Global Warming Potentials: 1. Climatic Implications of Emissions Reductions

The use of Global Warming Potentials (GWPs) to calculate equivalent carbon dioxide emissions reductions in the climate change context is examined. We find that GWPs are accurate only for short time horizons. Over long time horizons their use implicitly leads to tradeoffs between near-term and long-term climate change. For one of the most policy-relevant cases, comparing reductions in methane and carbon dioxide, the long-term effect on climate of reducing methane emissions is relatively small, at variance with the common perception based on published GWP values.     

Evaluating Global Warming Potentials with historical temperature

Global Warming Potentials (GWPs) are evaluated with historical temperature by applying them to convert historical CH₄ and N₂O emissions to equivalent CO₂ emissions. Our GWP analysis is based on an inverse estimation using the Aggregated Carbon Cycle, Atmospheric Chemistry, and Climate Model (ACC2). We find that, for both CH₄ and N₂O, indices higher than the Kyoto GWPs (100-year time horizon) would reproduce better the historical temperature. The CH₄ GWP provides a best fit to the historical temperature when it is calculated with a time horizon of 44 years. However, the N₂O GWP does not approximate well the historical temperature with any time horizon. We introduce a new exchange metric, TEMperature Proxy index (TEMP), that is defined so that it provides a best fit to the temperature projection of a given period. By comparing GWPs and TEMPs, we find that the inability of the N₂O GWP to reproduce the historical temperature is caused by the GWP calculation methodology in IPCC using simplifying assumptions for the background system dynamics and uncertain parameter estimations. Furthermore, our TEMP calculations demonstrate that indices have to be progressively updated upon the acquisition of new measurements and/or the advancement of our understanding of Earth system processes.     

Testing 100-Year Global Warming Potentials: Impacts on Compliance Costs and Abatement Profile

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 (CO<sub>2</sub>) 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.     

SF6气体的辐射强迫和全球增温潜能的研究

IPCC(2007)指出, 六氟化硫(SF6) 作为臭氧消耗物质 (ODSs) 的部分替代物质, 近年来排放量大大增加。它作为控制排放的人造长寿命温室气体之一已经被列入《京都议定书》。但是, 目前在臭氧消耗物质替代品中, 对SF6的辐射强迫和全球增温潜能的研究较少, 而且所用的谱吸收资料陈旧。本文采用最新的分子吸收数据库HITRAN2004中的SF6的吸收截面数据, 利用Shi(1981) 的吸收系数重排法, 建立了SF6的相关k分布的辐射计算方案, 在此基础上研究了SF6在晴空大气下的辐射效率和全球增温潜能, 并首次计算了SF6的全球温变潜能, 与其全球增温潜能进行了比较。本文的研究表明: SF6的辐射效率为0.512 W/m2, 经过大气寿命调整之后的辐射效率为0.506 W/m2, 二者差别不大; 根据IPCC (2007) 给出的排放情景, 到2100年, SF6在大气中的体积分数将达到35×10-12～70×10-12, 引起的相应辐射强迫将在0.004～0.028 W/m2之间变化; 相对于二氧化碳的100年全球增温潜能为2.33×104, 比IPCC(2007)的结果大2.2%; 100年的持续排放的全球增温潜能为2.26×104, 与其他长寿命人造温室气体一道, 其对全球变暖的长期影响不容忽视。     

The Cost of Using Global Warming Potentials: Analysing the Trade off Between CO2, CH4 and N2O

The metric governing the trade-off between different greenhouse gases in the Kyoto Protocol, the Global Warming Potentials (GWPs), has received ample critique from both scientific and economic points of view. Here we use an integrated climate-economic optimization model to estimate the cost-effective trade-off between CO₂, CH₄ and N₂O when meeting a temperature stabilization target. We then estimate the increased cost from using GWPs when meeting the same temperature target. Although the efficient valuation of the gases differs significantly from their respective GWPs, the potential economic benefit of valuing them in a more correct way amounts to 3.8 percent of the overall costs of meeting the temperature stabilization target in the base case. In absolute value, this corresponds to an additional net present value cost of US$₂₀₀₀100 billion. To corroborate our findings we perform a Monte Carlo-analysis where several key parameters are randomly varied simultaneously. The result from this exercise shows that our main result is robust to a wide range of changes in the key parameter values, giving a median economic loss from using GWPs of 4.2 percent.     

The Oxidation of Organic Compounds in the Troposphere and their Global Warming Potentials

Oxidation by hydroxyl radicals is the main removal process for organic compounds in the troposphere. This oxidation acts as a source of ozone and as a removal process for hydroxyl and peroxy radicals, thereby reducing the efficiency of methane oxidation and promoting the build-up of methane. Emissions of organic compounds may therefore lead to the build-up of two important radiatively-active trace gases: methane and ozone. Emission pulses of 10 organic compounds were followed in a global 3-D Lagrangian chemistry-transport model to quantify their indirect greenhouse gas impacts through changes induced in the tropospheric distributions of methane and ozone. The main factors influencing the global warming potentials of the 10 organic compounds were found to be their spatial emission patterns, chemical reactivity and transport, molecular complexity and oxidation products formed. The indirect radiative forcing impacts of organic compounds may be large enough that ozone precursors should be considered in the basket of trace gases through which policy-makers aim to combat global climate change.     

