[, ]a right to send out a measured amount of harmful gases such as carbon dioxide into the air二氧化碳排放配额◆Countries that fail to reduce their emissions sufficiently will have to buy carbon credits.不能有效降低排放量的国家不得不购买碳信用额度。ⓘ The word carbon is used because the harmful gases are measured in standard units ( carbon dioxide equivalents) based on the damage caused to the environment by carbon dioxide .采用 carbon 这一词，是因为有害气体是用标准单位（二氧化碳当量 carbon dioxide equivalents）量度的，而这一标准单位是基于二氧化碳对环境造成的损害程度而定的。➡ see note at emission unit