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.”

Without carbon dioxide in the atmosphere, the Earth would be a frozen orb.

It is known with a very high degree of certainty that carbon dioxide keeps the Earth warm and more of it will make the Earth warmer.

It is also known with a very high degree of confidence that humans activities have increased atmospheric CO₂ content by about 40% since the dawn of the industrial revolution.

There is close to universal consensus among well-informed climate scientists that most of the global warming over the past 50 years was associated with our greenhouse gas emissions.

There is substantial uncertainty regarding how sensitive our climate system is to added CO₂, where something like 3 C per CO₂ doubling (about 5 F) might be somewhere near the central expectations but with semi-reasonable people arguing for half this or double this.

There is very little consensus regarding how adaptable humans will be to these changes. Humans already live from the equator to the Arctic circle. Houston used to be a malarial hell-hole and now it is a modern air-conditioned city.

At the one end of the spectrum there are people thinking climate change will be an existential threat to human existence. At the other end, there are people who think most people will barely notice the effects of climate change. Neither end of this spectrum represents a tenable position.

My own view is that climate change will impose a substantial cost on society but that climate change is unlikely to be the biggest problem that most people will face in their lives.  This is less true for sensitive ecosystems such as coral reef systems.

Humans are like weeds. We are the invasive generalists par excellence. We spread rapidly, grow quickly, and successfully inhabit almost any environment.

Climate change will impact the delicate flowers tuned to a narrow range of environmental conditions; climate change will benefit many weeds, which can take advantage of disruption.

Carbon dioxide also acts as a fertilizer for plants, so there is potential for crop yields to increase under a high-CO₂ atmosphere.

When the dinosaurs were around, the atmosphere was rich with CO₂ and life flourished. We are not followers of Leibniz and do not think we are living in the best of all possible worlds. There is nothing particularly special about the climate of the pre-industrial era, although it does seem to have been a particularly stable climatic period.

The problem is not that greenhouse gases are pushing us from a better climate to a worse climate so much as the problem is one of rates of change. Will climate change occur so rapidly that the transition imposes costs that were not anticipated, costs that are larger than we would like to deal with?

[Just in case it is not clear, my answer to the final question is ‘yes’. Not only that, even anticipated changes are sufficient to motivate eliminating fossil-fuel CO₂ emissions as soon as is practicable.]