Keep in mind that in that roughly 150 year period we are talking about because of increased carbon dioxide concentrations, the world oceans are now 30% more acidic than they were then. The next 100 years will see a another 30% decrease in Hydronium ion concentrations even if humans don't add a single extra molecule of carbon dioxide themselves as the amount already in the atmosphere will take some time to reach equilibrium with that already there.
What's actually happened here is that there is a difference of 0.1pH between some proxy reconstructions related to 150 years ago and some actual measurements taken recently. Since modern pH meters, from different suppliers, can differ by up to 0.3 the difference is meaningless. Do climate scientists understand that pH is a log scale, thus ONE unit would equate to a 1000% change.
However, the reality is that although the baseline of annual carbon dioxide production by all the volcanoes in the world is about 250,000,000 metric tons, the amount humans now produce annually is 33,000,000,000 tons, so it is highly unlikely that humans will turn this around soon.
The figure for vulcanism is very difficult to verify. Since most of the Earth's surface, including some highly vocanically active areas, is covered with water. The likes of geothermal vents are likely to be difficult to spot under the ocean. These will be putting strong acids. Yet the oceans manage to buffer an unknown quantity of these. Carbon dioxide in water forms a weak acid. Even with all of the possible carbon dioxide on Earth in them the oceans would still be alkaline.