Soren wrote on Oct 30
th, 2009 at 9:08pm:
Don't be ridiculous. How did she measure acidification over 25 million years?
She didn't. She is guessing, or rather conjecturing from corals, probably. Anybody who is talking about that amount of change in pH over 25 million years as fact is bullsh!tting. And what is the margin of error of these guesstimates?
Aha! - deliberately spreading confusion again. Acidification is the recent process where increased production of CO2 is leading to reduction in ocean pH. The parameter measured over 25 million years is pH, not acidification. Soren, if you protest wildly about technical matters that you don't actually understand, then it doesn't matter how much impeccable rhetoric you use. You still end up looking foolish.
As far as the question of how you measure ocean pH over 25 million years, it is done by the use of proxies. Obviously an indirect method was used.
You are familar of course with the proxy data that is used to measure global temperature using Deuterium in ice cores? The one that is quite happily accepted and manipulated by denialists such as McIntyre? (I should add that he doesn't have the resources to produce his own data, so he manipulates that of others)
Anyway that's another example of proxy data. The proxy data matches quite well with recent data, and that gives us the confidence to use it over a longer period, especially if it's backed up by other proxy data. The boron isotope ratio of biogenic carbonate is well established as a proxy for ocean pH.
http://www.sciencemag.org/cgi/content/abstract/282/5393/1468There have been many other studies that corroborate that one of course. Corals? - no, bad guess, Soren. They usually use benthic foraminifera.
It's quite enlightening that you didn't ask the question "how did she measure ocean pH?" like most normal people would have done. Instead, you go on the attack immediately without any data to back you up. She was "guessing", you splutter, "conjecturing from corals" probably. In fact the only person doing the guessing is you

Now for the question of error bars. She could have used error bars, but to do so would have been difficult in this case. The error in this case is extremely low. A graph of pH is on a logarithmic scale. A pH increase from say 7 to 8 represents a
tenfold decrease (in hydrogen ion concentration), so any error in concentration would be reduced to being insignificant on a pH scale. Try it on your scientific calculator if you don't believe me. There is one built in to your operating system. I'm sure any highschool student worth his salt would be happy to demonstrate its use.
You do understand the concept of logarithm I take it?