CH4和N2O的辐射强迫与全球增温潜能

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。     

Thinking About Global Warming

Attitudes toward global warming are influenced by various heuristics, which may distort policy away from what is optimal for the well-being of people. These possible distortions, or biases, include: a focus on harms that we cause, as opposed to those that we can remedy more easily; a feeling that those who cause a problem should fix it; a desire to undo a problem rather than compensate for its presence; parochial concern with one’s own group (nation); and neglect of risks that are not available. Although most of these biases tend to make us attend relatively too much to global warming, other biases, such as wishful thinking, cause us to attend too little. I discuss these possible effects and illustrate some of them with an experiment conducted on the World Wide Web.     

全球变暖的科学

全球变暖已经是不争的事实.根据目前主要的3个全球温度序列,1910-2009年的变暖趋势为0.70 ～0.75℃/100a[1].粗略地讲,目前已经变暖了0.8℃.如果把气候变化的阈值限制为2℃,则今后只有1.2℃的上升空间,这就是我们面临的严峻形势[2].根据全球气候系统的概念[3],全球变暖不仅仅是地面温度的上升,还包含了冰雪的融化、海平面的上升、多年冻土的退化及全球植被的变化等等.这些变化已经、正在或将来可能影响到人类生活的方方面面.     

全球变暖趋缓研究进展

近十几年来,全球年平均表面温度上升趋势显示出停滞状态,即全球变暖趋缓,这引起了国际社会的广泛关注,同时也引发了对全球变暖的质疑,各国气候学家正努力就全球变暖趋缓的事实、原因及其可能影响展开研究。本文综述了目前国内外对全球变暖趋缓的研究结果。多数科学家认可近十几年来全球变暖停滞的事实,并认为太阳活动处于低位相、大气气溶胶（自然和人为）增加以及海洋吸收热量是变暖停滞的可能影响因子,其中海洋（尤其是700米以下的深海）对热量的储存可能是变暖停滞的关键。国际耦合模式比较计划第5阶段中的模式并未精确地描述各种有利降温影响因子的近期位相演变,因而其模拟的近期增暖趋势较观测偏强。由此推断,变暖停滞主要是自然因素造成的,并且预测变暖趋缓将在近几年或几十年内结束（依赖于太平洋年代际振荡的位相转变）,未来气温将仍主要受到温室气体增加的影响而表现出明显的上升趋势。因此,目前的全球变暖趋缓不大可能改变到本世纪末全球大幅度变暖带来的风险。本综述展望未来的研究热点包括:精确估算全球气温和海洋热含量的变率及其不确定性,海洋年代际信号（太平洋以及大西洋的年代际振荡）的转型机制,存储在深海的热量将在何时返回海洋表面及其对区域气候的潜在影响。     

Global Warming and Coastal Erosion

One of the most certain consequences of global warming is an increase of global (eustatic) sea level. The resulting inundation from rising seas will heavily impact low-lying areas; at least 100 million persons live within one meter of mean sea level and are at increased risk in the coming decades. The very existence of some island states and deltaic coasts is threatened by sea level rise. An additional threat affecting some of the most heavily developed and economically valuable real estate will come from an exacerbation of sandy beach erosion. As the beach is lost, fixed structures nearby are increasingly exposed to the direct impact of storm waves, and will ultimately be damaged or destroyed unless expensive protective measures are taken. It has long been speculated that the underlying rate of long-term sandy beach erosion is two orders of magnitude greater than the rate of rise of sea level, so that any significant increase of sea level has dire consequences for coastal inhabitants. We present in this paper an analytical treatment that indicates there is a highly multiplicative association between long-term sandy beach erosion and sea level rise, and use a large and consistent data base of shoreline position field data to show that there is reasonable quantitative agreement with observations of 19th and 20th century sea levels and coastal erosion. This result means that the already-severe coastal erosion problems witnessed in the 20th century will be exacerbated in the 21st century under plausible global warming scenarios.     

全球变暖预估的不确定性

根据IPCC第4次评估报告(AR4)第10章[1],到2100年全球平均温度相对于1980—1999年平均有可能上升1.1～6.4℃,最佳估计值为1.8～4.0℃。这里给出来的是一个变化范围,但是,要注意这并不是预估的不确定性。1.1℃是最低排放情景B1的下限,6.4℃是最高排放情景A1F1的上限。1.8℃是     

全球变暖在继续

基于全球和中国的观测资料指出,无论全球还是中国,2001-2010年都是有仪器观测记录以来最暖的10年。虽然这10年内的温度上升趋势很弱,但并不意味着气候变暖已经停止。分季节来看,近10年（2001-2010年）冬季中国东北及新疆的气温低于前10年（1991-2000年）。然而,这种区域性和季节性的温度下降并没有影响全国、全年保持变暖的趋势。