Some climate scientists believe that 400 ppm of CO2 in the atmosphere is already enough to take us past the tipping point at which we risk a climate catastrophe that will turn billions of people into refugees. They say that we need to get the amount of atmospheric CO2 back down to 350 ppm.
一些气象学家认为400 ppm的大气二氧化碳浓度已经超过了气候灾难触发点，数十亿人有成为难民的危险。他们说，我们需要让大气二氧化碳水平下降至350 ppm。这个数字被写入了草根运动350.org的名字，188个国家的志愿者参与了这个旨在解决气候变化问题的组织。