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1.
Agricultural GHG mitigation policies are important if ambitious climate change goals are to be achieved, and have the potential to significantly lower global mitigation costs [Reisinger, A., Havlik, P., Riahi, K., van Vliet, O., Obersteiner, M., & Herrero, M. (2013). Implications of alternative metrics for global mitigation costs and greenhouse gas emissions from agriculture. Climatic Change, 117, 677–690]. In the post-Paris world of ‘nationally determined contributions’ to mitigation, the prospects for agricultural mitigation policies may rest on whether they are in the national economic interest of large agricultural producers. New Zealand is a major exporter of livestock products; this article uses New Zealand as a case study to consider the policy implications of three global policy scenarios at the global, national and farm levels. Building on global modelling, a model dairy farm and a model sheep and beef farm are used to estimate the changes in profit when agricultural emissions are priced and mitigated globally or not, and priced domestically or not, in 2020. Related to these scenarios is the metric or GHG exchange rate. Most livestock emissions are non-CO2, with methane being particularly sensitive to the choice of metric. The results provide evidence that farm profitability is more sensitive to differing international policy scenarios than national economic welfare. The impact of the choice of metric is not as great as the impact of whether other countries mitigate agricultural emissions or not. Livestock farmers do best when agricultural emissions are not priced, as livestock commodity prices rise significantly due to competition for land from forestry. However, efficient farmers may still see a rise in profitability when agricultural emissions are fully priced worldwide.

Policy relevance

Exempting agricultural emissions from mitigation significantly increases the costs of limiting warming to 2 °C, placing the burden on other sectors. However, there may be a large impact on farmers if agricultural emissions are priced domestically when other countries are not doing the same. The impacts of global and national climate policies on farmers need to be better understood in order for climate policies to be politically sustainable. Transitional assistance that is not linked to emission levels could help, as long as the incentives to mitigate are maintained. In the long run, efficient farmers may benefit from climate policy; international efforts should focus on mitigation options and effective domestic policy development, rather than on metrics.  相似文献   

2.
Minimizing the future impacts of climate change requires reducing the greenhouse gas (GHG) load in the atmosphere. Anthropogenic emissions include many types of GHG’s as well as particulates such as black carbon and sulfate aerosols, each of which has a different effect on the atmosphere, and a different atmospheric lifetime. Several recent studies have advocated for the importance of short timescales when comparing the climate impact of different climate pollutants, placing a high relative value on short-lived pollutants, such as methane (CH4) and black carbon (BC) versus carbon dioxide (CO2). These studies have generated confusion over how to value changes in temperature that occur over short versus long timescales. We show the temperature changes that result from exchanging CO2 for CH4 using a variety of commonly suggested metrics to illustrate the trade-offs involved in potential carbon trading mechanisms that place a high value on CH4 emissions. Reducing CH4 emissions today would lead to a climate cooling of approximately ~0.5 °C, but this value will not change greatly if we delay reducing CH4 emissions by years or decades. This is not true for CO2, for which the climate is influenced by cumulative emissions. Any delay in reducing CO2 emissions is likely to lead to higher cumulative emissions, and more warming. The exact warming resulting from this delay depends on the trajectory of future CO2 emissions but using one business-as usual-projection we estimate an increase of 3/4 °C for every 15-year delay in CO2 mitigation. Overvaluing the influence of CH4 emissions on climate could easily result in our “locking” the earth into a warmer temperature trajectory, one that is temporarily masked by the short-term cooling effects of the CH4 reductions, but then persists for many generations.  相似文献   

3.
The global three-dimensional Lagrangian chemistry-transport model STOCHEM has been used to follow changes in the tropospheric distributions of methane CH4 and ozone O3 following the emission of pulses of the oxides of nitrogen NO x . Month-long emission pulses of NO x produce deficits in CH4 mixing ratios that bring about negative radiative forcing (climate cooling) and decay away with e-folding times of 10–15 years. They also produce short-term excesses in O3 mixing ratios that bring about positive radiative forcing (climate warming) that decay over several months to produce deficits, with their attendant negative radiative forcing (climate cooling) that decays away in step with the CH4 deficits. Total time-integrated net radiative forcing is markedly influenced by cancellation between the negative CH4 and long-term O3 contributions and the positive short-term O3 contribution to leave a small negative residual. Consequently, total net radiative forcing from NO x emission pulses and the global warming potentials derived from them, show a strong dependence on the magnitudes, locations and seasons of the emissions. These dependences are illustrated using the Asian continent as an example and demonstrate that there is no simple robust relationship between continental-scale NO x emissions and globally-integrated radiative forcing. We find that the magnitude of the time-integrated radiative forcing from NO x -driven CH4 depletion tends to approach and outweigh that from ozone enhancement, leaving net time-integrated radiative forcings and global warming potentials negative (climate cooling) in contrast to the situation for aircraft NO x (climate warming). Control of man-made surface NO x emissions alone may lead to positive radiative forcing (climate warming).  相似文献   

