Okay!
The more CO2 you have in the atmosphere, the more CO2 you have dissolved in the waters in contact with the atmosphere.
CO2 + H2O ----> H2CO3 (AKA Carbonic Acid) ----> H+ + HCO3
the more H+ (free hydrogen ions) you have in a solution, the more “acidic” that solution becomes.
Currently, the oceans are about 30% more acidic than they were a century ago, and are considerably more acidic than they have been in at least 800,000 years and possibly more than they've been in the last 50 million years or more.
And all it takes is one molecule of CO2 to turn the oceans acidic?
That is not what I stated, nor was this absurdity implicit in the question you asked which was for a "small word" simplification of the process (chemistry) of how atmospheric CO2 turns the oceans acidic. That said, technically water, regardless of the volume, would be made more acidic (have a higher concentration of cations) through the addition of a single extra free proton (hydrogen cation), of course, even in a small volume of water, that level of acidification is generally immeasurable. When, however, we are talking about adding 30+ gigatons of CO2/year to the atmosphere even bodies of water as large as the oceans on our planet, undergo measureable change when this much of an active chemical is introduced to those waters annually.
Can you continue you train of thought?
certainly, but given that you now understand the process, plugging the proper numbers into the equations for calculating the volume and mass of the ocean's surface (upper 30 meters) waters and then applying standard pH calculations given the volume of CO2 added to these surface waters each year, should yeild the results you seem to be seeking. (current measurements indicate an accelerating decadal average pH increase of about 0.02 units)
What does it mean that "the oceans are about 30% more acidic than they were a century ago"? If the ocean pH is 8, where does a 30% more acidic change take us?
(I have several more questions, but it's best to do this in small doses because I'm a layman)
At the start of the industrial revolution the average ocean pH was measured to be ~8.25, current measurements yield an average of ~8.135. A pH level change of 0.1 units is equivilant to a 30% change in cation concentration. Our actual measured change is a bit higher than 0.1 (.115), so my statement of 30% is a bit low and should be considered a conservative estimation. There is of course variation with less acidity in the tropical waters than in the higher latitude oceans due to the increased buffer capacity of tropical waters (and less ability of the warmer waters to hold onto dissolved CO2). this doesn't mean that sea water is going to start fizzing and acting like concentrated strong acids, but it does meant that much of the current base of the food chain which depends upon a higher, stable pH are at risk of disruption. There are issues occurring now, but it is the issues that come associated with the even higher levels that our increasing levels of atmospheric emissions portend which are the problem we must deal with.
Layman or expert, issues are generally best tackled in bite-size bits.
I have no problem sharing my understandings or any civil discussion of issues, even when there is an extreme difference of position and perspective; I generally turn the other cheek several times before the only cheeks I have left are gluteal.