrease in carbon emission quotas. Under the assumption of a fixed reduction rate of carbon emission quota in both scenario 1 and scenario 2,the carbon emission quotas would come down year on year, thus contributing to increases in trading price. From the demand perspective, it also makes sense that an increase in trading price follows an increase in demand (or perceived need) for greater carbon emissions. With future economic growth, demand for greater carbon emissions will increase, thus contributing to increases in trading price. Insert figure 5 here It should be noted that the trading prices for carbon emission in scenario 2 are higher than scenario 1. This is because global carbon emission quotas in the former are less than the latter. It should be note that the trading price of carbon emission by 2100 is quite high,2490$/tC in scenario 1 and 3307$/tC in scenario, requiring that new reduction technology, such as CCS, must be developed and disseminated to reduce the impact of carbon emission reduction on the global economy. Scenario 1 (figure 6) shows that for 2025-2100, only the ROW will have constant positive trading volumes, whilst the US, JP, and FSU will display constant negative trading volumes; CN will change from positive to negative in this period, while EU will change from negative to positive. Scenario 2 (figure 7) shows that for 2025-2100, again, only the ROW will have constant positive trading volume, while the US and JP will have constant negative trading volume; CN and FSU will change from positive to negative, while EU will change from negative to positive. Obviously, countries with positive trading volume (mainly ROW, CN and FSU) would be carbon emission permit sellers; while countries with negative trading volume (mainly US, JP and EU) would be carbon emission permit buyers. In other word, the mechanism of carbon emission trading is helpful for transferring allocated quotas from developing countriesto developed counties. Insert figure 6 and 7 here ※ Where positive value means that the carbon emission permits have a surplus after regional carbon emissions are subtracted from the allocated quotas, creating carbon emission permit seller; Negative value means that the carbon emission permits have a deficit, creating carbon emission permit buyer. Theoretically, the size of trading volumes depends on the gap between carbon emissions and allocated quotas. The larger the gap is, the more trade there would be. For regions with surplus quotas, increasing their quotas means increasing their positive gap, and in turn resulting in an increase in trading volumes; while for regions with deficit quotas, increasing their quotas mean decreasing their negative gap, and in turn resulting in a decrease in trading volumes. In other words, even if global quotas remain constant, differing quota allocations between regions will lead to different trading volumes. It is necessary to note that countries may change their trading roles in the future, for instance, in both scenarios China will change from a permit seller to permit buyer. Considering the expected rising trading prices, storing quotas for future use may provecost-efficient. In this case, if quota storage is considered, our model requires some corresponding improvements, an issue to be pursued in future research.. Insert figure 8 and 9 here Figure 8 shows, during both 2025-2050or 2051-2100, only the ROW has positive cumulative trading values in scenario 1. In scenario 2(figure 9) shows that in addition to ROW, CN and FSU have slightly positive cumulative trading values during 2025-2050; while it is also only ROW that has positive cumulative trading values during 2050-2100. These results indicate that developing countries, especially ROW can receive capital inflow under the implementation of carbon trading, and developed countries such as US, JP can achieve their reduction obligations by purchasing developing countries deficit permits. Overall, carbon emission trading is helpful for both developing countries and developed countries. For China, the cumulative trading values during 2025-2050 and 2051-2100 are -0.06 and -38trillion US dollars, respectively, in scenario 1; while 2.8 and -22 trillion US dollars, respectively, in scenario 2.Obviously, scenario 2 is more beneficial for protecting Chinese economic interests than scenario 1. From the point of view of the actual regional emissions, although the quota allocation mechanism assigns all regions’ quotas each year according to a given principle, the actual regional emissions are still differentiated from the allocated quotas due to the carbon trading mechanism. When the marginal abatement costs of a region are higher than the trading price, the region with deficit quotas would rather purchase the necessary additional quota from those with lower marginal abatement costs than abate by itself. In this case, under the carbon emissions trading the relative sizes of the actual regional carbon emissions per capita would display little change. For example, the actual regional carbon emissions per capita of the US, FSU, JP and CN in 2100 are still much higher than that of the ROW and EU in both scenarios 1 and 2 (see figure 10). Insert figure 10 here The reasons why actual regional carbon emissions per capita of EU and ROW in 2100 are lower than other regions could be as follows: For the EU, advanced technology and strong political will to reduce emissions contribute to its future lower emissions per capita; For the ROW, lower levels of economic development leads to its lower emission requirements, and in turn result in low future emissions per capita. Obviously, under the carbon emission trading process, the principle of “equal cumulative carbon emissions per capita” does not necessarily lead to regions’ actual carbon emissions per capita being equal. To further evaluate the global impacts of carbon trading, the Ramsey utility function is used for analysis. Unlike GDP, the Ramsey function considers both the total GDP and per capita welfare, which is a representation of comprehensive national power. Wang et al. (2010) described the formula for the Ramsey utility function, and considering the academic controversy over the discount rate, this article set 0.015 and 0.001 respectively for the discount rate (Nordhaus, 2007; Stern, 2008). Figure 11 shows the change rates of the global cumulative Ramsey utility in scenarios 1 and 2 with or without carbon trading, relative to that in scenario 0. Insert figure 11 here Figure 11shows that the size of the discount rate cannot change the relative size of the cumulative change rate of the Ramsey utility. In both scenarios 1 and 2, carbon emission trading always increases the global Ramsey utility. 4. Conclusions Based on agent modeling technology, this article establishes a global carbon-trading model and simulation system. By setting an “equal cumulative carbon emissions per capita” scenario and a “2°C target” scenario, simulation results shows that: (1) The results of carbon trading depend on quota allocation. To offset the numerous historic carbon emissions, developed countries such as US would face huge quota deficits in scenario 1. In this case, the principle of equal cumulative carbon emissions per capita may not be accepted easily by these countries. (2) With a decrease in global carbon emission quotas and an increase demand for carbon emissions, the global carbon price will rise in the future. (3) The implementation of carbon trading is helpful for transferring capital mainly from developed countries to developing countries. (4)Under the carbon emission trading process, developed countries will purchase a large number of emissions quotas from developing countries; therefore, the principle of equal cumulative carbon emissions per capita will not hold. 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