4.
CH4和N2O作为主要温室气体,自工业革命以来排放量急剧增加,已经被列入《京都议定书》要求控制它们的排放。本文利用高光谱分辨率的辐射传输模式,计算了CH4、N2O在晴空大气和有云大气条件下的瞬时辐射效率和平流层调整的辐射效率,以及它们的全球增温潜能(GWP)和全球温变潜能(GTP),并根据模式结果拟合了CH4和N2O的辐射强迫的简单计算公式。本文的研究表明:CH4和N2O在有云大气下的平流层调整的辐射效率分别为4.142×10-4 W m-2 ppb-1和3.125×10-3 W m-2 ppb-1 (1ppb=10-9),经大气寿命调整后的辐射效率分别为3.732×10-4 W m-2 ppb-1和2.987×10-3 W m-2 ppb-1,与IPCC(2007)的相应结果高度一致。CH4和N2O 100年的全球增温潜能GWP分别为16和266;100年的脉冲排放的全球温变潜能GTPP分别为0.24和233;持续排放的全球温变潜能GTPS分别为18和268。它们在未来全球变暖和气候变化中,影响仅次于CO2,仍然起着非常关键的作用。  相似文献   

5.
Substitution of natural gas for coal is one means of reducing carbon dioxide (CO2) emissions. However, natural gas and coal use also results in emissions of other radiatively active substances including methane (CH4), sulfur dioxide (SO2), a sulfate aerosolprecursor, and black carbon (BC) particles. Will switching from coal to gas reduce the net impact of fossil fuel use on global climate? Using the electric utility sector as an example, changes in emissions of CO2, CH4,SO2 and BC resulting from the replacement of coal by natural gas are evaluated, and their modeled net effect on global mean-annual temperature calculated. Coal-to-gas substitution initially produces higher temperatures relative to continued coal use. This warming is due to reduced SO2 emissionsand possible increases in CH4 emissions, and can last from 1 to 30years, depending on the sulfur controls assumed. This is followed by a net decrease in temperature relative to continued coal use, resulting from lower emissions of CO2 and BC. The length of this period and the extent of the warming or cooling expected from coal-to-gas substitution is found to depend on key uncertainties and characteristics of the substitutions, especially those related to: (1) SO2 emissions and consequentsulphate aerosol forcing; and (2) the relative efficiencies of the power plantsinvolved in the switch.  相似文献   

6.
This article assesses Japan's carbon budgets up to 2100 in the global efforts to achieve the 2?°C target under different effort-sharing approaches based on long-term GHG mitigation scenarios published in 13 studies. The article also presents exemplary emission trajectories for Japan to stay within the calculated budget.

The literature data allow for an in-depth analysis of four effort-sharing categories. For a 450?ppm CO2e stabilization level, the remaining carbon budgets for 2014–2100 were negative for the effort-sharing category that emphasizes historical responsibility and capability. For the other three, including the reference ‘Cost-effectiveness’ category, which showed the highest budget range among all categories, the calculated remaining budgets (20th and 80th percentile ranges) would run out in 21–29 years if the current emission levels were to continue. A 550?ppm CO2e stabilization level increases the budgets by 6–17 years-equivalent of the current emissions, depending on the effort-sharing category. Exemplary emissions trajectories staying within the calculated budgets were also analysed for ‘Equality’, ‘Staged’ and ‘Cost-effectiveness’ categories. For a 450?ppm CO2e stabilization level, Japan's GHG emissions would need to phase out sometime between 2045 and 2080, and the emission reductions in 2030 would be at least 16–29% below 1990 levels even for the most lenient ‘Cost-effectiveness’ category, and 29–36% for the ‘Equality’ category. The start year for accelerated emissions reductions and the emissions convergence level in the long term have major impact on the emissions reduction rates that need to be achieved, particularly in the case of smaller budgets.

