As noted by Dixon, the Guardian did eventually edit both the headline and the offending first sentence to reflect the reality that the source of all this was referring to the rate of acidification. Or, more accurately, to the rate at which the oceans are becoming slightly less alkaline. Whether that rate is really remarkable is another matter, but one thing seems agreed at the source linked to by Dixon (loc cit): the oceans have been appreciably less alkaline for much of the past 300 million years:
And, as illustrated in a well-known graphic reproduced here, CO2 levels were typically over 1,000ppm for much of that time:
Whatever, we now have another piece of climate junk in circulation. Keep an eye out for it coming your way. If you see it being aimed at children or teachers, please let me know and I'll add the details here.
Hat-tip re the Dixon post: Bishop Hill, http://www.bishop-hill.net/blog/2013/10/7/oceans-are-unprecedentedly-alkaline.html