Assessment of Alaska’s North Slope Oil Field Capacity to Sequester CO2

The capacity of 21 major fields containing more than 95% of the North Slope of Alaska’s oil were investigated for CO₂ storage by injecting CO₂ as an enhanced oil recovery (EOR) agent. These fields meet the criteria for the application of miscible and immiscible CO₂-EOR methods and contain about 40 billion barrels of oil after primary and secondary recovery. Volumetric calculations from this study indicate that these fields have a static storage capacity of 3 billion metric tons of CO₂, assuming 100% oil recovery, re-pressurizing the fields to pre-fracturing pressure and applying a 50% capacity reduction to compensate for heterogeneity and for water invasion from the underlying aquifer. A ranking produced from this study, mainly controlled by field size and fracture gradient, identifies Prudhoe, Kuparuk, and West Sak as possessing the largest storage capacities under a 20% safety factor on pressures applied during storage to avoid over-pressurization, fracturing, and gas leakage. Simulation studies were conducted using CO₂ Prophet to determine the amount of oil technically recoverable and CO₂ gas storage possible during this process. Fields were categorized as miscible, partially miscible, and immiscible based on the miscibility of CO₂ with their oil. Seven sample fields were selected across these categories for simulation studies comparing pure CO₂ and water-alternating-gas injection. Results showed that the top two fields in each category for recovery and CO₂ storage were Alpine and Point McIntyre (miscible), Prudhoe and Kuparuk (partially miscible), and West Sak and Lisburne (immiscible). The study concludes that 5 billion metric tons of CO₂ can be stored while recovering 14.2 billion barrels of the remaining oil.     

盐湖地下卤水的开采技术及其展望

我国是农业大国,钾肥的需求量巨大,目前钾肥供应主要来源于柴达木盆地。由于目前的技术限制,钾资源的开发还局限于浅部,无法满足我国钾肥的需求,大部分钾肥还依赖于进口。总结和对比井采技术、渠采技术和CO2地质封存与深部卤水联合注采技术(CO2-EWR)表明,对浅层地下卤水的开采,井采技术和渠采技术适用,但两种技术使采卤泵、采卤管道和输卤渠容易堵塞;并且井采技术投资较大,渠采技术可能导致地下水循环受阻,因而会出现大面积的疏干区。CO2-EWR适合开采深部卤水,虽然该技术的一次性投入较大,但该技术一方面将CO2存储在深部卤水层中,另一方面将卤水驱替出含水层,是一种新型的碳捕集、利用与封存的技术(CCUS)。随着浅层卤水资源的耗竭,开展深部卤水资源的开采利用势在必行,CO2-EWR技术应用会越来越广泛。     

Subsurface Sequestration of CO<Subscript>2</Subscript> in the U.S: Is it Money Best Spent?

The continuously decreasing average coal rank (heating value), inadequate investment, and ever stricter air-emission controls have caused the average efficiency of electricity generation from coal in the U.S. to plummet to a mere 32% by the year 2008. The U.S. gas-fired powerplants are 30% more efficient than the coal-fired ones, with average efficiency of 43% in 2008. Replacing each 1,000 MW _e generated by an average coal-fired powerplant with an average gas-fired powerplant would avoid today 7 million tonnes of CO₂ emissions, 1.2 million tonnes of toxic ash, and significant issues with water contamination. The parallel upgrades to the more efficient supercritical steam turbines would decrease current emissions by up to 50% (from the current average plant efficiency of 32% to over 45%). The CO₂ captured in the new combined-cycle powerplants might be used to enhance oil recovery in local fields, where feasible. The CO₂ enhanced oil recovery (EOR) can never become the main sink for the gigantic CO₂ volume generated each year by electric powerplants. Currently, EOR could absorb only 1% of that volume.     

