植物光合作用确实有重大影响大气中的氧气浓度,可能看到的情节(大气中的氧气研究)(http://scrippso2.ucsd.edu/plots)。在光合作用强烈的季节性变化,特别是在北半球高纬度地区,导致每年约20 ppm的氧气波动(ppm)。叠加在这是增加二氧化碳的“稀释效应”,主要是由于化石燃料的燃烧,这样我们实际上是失去大约19氧分子每年每百万。这些影响远小于短期波动可用氧气由天气引起的。你是正确的在说平均氧浓度约为21%。比较最优呼吸范围,对于人类来说,19.5 - 23.5%的氧气。人们往往失去意识大约10%的氧气,和死于窒息在5%左右或更少。上面的数据是海平面。在高山上海拔可以12%的氧气,这就是为什么它是如此难以攀登喜玛拉雅山最高的山峰。采取长远的角度来看,即使在海平面有大量大气中氧含量的变化在过去的5.5亿年里,变化在10%和35%之间。 Don't worry, the human physiology is more than capable of handling *normal* fluctuations and trends in the atmosphere's oxygen content. But here is something which you might want to worry about: Suppose international efforts to curb greenhouse gas emissions are negated by continued human population growth? A worst-case scenario can be contemplated in which the global mean temperature rise attains, or even exceeds, 4.5 degrees Celsius during some time next century. In this case, at least a billion people, mainly in the tropics, will be subjected to extreme seasonal heat-stress. At the same time the cumulative effects of oxygen dilution in the atmosphere might become sufficiently high to exacerbate that heat-stress. This is a scenario that *does* have the potential to kill people.