As the carbon dioxide in the atmosphere today reaches 380 parts per million (ppm), while the last few million years saw fluctuations between about 180 and 280 ppm, it is no surprise that the sea water is more acidic than during this recent period in Earth's history.
As always, it is not just the scale of change that is important, but its speed.
A new study attempted to measure the current rate of change, against what happened in pre-industrial times, but was dependent on computer models to provide historical estimates.
Despite this caveat, the survey numbers are surprising, suggesting that the current rate of acidification is two orders of magnitude larger than what happened at the end of the last Ice Age.
Do marine animals, plants and ecosystems can live with that? As the oceans will in the future? Is it still will be able to deliver the food we need?
Some laboratory experiments suggest problems. For example, last week, a team of Australian researchers found that increased levels of CO2 in seawater affect the brain chemistry of fish alter their behavior.
Some people may say that what is happening is not an increase in acidity, but a drop in alkalinity, so you can not call this acidification.
In a way, that is correct. With a pH of 8.1 and falling, sea water is alkaline to neutral path.
But this is irrelevant. Organisms and ecosystems adapt to any acidity or alkalinity are, but need time to do it, and in some cases, for example, for animals that need to form shells, such adaptation may be impossible.
Anyway, there is a wealth of evidence that ocean acidification is a concern - perhaps even more than the climatic effects of CO2 emissions.
Some climate conventions already mentioned the problems of acidification. The Rio +20 (United Nations Conference on Sustainable Development) offers a way of putting it on the tables of presidents and prime ministers, and a movement is being actively pursued.
The International Oceanographic Commission of UNESCO is a UN bodies dedicated to talking about the acidification in the Rio agenda
As with climate impacts, there is an agenda concerned with dealing with the impacts of acidification, as well as an agenda concerned with the reduction of the trend itself.
Some years ago, for example, scientists have shown that keeping the fish population in a balanced and healthy reef offers protection against impacts of temperature and acidity.