I wrote the following in response to this post:  http://news-oceanacidification-icc.org/2015/08/26/a-plea-to-ocean-acidification-scientists/

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The Arctic is cold. It will remain cold even with global warming.

However, it makes sense to talk about the warming of the Arctic despite its being cold. It also makes sense to talk about the Arctic being warmer than it was a century ago even though it is still cold. One might also say that the Arctic is ‘warm’ relative to what it was a century ago.

It is not making a mistake to use the word ‘warm’ or ‘warmer’ in this context. In these contexts, ‘warm’, ‘warming’ and ‘warmer’ refer to signs of change and not absolute values.

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Carbon dioxide in the ocean acts as a weak acid, in that it donates protons to solution.

The addition of a weak acid into the ocean is making the ocean more acidic, in that it is decreasing the pH of the ocean and bringing it closer to the acid end of the scale.

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It is as if I were to declare that I am not going to call anything ‘warm’ unless the temperature is greater than 25 C, and then you claim that nobody can talk about the warming of the Arctic until the temperature reaches 25 C.

This is an absurd position.

It makes sense to use terms like ‘acid’, ‘acidic’ and ‘acidification’ in reference to directions of change and in comparative contexts (c.f., the Arctic is warmer than it was a century ago; the ocean is more acidic than it was a century ago.) These statements do not mean that the Arctic is warm or the oceans are acid in any absolute sense; they are relative statements.

In this context, ‘warmer’ means ‘higher temperatures’ and ‘more acidic’ means lower pH.

This has been standard usage in the discussion of ocean acidification for over a decade. It is not helpful to try to change this usage at this time.

The post referred to above ends:

“Some of us have made this mistake in the past but let us ban the future use of “acid” or “acidic” in the context of our work.”

Better would have been,

“With regard to ocean acidification, let us reserve the use of terms such as ‘acid’ and ‘acidic’ to contexts where comparisons are being made or reference is being made to a sign of change; in most oceanographic contexts, it is incorrect to use these terms to describe seawater in an absolute sense.”