Cost Implications of Uncertainty in CO<Subscript>2</Subscript> Storage Resource Estimates: A Review

Carbon capture from stationary sources and geologic storage of carbon dioxide (CO₂) is an important option to include in strategies to mitigate greenhouse gas emissions. However, the potential costs of commercial-scale CO₂ storage are not well constrained, stemming from the inherent uncertainty in storage resource estimates coupled with a lack of detailed estimates of the infrastructure needed to access those resources. Storage resource estimates are highly dependent on storage efficiency values or storage coefficients, which are calculated based on ranges of uncertain geological and physical reservoir parameters. If dynamic factors (such as variability in storage efficiencies, pressure interference, and acceptable injection rates over time), reservoir pressure limitations, boundaries on migration of CO₂, consideration of closed or semi-closed saline reservoir systems, and other possible constraints on the technically accessible CO₂ storage resource (TASR) are accounted for, it is likely that only a fraction of the TASR could be available without incurring significant additional costs. Although storage resource estimates typically assume that any issues with pressure buildup due to CO₂ injection will be mitigated by reservoir pressure management, estimates of the costs of CO₂ storage generally do not include the costs of active pressure management. Production of saline waters (brines) could be essential to increasing the dynamic storage capacity of most reservoirs, but including the costs of this critical method of reservoir pressure management could increase current estimates of the costs of CO₂ storage by two times, or more. Even without considering the implications for reservoir pressure management, geologic uncertainty can significantly impact CO₂ storage capacities and costs, and contribute to uncertainty in carbon capture and storage (CCS) systems. Given the current state of available information and the scarcity of (data from) long-term commercial-scale CO₂ storage projects, decision makers may experience considerable difficulty in ascertaining the realistic potential, the likely costs, and the most beneficial pattern of deployment of CCS as an option to reduce CO₂ concentrations in the atmosphere.     

Specific Storage Volumes: A Useful Tool for CO2 Storage Capacity Assessment

Subsurface geologic strata have the potential to store billions of tons of anthropogenic CO₂; therefore, geologic carbon sequestration can be an effective mitigation tool used to slow the rate at which levels of atmospheric CO₂ are increasing. Oil and gas reservoirs, coal beds, and saline reservoirs can be used for CO₂ storage; however, it is difficult to assess and compare the relative storage capacities of these different settings. Typically, CO₂ emissions are reported in units of mass, which are not directly applicable to comparing the CO₂ storage capacities of the various storage targets. However, if the emission values are recalculated to volumes per unit mass (specific volume) then the volumes of geologic reservoirs necessary to store CO₂ emissions from large point sources can be estimated. The factors necessary to convert the mass of CO₂ emissions to geologic storage volume (referred to here as Specific Storage Volume or ‘SSV’) can be reported in units of cubic meters, cubic feet, and petroleum barrels. The SSVs can be used to estimate the reservoir volume needed to store CO₂ produced over the lifetime of an individual point source, and to identify CO₂ storage targets of sufficient size to meet the demand from that given point source. These storage volumes also can then be projected onto the land surface to outline a representative “footprint,” which marks the areal extent of storage. This footprint can be compared with the terrestrial carbon sequestration capacity of the same land area. The overall utility of this application is that the total storage capacity of any given parcel of land (from surface to basement) can be determined, and may assist in making land management decisions.     

Risk,Liability, and Economic Issues with Long-Term CO<Subscript>2</Subscript> Storage—A Review

Given a scarcity of commercial-scale carbon capture and storage (CCS) projects, there is a great deal of uncertainty in the risks, liability, and their cost implications for geologic storage of carbon dioxide (CO₂). The probabilities of leakage and the risk of induced seismicity could be remote, but the volume of geologic CO₂ storage (GCS) projected to be necessary to have a significant impact on increasing CO₂ concentrations in the atmosphere is far greater than the volumes of CO₂ injected thus far. National-level estimates of the technically accessible CO₂ storage resource (TASR) onshore in the United States are on the order of thousands of gigatons of CO₂ storage capacity, but such estimates generally assume away any pressure management issues. Pressure buildup in the storage reservoir is expected to be a primary source of risk associated with CO₂ storage, and only a fraction of the theoretical TASR could be available unless the storage operator extracts the saltwater brines or other formation fluids that are already present in the geologic pore space targeted for CO₂ storage. Institutions, legislation, and processes to manage the risk, liability, and economic issues with CO₂ storage in the United States are beginning to emerge, but will need to progress further in order to allow a commercial-scale CO₂ storage industry to develop in the country. The combination of economic tradeoffs, property rights definitions, liability issues, and risk considerations suggests that CO₂ storage offshore of the United States may be more feasible than onshore, especially during the current (early) stages of industry development.     