Policy relevance

In previous climate mitigation target formulation processes for 2020 and 2030 in Japan, neither equity principles nor long-term management of cumulative GHG emissions was at the centre of discussion. This article quantitatively assesses how much more GHGs Japan can emit by 2100 to achieve the 2?°C target in light of different effort-sharing approaches, and how Japan's GHG emissions can be managed up to 2100. The long-term implications of recent energy policy developments following the Fukushima nuclear disaster for the calculated carbon budgets are also discussed.  相似文献   

7.
A field study of trace gas emissions from biomass burning in Equatorial Africa gave methyl chloride emission ratios of 4.3×10–5±0.8×10–5 mol CH3Cl/mol CO2. Based on the global emission rates for CO2 from biomass burning we estimate a range of 226–904×109 g/y as global emission rate with a best estimate of 515×109 g/y. This is somewhat lower than a previous estimate which has been based on laboratory studies. Nevertheless, our emission rate estimates correspond to 10–40% of the global turnover of methyl chloride and thus support the importance of biomass burning as methyl chloride source. The emission ratios for other halocarbons (CH2Cl2, CHCl3, CCl4, CH3CCl3, C2HCl3, C2Cl4, F-113) are lower. In general there seems to be a substantial decrease with increasing complexity of the compounds and number of halogen atoms. For dichloromethane biomass burning still contributes significantly to the total global budget and in the Southern Hemisphere biomass burning is probably the most important source for atmospheric dichloromethane. For the global budgets of other halocarbons biomass burning is of very limited relevance.  相似文献   

8.
The comprehensive approach adopted in the Kyoto Protocol relies on the use of 100-year Global Warming Potentials (GWPs) to convert emissions of various gases to `carbon dioxide (CO2) equivalents'. This particular set of weights, or metric, has a limited capacity to handle the large variations in atmospheric adjustment times, and emissions of various gases that are equal in terms of `CO2 equivalents' will not result in equal climatic effects. In this study, the 100-year GWP metric is assessed in the context of implementing the Kyoto Protocol. Using data from Norway, we explore how abatement policy formulated on the basis of 100-year GWPs compares to policies based on other metrics in terms of compliance costs and abatement profile, that is, the composition of the basket of gases reduced. We found that the costs for Norway change significantly when other metrics are used, but changes in the composition of the basket of gases are moderate. However, since compliance costs can be controlled through other mechanisms for post-Kyoto Protocols, the use of 100-year GWPs versus other metrics has little impact on the general formulation of Norwegian climate policy.  相似文献   

9.
Sergio Pacca 《Climatic change》2007,84(3-4):281-294
Greenhouse gas (GHG) emissions from hydroelectric dams are often portrayed as nonexistent by the hydropower industry and have been largely ignored in global comparisons of different sources of electricity. However, the life cycle assessment (LCA) of any hydroelectric plant shows that GHG emissions occur at different phases of the power plant’s life. This work examines the role of decommissioning hydroelectric dams in greenhouse gas emissions. Accumulated sediments in reservoirs contain noticeable levels of carbon, which may be released to the atmosphere upon decommissioning of the dam. The rate of sediment accumulation and the sediment volume for six of the ten largest United States hydroelectric power plants is surveyed. The amount of sediments and the respective carbon content at the moment of dam decommissioning (100 years after construction) was estimated. The released carbon is partitioned into CO2 and CH4 emissions and converted to CO2 equivalent emissions using the global warming potential (GWP) method. The global warming effect (GWE) due to dam decommissioning is normalized to the total electricity produced over the lifetime of each power plant. The estimated GWE of the power plants range from 128–380 g of CO2eq./kWh when 11% of the total available sediment organic carbon (SOC) is mineralized and between 35 and 104 g of CO2eq./kWh when 3% of the total SOC is mineralized. Though these values are below emission factors for coal power plants (890 g of CO2eq./kWh), the amount of greenhouse gases emitted by the sediments upon dam decommissioning is a notable amount that should not be ignored and must be taken into account when considering construction and relicensing of hydroelectric dams.  相似文献   

