I think the author ignores several important facts. For one, humans are high on the food chain and in turn may not be as robust as say roaches, but we can construct pretty much everything. We will evolve and change, but the extinction of the human race would require several Unprecedented events. Even a large meteorite striking Earth would have trouble killing off humanity (obviously if it's big enough...). Furthr, algae reduce carbon much MUCH more efficiently than plants and can reproduce much faster. Even more we already have processes of turning algae to oil (although the oil is of poor quality). All that being said the more carbon dioxide is released the quicker/more algae will grow and the more oxygen and oil can be produced. In other words, obviously there are limits and I challenge you (the author or reader) to do research, but although humanity has problems. As a species we are doing alright.