拉果错盐湖卤水蒸发过程中Li+富集行为的分子动力学模拟

采用分子动力学模拟,研究了西藏拉果错盐湖卤水中阴、阳离子以及水分子间的相互作用行为。以盐湖卤水等温蒸发过程中粒子浓度变化的四个阶段为研究对象,分别计算了不同体系的扩散系数、配位数、均方位移和径向分布函数。计算结果表明,液相浓度越低时,H₂O分子对各离子之间的相互作用有抑制作用,液相中离子浓度越高时,SO₄2-易与CO₃2-竞争Li⁺形成离子对,从而影响盐湖卤水中Li⁺的富集。本文研究结果对盐湖卤水中Li⁺的迁移行为作出了机理解释,为盐湖卤水提锂的发展奠定了理论基础。     

Chemical weathering and CO2 consumption in the Xijiang River basin, South China

Monthly samples of riverine water were collected and analyzed for the concentrations of major ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, HCO₃⁻, SO₄²⁻, Cl⁻, NO₃⁻), dissolved silicon, and total dissolved solids (TDS) at Wuzhou hydrological station located between the middle and lower reaches of the Xijiang River (XJR) from March 2005 to April 2006. More frequent sampling and analysis were carried out during the catastrophic flooding in June 2005. Stoichiometric analysis was applied for tracing sources of major ions and estimating CO₂ consumption from the chemical weathering of rocks. The results demonstrate that the chemical weathering of carbonate and silicate rocks within the drainage basin is the main source of the dissolved chemical substances in the XJR. Some 81.20% of the riverine cations originated from the chemical weathering processes induced by carbonic acid, 11.32% by sulfuric acid, and the other 7.48% from the dissolution of gypsum and precipitates of sea salts within the drainage basin. The CO₂ flux consumed by the rock chemical weathering within the XJR basin is 2.37 × 10¹¹ mol y^− 1, of which 0.64 × 10¹¹ mol y^− 1 results from silicate rock chemical weathering, and 1.73 × 10¹¹ mol y^− 1 results from carbonate rock chemical weathering. The CO₂ consumption comprises 0.38 × 10¹¹ mol during the 9-d catastrophic flooding. The CO₂ consumption from rock chemical weathering in humid subtropical zones regulates atmospheric CO₂ level and constitutes a significant part of the global carbon budget. The carbon sink potential of rock chemical weathering processes in the humid subtropical zones deserves extra attention.     

An Analysis of Environmental and Economic Impacts of Fossil Fuel Production in the U.S. from 2001 to 2015

The production and burning of fossil fuels is the primary contributor to CO₂ emissions for the U.S. We assess the impact of producing coal, crude oil, and natural gas on the environment and economic well-being by analyzing state-level data from 2001 to 2015. Our findings show that coal production has led to more CO₂ emissions and no significant benefit to economic well-being. Crude oil production has a non-significant impact on CO₂ emissions but is related to a lower poverty rate, a higher median household income, and a higher employment rate. Natural gas withdrawals have a positive impact on median household income. We discuss these findings in the context of current U.S. energy policies and then provide directions for future research.     

含锂卤水中锂资源高效利用与绿色分离的新型萃取体系

针对现有高镁锂比盐湖卤水、碳酸锂产业排放的碱性料液、废旧锂电池回收液等含锂溶液的萃取分离技术现状以及高效、清洁、高值化利用的重大需求及关键基础科学问题,设计合成出数十种酰胺类、磷酸酯类以及双酮类锂特效萃取剂,通过对该类萃取剂的表征与不同放大规模的研究,筛选出多个具有工业应用前景的锂萃取体系,研发出适合我国盐湖卤水锂资源特点的、经济上可行的具有自主知识产权的分离提取锂的新萃取体系与工艺,突破高镁锂比盐湖卤水提锂这一世界性技术难题。经过产业化应用研究,萃取法从高镁锂比盐湖卤水中分离提取锂的技术,在锂镁选择性分离以及资源高效利用率方面已经凸显出了比现有任何提锂工艺更加优异的效果,为我国盐湖资源高效、清洁、高值化利用提供科学依据,提升我国在盐湖锂分离领域的国际地位和竞争力。     

Water content and land use history controlling soil CO2 respiration and carbon stock in savanna soil and groundnut fields in semi-arid Senegal

