Re: yes but (@Matt Bryant)
but that 2% excess CO2 emission has increased the atmospheric concentration of CO2 from ~280ppm to ~380ppm. An increase of about 35%.
The CO2 in the atmosphere is in equilibrium with the CO2 dissolved in the oceans. That is a 35% uptick in atmospheric CO2 will eventually lead to a similar uptick in CO2 concentration in the ocean (it's far from saturated in this regard, it's not a fizzy drink yet). However this step is lagging, it takes time for the CO2 concentration of the ocean bulk to even out, quite a lot of it is more than a mile from the surface.
In turn the dissolved CO2 is also in reversible equilibrium (by reaction with water) with carbonic acid (H2O + CO2 <-> H2CO3). Pushing in more CO2 drives the equilibrium over to the H2CO3 side. H2CO3 is acidic (weakly), in that it disassociates into "free protons"* and bicarbonate.
pH is the negative logarithm of "free proton"* concentration... so increasing atmospheric CO2 inevitably leads to the pH of sea water decreasing, that is acidification (by definition, frankly).
* I'm forced to point out at this point that "free protons" do not exist in even very acidic water solutions. Assuming they exist is a gross simplification. The acidic species in aqueous solution is actually H3O+, that is the acidic proton attaches itself to a near by water molecule.