Calling a decline in pH of ocean water from 8.2 to 8.1 (which is calculated to have happened over recent decades, perhaps in response to rising atmospheric carbon dioxide concentration though other causes are possible) “acidification,” meaning “becoming more acidic,” is misleading at best.
Something can’t become “more acidic” unless it’s already acidic, and a solution with a pH higher than 7.0 is by definition not acidic but basic. Earth’s five oceans vary in pH from about ~7.9 to ~8.3, and pH is measured on a logarithmic scale. That means a pH of 10 is 10 times more basic than one of 9; and 9 is 10 times more basic than 8; etc.
A pH of 8.1 is still about 10.26 times more basic than the neutral 7, which is the dividing line between acid and basic. Hydronium ions (H+), which make solutions acidic, are minisculy present but are vastly overwhelmed—by many orders of magnitude in concentration—by hydroxyl ions (OH–), which make solutions basic. (By the way, when you combine an H+ ion with an OH– ion, you get H2O, water!)
A decline in average ocean pH from 8.2 to 8.1 represents an increase in hydronium ions (H+) of about 26 percent, which sounds alarming until you realize that with a measurement margin of error several times that, and with pH levels at given points swinging markedly every day along a continuum four times as wide, it isn’t likely to be highly consequential.
Featured image by U.S. Geological Survey, Creative Commons.