Decomposition of soil organic carbon (SOC) regulates the partitioning between soil C-stock and release of CO₂ to the atmosphere and is vital for soil fertility. Agricultural expansion followed by decreasing amounts of SOC and soil fertility is a problem mainly seen in tropical agro-ecosystems where fertilizers are in short supply. This paper focuses on factors influencing temporal trends in soil respiration measured as CO₂ effluxes in grass savanna compared with groundnut (Arachis hypogaea L.) fields in the semi-arid part of Senegal in West Africa. Based on laboratory experiments, soil CO₂ production has been expressed as a function of temperature and soil water content by fit equations. Field measurements included soil CO₂ effluxes, soil temperatures and water contents. Effluxes in grass savanna and groundnut fields during the dry season were negligible, while effluxes during the rainy season were about 3–8 μmol CO₂ m^?2 s^?1, decreasing to less than 1 μmol by the end of the growing season. Annual soil CO₂ production was simulated to be in the range of 31–38 mol C m^?2. Furthermore, a controlled water addition experiment revealed the importance of rain during the dry season for the overall turnover of soil organic matter.     

Chemical composition of saline and subsaline lakes of the northern Great Plains,western Canada

The northern Great Plains of Canada stretch from the Precambrian Shield near Winnipeg, Manitoba, westward for ∼1,700 km to the Rocky Mountains foothills. This vast region of flat to gently rolling terrain contains a very large number of salt lakes. Major ion chemical data on ∼500 of them are available. Although the average brine (salinity, 37 ppt) is a Na⁺−SO₄ ²⁻ type of water, the lakes exhibit a wide range of salinities and ionic compositions. This diversity is confirmed by Q-mode cluster analysis; it identified thirteen major water chemistry types. Most ions display distinct trends, both spatially and with increasing salinity. All dissolved components increase with increasing salinity, but at different rates. The relative proportions of Ca²⁺ and HCO₃ ⁻+CO₃ ²⁻ ions show a strong decrease with increasing brine salinity, whereas SO₄ ²⁻ ions increase with increasing salinity. The ionic proportions of Na⁺, Mg²⁺, K⁺ and Cl⁻ exhibit no significant relationship with salinity. R-mode factor analysis of the lake water chemistry, combined with selected environmental parameters, identifies groundwater composition, climate, and the elevation of the lake within the drainage system as most important in controlling brine chemistry and salinity on a regional basis. Variability in source of ions, reaction processes and products are undoubtedly key factors in helping to explain brine chemistry of an individual basin or variation from a local perspective, but these factors are generally poorly understood and not quantified on a regional basis. Palliser Triangle Global Change Project Contribution Number 3.     

Trona resources in southwest Wyoming

Bedded trona (Na₂CO₃·NaHCO₃·2H₂O) in the lacustrine Green River Formation of Eocene age in the Green River Basin, southwest Wyoming, constitutes the largest known resource of natural sodium carbonate in the world. In this study, 116 gigatons (Gt) of trona ore are estimated to be present in 22 beds, ranging from 1.2 to 11 meters (m) in thickness. Of this total, 69 Gt of trona ore are estimated to be in beds containing less than 2 percent halite and 47 Gt in beds containing 2 or more percent halite. These 22 beds underlie areas of about 130 to more than 2,000 km² at depths ranging from about 200 m to more than 900 m below the surface. The total resource of trona ore in the basin for which drilling information is available is estimated to be about 135 Gt.Underveloped trona beds in the deeper southern part of the basin may be best developed by solution mining. Additional unevaluated sodium carbonate resources are present in disseminated shortite (Na₂CO₃·2CaCO₃) in strata interbedded with the trona and in shallow sodium carbonate brines in the northeast part of the basin. Estimates of the shortite and brine resources were not made.     

过去陆地生态系统碳储量估算研究

准确估算陆地生态系统碳储量并认识其空间分布和时间演变规律是碳循环研究的关键 问题。本文回顾了全球与中国陆地生态系统在碳储量估算研究方面的若干进展, 包括基于各种方 法和资料的主要估算结果及其尚存在的不确定性。重点评述了末次盛冰期和中全新世两个时期 陆地生态系统碳储量的变化及其影响因素, 对8.2kaB.P.以来全球大气CO₂ 浓度呈现升高的现象 及其可能原因进行了讨论。全新世中晚期全球大气CO₂ 浓度逐渐升高与旧大陆地区陆地生态系 统碳储量减少的事实是一致的, 新石器时期特别是农业文明开始以后人类活动对陆地植被的持 续干预可能是造成陆地生态系统碳储量减少的原因之一。     

Limnogeology in Brazil’s “forgotten wilderness”: a synthesis from the large floodplain lakes of the Pantanal

