This implies that before 2050 global emissions of CO2 must be reduced to below 50% of the 1990 level (they are currently 15% above that level), and that average emissions in developed countries must be reduced by at least 80% of the 1990 level. The United Kingdom has already committed itself to a binding target to reduce emissions by that amount, and President Barack Obama has expressed intention that the United States should also set that target.
如果我们想比较有把握地实现这一目标， 那么CO2浓度决不允许超过百万分之450（现在是将近百万分之390） 。这意味着， 2050年前全球的二氧化碳排放量必须比1990年的水平减少50 ％以上（目前是超过了该水平的15 ％以上） ，而且发达国家的平均排放量必须至少比1990年的水平减少80 ％。英国已经承诺了一项具有约束力的目标，以减少排放量，而奥巴马总统也已表示，美国也打算建立这样的目标。