10.
Strategies for mitigating the increasing concentration of carbon dioxide (CO2) in the atmosphere include sequestering carbon (C) in soils and vegetation of terrestrial ecosystems. Carbon and nitrogen (N) move through terrestrial ecosystems in coupled biogeochemical cycles, and increasing C stocks in soils and vegetation will have an impact on the N cycle. We conducted simulations with a biogeochemical model to evaluate the impact of different cropland management strategies on the coupled cycles of C and N, with special emphasis on C-sequestration and emission of the greenhouse gases methane (CH4) and nitrous oxide (N2O). Reduced tillage, enhanced crop residue incorporation, and farmyard manure application each increased soil C-sequestration, increased N2O emissions, and had little effect on CH4 uptake. Over 20 years, increases in N2O emissions, which were converted into CO2-equivalent emissions with 100-year global warming potential multipliers, offset 75–310% of the carbon sequestered, depending on the scenario. Quantification of these types of biogeochemical interactions must be incorporated into assessment frameworks and trading mechanisms to accurately evaluate the value of agricultural systems in strategies for climate protection.  相似文献   

11.
In order to estimate the benefit attributable to alleviating global warming for a kind of cost–benefit analysis of global warming mitigation, global warming impacts were quantitatively evaluated for a pathway of unmitigated CO2 emissions and three pathways to stabilize the atmospheric CO2 concentration at different levels, keeping unchanged the assumed conditions on population and GDP growths, although the GDP losses which will be caused due to the warming mitigation for the three stabilization pathways are taken into account. The evaluation results show that global warming will reduce the world total number of deaths caused by thermal stress owing to the large decrease in the cold-related deaths; it will increase the water stress in some regions, while it will decrease the stress in other regions; reductions in CO2 emissions will decrease the probability of THC collapse and terrestrial biodiversity loss; and it will enhance an increase in the wheat production potential.  相似文献   

12.
Anthropogenic emissions of methane (CH4) and nitrous oxide (N2O) from livestock agriculture (enteric fermentation, animal waste management systems, and pasture manure) and plant growing of the Russia (CH4 emissions from rice fields, direct and indirect N2O emissions from agricultural lands) are considered. In 2004, the total emissions of these greenhouse gases in the agricultural sector amounted to 1.4 × 105 thousand t CO2-equivalent, which corresponds to 45% of the 1990 level (3.1 × 105 thousand t CO2-equivalent). In 2004, the contribution of N2O to the total agricultural emissions was approximately twice (67.0%) that of CH4 (33.0%). Direct N2O emissions from agricultural soils (0.5 × 105 thousand t CO2-equivalent) and CH4 emissions from the internal fermentation of domestic animals (0.4 × 105 thousand t CO2-equivalent) are the most significant sources in the agricultural sector of the Russian Federation. In 2004, all these agricultural sources emitting methane and nitrous oxide contributed about 7% CO2-equivalent to the total emission of the anthropogenic greenhouse gases in Russia.  相似文献   

13.
Approximately 1700 Pg of soil carbon (C) are stored in the northern circumpolar permafrost zone, more than twice as much C than in the atmosphere. The overall amount, rate, and form of C released to the atmosphere in a warmer world will influence the strength of the permafrost C feedback to climate change. We used a survey to quantify variability in the perception of the vulnerability of permafrost C to climate change. Experts were asked to provide quantitative estimates of permafrost change in response to four scenarios of warming. For the highest warming scenario (RCP 8.5), experts hypothesized that C release from permafrost zone soils could be 19–45 Pg C by 2040, 162–288 Pg C by 2100, and 381–616 Pg C by 2300 in CO2 equivalent using 100-year CH4 global warming potential (GWP). These values become 50 % larger using 20-year CH4 GWP, with a third to a half of expected climate forcing coming from CH4 even though CH4 was only 2.3 % of the expected C release. Experts projected that two-thirds of this release could be avoided under the lowest warming scenario (RCP 2.6). These results highlight the potential risk from permafrost thaw and serve to frame a hypothesis about the magnitude of this feedback to climate change. However, the level of emissions proposed here are unlikely to overshadow the impact of fossil fuel burning, which will continue to be the main source of C emissions and climate forcing.  相似文献   

