"more acidic" is not entirely correct as the ocean is strictly speaking still alkaline (pH>7) and will remain so in the future. It is nevertheless true that the pH will most likely decrease (and has already done so in the past). A small change in the pH leads to large shifts in seawater carbonate chemistry (as the author correctly mentions later in the main text).

The pH change will affect many species. I am not sure if the statement "all sea life" is justified at this stage. Indirect effects will likely play a major role here (as mentioned later in the text) but this still lacks evidence. This is more like "work in progress" I would say.

This sentence is not really wrong but imprecise. First, plants use carbon dioxide (or in the case of aquatic photosynthetic organisms CO2 and often bicarbonate). The term "carbon" is to general. Second, the sentence implies that only some plants use carbon dioxide. I am sure the author is aware that "all" plants use CO2 for photosynthesis.

This is a correct statement but I found it a bit weird that the author selectively referred to barnacles. There a many species which do not respond directly (i.e. physiologically) to end-of-the-century pH values (although they may respond indirectly; see comment above).

a very important statement which is often neglected. It is good that the author included this statement.

correct.

This statement is based on on a study by Stiasny et al., 2016. The authors write: "Here, we obtain first experimental mortality estimates for Atlantic cod larvae under OA and incorporate these effects into recruitment models. End-of-century levels of ocean acidification (~1100 μatm according to the IPCC RCP 8.5) resulted in a doubling of daily mortality rates compared to present-day CO2 concentrations during the first 25 days post hatching (dph), a critical phase for population recruitment. These results were consistent under different feeding regimes, stocking densities and in two cod populations (Western Baltic and Barents Sea stock). When mortality data were included into Ricker-type stock-recruitment models, recruitment was reduced to an average of 8 and 24% of current recruitment for the two populations, respectively. Our results highlight the importance of including vulnerable early life stages when addressing effects of climate change on fish stocks." The author of the BBC article referred to their work correctly.

It could also be said that eventually we must switch to renewables since all fossil resources are exploited. There is no long term alternative to renewable (as far as I know).

I agree with dlswain. "Ever" is kind of right from a human perspective but it may not be totally right.

Indeed! I get to a slightly different number, however, (i.e. 45 %) maybe because I used a different basis (280 ppm) and/or current CO2 value (i.e. 405 ppm from Maona Loa, August 2017). The message is correct!