Meinshausen Malte, Meinshausen Nicolai, Hare William, Raper Sarah C B, Frieler Katja, Knutti Reto, Frame David J, Allen Myles R
Potsdam Institute for Climate Impact Research, Telegraphenberg, 14412 Potsdam, Germany.
Nature. 2009 Apr 30;458(7242):1158-62. doi: 10.1038/nature08017.
More than 100 countries have adopted a global warming limit of 2 degrees C or below (relative to pre-industrial levels) as a guiding principle for mitigation efforts to reduce climate change risks, impacts and damages. However, the greenhouse gas (GHG) emissions corresponding to a specified maximum warming are poorly known owing to uncertainties in the carbon cycle and the climate response. Here we provide a comprehensive probabilistic analysis aimed at quantifying GHG emission budgets for the 2000-50 period that would limit warming throughout the twenty-first century to below 2 degrees C, based on a combination of published distributions of climate system properties and observational constraints. We show that, for the chosen class of emission scenarios, both cumulative emissions up to 2050 and emission levels in 2050 are robust indicators of the probability that twenty-first century warming will not exceed 2 degrees C relative to pre-industrial temperatures. Limiting cumulative CO(2) emissions over 2000-50 to 1,000 Gt CO(2) yields a 25% probability of warming exceeding 2 degrees C-and a limit of 1,440 Gt CO(2) yields a 50% probability-given a representative estimate of the distribution of climate system properties. As known 2000-06 CO(2) emissions were approximately 234 Gt CO(2), less than half the proven economically recoverable oil, gas and coal reserves can still be emitted up to 2050 to achieve such a goal. Recent G8 Communiqués envisage halved global GHG emissions by 2050, for which we estimate a 12-45% probability of exceeding 2 degrees C-assuming 1990 as emission base year and a range of published climate sensitivity distributions. Emissions levels in 2020 are a less robust indicator, but for the scenarios considered, the probability of exceeding 2 degrees C rises to 53-87% if global GHG emissions are still more than 25% above 2000 levels in 2020.
100多个国家已采用将全球变暖限制在2摄氏度或更低（相对于工业化前水平）的目标，作为减轻气候变化风险、影响和破坏的缓解努力的指导原则。然而，由于碳循环和气候响应的不确定性，与特定最大变暖相对应的温室气体（GHG）排放量却鲜为人知。在此，我们基于气候系统属性的已发表分布和观测约束条件，进行了一项全面的概率分析，旨在量化2000年至2050年期间的温室气体排放预算，该预算将把整个21世纪的变暖限制在2摄氏度以下。我们表明，对于所选的排放情景类别，到2050年的累计排放量以及2050年的排放水平，都是21世纪变暖相对于工业化前温度不超过2摄氏度的概率的可靠指标。考虑到气候系统属性分布的代表性估计，如果将2000年至2050年期间的累计二氧化碳排放量限制在10000亿吨二氧化碳，变暖超过2摄氏度的概率为25%；而限制在14400亿吨二氧化碳时，概率为50%。已知2000年至2006年的二氧化碳排放量约为2340亿吨二氧化碳，要实现这一目标，到2050年仍可排放不到已探明经济可采石油、天然气和煤炭储量的一半。最近的八国集团公报设想到2050年将全球温室气体排放量减半，假设以1990年为排放基准年并采用一系列已发表的气候敏感性分布，我们估计届时超过2摄氏度的概率为12%至45%。2020年的排放水平是一个不太可靠的指标，但对于所考虑的情景，如果2020年全球温室气体排放量仍比2000年水平高出25%以上，超过2摄氏度的概率将升至53%至87%。