Sediment records from floodplain lakes have a large and commonly untapped potential for inferring wetland response to global change. The Brazilian Pantanal is a vast, seasonally inundated savanna floodplain system controlled by the flood pulse of the Upper Paraguay River. Little is known, however, about how floodplain lakes within the Pantanal act as sedimentary basins, or what influence hydroclimatic variables exert on limnogeological processes. This knowledge gap was addressed through an actualistic analysis of three large, shallow (<5 m) floodplain lakes in the western Pantanal: Lagoa Gaíva, Lagoa Mandioré and Baia Vermelha. The lakes are dilute (CO₃ ²⁻ > Si⁴⁺ > Ca²⁺), mildly alkaline, freshwater systems, the chemistries and morphometrics of which evolve with seasonal flooding. Lake sills are bathymetric shoals marked by siliciclastic fans and marsh vegetation. Flows at the sills likely undergo seasonal reversals with the changing stage of the Upper Paraguay River. Deposition in deeper waters, typically encountered in proximity to margin-coincident topography, is dominated by reduced silty-clays with abundant siliceous microfossils and organic matter. Stable isotopes of carbon and nitrogen, plus hydrogen index measured on bulk organic matter, suggest that contributions from algae (including cyanobacteria) and other C₃-vegetation dominate in these environments. The presence of lotic sponge spicules, together with patterns of terrigenous sand deposition and geochemical indicators of productivity, points to the importance of the flood pulse for sediment and nutrient delivery to the lakes. Flood-pulse plumes, waves and bioturbation likewise affect the continuity of sedimentation. Short-lived radioisotopes indicate rates of 0.11–0.24 cm year⁻¹ at sites of uninterrupted deposition. A conceptual facies model, developed from insights gained from modern seasonal processes, can be used to predict limnogeological change when the lakes become isolated on the floodplain or during intervals associated with a strengthened flood pulse. Amplification of the seasonal cycle over longer time scales suggests carbonate, sandy lowstand fan and terrestrial organic matter deposition during arid periods, whereas deposition of lotic sponges, mixed aquatic organic matter, and highstand deltas characterizes wet intervals. The results hold substantial value for interpreting paleolimnological records from floodplain lakes linked to large tropical rivers with annual flooding cycles.     

Geochemistry of waters and brines from the Salinas Grandes basin,Córdoba,Argentina. II. Gypsum dissolution-calcite precipitation,and brine evolution

Rivers and streams originating in the surrounding mountainous area are the major sources of salt in the Salinas Grandes basin (Córdoba, Argentina). These rivers infiltrate when they reach the sandflat or in the fringes of the mudflat, feeding springs which often form shallow lakes. Presently, the lakes are distant from the playa edge, thus allowing inflow waters to dissolve ancient (Pleistocene?) evaporite beds. In the sandflat environment, two dominant types of water have been recognized (SO ₄ ^2? -Cl^?-HCO ₃ ^? -Na⁺, and Cl^?-SO ₄ ^2? -HCO ₃ ^2? -Na⁺), both considered as original members of the brine in the saline complex. Two main sources of solutes were distinguished, one related to the waters supplied by the southern sector and another to waters of the eastern sector. As a result of the chemical evolution in the playa environment, all brines belong to the neutral type (Cl^?-SO ₄ ^2? -Na⁺). Following Hardie and Eugster's (1970) model, waters from the southern sector should evolve towards an alkaline brine (Cl^?-SO ₄ ^2? -HCO ₃ ^? -Na⁺), whereas those from to the eastern sector should evolve towards a neutral one (Cl^?-SO ₄ ^2? -Na⁺). A computer simulation was carried out to model the chemical evolution of source waters. The results obtained by this methodology showed the same dichotomy (alkaline vs. neutral) established by Hardie and Eugster's (1970) model. The deficit in alkalinity could not be explained by any of the mechanisms published until now. Gypsum dissolution is the most likely mechanism which accounts for the chemical evolution of the waters investigated. When such a process is included in the computations, the Ca²⁺ supplied by gypsum beds generates an increase in the ion activity product (aCa⁺²·aCO ₃ ^2? ) and produces a significant change in the 2Ca⁺²/(2CO ₃ ^2? +HCO ₃ ^? ) ratio, switching from values less than 1 to values greater than 1. This process determines the precipitation of calcite, and leads to a decrease in alkalinity, which in turn would explain the existence of a neutral brine in the saline complex. An intermediate salinity brine was detected in the mudflat, which, according to the model (Hardie and Eugster, 1970), should evolve towards a SO ₄ ^2? -free neutral brine (Cl^?-Na⁺-Ca²⁺). The absence of this type of brine may be explained through mixing processes.     

