Acid test for local action
Whether you prefer the term "ocean acidification" or the less compelling but more accurate "ocean de-alkalisation", there's little doubt that the addition of carbon dioxide to the seas threatens to change them fundamentally over the course of the century.
Ocean acidification 101 says that the oceans absorb some of the extra CO2 going into the atmosphere.
That slowly makes seawater less alkali - or more acid, as you prefer - with major and potentially catastrophic impacts on sea life.
The science is well documented, so I won't go over that ground again except to raise an alert to look out for an interesting study coming out in the next few days.
If global ocean acidification from global CO2 emissions is the issue, you might think that the solution would necessarily be global as well.
That's certainly the way it's mainly been talked about - and in the long run, curbing carbon emissions probably is the only way to protect the coral and other shell-forming creatures that depend on seawater maintaining a constant average pH around 8.2.
But in an article in the journal Science this week, a group of US-based scientists and lawyers is making a different argument: local initiatives can be effective too, they say.
There are a couple of main strands to their argument.
Firstly, the pH of seawater varies from place to place; and in some coastal zones, it's already been pushed toward the acid by local pollution.
- The oceans are thought to have absorbed about half of the extra CO2 put into the atmosphere in the industrial age
- This has lowered its pH by 0.1
- pH is the measure of acidity and alkalinity
- The vast majority of liquids lie between pH 0 (very acidic) and pH 14 (very alkaline); 7 is neutral
- Seawater is mildly alkaline with a "natural" pH of about 8.2
- The IPCC forecasts that ocean pH will fall by "between 0.14 and 0.35 units over the 21st Century, adding to the present decrease of 0.1 units since pre-industrial times"
Secondly, there's a large and growing mound of evidence to suggest that keeping reefs, for example, safe from disease and destructive fishing and local pollution and invasive species gives them greater resistance to climate-related threats.
A couple of years ago, in sediments around Chesapeake Bay on the eastern US coast, scientists found that the northern quahog - a type of clam whose name will resonate with fans of the Family Guy cartoon series - were in trouble.
The problem was a lack of the calcium carbonate minerals from which they fashion shells.
Putting crushed-up old shells into the sediments raised the amounts available to them, which led to an increase in the number of live clams.
One of the projected impacts of ocean acidification is a decline in the availability of carbonate, which many sea creatures extract to form aragonite and calcite.
So here in Chesapeake Bay, the authors of the Science article suggest, is evidence that localised measures could provide some defence against the global trend.
If that's a science-based approach, laws and regulations may also help.
Enforcing rules on coastal erosion, and the quality of water in rivers running into the sea, can reduce local pollution that's pushing in an acidifying direction, the article argues.
And they imply that anyone who takes an interest in the issue should scrutinise local laws to see what remedies may be available.
The US, for example, has the Clean Air Act, Clean Water Act, Coastal Zone Management Act and many others at federal and state level that might be deployable.
As discussed here a few weeks ago (and more recently by David Adam in Nature Climate Change), campaign groups have regularly attempted to use legal avenues to force action on emissions - not, it should be said, with a vast amount of success.
Whatever the merits of the case, it's clearly one where lawyers will have ample scope to argue about the limits of jurisdiction, the attribution of climate impacts, and indeed the scale of impacts given that projections of sea level rise are far from accurate.
Lots of the difficulties melt away when local laws are used for local change.
It might not be a strategy that solves the problem - but it could bring some relief to beleaguered bivalves.