Scientists in Belgrade came up with the idea of “planting” large tanks of water and algae in places where trees can’t grow. The tanks are 10-50x more efficient than a normal tree for the space it takes up and is in general highly sustainable, even creating excellent fertilizer in the process. You can skip about halfway through the video for the actual information about them.
That’s without mentioning the resources invested into building those oxigen farms. The fact that this is done on a rich country already tells a lot. Solar panels aren’t made with love and care, but minerals extracted from the earth.
Also, our problem isn’t lack of O2 or excessive CO2. Our problem is a series of ideas and decisions we make about how we treat the world we’re a part of. One of those ideas, is precisely efficiency above all other things. It’s the same idea that makes market speculators fall in love with “line goes up”. She even makes a point of saying how much more efficient than trees those are.
Sure, those are efficient in making the air safer for humans, but do they help with other local biodiversity? Do they help fixing the soil? Do they help the global ecosystem as a whole?