14.
This paper provides estimates of emissions of two important but often not well-characterized greenhouse gas (GHG) emissions related to transportation energy use: methane (CH4) and nitrous oxide (N2O). The paper focuses on emissions of CH4 and N2O from motor vehicles because unlike emissions of CO2, which are relatively easy to estimate, emissions of CH4 and N2O are a function of many complex aspects of combustion dynamics and of the type of emission control systems used. They therefore cannot be derived easily and instead must be determined through the use of published emission factors for each combination of fuel, end-use technology, combustion conditions, and emission control system. Furthermore, emissions of CH4 and N2O may be particularly important with regard to the relative CO2-equivalent GHG emissions of the use of alternative transportation fuels, in comparison with the use of conventional fuels. By analyzing a database of emission estimates, we develop emission factors for N2O and CH4 from conventional vehicles, in order to supplement recent EPA and IPCC estimates, and we estimate relative emissions of N2O and CH4 from different alternative fuel passenger cars, light-duty trucks, and heavy-duty vehicles.  相似文献   

15.
The non-CO2 climate impact of aviation (NOx and contrails) is assessed and emissions weighting factors (EWFs) i.e., the factor by which aviation CO2 emissions should be multiplied to get the CO2-equivalent emissions for annual fleet average conditions are estimated. The EWFs are estimated using two economic metrics. One is based on the relative damage cost between non-CO2 forcers and CO2. The other is based on the cost-effective valuation between the non-CO2 forcers and CO2 given an upper ceiling on the global annual average surface temperature (set at 2?K above pre-industrial levels). We also estimate EWFs using three physical metrics, Global Warming Potential (GWP), Global Temperature change Potential (GTP) and Sustained GTP (SGTP) and compare our results with the economics based metrics. Given best estimates on the forcing contributions from CO2, contrails and NOx from aviation and by using a discount rate of 3%/year, the RDC based metric gives an EWF equal to 1.4 (slightly higher than EWFs based on GWP and SGTP using a 100?year time horizon). EWF using the cost-effective approach depends on the time that remains before stabilization occurs. It is roughly equal to unity until a few years before the temperature reaches its ceiling, and approximately 2 when stabilization has taken place. EWFs based on GTP resemble those based on CETO when the time left to when stabilization occurs is sufficiently large. Once stabilization has occurred CETO values resemble RDC based values. If aviation-induced cirrus clouds are included, uncertainties increase and the EWFs for GWP, SGTP and RDC based metrics end up in the range 1.3–2.9, while EWFs for GTP and CETO remain close to unity in the near term.  相似文献   

16.
Global cooling: increasing world-wide urban albedos to offset CO2   总被引：2，自引：0，他引：2  
Increasing urban albedo can reduce summertime temperatures, resulting in better air quality and savings from reduced air-conditioning costs. In addition, increasing urban albedo can result in less absorption of incoming solar radiation by the surface-troposphere system, countering to some extent the global scale effects of increasing greenhouse gas concentrations. Pavements and roofs typically constitute over 60% of urban surfaces (roof 20–25%, pavements about 40%). Using reflective materials, both roof and pavement albedos can be increased by about 0.25 and 0.15, respectively, resulting in a net albedo increase for urban areas of about 0.1. On a global basis, we estimate that increasing the world-wide albedos of urban roofs and paved surfaces will induce a negative radiative forcing on the earth equivalent to offsetting about 44 Gt of CO2 emissions. At ～$25/tonne of CO2, a 44 Gt CO2 emission offset from changing the albedo of roofs and paved surfaces is worth about $1,100 billion. Furthermore, many studies have demonstrated reductions of more than 20% in cooling costs for buildings whose rooftop albedo has been increased from 10–20% to about 60% (in the US, potential savings exceed $1 billion per year). Our estimated CO2 offsets from albedo modifications are dependent on assumptions used in this study, but nevertheless demonstrate remarkable global cooling potentials that may be obtained from cooler roofs and pavements.  相似文献   

