A nice response, and interesting. But if you dig a little deeper, you'll see it's not that trivial.
Yes it is.
I would note that your post didn't address the relative orders of magnitude of CO2.
Calculations, please. Making stuff up isn't science. Calculating effects is. If you think that relative magnitude of CO2 is relevant, give me a back of the envelope showing plausibility. You can use as a starting point the fact all the volcanoes worldwide emit, on average, an estimated 130 to 440 million metric tons of CO2 each year. (Sounds like a lot, doesn't it?)
My revised argument (I didn't type the following in the earlier post) is that natural CO2 dominates anthropogenic CO2,
and any changes we induce to the overall temperature are overshadowed by natural variations.
Nope. They add to the natural variations... but the natural variations tend to average out with time, while the anthropogenic CO2 is monotonic upward.
In particular, the variations in chemistry and temperature of the ocean dominate the chemical equilibrium.
Don't speculate, calculate. About two minutes of work should show you that this is not even within a few orders of magnitude of being relevant. You need a back of the envelope calculation showing plausibility.
What I didn't add about the undersea volcanoes is when heat and acid are added to water, LeChatlier's principle states that the alkaline ocean (remember, ocean pH varies from 7.0 to 8.0) will go slightly more acidic (sulfuric acid is a much stronger acid than carbon dioxide) and push the carbon dioxide out of the water, and increasing temperature raises the dissociation constant of water (or lowers the pKw, take your pick) and also forces out more CO2.
Now you're talking effects that aren't even close to being relevant. Don't speculate, calculate.
Anyone who has drunk a warm, flat beer, or poured vinegar into soda water and watch it fizz, can observe this. The assumed heat added by volcanoes is 525,000 TW-h, [check your numbers too ;-)], and the acidity from sulfuric acid is enough energy (in terms of chemical potential) to affect the solubility and cause the ocean to release more CO2 into the atmosphere, or absorb more if the volcanic activity decreases.
Show me an order of magnitude. How much is the effect?
If there is a 10% variation in the volcanic releases of heat and SO4 (or 52,000 TW-h, compared to 142 TW-h from anthropogenic sources), that will affect the environment more than what we add, and it can be argued that from the energy balance difference (recall the worlds energy demand is another way of showing the chemical potential differences between the hydrocarbons and CO2 + H2O). This is significant,
Sorry, but your numbers fail a check of units. The units needed are warming in degrees K. Any other numbers need to, eventually, be turned into warming in K by a calculation.
and the argument cannot be dismissed by calling me a denier.
You have stopped being a denier when you started doing calculations with actual numbers. You may be wrong... but you have now demonstrated that you are not a denier.
It could be dismissed if all volcanoes were identified and their activity cataloged.
Unnecessary. If the effect is many orders of magnitude too small to think about, no need to pay further attention.