<i>&gt; the current concentrations are 209 460 ppm of O2 compared with around 380 ppm of CO2. So, it&#x27;s currently a non issue.</i><p>I certainly agree it&#x27;s &quot;currently&quot; a non-issue; but I would add that given the numbers in the article it&#x27;s going to continue to be a non-issue for the foreseeable future. The key fact from the article is that the rates of change of O2 and CO2 are of the same order of magnitude: a few ppm&#x2F;year. That change is a percent or so of total CO2 concentration, but only a thousandth of a percent or so (1 part in 10^5) of total O2 concentration. So it would take a thousand years at current rates for the O2 concentration to decrease by 1 percent of its current value (which is still negligible in human terms).<p>Plus, that assumes a linear decrease over a thousand years, which is highly implausible. The article notes that we have only been measuring atmospheric O2 concentrations for a couple of decades. No meaningful conclusions can be drawn from that about what will happen to O2 concentrations over a thousand years. The best current model we have is the simple and obvious one that O2 concentrations in Earth&#x27;s atmosphere are maintained at appropriate levels for oxygen-breathing animals as part of the cycle of plant and animal respiration, which has been going on for hundreds of millions of years, including periods when CO2 concentrations were much higher than they are now.