17.
Dietary Guidelines for many countries recommend that people should eat ‘nutrient dense’ foods, which are foods with a high nutrient to energy ratio; and that people should limit their intake of saturated fat, added salt or added sugar. In addition, consumers and environmentalists increasingly want their food to be produced with a low impact on the environment, including reduced greenhouse gas emissions (GHGE), yet agriculture is a major source of CH4 and N2O emissions, as well as producing CO2 emissions. Current research on GHGE from agriculture does not incorporate the nutritional value of the foods studied. However, the nutritional content of food is important, given the prevalence of malnutrition, including obesity (due to over-consumption of foods high in energy yet low nutritional density), and the negative health impacts they produce. This paper introduces the metric, emissions/unit nutrient density, and compares the results with three other metrics: emissions intensity (t CO2e/t product), emissions/t protein and emissions/GJ. The food products examined are wheat flour, milk, canola oil, lean lamb, lean beef, untrimmed lamb and untrimmed beef. The metric t CO2e/unit nutrient density was the preferred metric to use when examining GHGE from food production because it compares different types of products based on their nutritional value, rather than according to singular nutrients such as protein, or specific attributes such as product weight or energy content. Emissions/unit nutrient density has the potential to inform consumer choices regarding foods that have a higher nutritional content relative to the GHGE generated. Further analysis would be useful to develop and expand the use of this metric further.  相似文献   

18.
This paper synthesizes results of the multi-model Energy Modeling Forum 27 (EMF27) with a focus on climate policy scenarios. The study included two harmonized long-term climate targets of 450 ppm CO2-e (enforced in 2100) and 550 pm CO2-e (not-to-exceed) as well as two more fragmented policies based on national and regional emissions targets. Stabilizing atmospheric GHG concentrations at 450 and 550 ppm CO2-e requires a dramatic reduction of carbon emissions compared to baseline levels. Mitigation pathways for the 450 CO2-e target are largely overlapping with the 550 CO2-e pathways in the first half of the century, and the lower level is achieved through rapid reductions in atmospheric concentrations in the second half of the century aided by negative anthropogenic carbon flows. A fragmented scenario designed to extrapolate current levels of ambition into the future falls short of the emissions reductions required under the harmonized targets. In a more aggressive scenario intended to capture a break from observed levels of stringency, emissions are still somewhat higher in the second half due to unabated emissions from non-participating countries, emphasizing that a phase-out of global emissions in the long term can only be reached with full global participation. A key finding is that a large range of energy-related CO2 emissions can be compatible with a given long-term target, depending on assumptions about carbon cycle response, non-CO2 and land use CO2 emissions abatement, partly explaining the spread in mitigation costs.  相似文献   

19.
This paper compares the results of the three state of the art climate-energy-economy models IMACLIM-R, ReMIND-R, and WITCH to assess the costs of climate change mitigation in scenarios in which the implementation of a global climate agreement is delayed or major emitters decide to participate in the agreement at a later stage only. We find that for stabilizing atmospheric GHG concentrations at 450?ppm CO2-only, postponing a global agreement to 2020 raises global mitigation costs by at least about half and a delay to 2030 renders ambitious climate targets infeasible to achieve. In the standard policy scenario??in which allocation of emission permits is aimed at equal per-capita levels in the year 2050??regions with above average emissions (such as the EU and the US alongside the rest of Annex-I countries) incur lower mitigation costs by taking early action, even if mitigation efforts in the rest of the world experience a delay. However, regions with low per-capita emissions which are net exporters of emission permits (such as India) can possibly benefit from higher future carbon prices resulting from a delay. We illustrate the economic mechanism behind these observations and analyze how (1) lock-in of carbon intensive infrastructure, (2) differences in global carbon prices, and (3) changes in reduction commitments resulting from delayed action influence mitigation costs.  相似文献   

20.
Abstract

This article presents a set of multi-gas emission pathways for different CO2-equivalent concentration stabilization levels, i.e. 400, 450, 500 and 550 ppm CO2-equivalent, along with an analysis of their global and regional reduction implications and implied probability of achieving the EU climate target of 2°C. For achieving the 2°C target with a probability of more than 60%, greenhouse gas concentrations need to be stabilized at 450 ppm CO2-equivalent or below, if the 90% uncertainty range for climate sensitivity is believed to be 1.5–4.5°C. A stabilization at 450 ppm CO2-equivalent or below (400 ppm) requires global emissions to peak around 2015, followed by substantial overall reductions of as much as 25% (45% for 400 ppm) compared to 1990 levels in 2050. In 2020, Annex I emissions need to be approximately 15% (30%) below 1990 levels, and non-Annex I emissions also need to be reduced by 15–20% compared to their baseline emissions. A further delay in peaking of global emissions by 10 years doubles maximum reduction rates to about 5% per year, and very probably leads to high costs. In order to keep the option open of stabilizing at 400 and 450 ppm CO2-equivalent, the USA and major advanced non-Annex I countries will have to participate in the reductions within the next 10–15 years.  相似文献   

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