CO2 persists in the atmosphere for 50-200 years. Our current level of emissions (8 billion tons in 2008) and the world's rate of population growth suggest that if nothing is done emissions will rise to 16 billion tons by 2050. But temperature tolerance forecasts suggest that emissions at that time cannot exceed 9 billion tons.
鑑於二氧化碳會在大氣中存留 50-200 年，以目前人類碳排放（2008 年為 80 億噸）和人口成長情況預估，若什麼都不做，2050 年的全球碳排放量將倍增為 160 億噸；但依容忍溫度預估，當年的排放量絕不能超過 90 億噸。