青藏高原高硼卤水的水化学特征及其成因

本文就青藏高原高硼卤水的分布、水化学特征、硼与共生元素的相关性及硼矿沉积的某些规律作了阐述,进而探讨了高硼卤水的成因。     

Graphical Planning Envelopes for Estimating the Surface Footprint of CO<Subscript>2</Subscript> Plumes during CO<Subscript>2</Subscript> Injection into Saline Aquifers

This article presents research regarding the storage or sequestration of carbon dioxide in deep, saline aquifers. Building upon existing research and supplementing it with new numerical modeling simulations, a set of graphical planning curves was developed. Each graphical planning curve plots the value of Ω or the normalized surface footprint per kilogram of CO₂ injected versus the aquifer anisotropy ratio. The planning curves present one planning envelope that is subdivided into two parts. One portion of the envelope governs the planning for active injection operations of geologic storage projects typically lasting less than 100 years. The second portion of the envelope governs the planning for long-term monitoring of the carbon dioxide plume as it evolves from mostly free-phase or highly concentrated aqueous-phase carbon dioxide to entirely dilute aqueous-phase carbon dioxide. This approach is innovative and useful for practitioners since it provides a simple way to estimate the CO₂ surface footprint regardless of the aquifer anisotropy. Previous approaches for estimating the footprint usually assumed an isotropic and homogeneous aquifer storage zone.     

Photosynthetic responses of Larrea tridentata to a step-increase in atmospheric CO2at the Nevada Desert FACE Facility

Of all terrestrial ecosystems, the productivity of deserts has been suggested to be the most responsive to increasing atmospheric CO₂. The extent to which this prediction holds will depend in part on plant responses to elevated CO₂under the highly variable conditions characteristic of arid regions. The photosynthetic responses ofLarrea tridentata , an evergreen shrub, to a step-increase in atmospheric CO₂(to 550 μmolmol⁻¹) were examined in the field using Free-Air CO₂Enrichment (FACE) under seasonally varying moisture conditions. Elevated CO₂substantially increased net assimilation rate (A_net) in Larrea during both moist and dry periods of the potential growing season, while stomatal conductance (g_s) did not differ between elevated and ambient CO₂treatments. Seasonal and diurnal gas exchange dynamics in elevated CO₂mirrored patterns in ambient CO₂, indicating that elevated CO₂did not extend photosynthetic activity longer into the dry season or during more stressful times of the day. Net assimilation vs. internal CO₂(A/C_i) responses showed no evidence of photosynthetic down-regulation during the dry season. In contrast, after significant autumn rains, A_max(the CO₂saturated rate of photosynthesis) and CE (carboxylation efficiency) were lower in Larrea under elevated CO₂. In situ chlorophyll fluorescence estimation ofLarrea Photosystem II efficiency (F_v/F_m) responded more to water limitation than to elevated CO₂. These findings suggest that predictions regarding desert plant responses to elevated CO₂should account for seasonal patterns of photosynthetic regulatory responses, which may vary across species and plant functional types.     

Carbon emissions trends with optimal balanced economic growth of China and the USA and some abatement options for China

It is believed that the global CO2 emissions have to begin dropping in the near fu- ture to limit the temperature increase within 2 degrees by 2100. So it is of great concern to environmentalists and national decision-makers to know how the global or national CO2 emissions would trend. This paper presented an approach to project the future CO2 emissions from the perspective of optimal economic growth, and applied this model to the cases of China and the United States, whose CO2 emissions together contributed to more than 40% of the global emissions. The projection results under the balanced and optimal economic growth path reveal that the CO2 emissions will peak in 2029 for China and 2024 for the USA owing to their empirically implied pace of energy efficiency improvement. Moreover, some abatement options are analyzed for China, which indicate that 1） putting up the energy price will de- crease the emissions at a high cost; 2） enhancing the decline rate of energy intensity can significantly mitigate the emissions with a modest cost; and 3） the energy substitution policy of replacing carbon intensive energies with clean ones has considerable potential to alleviate emissions without compromising the economic development.