Carbon dioxide (CO 2 ) from fossil fuels burning and land-use change is accumulating in the atmosphere. Current levels are over 40% higher than in the pre-industrial era and a continued increase of atmospheric CO 2 will lead to further warming of the planet. In the Paris Agreement, countries set out to hold the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C. There is an upper limit to CO 2 emissions compatible with these objectives. Current knowledge from climate models indicates that the relationship between total or ‘cumulative’ CO 2 emissions and surface warming is broadly linear, meaning that if we double the total amount of CO 2 emissions, we would see a doubling of the warming. From this relationship, one can estimate the remaining carbon budget that could be emitted to the atmosphere in order to remain below +1.5 or +2.0 degC. These carbon budgets were first assessed in the IPCC 5th Assessment Report in 2013, but were revisited in recent publications and in the IPCC Special Report on Global Warming of 1.5°C released in October 2018. These newer estimates better account for the historical CO 2 emissions and level of warming already observed. Given a present-day warming of about +1.0 degC above pre-industrial levels and historical emissions of about 2200GtCO 2 , these studies broadly agree that the +1.5 and +2.0 degC limits would impose a remaining budget from 2018 of less than about 580GtCO 2 and 1500GtCO 2 , respectively. These remaining carbon budgets would be used up in less than about 15 years and 35 years, respectively, at current rate of global CO 2 emissions. How are these carbon budgets developed?

中文翻译：

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全球碳预算：确定化石燃料排放的限制

来自化石燃料燃烧和土地利用变化的二氧化碳 (CO 2 ) 正在大气中积累。目前的水平比工业化前时代高出 40% 以上，大气中 CO 2 的持续增加将导致地球进一步变暖。在《巴黎协定》中，各国着手将全球平均气温升幅控制在远低于工业化前水平 2°C 的范围内，并努力将气温升幅限制在 1.5°C 以内。与这些目标相符的 CO 2 排放有一个上限。当前来自气候模型的知识表明，CO 2 总排放量或“累积”CO 2 排放量与地表变暖之间的关系大致呈线性关系，这意味着如果我们将 CO 2 排放总量增加一倍，我们将看到变暖增加一倍。从这段关系来看，人们可以估计可以排放到大气中的剩余碳预算，以保持在 +1.5 或 +2.0 摄氏度以下。这些碳预算首先在 2013 年 IPCC 第 5 次评估报告中进行了评估，但在最近的出版物和 2018 年 10 月发布的 IPCC 全球变暖 1.5°C 特别报告中重新进行了评估。这些较新的估计更好地解释了历史 CO 2 排放和已经观察到的变暖水平。鉴于目前气温比工业化前水平高出约 +1.0 摄氏度，历史排放量约为 2200GtCO 2 ，​​这些研究大致同意，+1.5 和 +2.0 摄氏度的限制将使 2018 年的剩余预算低于约 580GtCO 2和 1500GtCO 2 ，​​分别。这些剩余的碳预算将分别在不到 15 年和 35 年的时间内用完，以目前的全球 CO 2 排放速度。这些碳预算是如何制定的？