We also know beyond doubt that emissions from human activities have substantially increased the amount of greenhouse gases (especially carbon dioxide) in our atmosphere. When the first IPCC report was published in 1990, the concentration of CO2 in the atmosphere had reached 354 parts per million (up from the preindustrial baseline of 280 ppm).
我们还不带任何疑问地知道，人类活动所产生的排放大大增加了大气中的温室气体（特别是二氧化碳）数量。1990年，当第一份IPCC报告出台时，大气二氧化碳浓度已经达到了百万分之354（工业化前的基准水平为280ppm）。今年，大气浓度第一次超过了400ppm大关。从采集自南极冰盖的远古气体中我们得知，二氧化碳正水平处于一百万年来的最高值。